Isolation, Cultivation, and Diversity of Deep-Sea Piezophiles

Abstract

This chapter focuses on the isolation, taxonomy, and diversity of piezophilic microorganisms and their habitats. Based upon several studies the authors have indicated that cultivated psychrophilic and piezophilic deep-sea bacteria could be affiliated with one of five genera within the Gammaproteobacteria subgroup: Shewanella, Photobacterium, Colwellia, Moritella, and Psychromonas, which was formally classified as ‘’an unidentified genus’’. The chapter describes taxonomic features of the piezophilic genera. For handling piezophiles for further study, JAMSTEC developed a deep-sea baropiezophile and thermophile isolation and cultivation system, referred to as the DEEPBATH system. The DEEPBATH system consists of four separate devices: (1) a pressure-retaining sampling device, (2) a dilution device under pressure conditions, (3) an isolation device, and (4) a cultivation device. From the analyses of 16S rRNA gene sequences after cultivation at 65 MPa, two groups of the bacterial genera Shewanella and Moritella were identified. The authors have analyzed the microbial community structures by the terminal restriction fragment length polymorphism for the bacterial 16S rRNA gene and determined that the community is drastically changed at different pressure conditions of cultivation using the DEEPBATH system. Piezophiles are characterized by high levels of unsaturated fatty acids in their cell membrane layers, but long-chain polyunsaturated fatty acid (PUFA) like EPA and DHA are not necessarily required for high-pressure growth. The diversity of piezophilic bacteria is closely linked with the global deep-sea ocean circulation, but some of the closed oceans, like the Japan Sea, also contain piezophilic bacteria taxonomically similar to deep-sea microbes in the open oceans.