Environmental Microbiology: Advanced Research and Multidisciplinary Applications E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Environmental Microbiology: Advanced Research and Multidisciplinary Applications focus on the current research on microorganisms in the environment. Contributions in the volume cover several aspects of applied microbial research, basic research on microbial ecology and molecular genetics.
The reader will find a collection of topics with theoretical and practical value, allowing them to connect environmental microbiology to a variety of subjects in life sciences, ecology, and environmental science topics. Advanced topics including biogeochemical cycling, microbial biosensors, bioremediation, application of microbial biofilms in bioremediation, application of microbial surfactants, microbes for mining and metallurgical operations, valorization of waste, and biodegradation of aromatic waste, microbial communication, nutrient cycling and biotransformation are also covered.
The content is designed for advanced undergraduate students, graduate students, and environmental professionals, with a comprehensive and up-to-date discussion of environmental microbiology as a discipline that has greatly expanded in scope and interest over the past several decades.
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Seitenzahl: 404
Veröffentlichungsjahr: 2002
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PREFACE
Environmental microbiology is a subfield of microbiology that studies the role of microorganisms in maintaining a healthy, viable, and habitable environment. The role of micro-organisms aims to foster a prosperous, viable and inhabited environment. Microbes are considered to have both negative and positive effects on the environment, as their pollution can cause severe health problems, while on the other hand, they have various beneficial uses such as organic material degradation, being a source of nutrients in food chains, nutrient recycling, and pollutant bioremediation. This book offers an introduction to the discipline of environmental microbiology. It also demonstrates the importance of environmental microbes in our daily lives. It describes the main microorganisms that are found in environmental microbiology, their methodological options, and possible human impact. There is more to the successful exploitation of a given environment than can be explained exclusively in terms of environmental microbiology. An important thrust in this book is the new challenges of modern environmental microbiology, where pathogens and bioremediation are still important topics. This book is the result of hard work and the many efforts of the different authors. We pay them a warm thanks. This book provides a comprehensive review on environmental microbiology. The chapters, each written by subject matter specialists, help scientists, teachers, students, extension workers, farmers, consumers, administrators, traders and NGOs in increasing their understanding of environmental microbiology. This book on environmental microbiology comprises 10 chapters. The topics of our chapters are as follows: (1) Environmental microbiology: introduction and scope, (2) Impact of microbial diversity on the environment, (3) Rhizospheric microbial communication, (4) Microbial communication: a significant approach to understand microbial activities, and interactions, (5) Nutrient cycling: an approach to environmental sustainability, (6) Microbial biosensors for environmental monitoring, (7) Microbial degradation, bioremediation and biotransformation, (8) Bioremediation of hazardous organics in industrial refuses, (9) Role of microbial biofilms in bioremediation, (10) Microbial processing for the valorization of waste and application. Internationally, the interdisciplinary and multifactor global modern system of teamwork has been recognized for scientific excellence. Therefore, most chapters have involved the collaboration of 4–8 or more diverse international authors from different countries. Thus the book represents a truly global perspective consistent with the nature of environmental microbiology.
List of Contributors
Environmental Microbiology: Introduction and Scope
Dhriti Sharma1,2,#,Savita Bhardwaj1,#,Mamta Pujari1,Renu Bhardwaj3,Dhriti Kapoor1,*Abstract
Environmental microbiology deals with the role of microorganisms in supporting a thriving, viable and inhabitable environment. It helps to figure out the nature and functioning of the microbial population residing in all parts of the biosphere, i.e., air, water, and soil. Microbes are known to affect the environment both negatively and positively, as their contamination may lead to serious health issues on one hand, whereas various welfare activities like degradation of organic material, being a source of nutrients in food chains, recycling of nutrients, and bioremediation of pollutants are also associated with them on the other hand. In a way, their practical importance makes them a special tool in the hands of environment microbiologists to lessen the deleterious impact of different environmental problems. The degradation potential of microbes earns them a place in treating wastewater, containing organic and inorganic impurities being originated in public and industrial arenas whereby minerals, nutrients, and a number of other eco-friendly by-products are also generated. Microbial species like Pseudomonas, Sphingomonas, and Wolinella are few among those species which are commonly engaged in this process of degradation of harmful effluents being continuously added into the environment, thus ensuring the safety and sustenance of the latter.
Furthermore, their degradative abilities also help them to effectively confront and conquer the problem of oil spillage in sea waters resulting in less ecological damage. The manipulation of microbes in the present times has gained quite an important place in our lives in which this discipline of environmental microbiology contributes by unraveling all such possibilities of utilizing the microbes to our benefit. The present chapter provides a deep insight into this important branch of microbiology and its scope, which will help better understand its role in other fields such as agriculture, medicine, pharmacy, clinical research, and chemical and water industries.
Introduction
The invisible world of microorganisms, belonging to three principal life realms- Archaea, Bacteria, and Eukaryota and viruses- has played a pivotal role in the evolutionary process of the rest of the organisms dwelling on earth [1]. Being the earliest life forms, they have brought about major changes in the primitive reducing atmosphere; turning it into an oxidizing one with the help of oxygenic photosynthesis. Further, by developing adaptive mechanisms, they have colonized almost all the inhabitable areas on the earth, even those that offer the most unusual and extreme circumstances in terms of temperature, pressure, salinity, radiation, and pH [2]. The intriguing cosmopolitan nature, diversity, and immensity coupled with longevity have made the microbes' interactions with their surroundings more interesting. The study of these interactions between microorganisms and macroorganisms, including their environment, has now been upgraded to a new discipline of ‘Environmental Microbiology’ or ‘Applied Microbial Ecology’.
Environmental impacts of microbial activities are beneficial as well as harmful. A plethora of essential ecosystem services are carried out by these microbes; all the existing life forms and the biosphere at large, exhibit direct or indirect dependency upon the microbial activities. The microorganisms regulate biogeochemical cycles around the globe via having a major say over the important assimilative processes like fixation of Carbon and Nitrogen along with metabolism of Sulphur, Methane, etc. [3]. On the other hand, the baneful aspects of microbial existence in our surroundings involve the decomposition of our food items, textiles, and dwellings; disease in animals and crop plants. The credit for most of the progress made so far in this field goes to the advent of new technologies like the availability of radioisotopes, chemical-sensitive microelectrodes, and cultivation-independent techniques. New branches like metagenomics and metatranscriptomics plus metaproteomics wherein sequencing of the complete DNA complement recovered from the environment and quantification of actual expression of genetic potential are performed, have taken the science of environmental microbiology to a massive leap forward [4].
History of Environmental Microbiology
Microbe-based studies date back as early as the seventeenth century when an amateur, Anton von Leeuwenhoek reported their existence and named them animalcules. However, initially, research activities regarding microbes were carried out only in the context of a physiological perspective without giving much importance to the ecological aspects involved. This is revealed in the works of Louis Pasteur and M. Beijerinck who studied the distribution of microbes and invented the enrichment culture technique for microbes [5]. Among a few others, S. Winogradsky attempted microbial studies keeping their medical aspects aside; developed the Winogradsky column, and discovered chemosynthesis. He is credited to be among the first students of Environmental Microbiology [6]. But, Hungate and co-workers in the 20th century pioneered this new discipline of environmental microbiology by including quantitative aspects of ecological activities performed by microbes. In its initial stages, the center point of environmental microbiology was on public health, owing to a number of microbial disease outbreaks caused due to contaminated food and water like food poisoning, typhoid, cholera, etc. However, in the 1960s, a famous literary work ‘Silent Spring’ by Rachel Carlson shifted this focus to the presence of chemical pollutants in natural resources and their ill effects on health. This eventually led to the discovery of clean-up mechanisms by employing microbes and a whole new aspect of environmental microbiology i.e., bioremediation. Further, the inclusion of molecular genetics and the advent of other biotechnological applications have modernized this field.
Biotic Interactions- The Basis of the Science of Environmental Microbiology
Microbial diversity inhabiting almost all the existent habitats on the earth is a cumulative result of key interactions exhibited by microorganisms among themselves and with macroorganisms. These interactive associations hint at the co-evolution of the partners involved making them well-adapted and specialized (Table 1). Major biotic interactions of microbes are summarized as follows:
1) Symbiosis: It is a type of biotic interaction where microbes, particularly bacteria, get involved with other microbes or organisms of higher groups. Though microbes are quite small, but they contribute significantly to the physiological and evolutionary processes of eukaryotes [7]. Further, the symbiotic relationships exhibited by microbes can be categorized into a) Mutualism b) Commensalism c) Ammensalism, which in turn cast major impacts on the ecosystem of which they are a part [8].
a) Mutualism: It comprises the mutually beneficial relationship between the involved microbes and their partners [9]. Besides lichens (alga + fungus) and mycorrhiza (fungus + roots of plants), a classic example of microbial mutualism is a consortium formed between a methane-producing archaebacteria (Methanobacterium omelianskii) and an ethyl alcohol fermenting organism where the latter provides hydrogen to the former so that proper growth and production of methane occurs, this process is known as cross-feeding or Syntrophy [10]. Ethanol fermenting partners exhibit thermodynamically unfavoured endergonic reactions but the association with archaebacterial partners turns the nature of the overall reaction into an exergonic one, thus their existence in extreme environments is ensured which is not possible for them to do individually [11, 12]. In ecosystems with inadequate energy and nutrient resources like deep subsurfaces of soil or water bodies, this type of mutualistic interaction is believed to assist the growth and survival of microorganisms along with the production of energy in higher quantities [13, 14].
b) Commensalism: This symbiotic relation is quite common where one microbial partner benefits from the other partner's metabolic products without the latter exhibiting any good or bad impact. For example, two microbial species- fungus Saccharomyces cerevisiae (A fungus) support the growth of bacteria Proteus vulgaris in a mixed culture by providing it with niacin like growth factor, which is not possible in growing the bacteria in pure culture; the fungal partner is neither harmed nor benefitted from this interaction [15]. Some of the microbial flora thriving upon different body parts of human beings also come under the helm of commensalistic interactions like E. coli residing in the intestine.
c) Ammensalism: It is a type of antagonistic interaction wherein one partner is negatively affected while the other one exhibits indifference to this relationship by remaining unaffected. A peculiar example substantiating this interaction is between the microbial organisms Lactobacillus casei and Pseudomonas taetrolens where the former owing to the by-products synthesized during the production of lactic acid inhibits the growth of the latter via inducing a reduction in the overall yield of its main product i.e. lactobionic acid without itself getting least affected in terms of growth and behavior [16]. One more such example is between Staphylococcus xylosus and Kocuria varians involved in the fermentation of meat and vegetables and the former casts an inhibitory effect on the latter [17].
2) Parasitism: In negative interaction, the smaller partner, called the parasite, derives nutrition and shelter from, in, or, on the body of the larger partner, called the host, and casts an inhibitory effect on the survival of the host. A parasite is unable to exist without its host, however, the parasitism can be temporary or permanent, external or internal in nature. A large number of microbes find their place in medical microbiology pertaining to their parasitic nature and therefore being the causative agent of several diseases of viral, bacterial, fungal, or protozoan origin. In terms of microbial interactions, the viruses- bacteriophages parasitize upon bacteria, especially those involved in the fermentation of food items [18].
Importance of Microorganisms
Owing to their cosmopolitan nature, a plethora of roles are performed by microorganisms in the environment. All interactions occur between these microbes and macroorganisms (from symbiotic, neutral, commensalistic, exploitative, and competitive) which are discussed under two broad heads i) Useful activities and ii) Harmful activities.
Useful Activities
Nutrient Cycling
An intricate complex of microorganisms (bacteria, fungi, protists) is the potential source of nutrients to their biotic surroundings (macro-organisms like plants and animals) instead of soil, as considered in plant physiology [19, 20]. The microbial richness in the environment has been found to promote plant growth via different mechanisms like modulating the hormone signaling inside the plants, outsmarting or expelling the disease-producing microbes, and adding nutrients into the soil [21, 22].
In the last activity, nutrients like Carbon, Nitrogen, Phosphorus and sulfur, etc. which are otherwise organically held in living forms get released and added back into the ecosystem upon their death and decay through the process of biodegradation by the microorganisms (mostly via saprotrophic bacteria and fungi).They are then converted into more favored ionic forms such as ammonium, nitrate, phosphate, and sulfate as depicted in Fig. (1) [23]. All the major biogeochemical cycles (Carbon cycle, Nitrogen cycle, Sulphur, and Phosphorus cycle) rely on this biodegrading potential of microbes for their completion [24] For example, the nitrifying and ammonifying bacteria (Nitrosomonas, Nitrosococcus, Nitrocystis, and Bacillus sp.) release and perform the fixation of the naturally unavailable form of molecular nitrogen into the preferred and bioavailable nutrient forms. This nutrient cycling followed by transformation boosts the growth of plants and in turn those dependent upon plants. The overall productivity of an ecosystem, in a way, depends upon the microbial activities in the recycling of nutrients [25].
Chemosynthesis
Microbes are crucial to all the world's ecosystems for ensuring their sustenance and survivability, especially the ones where the possibility of photosynthesis is ruled out owing to the absence of light such as in deep marine biomes and hydrothermal vents. In these areas, microbes such as Beggiatoa, Ferrobacillus, Gallionella, and Thiovirga provide nutrition to other organisms by performing chemosynthesis. The genus Sulfurihydrogenibium has maximum carbon dioxide fixation rates in the dark at high temperatures whereas Thiovirga sufurooxydans bacterium excels at comparatively lower temperatures and shows chemolithotrophic activity to produce energy by oxidizing sulphur, sulfide, and thiosulphate [26]. Moreover, some of these chemotrophic microbes can also perform well under anoxygenic environments.
Fig. (1)) A generalized scheme of nutrient cycling in an ecosystem depicting the important role of microbes.Soil Formation
Microorganisms residing in the soil serve in multiple ways. The process of formation of soil, however, involves the contribution of biological, physical, and chemical factors but microbes perform the major role. The microbes are the chief driving force behind many transformations in the reservoir pool of nutrients of the soil and they also give rise to stable and labile forms of carbon, affect the formation of bedrocks, and enhance the soil porosity and glomalin content which in turn help in the establishment of subsequent plant communities [27].
Contribution to the Evolutionary Process
Major transfer of genes in a horizontal manner occurs in microbial populations which holds evolutionary significance [28, 29]. Evidence of this horizontal gene transfer came forth first from Griffith’s transformation experiment in 1928 in which the Pneumococcus bacteria got modified from the non-virulent form into a virulent one upon horizontally taking up the genes from its close relatives. Other methods of recombination in prokaryotes like conjugation and transduction also work upon the principle of horizontal gene transfer. Moreover, during the evolution of prokaryotic and the eukaryotic domain, extensive horizontal transfer has taken place, which will help restructure phylogenetic trees while comparing these with the ones constructed based on genome histories created from the fossil records [30, 31].
Harmful Activities
Spoilage of Food Products
Every year huge economic losses are incurred due to food spoilage with the significant contribution of microorganisms [32]. As per the reports of USDA Economic Research Service estimates, food close to 96 billion pounds of weight in the United States alone, is rendered unfit for human consumption either at retail, food service, or consumer level of marketing. The Flavour and shape of these consumables are changed due to microbial activity and about 25% of global food production is estimated to be lost due to this spoilage [33]. Further, the demand for fresh and pesticide-free food items, along with enhanced shelf life, has left the food articles more prone to microbial. The rotting of vegetables, fruits, meat, bread, or souring of milk and milk products is caused by saprotrophic bacteria, which are always present in the air and settle down on exposed food articles. Given their extremely small size, food infestation with microbes, especially bacteria and yeast, is hard to notice except for molds. The nature of food also contributes to this spoilage by microorganisms like the food items with more water content (meat, milk, and seafood) are spoiled comparatively more often as compared to those with less water content. However, the cereals constituting our staple diet are spoiled mainly by fungi like molds and yeasts. Common examples of food spoiling bacteria and fungi are Acinetobacter, Brochothrix, Clostridium, Flavobacterium, Micrococcus, Pseudomonas, Staphylococcus, lactic acid bacteria, members of Enterobacteriaceae, Aspergillus flavus, Aspergillus niger, Penicillium and Rhizopus sp [34].
Spoilage of Household Products
Domestic articles like textiles, paper, plastic, paint optical instruments, leather, canvas, and wooden articles are also exposed to microbial spoilage. Bacteria like Spirochaete cytophaga, Cellulomonas sp., and fungi like Alternaria, Aspergillus, Chaetomium, Cladosporium, Penicillium, and Rhizopus contribute majorly to the deterioration of these articles.
Diseases in Plants and Animals
Microbes are also pathogenic, causing serious inflictions to the biotic component of the ecosystem. The majority of the plant and animal diseases are of bacterial origin in about 90% of human diseases are caused by bacteria. Some of the examples of bacterial, fungal, and viral diseases are summarised in Table 2.
Scope of Environmental Microbiology
The emerging field of environmental microbiology has a plentitude of scope which in turn makes its applications extensive in diverse fields like industrial microbiology, soil microbiology, food safety, diagnostic microbiology, aquatic microbiology, water industries, safely disposing off hazardous wastes, biotechnology, occupational health/infection control, and aero microbiology. Here, a few of them are described to give a clear idea about the important role the microbes play in preserving the environment and human welfare at large.
Bioremediation: Besides being quite efficient in degrading naturally occurring material substances, the microorganisms have also been found to decompose some chemically synthesized compounds known as xenobiotics. Increased cognizance regarding the harmful impacts of these chemical pollutants produced as by-products in food, agricultural, chemical and pharmaceutical industries and are continuously added to the environment has kindled the research activities centered on manufacturing easily degradable substances or the techniques which help in degrading the contaminants in an eco-friendly manner. The application of diverse microbes individually or in a collective manner for this purpose by utilizing their biodegradation potential is known as bioremediation. Both in situ (on the actual site) and ex-situ (away from the actual site of contamination) strategies are practiced in it. Metal biosorption, biostimulation, bioaugmentation, and bioventing are some of the in situ techniques, whereas landfarming, biopiling, and composting come under the helm of ex-situ remediation. Still, some of these methods can be adopted both in situ and ex-situ conditions, so cannot be demarcated into one type.
Out of all of these, biostimulation stands apart in terms of its wide application and advantages; in it, the growth of otherwise naturally occurring microorganisms is boosted through the external supplementation with nutrients to help them to degrade pollutants more effectively [35]. Biostimulation can be concertedly used with a related technique of bioaugmentation in which the microbes with high degradative potential are inoculated into the affected site to fasten the process of remediation. The biotic interactions between the microbes and the environment affect the degradative abilities of remedial techniques which work together on the substrate (contaminant).
Examples of some of the microorganisms possessing biodegradation potential for contaminants are:
Arhaebacteria like Halobacterium, Haloferax, Halococcus;Bacteria like Pseudomonas putida, Dechloromonas aromatica, Nitrosomonas europaea, Nitrobacter hamburgensis, Deinococcus radiodurans, Sphingomonas, Wolinella;Fungi like White rot fungi- Phanerochaete chrysosporium, Pleurotus ostreatus and Trametes versicolor [36-38].Some Pollutant-specific Bioremediation Techniques
Degradation of Oil Spills
All the major economies of the world witness competition for the most valuable energy source of present times i.e. petroleum oil [39]. However, during the multiple stages of petroleum oil production, refining, processing, and at the time of its storage and transportation, there is an imminent danger of oil spill accidents which result in environmental degradation [40, 41]. Oil spills in peculiar environments such as deep-sea areas, deserts, polar regions, and wetlands, further aggravate the difficulty level of this problem. But this knotty issue of oil contamination in the ecosystem can be readily rectified by the use of petroleum hydrocarbon-degrading bacteria like Achromobacter, Alkanindiges, Dietzia, Enterobacter, Mycobacterium, Pandoraea [42-45]. Types, requirements in different environments, and the basic process of bioremediation of oil spills are briefly summarised in Fig. (2).
Biomineralization
New mineral technologies involve the use of microorganisms for on-site sequestering of inorganic pollutants such as those present in acid mine drainages [46, 47]. Microbes affect the process of mineral formation in various ways like they can either coprecipitate or simply adsorb the inorganic metals. For example, the Iron oxidizing bacteria change the ferrous (Fe2+) form of iron into ferric (Fe3+), which precipitates more easily, forming ferrihydrites for trapping inorganic pollutants [48, 49].
Several different bacterial strains have been recognized of Fe-oxidizing bacteria (Gallionella ferruginea, Acidithiobacillus ferrooxidans) and Fe- and As-oxidizing bacteria (Thiomonas sp.) which assist in Iron and Arsenic holding mineral phases for biomineralization. Some of the other microbes have been reported to synthesize Manganese oxides to sequester these pollutants [50, 51].
Microscopic studies have revealed the direct connection between microbial cells and mineral phases where the trapping of inorganic pollutants leading to biomineralization occurs either inside the periplasm or at the extracellular level via the formation of extracellular polymeric substances [52]. Microbial phosphatases are also employed to trap metal pollutants like Cr, U, Pb, and Sr through oxidizing organic phosphates which release harmless inorganic phosphates by precipitation [53-55]. Though these practices are quite economical and promising, bioremediation still needs to be popularised on a larger scale.
Fig. (2)) Summing up different aspects of cleaning of oil spills by microbes.Biofertilizers
Rhizosphere colonizing microorganisms, especially bacteria and fungi which enhance the availability of primary nutrients to the target plant crops are categorized as biofertilizers. These are also known as plant growth-promoting microbes which can be of several types like Nitrogen fixers, Phosphate solubilizers, Potash, and Zinc mobilizers, depending upon the activity they perform inside the soil. Live formulations or carrier-based inoculums of a number of microbes when applied to different plant parts like roots, and seeds, or simply added to the soil increase the phytoavailability of soil nutrients by changing them from unstable to accessible forms. Some major examples of biofertilizers are photosynthetic bacteria, nitrogen-fixing bacteria plus cyanobacteria (Rhizobium, Nostoc, Anabaena), and other bacteria like Actinomyces, Azotobacter, Bacillus, Pseudomonas, Lactobacillus sp. along with microbes of fungal origin such as yeast, Trichoderma and mycorrhizal associations. Rhizobium is one of the extensively studied nitrogen-fixing bacteria in legume plants whereas Azospirillum fixes the nitrogen in cereal and fodder crops besides enhancing the water and mineral uptake rate. These biofertilizers improve the crop yield sustainably besides being cost-effective, handy to use, harmless to the environment, renewable, and eco-friendly [56]. All these features make them an irreplaceable and essential part of the Integrated Nutrition System (INS) and Integrated Plant Nutrition System (IPNS) [57].
Wastewater Treatment
Wastewater has been generated in huge quantity primarily due to anthropogenic actions, for instance, increased industrial effluents, agronomic techniques, and urbanization; however, simultaneous release of wastewater without proper handling creates severe contamination issues [58]. Bioaerosol is diffused into the atmosphere in the form of small water particles, which act as microbe transporters during wastewater remediation [59]. Various microbes are recognized as potential candidates for the remediation of wastewater, e.g. Lipomyces starkeyi yeast was used to clean sewage disposal and produce lipids which are then used as a moiety for the generation of biodiesel [60]. Yeasts such as Rhodotorula glutinis, Rhorosporidium toruloides, and Cryptococcus curvatus can also be used to remediate wastewater [61]. The combination of different microbes, such as yeast and algae, is also an important technique for biological wastewater treatment [62]. This treatment is of two major types- i) Aerobic and ii) Anaerobic depending upon the requirement of oxygen, a comparative account of these two is summarised in Table 3. Anaerobic remediation methods have also been used for the salinity removal from wastewater e.g. Haloferax denitrificans, and H. mediterranei removed nitrate and nitrite from salinity water sources [63]. The co-immobilized application of Chlorella vulgaris and Pseudomonas putida exhibited efficient exclusion of ammonium, phosphate, and organic carbon, showing that the nutrient accumulation capacity of C. vulgaris and P. putida was increased from wastewater when used in combination [64]. Microbial immobilized media was produced by combining polyvinyl alcohol, polyethylene glycol, and activated sludge which showed 99% nitrification and denitrification activity and eliminated 85% of the organic matter from wastewater [65]. Bacillus salmalaya 139SI bacteria improved the removal efficiency of Cr6+ and increased crude oil - waste's water solubility [66, 67].
Biofilms
Since the beginning of microbiology, microbes have been mainly recognized as planktonic, free-floating cells and designated based on their growth, phenological, and biochemical aspects in nutritionally rich culture media. However, in all major natural ecosystems, these microorganisms are usually seen in tight interaction with substrates in the form of multicellular masses, known as biofilms, which are attached to the mucus they release [68]. During biofilm formation, microbe assembly is immobilized on a solid structure via electrostatic, hydrophobic, and covalent bonds carried out by the microbe itself and its constituents, for instance, cilia, fimbriae, cell wall, and EPS [69]. Biofilms are found almost in all humid ecosystems where surface attachment source is available and proper nutrient amount is accessible. A biofilm comprises an individual bacterial moiety as well as also made up of several bacteria, fungi, algae, and protozoa species, in which around 97% of the biofilm matrix is either H2O or solvent, the physical characteristics of which are controlled by the solutes added in it [70]. In a biofilm, mass transference relies upon diffusion whereas, its thickness relies upon the potential of constituents and O2 penetration [70].
Bioenergy Production
The energy generated from biofuels and waste contributes to 10% of the global energy demand compared to other resources. Hence, biofuels are recognized as vital sources for future sustainable energy generation, and bioenergy generation via microbes is considered a promising source. For example, microbes like microalgae, bacteria, fungi, and yeast have the potential to produce CH4, H2 gas, biodiesel, or bioethanol [71] (Fig. 3). Nannochloropsis gaditana produced biodiesel through transesterification with methanol under supercritical circumstances with the highest amount of 0.48 g g−1 biodiesel at a temperature of 255–265 °C and a reaction period of 50 min [72].Microalgae biomass of Chlorella sp. was pre-treated with anaerobic acterium Bacillus licheniformis for the production of biogas, where methane generation was enhanced from 9.2 to 22.7% by altering the amount of B. licheniformis [73].
Fig. (3)) Bioenergy production by using microbes (algae) (modified from Baicha et al. [71]).Oleaginous microbes, for instance, microalgae, yeasts, and bacteria are also utilized as an alternative technique for biodiesel generation due to their characteristics like decreased land demand, small farming time, and also accumulation of greater amounts of lipids in their cells through utilizing organic carbon sources i.e. carbohydrates and organic acids [74]. Clostridium butyricum uses POME as a substrate produced H2 at a pH of 5.5 with an H2 amount of 3.2 L per liter of POME [75]. Anaerobic bacteria Clostridium paraputrificum significantly converted N-acetyl-D-glucosamine to H2 with an amount of hydrogen 2.2 mol H2/mol of GlcNAc [76]. Certain bacterial and fungal strains improve the formation of biogas by triggering the action of specific enzymes, for example, cellulolytic strains like Actinomycetes enhance biogas formation in the range of 8.4–44% [77].
CONCLUSION
Though invisible, the microorganisms are all around us, residing in every possible habitat, and have largely contributed to making the environment what it is today by helping in the evolutionary process of the rest of the organisms and transforming the primitive anoxygenic conditions on this planet. These earliest life forms continue to rule over us by causing serious disease outbreaks, spoiling a large number of economically important articles but at the same time also act as saviors by giving us provisions essential for sustaining life and preserving the environment. This particular arena dealing with applied part of microorganisms in our surroundings has helped in its elevation to a new discipline of environmental microbiology. Biotic and abiotic components of the ecosystem are in a way regulated by the activities of these microorganisms. Microbes interact among themselves and with other microorganisms in various manners and confer the environment with their beneficial and baneful services. Anthropogenic interventions have interfered with the ecosystem's natural harmony, giving rise to the problem of pollution in almost all the natural resources found in soil, air, and water. Over the years, environmental microbiology has become a science that shares its interfaces with a large number of specialties like agriculture, industries, and health and offers services that can rectify this imbalance in the environment. Bioremediation, biofertilizers, bioenergy, biofilms, and biological sewage treatment are some of the emerging and unique services which use microorganisms to preserve the environment and assist its other biotic inhabitants to lead a healthy and quality life.
CONSENT FOR PUBLICATION
Not applicable.
CONFLICT OF INTEREST
The author declares no conflict of interest, financial or otherwise.
ACKNOWLEDGEMENT
Declared none.
