Life on Earth is possible due to the vital elements and energy transformations referred as biogeochemical cycle. Microorganisms play an essential role in moderating the Earth's biogeochemical cycles; nevertheless, despite our fastincreasing ability to investigate highly complex microbial communities and ecosystem processes, they remain unknown. Microbes are crucial in nutrient cycling and energy transfers between ecosystems and the tropics, but research on their intricate functions is still restricted due to technological inabilities. A better understanding of microbial communities based on ecological principles may improve our ability to predict ecosystem process rates using environmental variables and microbial physiology. We explored the ecological role of microorganisms participating in biogeochemical cycles, hoping to delineate the role of microbes and microbiomes in biogeochemical cycles. Insights into these aspects can help us mitigate the effects of climate change and other future uncertainties by regulating the microbial-dependent biogeochemical cycle.

In an environmental degradation era, improving microbial activity in sustainable mining and pollutant removal has become necessary for the green economy's future. Bioleaching (microbial leaching) is being studied intensively for metal extraction since it is a cost-effective and environmentally benign technique. Bioleaching with acidophiles involves the production of ferric (Fe III) and sulfuric acid. Cyanogenic microorganisms, in particular, can extract metal(s) by creating hydrogen cyanide. Furthermore, environmental degradation and its rehabilitation are serious issues worldwide. Hydrocarbons, pesticides, heavy metals, dyes, and other contaminants are the principal factors significantly degrading the environment. Residual pollutants might also be challenging to remove. Bioremediation is one of the most effective approaches for reducing environmental contaminants since it restores the damaged site to its original state. So yet, only a tiny number of microorganisms (culturable bacteria) have been used, leaving a vast amount of microbial diversity undiscovered. Various bioremediation approaches, such as chemotaxis, bioaugmentation, biostimulation, genetically engineered microbes, biofilm formation, and advanced omics, have been widely used to improve the microbe’s metabolic activity, degradation potential of persistent pollutants and restoration of polluted habitats. Microorganisms contribute to the rehabilitation of polluted ecosystems by cleaning up trash in an ecologically friendly way and producing harmless products. This chapter addresses the critical processes in improving bioremediation and current breakthroughs in bioremediation, including bacteria and plants.

Over the recent decades, there has been a tremendous need to develop alternative, sustainable, clean, and renewable energy resources. This demand is attributed to the exhaustion of fossil fuel reserves and the associated economic risks, the impact of fossil fuel use on the environment, and the associated global warming. Bioelectrochemical systems (BES), which use biological entities to generate electricity, are promising alternative clean renewable energy. Microbial fuel cell (MFC), a type of BES, exploits the potential of electro-active microorganisms for extracellular electron transfer to generate electricity. In an MFC, microbes oxidize the organic substrates fed into the anode chamber into electrons, protons, and CO2 . The electrons flow through the connected external load/circuit towards the cathode, creating the potential difference across the electrode and subsequent current output. A terminal electron acceptor at the cathode accepts the electrons and protons. In addition to electricity generation, MFC has extended applications in wastewater treatment, heavy metal remediation, bioremediation of environmental pollutants, biosensors for monitoring the environment, etc. This chapter will help understand the basic principle of an MFC and the role of microbes in a microbial fuel cell, genetic engineering, biofilm engineering approaches, and electrode engineering approaches for increasing the overall efficiency of an MFC for its practical implementation.

Energy crises resulting from the depletion of petroleum resources, hikes in the price of fossil fuel, and unpredictable climate change are some of the recent concerns that have provoked serious research on alternative energy sources that would be sustainable. This book chapter reviews how sustainable bioenergy production through microbes using feedstocks can provide clean and green energy that can consequently facilitate ecosystem restoration. Feedstocks are pivotal to this biotechnological process. Microbes are also equally very vital. Therefore, changing from fossil fuel to bioenergy resource options is essential. Energy transition can, therefore, create emerging opportunities in bioenergy rendering and bioeconomy that will result in the possible use of clean and green energy. In this regard, biofuels are a straightforward substitute for fossil fuels. Renewable feedstocks are suitable ingredients that sustainably produce biofuels using microbial-based bioconversion processes. Microorganisms can massively secrete industrially important enzymes capable of degrading long-chained biopolymers into short-chained monomeric sugars and fermenting them into energy-dense biomolecules. Microbes play a crucial role in the sustainable generation of biofuels and bioenergy. Bioenergy research is, therefore, crucial for a nation's economic stability and energy security. Additionally, reducing greenhouse gas emissions while promoting the use of renewable energies and the creation of livelihoods aids in the worldwide effort. Anthropogenic activities are highly reduced, thereby enhancing ecosystem restoration.

Microbes are crucial for the survival of life on Earth as they affect the major biogeochemical cycles that make our planet congenial for life, providing essential elements like carbon and nitrogen in required forms and quantities. Microbes also play a significant role as either generators or consumers of greenhouse gases, such as carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2O), through various processes in our environment. The distribution of these chemicals on the Earth and in the atmosphere is severely reliant on the equilibrium of these microbial progressions. The consumption of GHGs by microbes is facilitated through their use as substrates in processes like photo/chemoautotrophy, methanotrophy, and nitrous oxide reduction. The CO2 emitted from the organic matter decomposition and terrestrial respiration is subsequently subjected to photosynthetic fixation partially and is mitigated through carbon sequestration into soil and biomass. The biogenic release of methane through the biological anaerobic decomposition of organic materials by methanogens constitutes an important source of atmospheric CH4, while methanotrophs, through CH4 oxidation, facilitate methane emission mitigation. The microbial nitrification denitrification processes are the significant source of N2O emission, while the N2Oreducing bacteria are responsible for decreasing N2O emissions via nitrous oxide reduction enzymatic processes. The complexity of the interactions between these microbes with neighboring biotic and bacterial variables in order to regulate Earth's greenhouse gas emissions is a factor that affects their activity. Hence, interdisciplinary approaches, including microbial ecology, environmental genomics, soil and plant sciences, etc., should be concentrated on mitigating greenhouse gases.

The most significant threat to civilization is climate change. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the three predominant greenhouse gases generated and utilized by microbes. Certain bacteria can induce diseases in humans, animals, and plants, exacerbating climate change. When conditions allow, microbes that utilize light- or chemoautotrophic activities (such as cyanobacteria and algae) and methanotrophic processes (which oxidize CH4) and those that reduce N2O can also metabolize these three gases (denitrifies). The production or consumption of these gases by bacteria is contingent upon their environment and interactions, which humans frequently modify. At times, we can manipulate environmental variables to enhance the microbial degradation of these gasses. According to a recent Intergovernmental Panel on Climate Change (IPCC) study, 3.3 billion individuals globally are subjected to environmental change. At the same time, unsustainable growth patterns exacerbate ecological and human vulnerability to environmental hazards. As individuals, societal change agents, and microbiologists with expertise, we may assist in identifying methods to reverse the prevailing tendency. This chapter argues that understanding both the direct and indirect effects of climate change on microorganisms is essential to evaluate their potential positive and negative impacts on land-atmosphere carbon exchange and global warming. Furthermore, we suggest that this encompasses examining the complex interactions and feedback mechanisms that emerge during communication among microorganisms, plants, and their physical environment within the climate change framework. Furthermore, the influence of further global changes may exacerbate the effects of the environment on soil bacteria

Marine environments are among the most unfavorable due to salinity, pH, sea surface temperature, wind patterns, ocean currents, and precipitation regimes. Due to the frequent changes in environmental conditions, the microorganisms that live there are better suited to adjusting to unfavorable conditions, which is why they have complex characteristic qualities of adaptation. Consequently, by forming biofilms and producing extracellular polymeric substances, the microorganisms isolated from marine habitats are intended to be better exploited in the bioremediation of soils and water bodies contaminated with toxic pollutants. Many marine bacteria have also been reported to produce bioactive compounds, which found their use in many biotechnological applications. This chapter explores marine microbial diversity, its utilization in bioremediation, and understanding their role in ecosystem sustainability.

Mangroves and wetlands are critical intermediary ecosystems between terrestrial and marine environments. These ecosystems offer a wide range of invaluable ecological and economic services. However, under the influence of natural and anthropogenic threats, mangroves and wetlands face rapid degradation. Microbes and microbiomes are integral components of a mangrove, playing key roles in the stability of the ecosystem. The present chapter compiles a comprehensive review of the classification and the role of microorganisms in the sustainability of mangrove and wetland ecosystems. The chapter discusses the most critical features of microbial groups, including archaea, bacteria, algae, and fungi in mangroves and wetlands. Bacterial groups under discussion consist of sulfur-related bacteria, nitrogen-related bacteria, phosphate-solubilizing bacteria, and photosynthetic bacteria. A separate section is dedicated to periphytic communities encompassing a microhabitat involving various prokaryotic and eukaryotic microorganisms. Moreover, biochemical transformations brought about by wetlands' microbial groups are explained. In addition, the following chapter emphasizes the degree of complexity in microbial interactions and draws attention to how alterations to these interactions ultimately impact ecosystems' health status. Furthermore, the role of wetland microorganisms in processes, such as detoxification, bioremediation, methanogenesis, carbon sequestration, nutrient cycling and transformations, and primary production is articulated.

A forest is a large area of land covered with big trees of different species, approximately covering one-third of the Earth's surface. Forest ecosystems are more than what can be seen physically (aboveground); below the ground level, they are extraordinarily diverse and have unique communities of microbiomes with a large population of bacteria and fungi species. These microorganisms are essential to how plants interact with the soil environment and are necessary to access critically limiting soil resources. This book chapter focuses on the ecosystems below and above ground level of a forest microbiome, including the soil microorganisms, their importance, and the diverse interrelationships among soil microorganisms (parasitism, mutualism, commensalism). The aboveground part of a plant is known as the phyllosphere, harboring diverse microorganisms, such as viruses, bacteria, filamentous fungi, yeast, algae, and rarely protozoa and nematodes with a role in disease resistance that is critical to plant health and development. The rhizosphere is the soil region immediately adjacent to and affected by plant roots where plants, soil, microorganisms, nutrients, and water meet and interact. In this region, plants and microbes coordinate and show a symbiotic relationship by fulfilling each other's nutrient requirements, roles, and functions. The endosphere is the plant interior and is colonized by endophytes, and their functions range from mutualism to pathogenicity. Archaebacteria, anaerobic bacteria, aerobic prokaryotes, fungi, and viruses exist as forest biomes. Examples of fungi include Trichoderma harzianum and obligate parasites Puccinia striiformis and Gremmeniella abietina. Plants, fungal endophytes, mycoviruses, and the environment all participate in a four-way interactive system.

The sustainable industrial revolution is the way forward to help humankind prolong its existence on Earth. The first step could be facilitating the natural process under a controlled environment to produce the desired products instead of chemicals. The industrial sectors, especially food and pharmaceuticals, depend on microbes for most of their production. Biocontrol, enzyme, and fuel production have been explored in recent years. Microbial production systems encompass the metabolites produced by bacteria, fungi, or viruses that facilitate industrial processes. These secondary metabolites have been noted to pose implications in many fields, including agriculture. After the advent of modern genetic engineering techniques, the utilization of microbiota in various activities is increasing due to their simplicity and costeffectiveness. The gene mounting and biotechnological tolls have aided in manipulating these microbes' secondary metabolites, thereby improving productivity. Furthermore, multi-disciplinary and comprehensive approaches directed towards improving microbial production are described in this chapter. 

Most of the various categories of bacteria and fungi that comprise the human microbiota are primarily incapable of causing diseases. Human beings and animal microbiomes can influence their health and homeostasis through the synthesis of necessary nutrients and vitamins, metabolism of drugs, guarding against pathogenic microbes, additional production of bile acids from the host, immune response, vulnerability to illness, and consistent behavior change. Animal species harbor distinctive microbiomes and possess greater complexity compared to the human microbiome. Living organisms are somewhat exposed to microbes in the newborn stage, at the time of delivery from the birth passage or vagina, and through breastfeeding. The kind of microbes the infant carries relies exclusively on the species seen in the mother. Further, changes in the microbiota of animals and humans depend on exposure to the environment and type of diet. This change can help benefit the health of the host or put one at a more significant chance for disease. This transformation of the microbiome in earlier life holds possible health importance to developing the immune system, influencing health effects including gastroenteritis, asthma, hay fever (allergic rhinitis), and chronic illnesses like diabetes. In addition to the genes of the family, surroundings, medication use, and diet greatly determine what microbiota is present in animals and humans. All of these aspects construct a particular microbiome from individual to individual. An adult living being is colonized by multiple species of bacteria. The total biomass of these microorganisms is typically estimated at around 0.2 kg in adults. The microbiomes present in human and animal bodies serve several functions. They contribute to the breakdown of food, allowing for the digestion of complex carbohydrates, fiber, and other substances that our bodies cannot process alone. Additionally, these microbiomes produce essential nutrients that are made available to us. They also play a vital role in neutralizing toxins or harmful compounds, promoting detoxification, and safeguarding our well-being. Using microorganisms in therapies is one of the clinical revolutions in the 21st century. Numerous research studies have revealed the crucial functions of microbes and microbiomes in human and animal health security.