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 ؋ 10 6 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 m in length and 0.59 m 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.High hydrostatic pressure is one of the most unique physical parameters in deep-ocean environments and plays a significant, albeit underappreciated, role in the distribution of life in the biosphere. The effects of high hydrostatic pressure on microbial physiology are pervasive, with influences ranging from macromolecular structures to diverse cellular processes such as cell division and motility (8).Studies of microbial assemblages from the abyssal (4,000 m to 6,000 m) and hadopelagic (Ͼ6,000 m) environments are riddled with methodological issues, including but not limited to (i) difficulty and expense of sample collection, (ii) bulk seawater collection that mechanically disrupts delicate colloidal and particulate microenvironments, and (iii) specialized high-pressure equipment to maintain samples at in situ pressure and temperature once shipboard (6, 51, 89). Intrinsic biological factors similarly compound the complications of sampling from depth, the most challenging of which is the mixing of allochthonous microbial members from the overlying surface seawater derived from the vertical transport of aggregated material.These "hitchhiking" microorganisms, which are not adapted to the prevailing conditions of the deep, render taxonomic cataloguing and diversity estimates o...

Resource quality affects carbon cycling in deep-sea sediments

“…This results in reduced BGE when growth is constrained by factors such as temperature and nutrient supply, rather than organic carbon (energy) (del Giorgio and Cole, 1998). Previous studies have demonstrated that the growth of barophilic bacteria isolated from depths X3584 m is affected by temperature, pressure and substrate supply (Yayanos, 1986;Wirsen and Molyneaux, 1999;Eloe et al, 2011), with the production of new biomass declining rapidly as temperatures drop below 0 1C (Yayanos, 1986). Experiments conducted on barotolerant microbial communities from much shallower (p2003 m), Arctic sediments have demonstrated that the effects of labile substrate supply on bacterial catabolic activities predominate over those of temperature, salinity and pressure (MeyerReil and Kö ster, 1992;Arnosti et al, 1998).…”

Evolutionary Ecology of the Marine Roseobacter Clade

“…Clade members are ubiquitous in temperate and polar oceans (30); the latter include sea ice habitats, in which Roseobacter is a major bacterial phylotype (31,32). Roseobacters are also abundant in coastal sediments (33), deep pelagic ocean (34), and deep-sea sediments (35).…”

Bacterial Diversity of the Deep Sea of Sangihe Talaud, Sulawesi

“…Rhodobacterales bacterium belonging to the class of α-proteobacteria that is known living in a low temperature and high pressure (Psychropiezophiles) were f ound in site II, while Aphanothece sp. (Chroococcales class) which are able to live in high salinity (halophiles) were found in site I (Sarma & Arora, 2001;Eloe et al, 2011). There were types of Roseovarius sp.…”