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Chapter 18 : Adaptations of the Psychrotolerant Piezophile Photobacterium profundum Strain SS9
Category: Applied and Industrial Microbiology
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Strains of Photobacterium profundum and Shewanella violacea have become the work-horses for examining the adaptations of cold-adapted deep-sea microbes to high pressure. The chapter focuses on P. profundum, with an emphasis on strain SS9. Transposon mutagenesis, insertional mutagenesis, lacZ-based transcriptional reporter studies, allelic exchange, and complementation are all possible. SS9 is both the most psychrotolerant and the most piezophilic microorganism for which such studies have been reported. More recently its entire genome sequence has been determined, and transcriptome and comparative genomic analyses have been undertaken. The sections describe the roles of the membrane, membrane-associated signaling systems, and DNA recombination in SS9 piezoadaptation, and provide recent insights obtained from the SS9 genome sequence and functional and comparative genomics. Advances in genomic approaches have dramatically altered the understanding of the evolution, diversity, biochemistry, and physiology of life. These technologies have also been applied to two piezophiles: P. profundum strain SS9 and Shewanella violaceae strain DSS12, and additional sequencing projects are in the works. Genetic manipulations are needed to establish which genes actually influence growth ability at high pressure. Additional important issues are which piezophile-specific genes were acquired by horizontal gene transfer (HGT) and which were lost by the mesophilic strain 3TCK, which genes 3TCK might have needed to acquire for adaptation to shallow-water and atmospheric pressure, and whether the last common ancestor to the P. profundum strains was piezophilic or mesophilic.
NanoOrange fluorescent image of a P. profundum strain SS9 cell from a culture grown at 30 MPa. The body of the cell is approximately 2.5 µm in length. A single unsheathed polar flagellum is present.
Locations in which P. profundum isolates have been reported ( 14 , 21 , 23 , 75 , 82 ). Stars indicate eastern Antarctica, the northwestern Pacific Ocean, the Peru Margin, the Ryukyu Trench, the San Diego Bay, and the Sulu Sea.
Many membrane components could be important for integrity and function at high pressure. Shown in schematic format is the outer membrane of a gram-negative bacterial cell. The outer leaflet is composed of LPS with its lipid A (vertical lines, some with branches), core oligosaccharide (horizontal oval), and O-antigen polysaccharide (wavy line) regions. The inner leaflet contains phospholipids containing head groups (shown as open circles) attached to different types of fatty acids at their sn-1 and sn-2 positions. Straight lines are used to depict saturated fatty acids, lines with one bend are used to depict MUFAs such as cis-vaccenic acid, and lines with multiple bends are used to depict the PUFA EPA. A porin protein is shown spanning the entire outer membrane. Lipoprotein is shown connecting the outer membrane to the cell wall below. Phospholipid composition is also important for inner membrane function (not shown). Many lipid-protein interactions, and thus many essential cellular processes, could be subject to strong influences by pressure.