Preface

The book “Role of Microbes and Microbiomes in Ecosystem Restoration” focuses on basic to advanced techniques in various roles of microbes and microbiomes in the abatement and restoration of polluted ecosystems, climate change, production of renewable energy sources, and waste management. It covers ecosystem sustainability, the UN decade of ecosystem restoration, efficient utilization of microbes and microbiomes and their role in socio-economic development, and the current status of polluted and degraded ecosystems.

Stepping into an unusual era of concurrent buffer leads to a shifting global climate. At the beginning of the twenty-first century, one of the active concerns in the human ecological background is the destruction of ecology and ecosystems. Human actions have evolved a remarkable power to affect the ecosystem. To address this developing issue, the science of restoration ecology and its applied practices provide a potentially cost-effective, buoyant answer. The notion of restoration has emerged as the dominant subject in the global environmental context. One of the most important goals of the UN Convention on Biological Diversity from 2011 to 2020 is to restore at least 15% of the world's damaged ecosystems. World leaders adopted the “Bonn Challenge” in 2011, which is a global commitment to rehabilitate 150 million hectares of deforested and damaged land by 2020. Most significantly, in 2015, the UN formalized these worldwide pledges by endorsing the 2030 Sustainable Development Goals, one of which focuses on ecological restoration. Microbes are ubiquitous, providing many critical services to the ecosystem, such as sustainable plant productivity and a stable environment for human life. They help to keep atmospheric CO₂ and nitrogen levels stable, which are now reduced due to greenhouse gases and other hazardous pollutants. On a global scale, microbial organisms are extremely strong. Bacteria create approximately 50% of total oxygen, 75% of added nitrogen to the atmosphere, and 92% of nitrogen removal from the environment. As a result, this book covers the potential of bacteria and microbiomes in many ecosystems.

In Chapter 1, Prasad et al. provide an overview of the causes of ecosystem destruction, the need for ecosystem restoration, the significance of microbiome in biomining, restoration of farm and degraded land, control of heavy metals, production of renewable energy, crop growth, biofertilizer production, mitigation of greenhouse gases, and waste management. It also encompasses the role of molecular techniques in ecosystem restoration and the challenges involved in adopting microbiomes for ecosystem restoration.

Microbes are the crucial living elements of soils that contribute to the sustainability of ecosystems because of their capacity for stress tolerance, vast effective genetic pool, ability to survive in various conditions, and capacity for catabolism. However, various factors like soil conditions, geographical and climatic factors, and soil stressors (drought, submersion, pollutants, and salinity) may result in distinct microbial composition and characteristics, as well as its mechanism to support ecosystem restoration and defense against all of these stressors. Hence, Pooja et al., in Chapter 2, deliver the vital edaphic (pH, temperature, oxygen, nutrients, and moisture), geographical, climatic (UV radiation, elevated CO₂, temperature, permafrost thaw), and abiotic factors (drought, submergence, salinity, pollutants) involved in the establishment of microbes and microbiome.

In Chapter 3, Sinduja et al. discuss the ecological role of microorganisms participating in biogeochemical cycles, hoping to delineate the role of microbes and microbiomes in biogeochemical cycles. Microorganisms play an essential role in moderating the Earth's biogeochemical cycles; nevertheless, despite our fast-increasing ability to investigate highly complex microbial communities and ecosystem processes, they remain unknown. Hence, this chapter covers the strategies for proper management of prevailing natural resources, considerations for management, its role in the biogeochemical cycle, and the influence of beneficial soil microbes, such as plant growth promoting rhizobacteria and cyanobacteria, on natural resource management, with special emphasis on the role of soil enzymes in nutrient cycling.

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. Besides, bioremediation is one of the most effective approaches for reducing environmental contaminants since it restores the damaged site to its original state. Hence, Chapter 4 by Poornima et al. provides a baseline on bioleaching, its types, microbes involved in bioleaching, bioleaching pathways, and the role of microbes in the bioremediation of polluted habitats.

In recent years, microbial-assisted bioremediation has emerged as a promising and eco-friendly alternative for HM remediation. This approach utilizes microorganisms to transform, immobilize, or detoxify HMs, making them less harmful and more accessible for removal. Hence, Naik et al., in Chapter 5, highlight the eco-friendly use of microorganisms, their mechanisms that contribute to the bioremediation of HMs, and their potential use in the future.

In Chapter 6, Sajish et al. present 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. Microbial fuel cell, a type of BES, is a budding technology that exploits the potential of electroactive microorganisms for extracellular electron transfer to generate electricity. Hence, this chapter encompasses the history of MFC, bio-electrochemically active microorganisms, electroactive microbial genera in microbial fuel cells, factors affecting the development of anode biofilm, biofilm engineering, and the recent advances in strain improvement for improved MFC performance.

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 will be sustainable. 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. Industrially important enzymes are capable of degrading long-chained biopolymers into short-chained monomeric sugars and fermenting them into energy-dense biomolecules. Hence, Chapter 7, authored by Oyelade et al., comprehensively 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.

In recent decades, biofertilizers have gained popularity as a viable alternative to unsafe chemical fertilizers in pursuing sustainable agriculture. They have an essential role in enhancing crop output and preserving long-term soil fertility, both of which are critical for fulfilling global food demand. Therefore, Chavada et al., in Chapter 8, deliver the various microbes involved in nitrogen fixing, phosphorus and potassium solubilizing and mobilizing, sulfur oxidizing, and zinc solubilizing. The role of arbuscular fungi and plant growth-promoting rhizobacteria in biofertilizer production is also discussed.

Knowingly or unknowingly, agricultural systems face stress and resource quality degradation and their depletion by the activities of humans. Abiotic stresses, such as nutrient deficiency, water logging, extreme cold, frost, heat, and drought, affect agricultural productivity. Similarly, biotic factors like insects, weeds, herbivores, pathogens, bacteria, viruses, fungi, parasites, algae, and other microbes also limit good-quality products. Thus, Vijayalakshmi et al. discuss the application of microbes and microbiomes in biotic and abiotic stress management in Chapter 9. This chapter especially discusses the adaptive mechanisms of salt tolerance in plants, tolerance to abiotic stress, the emerging microbiome in soil biota, and nanomaterials' efficacy on stress.

Microbes 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. Sethupathi et al., in Chapter 10, discuss the role of microbes and microbiomes in the emission of major greenhouse gases like CO₂, CH₄, N₂O, and NH₃. The potential of the microbiome in mitigating these greenhouse gases is also delivered in this chapter.

Given that there is potential for warmth to boost the release of carbon dioxide from dirt to the atmosphere due to better microbial disintegration of dirt raw material, the impact of environmental change on the soil carbon sink remains uncertain. If forecasted climate modification situations are precise, this boost in soil carbon loss might significantly worsen the dirt carbon cycle responses. Therefore, Chapter 11 by Al-Jawhari introduces us to the soil CO2 balance, environmental effects, and the significance of the soil carbon cycle and microbial decomposers, carbon cycle in soil, ocean, and ecosystem restoration under climate change perspective.

The generation of wastewater increases multi-fold because of industries and the overexploitation of freshwater resources. Wastewater treatment is always linked with waste recovery and its optimum utilization, which broadens the amplitude of wastewater treatment, enhancing the quality of the byproducts and as an efficient alternative for non-potable purposes. Microbiomes are crucial in biological wastewater treatment methods such as activated sludge, anaerobic digestion, and bioelectrochemical systems. The microbial population's activity and resilience in the microbiome significantly impact the performance and stability of these activities. Suganthi et al. present the biological wastewater treatment, growth and kinetics, and different microbial community types, including bacteria and fungus, actinomycetes, algae, plants, and the range of microbial wastewater treatment in Chapter 12.

Solid waste disposal is a significant issue that worsens daily as more people move into cities. In Chapter 13, Velusamy et al. provide the status of solid waste management in India, sources and types of solid wastes, various conventional solid waste management techniques, and the role of microbes in solid waste management through composting and anaerobic digestion.

Microorganisms are pervasive and genuinely make up the “unseen majority” in the marine environment. Although marine isolates have been the subject of laboratory-based culture methods for more than ten years, we still do not completely understand the ecology of marine microorganisms. Thus, in Chapter 14, Poornachandhra et al. explore 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. Hence, Chapter 15 by Haghani et al. is dedicated to enlightening us regarding the most critical features of microbial groups, including archaea, bacteria, algae, and fungi in mangroves and wetlands. Moreover, the biochemical transformations brought about by wetlands' microbial groups and the degree of complexity in microbial interactions are explained.

Jerome et al., in Chapter 16, articulate the significance of forest microbiomes in ecosystem restoration and sustainability. Generally, forest microorganisms are essential to how plants interact with the soil environment and are necessary to access critically limiting soil resources. This 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).

Employing field-based monitoring and restoration assessment techniques, surveying microbes or microbial populations is challenging or impossible. In contrast, it is now possible to precisely and quickly describe and quantify these diverse and functional taxonomic groups by sequencing large quantities of environmental DNA or RNA utilizing genomic and, in particular, meta-omic technologies. Hence, Nagendran et al., in Chapter 17, throw light on using meta-omics techniques to monitor and assess the outcomes of ecological restoration projects and to monitor and evaluate interactions between the various organisms that make up these networks, such as metabolic network mapping. An overview of functional gene editing with CRISPR/Cas technology to improve microbial bioremediation is also provided herewith.

Chapter 18 by Satpathy et al. provides details on metagenomic approaches like Multi-Locus Sequence Typing (MLST), MOTHUR, Quantitative Insight into Microbial Ecology (QIIME), and PHAge Communities From Contig Spectrum (PHACCS) in the restoration of the temperate and tropical ecosystem.

Soil microorganisms also play a fundamental role in ecosystem functioning and conserving plant diversity. Exploring voluminous beneficial microorganisms and promoting the reestablishing of those beneficial microbes in the soil will preserve Earth's diverse native plant populations. Hence, Prasad et al., in Chapter 19, delve into fundamental and conventional techniques and approaches that can be employed to maintain soil microbial populations. Furthermore, the chapter investigates the possibility of creating protocols for regulatory or commercial objectives, emphasizing the significance of ecological restoration by using bioinoculants or microbial colonies in degraded sites.

In Chapter 20, Shivakumar et al. examine the application of molecular methods to ecosystem regeneration. The various available molecular methods and how they have been applied to monitor ecosystem health, identify microbial communities in ecosystems, and comprehend interactions between microbes and plants are discussed. The chapter also discusses the application of molecular methods to the restoration of ecosystems that have been damaged, including the use of plant-microbe interactions to promote plant development in contaminated soils.

The sustainable industrial revolution is the way forward to help humankind to prolong its existence on Earth. John et al. enlighten us with the role of the microbiome in a sustainable industrial production system. In Chapter 21, they disclose the energy sector's current status, microbes' role in organic and amino acid production, and the role of microalgae in sustainable agriculture.

The human microbiome plays a vital role in human development, immunity, and nutrition, where beneficial bacteria establish themselves as colonizers rather than destructive invaders. In Chapter 22, Pradyutha et al. introduce microbes' role in human and animal health security. The various human and animal diseases and the potential of microbiota, such as probiotics, in disease treatment are also discussed in this chapter.