Adaptations of cold- and pressure-loving bacteria to the deep-sea environment: cell envelope and flagella

Compared to terrestrial environments our knowledge of microorganisms inhabiting oceans, the largest ecosystem on Earth, is limited. Deep oceans contain bacteria that thrive at high pressure and low temperature. For them, as for all bacteria, the outer structures of the cell are the first point of contact with the environment, both sensing and being modified in response to it. The vast majority of studied cold- and pressure-loving bacteria are Gram-negative and so in this chapter, the adaptations of their cell envelope and flagella are presented. In deep-sea bacteria, the structure of phospholipids and lipopolysaccharides is modified in order to maintain membrane fluidity and enable membrane-localised proteins to perform their functions. Many of the membrane proteins involved in nutrient acquisition, transport, respiration, sensing and signalling are also specifically adapted to function at high pressure and low temperature. The ability to move towards nutrients or away from hostile environment is extremely important for bacterial survival and yet very vulnerable to increased pressure. Deep-sea bacteria are capable of swimming even at 150 MPa, which suggests their motility systems are specifically adapted to high pressure. Moreover, some bacteria have been shown to produce a second type of flagella (lateral flagella) in response to high pressure or low temperature. The findings presented in this chapter are a result of many techniques and analyses applied to whole microbial communities, single species as well as particular genes and proteins. Investigation of the adaptations to high pressure and low temperature not only expands basic knowledge but also identifies targets that could have biotechnological and industrial application. Deep-sea bacteria could be used for production of biofuels, secondary metabolites of value for drug development, and various pressure and temperature adapted enzymes.