Isolation and Characterization of Novel Psychrophilic, Neutrophilic, Fe-Oxidizing, Chemolithoautotrophic α- and γ- Proteobacteria from the Deep Sea

Abstract

We report the isolation and physiological characterization of novel, psychrophilic, iron-oxidizing bacteria (FeOB) from low-temperature weathering habitats in the vicinity of the Juan de Fuca deep-sea hydrothermal area. The FeOB were cultured from the surfaces of weathered rock and metalliferous sediments. They are capable of growth on a variety of natural and synthetic solid rock and mineral substrates, such as pyrite (FeS 2 ), basalt glass (ϳ10 wt% FeO), and siderite (FeCO 3 ), as their sole energy source, as well as numerous aqueous Fe substrates. Growth temperature characteristics correspond to the in situ environmental conditions of sample origin; the FeOB grow optimally at 3 to 10°C and at generation times ranging from 57 to 74 h. They are obligate chemolithoautotrophs and grow optimally under microaerobic conditions in the presence of an oxygen gradient or anaerobically in the presence of nitrate. None of the strains are capable of using any organic or alternate inorganic substrates tested. The bacteria are phylogenetically diverse and have no close Fe-oxidizing or autotrophic relatives represented in pure culture. One group of isolates are ␥-Proteobacteria most closely related to the heterotrophic bacterium Marinobacter aquaeolei (87 to 94% sequence similarity). A second group of isolates are ␣-Proteobacteria most closely related to the deep-sea heterotrophic bacterium Hyphomonas jannaschiana (81 to 89% sequence similarity). This study provides further evidence for the evolutionarily widespread capacity for Fe oxidation among bacteria and suggests that FeOB may play an unrecognized geomicrobiological role in rock weathering in the deep sea.In the deep-sea environment, hydrothermal habitats are recognized as sites that harbor unique biological ecosystems that are underpinned by chemosynthetic microbial primary production (22, 26). These prokaryotes derive energy from oxidation of reduced chemicals emanating from these sites (e.g., hydrogen sulfide [H 2 S]) and fix ambient CO 2 for cellular organic carbon needs. However, not all reduced chemicals released at these sites are available for immediate conversion to biomass. Rather, the interaction between geothermally heated fluids and cold seawater results in the precipitation of massive mineral deposits, primarily metal sulfides (40). Sulfides occur as chimney structures, brecciated rubble, particulate material (black smoke), and metalliferous sediment formed by settling particles. These deposits are composed of minerals such as pyrite (FeS 2 ), chalcopyrite (CuFeS 2 ), sphalerite (ZnS), marcasite (FeS 2 ), and pyrrhotite (FeS). At circumneutral pH in the presence of O 2 (and other suitable oxidants, e.g., Fe 3ϩ ), these minerals will oxidize abiogenically (33-35). Similar to the oxidation of reduced aqueous chemical species, oxidation of these minerals releases energy, which if mediated or catalyzed by microorganisms can be harnessed for cellular processes.On a quantitative basis, sulfide and sulfur oxidation may account for a large portion of the geochemic...

Potential for Microscale Bacterial Fe Redox Cycling at the Aerobic-Anaerobic Interface

“…Recent enrichment and isolation studies with Fe(II)-O 2 opposing gradient systems (Kucera and Wolfe 1957;Jones 1983) have expanded the range of organisms known to be involved in aerobic circumneutral Fe(II) oxidation beyond the traditional stalk-forming Gallionella and sheathed bacteria of SphaerotilusLeptothrix group, to include unicellular organisms from the α-, β-, and γ -Proteobacteria (Emerson and Moyer 1997;Emerson 2000;Edwards et al 2003;Sobolev and Roden 2004). The involvement of unicellular bacteria in circumneutral Fe(II) oxidation is consistent with the observation of high numbers of unicellular organisms closely associated with Fe(III) oxides in microbial mats present at a groundwater Fe seep in Denmark (Emerson and Revsbech 1994a), and the Fe(III) oxide-rich plaque of aquatic macrophyte roots (Emerson, Weiss, and Megonigal 1999).…”

Prokaryotic diversity, distribution, and insights into their role in biogeochemical cycling in marine basalts

“…The increasing oxidation of reduced iron with time could lead to a shift in the microbial community from oxidizers to reducers. In fact, Edwards et al (2003b) demonstrated that chemolithoautotrophic, iron-oxidizing a-and g-Proteobacteria isolated from sulfides and metalliferous sediments are able to grow on basalt glass. These isolates are capable of using oxygen and nitrate as electron acceptors.…”

“…In fact, we found numerous genes coding for nitrate and nitrite reduction; therefore, the genetic potential for denitrification is present in this environment. Recently, Edwards et al (2003b) demonstrated that chemolithoautotrophic iron-oxidizing bacteria are able to grow on basalt glass using nitrate as the electron acceptor. Whether anaerobic ammonium oxidation is occurring in basalts remains unclear.…”

Life in the lithosphere, kinetics and the prospects for life elsewhere

“…These data must be reconciled with the enrichment and culture of iron-oxidizing bacteria from deep ocean basalts reported by others (e.g. [44,[102][103][104]). Previous observations of iron-oxidizing micro-organisms in deep ocean basaltic rocks have generally been made where active circulation through rocks and hydrothermal systems generates sufficient reduced iron to sustain these communities, demonstrating the importance of an active hydrological cycle in overcoming the kinetic limitations to iron oxidation in the deep ocean.…”

“…Iron-oxidizing bacteria have been described in a number of environments around the world, but most of these are deep-sea, temperate or tropical environments [41][42][43][44][45][46][47][48][49][50][51].…”