In-situ incubation of iron-sulfur mineral reveals a diverse chemolithoautotrophic community and a new biogeochemical role for Thiomicrospira.

Sulfide mineral precipitation occurs at mid-ocean ridge (MOR) spreading centers, both in the form of plume particles and seafloor massive sulfide structures. A common constituent of MOR is the iron-bearing sulfide mineral pyrrhotite, which was chosen as a substrate for in-situ incubation studies in shallow waters of Catalina Island, CA to investigate the colonization of iron-oxidizing bacteria. Microbial community datasets were obtained from in-situ incubated pyrrhotite, allowing for direct comparison to microbial communities of iron-sulfides from active and inactive chimneys in deep-sea environments. Unclassified Gammaproteobacteria and Alphaproteobacteria (Magnetovibrio) largely dominated the bacterial community on pyrrhotite samples incubated in the water column while samples incubated at the surface sediment showed more even dominance by Deltaproteobacteria (Desulfobulbus), Gammaproteobacteria (Piscirickettsiaceae), Alphaproteobacteria (Rhodobacteraceae), and Bacteroidetes (Flavobacteriia). Cultivations that originated from pyrrhotite samples resulted in the enrichment of both, sheath-forming and stalk-forming Zetaproteobacteria. Additionally, a putative novel species of Thiomicrospira was isolated and shown to grow autotrophically with iron, indicating a new biogeochemical role for this ubiquitous microorganism.

Redox potential as a master variable controlling pathways of metal reduction by Geobacter sulfurreducens.

Geobacter sulfurreducens uses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of -0.10 V vs the standard hydrogen electrode, whereas the ImcH-dependent pathway operates only above this value. Here, we provide evidence that G. sulfurreducens also requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)-(oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high-potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment.

Assessing Marine Microbial Induced Corrosion at Santa Catalina Island, California.

High iron and eutrophic conditions are reported as environmental factors leading to accelerated low-water corrosion, an enhanced form of near-shore microbial induced corrosion. To explore this hypothesis, we deployed flow-through colonization systems in laboratory-based aquarium tanks under a continuous flow of surface seawater from Santa Catalina Island, CA, USA, for periods of 2 and 6 months. Substrates consisted of mild steel - a major constituent of maritime infrastructure - and the naturally occurring iron sulfide mineral pyrite. Four conditions were tested: free-venting "high-flux" conditions; a "stagnant" condition; an "active" flow-through condition with seawater slowly pumped over the substrates; and an "enrichment" condition where the slow pumping of seawater was supplemented with nutrient rich medium. Electron microscopy analyses of the 2-month high flux incubations document coating of substrates with "twisted stalks," resembling iron oxyhydroxide bioprecipitates made by marine neutrophilic Fe-oxidizing bacteria (FeOB). Six-month incubations exhibit increased biofilm and substrate corrosion in the active flow and nutrient enriched conditions relative to the stagnant condition. A scarcity of twisted stalks was observed for all 6 month slow-flow conditions compared to the high-flux condition, which may be attributable to oxygen concentrations in the slow-flux conditions being prohibitively low for sustained growth of stalk-producing bacteria. All substrates developed microbial communities reflective of the original seawater input, as based on 16S rRNA gene sequencing. Deltaproteobacteria sequences increased in relative abundance in the active flow and nutrient enrichment conditions, whereas Gammaproteobacteria sequences were relatively more abundant in the stagnant condition. These results indicate that (i) high-flux incubations with higher oxygen availability favor the development of biofilms with twisted stalks resembling those of marine neutrophilic FeOB and (ii) long-term nutrient stimulation results in substrate corrosion and biofilms with different bacterial community composition and structure relative to stagnant and non-nutritionally enhanced incubations. Similar microbial succession scenarios, involving increases in nutritional input leading to the proliferation of anaerobic iron and sulfur-cycling guilds, may occur at the nearby Port of Los Angeles and cause potential damage to maritime port infrastructure.

Bacillus rigiliprofundi sp. nov., an endospore-forming, Mn-oxidizing, moderately halophilic bacterium isolated from deep subseafloor basaltic crust.

A facultatively anaerobic bacterium, designated strain 1MBB1T, was isolated from basaltic breccia collected from 341 m below the seafloor by seafloor drilling of Rigil Guyot during Integrated Ocean Drilling Program Expedition 330. The cells were straight rods, 0.5 µm wide and 1-3 µm long, that occurred singly and in chains. Strain 1MBB1T stained Gram-positive. Catalase and oxidase were produced. The isolate grew optimally at 30 °C and pH 7.5, and could grow with up to 12 % (w/v) NaCl. The DNA G+C content was 40.5 mol%. The major cellular fatty acids were C16:1ω11c (26.5 %), anteiso-C15:0 (19.5 %), C16:0 (18.7 %) and iso-C15:0 (10.4 %), and the cell-wall diamino acid was meso-diaminopimelic acid. Endospores of strain 1MBB1T oxidized Mn(II) to Mn(IV), and siderophore production by vegetative cells was positive. Phylogenetic analysis of the 16S rRNA gene indicated that strain 1MBB1T was a member of the family Bacillaceae, with Bacillus foraminis CV53T and Bacillus novalis LMG 21837T being the closest phylogenetic neighbours (96.5 and 96.2 % similarity, respectively). This is the first novel species described from deep subseafloor basaltic crust. On the basis of our polyphasic analysis, we conclude that strain 1MBB1T represents a novel species of the genus Bacillus, for which we propose the name Bacillus rigiliprofundi sp. nov. The type strain is 1MBB1T ( = NCMA B78T = LMG 28275T).

Growth detection failures by the nonradiometric Bactec MGIT 960 mycobacterial culture system.

Mycobacterial growth in liquid culture can go undetected by automated, nonradiometric growth detection systems. In our laboratory, instrument-negative tubes from the Bactec MGIT 960 system are inspected visually for clumps suggestive of mycobacterial growth, which (if present) are examined by acid-fast smear analysis. A 3-year review demonstrated that ∼1% of instrument-negative MGIT cultures contained mycobacterial growth and that 10% of all cultures yielding mycobacteria were instrument negative. Isolates from instrument-negative MGIT cultures included both tuberculous and nontuberculous mycobacteria.