Microbial electrosynthesis, a process in which microorganisms use electrons derived from electrodes to reduce carbon dioxide to multicarbon, extracellular organic compounds, is a potential strategy for capturing electrical energy in carbon-carbon bonds of readily stored and easily distributed products, such as transportation fuels. To date, only one organism, the acetogen Sporomusa ovata, has been shown to be capable of electrosynthesis. The purpose of this study was to determine if a wider range of microorganisms is capable of this process. Several other acetogenic bacteria, including two other Sporomusa species, Clostridium ljungdahlii, Clostridium aceticum, and Moorella thermoacetica, consumed current with the production of organic acids. In general acetate was the primary product, but 2-oxobutyrate and formate also were formed, with 2-oxobutyrate being the predominant identified product of electrosynthesis by C. aceticum. S. sphaeroides, C. ljungdahlii, and M. thermoacetica had high (>80%) efficiencies of electrons consumed and recovered in identified products. The acetogen Acetobacterium woodii was unable to consume current. These results expand the known range of microorganisms capable of electrosynthesis, providing multiple options for the further optimization of this process.
Thermococcus may be an important alternative source of H2 in the hot subseafloor in otherwise low H2 environments such as some hydrothermal vents and oil reservoirs. It may also be useful in industry for rapid agricultural waste treatment and concomitant H2 production. Thermococcus paralvinellae grown at 82°C without sulfur produced up to 5 mmol of H2 L−1 at rates of 5–36 fmol H2 cell−1 h−1 on 0.5% (wt vol−1) maltose, 0.5% (wt vol−1) tryptone, and 0.5% maltose + 0.05% tryptone media. Two potentially inhibiting conditions, the presence of 10 mM acetate and low pH (pH 5) in maltose-only medium, did not significantly affect growth or H2 production. Growth rates, H2 production rates, and cell yields based on H2 production were the same as those for Pyrococcus furiosus grown at 95°C on the same media for comparison. Acetate, butyrate, succinate, isovalerate, and formate were also detected as end products. After 100 h, T. paralvinellae produced up to 5 mmol of H2 L−1 of medium when grown on up to 70% (vol vol−1) waste milk from cows undergoing treatment for mastitis with the bacterial antibiotic Ceftiofur and from untreated cows. The amount of H2 produced by T. paralvinellae increased with increasing waste concentrations, but decreased in P. furiosus cultures supplemented with waste milk above 1% concentration. All mesophilic bacteria from the waste milk that grew on Luria Bertani, Sheep's Blood (selective for Staphylococcus, the typical cause of mastitis), and MacConkey (selective for Gram-negative enteric bacteria) agar plates were killed by heat during incubation at 82°C. Ceftiofur, which is heat labile, was below the detection limit following incubation at 82°C. T. paralvinellae also produced up to 6 mmol of H2 L−1 of medium when grown on 0.1–10% (wt vol−1) spent brewery grain while P. furiosus produced < 1 mmol of H2 L−1. Twelve of 13 enzyme activities in T. paralvinellae showed significant (p < 0.05) differences across six different growth conditions; however, methyl viologen-dependent membrane hydrogenase activity remained constant across all media types. The results demonstrate the potential of at least some Thermococcus species to produce H2 if protein and α-glucosides are present as substrates.
Two heterotrophic hyperthermophilic strains, ES1 T and CL1 T , were isolated from Paralvinella sp. polychaete worms collected from active hydrothermal vent chimneys in the north-eastern Pacific Ocean. Both were obligately anaerobic and produced H 2 S in the presence of elemental sulfur and H 2 . Complete genome sequences are available for both strains. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strains are more than 97 % similar to most other species of the genus Thermococcus. Therefore, overall genome relatedness index analyses were performed to establish that these strains are novel species. For each analysis, strain ES1 T was determined to be most similar to Thermococcus barophilus MP T , while strain CL1 T was determined to be most similar to Thermococcus sp. 4557. The average nucleotide identity scores for these strains were 84 % for strain ES1 T and 81 % for strain CL1 T , genome-to-genome direct comparison scores were 23 % for strain ES1 T and 47 % for strain CL1 T , and the species identification scores were 89 % for strain ES1 T and 88 % for strain CL1 T . For each analysis, strains ES1 T and CL1 T were below the species delineation cut-off. Therefore, based on their whole genome sequences, strains ES1 T and CL1 T are suggested to represent novel species of the genus Thermococcus for which the names Thermococcus paralvinellae sp. nov. and Thermococcus cleftensis sp. nov. are proposed, respectively. The type strains are ES1 T (5DSM 27261 T 5KACC 17923 T ) and CL1 T (5DSM 27260 T 5KACC 17922 T ).The genus Thermococcus is composed of hyperthermophilic obligate anaerobes that couple the oxidation of peptides and polysaccharides to the reduction of elemental sulfur (S u ) and protons (Bertoldo & Antranikian, 2006). In this study, the complete genome sequences of two strains of the genus Thermococcus, strain ES1 T and strain CL1 T (Jung et al., 2012, were used to establish the novelty of these strains. Both strains were isolated from Paralvinella sp. polychaete worms collected from active hydrothermal vent chimneys on the Juan de Fuca Ridge in the northeastern Pacific Ocean (Pledger & Baross, 1989;Holden et al., 2001). Notably, in a survey of 20 species of the genera Thermococcus and Pyrococcus, both strains produced noticeable amounts of H 2 even when grown on S u (Oslowski et al., 2011). In this study, strains ES1 T and CL1 T were adapted for growth without S u at 82 u C through serial transfers on 0.5 % (w/v) maltose and tryptone medium as previously described (Adams et al., 2001). The concentrations of cells and H 2 were monitored in duplicate at certain time intervals by phase-contrast microscopy (Nikon 55i) and GC (Shimadzu GC-8A). The growth rate of strain ES1 T was the same despite the presence or absence of S u (doubling times of 65 and 72 min, respectively) (Fig. 1a) while strain CL1 T grew much slower without S u (doubling time of 190 min) relative to cultures with S u (doubling time of 52 min) (Fig. 1b). Both strains grew and produced 3.25-5.05 millimoles of H 2 per Abb...
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