Fig 1.
Photographs of strain VROV1 isolated from marine sediments collected on the northern Central Indian Ridge.
(A) A typical turquoise–blue color developed in vanadate-reducing VROV1 cultures. (B) Epifluorescence photomicrograph of bacterial cells entering the stationary phase and initiating endospore formation. (C) Epifluorescence photomicrograph showing vegetative cells in the exponential growth phase.
Fig 2.
Reductive precipitation of vanadium by strain VROV1.
The removal of vanadium due to precipitation accounts quantitatively for the decrease in dissolved vanadium (left). Comparison of the V2p XPS spectra between culture precipitate and reference vanadium compounds confirmed the biological reduction of vanadate to vanadyl (right). The relative error in vanadium determination by ICP‒AES was 10%. Abbreviations: ppt., precipitate; arb., arbitrary.
Table 1.
Growth and vanadate reduction in basal medium with specific supplements.
Fig 3.
Neighbor-joining phylogenetic tree of 16S rRNA gene sequences showing the relationship of T. mesophilus VROV1 to representative species within the order Clostridiales.
Node support was evaluated with 1,000 bootstrap replicates.
Fig 4.
Growth and metabolic characteristics of strain VROV1 in vanadate-free (upper panels) and vanadate-containing (lower panels) media.
Growth and consumption of glucose and vanadate (A, E). Production of primary metabolites excluding amino acids (B, F). Consumption of amino acids in a medium supplemented with a MEM amino acid mixture (C, G). Production of amino acids not included in the MEM amino acid mixture (D, H). Note the prolonged lag phase in the presence of vanadate. The error bars for the cell density reflect the standard deviation of the cell counts, whereas the concentrations determined via colorimetry and chromatography are subject to analytical errors of ±10% and ±5%, respectively.
Fig 5.
Proposed metabolic pathways related to vanadate reduction and alanine production by T. mesophilus VROV1.
The transamination of pyruvate to alanine bridges glycolysis and Stickland fermentation, maintaining the redox and nitrogen balances of overall fermentation reactions [31]. A metabolic shunt toward vanadate reduction can disrupt this coupling.
Table 2.
Comparison of vanadate reduction by different bacterial strains.