title: Isolation and characterization of a psychropiezophilic alphaproteobacterium.
abstract: Cultivated psychropiezophilic (low-temperature- and high-pressure-adapted) bacteria are currently restricted to phylogenetically narrow groupings capable of growth under nutrient-replete conditions, limiting current knowledge of the extant functional attributes and evolutionary constraints of diverse microorganisms inhabiting the cold, deep ocean. This study documents the isolation of a deep-sea bacterium following dilution-to-extinction cultivation using a natural seawater medium at high hydrostatic pressure and low temperature. To our knowledge, this isolate, designated PRT1, is the slowest-growing (minimal doubling time, 36 h) and lowest cell density-producing (maximal densities of 5.0 × 10⁶ cells ml⁻¹) piezophile yet obtained. Optimal growth was at 80 MPa, correlating with the depth of capture (8,350 m), and 10°C, with average cell sizes of 1.46 μm in length and 0.59 μm in width. Through detailed growth studies, we provide further evidence for the temperature-pressure dependence of the growth rate for deep-ocean bacteria. PRT1 was phylogenetically placed within the Roseobacter clade, a bacterial lineage known for widespread geographic distribution and assorted lifestyle strategies in the marine environment. Additionally, the gene transfer agent (GTA) g5 capsid protein gene was amplified from PRT1, indicating a potential mechanism for increased genetic diversification through horizontal gene transfer within the hadopelagic environment. This study provides a phylogenetically novel isolate for future investigations of high-pressure adaptation, expands the known physiological traits of cultivated members of the Roseobacter lineage, and demonstrates the feasibility of cultivating novel microbial members from the deep ocean using natural seawater.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0202, USA.
authors.forename: Emiley A
authors.initials: EA
authors.lastname: Eloe
authors.forename: Francesca
authors.initials: F
authors.lastname: Malfatti
authors.forename: Jennifer
authors.initials: J
authors.lastname: Gutierrez
authors.forename: Kevin
authors.initials: K
authors.lastname: Hardy
authors.forename: Wilford E
authors.initials: WE
authors.lastname: Schmidt
authors.forename: Kit
authors.initials: K
authors.lastname: Pogliano
authors.forename: Joe
authors.initials: J
authors.lastname: Pogliano
authors.forename: Farooq
authors.initials: F
authors.lastname: Azam
authors.forename: Douglas H
authors.initials: DH
authors.lastname: Bartlett
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D016000:Cluster Analysis; D003080:Cold Temperature; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D006874:Hydrostatic Pressure; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D041904:Roseobacter / Q000145:classification* / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S