Microorganisms and Their Metabolic Capabilities in the Context of the Biogeochemical Nitrogen Cycle at Extreme Environments.

Rosa María Martínez-Espinosa

doi:10.3390/ijms21124228

Abstract

Extreme microorganisms (extremophile) are organisms that inhabit environments characterized by inhospitable parameters for most live beings (extreme temperatures and pH values, high or low ionic strength, pressure, or scarcity of nutrients). To grow optimally under these conditions, extremophiles have evolved molecular adaptations affecting their physiology, metabolism, cell signaling, etc. Due to their peculiarities in terms of physiology and metabolism, they have become good models for (i) understanding the limits of life on Earth, (ii) exploring the possible existence of extraterrestrial life (Astrobiology), or (iii) to look for potential applications in biotechnology. Recent research has revealed that extremophilic microbes play key roles in all biogeochemical cycles on Earth. Nitrogen cycle (N-cycle) is one of the most important biogeochemical cycles in nature; thanks to it, nitrogen is converted into multiple chemical forms, which circulate among atmospheric, terrestrial and aquatic ecosystems. This review summarizes recent knowledge on the role of extreme microorganisms in the N-cycle in extremophilic ecosystems, with special emphasis on members of the Archaea domain. Potential implications of these microbes in global warming and nitrogen balance, as well as their biotechnological applications are also discussed.

Highlights

Extreme microorganisms, called “extremophiles” (from Latin extremus meaning “extreme” and Greek philia meaning “love”) are organisms that thrive in physically or geochemically extreme conditions that are usually detrimental to most life on Earth [1,2]
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Considering that Nitrogen cycle (N-cycle) pathways are mainly driven by microorganisms, more efforts must be made to understand their physiology and metabolism as well as their ecological relevance to modulate N:P:K balances and the interconversion of nitrogenous compounds in extreme ecosystems

Summary

Introduction

Called “extremophiles” (from Latin extremus meaning “extreme” and Greek philia (φιλια) meaning “love”) are organisms that thrive in physically or geochemically extreme conditions that are usually detrimental to most life on Earth [1,2]. (ii) Exploring the possible existence of extraterrestrial life (Astrobiology) Extremophiles, especially those thriving under multiple extremes, are good model organisms to carry out research in multiple disciplines, spanning areas such as the study of adaptations to harsh conditions, to the biogeochemical cycling of elements. The contribution of microorganisms at a global scale in the interchange between nitrogen forms is relevant and considering that extreme habitats are mostly occupied by extremophilic microbes, it is possible to assume that they could play relevant roles catalyzing reactions of the N-cycle in several extreme ecosystems, such as salty environments, soda lakes, mine sites, hot springs, volcano, etc. Some of the main applications of N-cycle reactions carried out by extremophilic archaea are discussed

Classification of Extreme Microorganisms

General Overview of the Role of Microorganisms in N-Cycle

Wastewater Treatments and Bioremediation

Environmental Studies

N-Cycle Enzymes

Conclusions