Molecular and Cellular Mechanisms Underlying the Microbial Survival Strategies: Insights into Temperature and Nitrogen Adaptations

Bacteria inhabit almost all ecological niches, including harsh environments of desert, oceans, hypersaline, volcanic and thermal biospheres, representing therefore one of the quantitatively most abundant organisms on earth. To survive under such a variety of ecological habitats, bacteria developed a number of strategies to rapidly adapt and respond to environmental changes by tuning down their metabolic activities, thus overcoming periods of unfavorable growth conditions. Generally, the processes of entering into and exiting from the metabolic stand-by mode are tightly regulated and characterized by a series of signaling events involving various secondary messenger molecules, signaling proteins, and regulatory RNAs. For example, the availability of nitrogen is highly variable in nature and, hence, considered as the limiting factor of microbial growth and development. Therefore, the nitrogen assimilation reactions require a tight regulation and a constant sensing of the quantity and quality of the available nitrogen. Temperature sensing is also essential for microbial survival. Consistently, microbes have developed diverse molecular strategies to sense temperature fluctuations and readjust their metabolism to survive and resume growth at a different temperature. In this chapter, we summarize the recent advances in our understanding of the microbial adaptation strategies toward environmental changes, specifically those related to temperature fluctuations and changes in nitrogen availability.