Preface

Extremophiles are nature’s ultimate survivors, thriving in environments ranging from the frozen Antarctic to abyssal hot hydrothermal vents. Interestingly, the discovery of several habitats/environments, resembling that of outer space, on the surface of Earth, and the discovery of organisms that thrive in such extreme environments have given many of the clues to find ‘life’ outside the Earth’s environment. Though life is believed to be originated amidst high temperature, highly reducing and acidic conditions of early Earth, many of these sites on the surface of our planet have been explored only recently, which contain environmental extremes that were unimaginable to our forefathers. The organisms that survive and grow under such harsh environmental conditions, which are uninhabitable to other organisms, are called extremophiles.

High-temperature environments occur in terrestrial hot springs and marine hydrothermal vents where the temperature could reach 100°C to 350°C. Several thermophilic (optima between 55°C and 65°C) and hyperthermophilic (optima between 80°C and 113°C) bacteria and archaea have been isolated that can grow optimally at temperatures above the boiling point of water. Psychrophiles on the other hand can grow optimally below the freezing point of water. Bacteria, like Deinococcus radiodurans is one of the most radiation-resistant organisms known and is capable of withstanding acute doses of gamma radiation. Environments with extreme atmospheric pressure, for example, deepest sea floor environments (e.g., Mariana trench, 10,898m deep), having a pressure of almost 1200 atm, harbor barophilic/piezophilic microbial community. Xerophiles can tolerate extreme desiccation by entering anhydrobiosis, a state characterized by little intracellular water and no metabolic activity. A number of gram-positive bacteria can form a special resistant, dormant structure called an endospore. These structures are extraordinarily resistant to environmental stresses such as desiccation, heat, ultraviolet radiation, gamma radiation, chemical disinfectants, etc. Environments, like the Dead Sea (a salt lake between Israel and Jordan and the lowest lake in the world) and the Great Salt Lake in Utah, despite having saturated salt (NaCl) concentrations, holds extreme halophiles, like Halobacterium salinarum which can grow at a salt concentration of 6.2 M. Highly acidic environments, like Rio Tinto river in Spain which has a pH of 1 to 2, and Danakil depression in Ethiopia which has a pH of 0, harbor acidophiles (e.g. Sulfolobus acidocaldarius , Ferroplasma acidarmanus and Picrophilus oshimae) which have their growth optimum of pH 0 or closer to it. Bacillus alcalophilus, and Microcystis aeruginosa on the other hand inhabit natural alkaline soda lakes where pH can reach about 12.0. There are a number of anaerobic bacteria and archaea that can live in complete anoxic environments by using terminal electron acceptors other than oxygen. Some microorganisms, called poly-extremophiles, are adapted to multiple environmental extremities. Thus far hundreds of phylogenetically diverse extremophiles have been isolated or identified from diverse environmental extremes.

In the last few decades, the research on extremophiles has not only provided ground-breaking discoveries that challenge our understanding of biochemistry and molecular biology but also has boosted the biotech industry to search for new products from them. On the applied side, extremophiles and their enzymes have spawned a multibillion-dollar biotechnology industry, with applications spanning biomedical, pharmaceutical, industrial, environmental, and agricultural sectors. The mechanism of adaptation to such environments by the extremophiles has also been well studied in the last few decades. Thus, the book aims to provide the most comprehensive and reliable current state of knowledge on the diversity of extremophiles along with the descriptions of the environments from which they have been isolated, mechanisms of their adaptation to such harsh environments, their applications in human welfare, and future scope. Indeed, the application of extremophiles and their biologically active compounds has opened a new era in biotechnology. However, despite the latest advances, we are just at the beginning of exploring the biotechnological potentials of extremophiles.

This book consists of fourteen chapters that explore the fascinating world of microbes in extreme environments. The first chapter deals with the overview of extremophiles and their strategies of adaptations in extreme environments. The rest of the chapters of the book cover the details including recent scientific information and future prospects of all types of extremophiles, including hyperthermophiles, psychrophiles, halophiles, acidophiles, alkaliphiles, xerophiles, chemolithotrophs, oligotrophs and anaerobic and other extremophiles. Each chapter is organized in such a way to cater to the knowledge of extremophiles (underrated fascinating microbes) including diversity, adaptations, and applications to the scientific community.

This book provides an overview of the current state of knowledge and all major developments in research of all types of the fascinating group of life-forms i.e., extremophiles. This book is an essential read for microbiologists working with extremophiles and their potential biotechnological applications, as well as for all budding microbiologists. The book is also recommended as a reference text for anyone interested in the field of research encouraging readers to reach out to new worlds and discoveries.

Finally, we express our gratitude to Professor Ramesh Kumar Pandey, Vice-Chancellor, Usha Martin University, Ranchi, Jharkhand, India, who has always been an inspirational persona to the young scientific community. With his profound knowledge on the subject, he prudently intuited the importance of the work and kindly wrote the foreword of this edited book. We are also grateful to Prof. Mahammad Ali, Vice Chancellor, Aliah University, Kolkata, India, for providing all necessary facilities and a conducive academic ambience ensuring smooth completion of the book. We are extremely grateful to Fr. Dr. Lalit P Tirkey, Principal, North Bengal St. Xavier’s College, West Bengal, India, for his enthusiastic support and encouragement in the completion of the project. We are also thankful to all authors for their hard work and professionalism in making this book a reality. Their expertise in the contributed chapters is acknowledged and appreciated. Our appreciation and credit go to Mrs. Humaira Hashmi, Editorial Manager Publications, Bentham Books for generous assistance, constant support, and patience in materializing the book. Lastly, we thank everybody who helped us in the successful realization of this book and express our apology that their names could not be mentioned personally.