School of Fisheries and Life, Shanghai Ocean University, Shanghai 201306, PR China
2.
Key Laboratory of Marine Biogenetic Resources, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China
3.
Faculty of Marine Biology, Xiamen Ocean Vocational College, Xiamen 361100, China
Funds:
Fundation item: The National Key R&D Program of China under contract No. 2021YFF0501304; The National Natural Science Foundation of China under contract Nos 91951201 and 42030412; Scientific Research Foundation of Third Institute of Oceanography, MNR No.2019021.
The genus Marinobacter is very broadly distributed in global environments and is considered as aerobic heterotroph. In this study, six Marinobacter strains were identified with autotrophic thiosulfate oxidation capacity. These strains, namely Marinobacter guineae M3BT, Marinobacter aromaticivorans D15-8PT, Marinobacter vulgaris F01T, Marinobacter profundi PWS21T, Marinobacter denitrificans JB02H27T, and Marinobacter sp. ST-1M (with a 99.93 % similarity to the 16S rDNA sequences of Marinobacter salsuginis SD-14BT), were screened out of 32 Marinobacter strains by autotrophic thiosulfate oxidization medium. The population of cells grew in a chemolithotrophic medium, increasing from 105 to 107 cells /mL within 5 days. This growth was accompanied by the consumption of thiosulfate 3.59 mM to 9.64 mM and the accumulation of sulfate up to 0.96 mM, and occasionally produced sulfur containing complex particles. Among these Marinobacter strains, it was also found their capability of oxidizing thiosulfate to sulfate in a heterotrophic medium. Notably, M. vulgaris F01T and M. antarcticus ZS2-30T showed highly significant production of sulfate at 9.45 mM and 3.10 mM. Genome annotation indicated that these Marinobacter strains possess a complete Sox cluster for thiosulfate oxidation. Further phylogenetic analysis of the soxB gene revealed that six Marinobacter strains formed a separate lineage within Gammaproteobacteria and close to obligate chemolithoautotroph Thiomicrorhabdus arctica. The results indicated that thiosulfate oxidizing and chemolithoautotrophic potential in Marinobacter genus, which may contribute to the widespread of Marinobacter in the global ocean.
Figure 1. Profile of cell density, thiosulfate, sulfate concentrations during autotrophic thiosulfate oxidizing growth over 5 days of Marinobacter type strains including Marinoabcter guineae M3BT, Marinobacter aromaticivorans D15-8PT, Marinobacter vulgaris F01T, Marinobacter profundi PWS21T and Marinobacter denitrificans JB02H27T. (A) Cell density. (B) Thiosulfate and sulfate concentration on the 5th day. NC, negative control without inoculums.
Figure 2. Sulfate concentrations and pH values in heterotrophic sulfur oxidation medium of 27 Marinoabcter type strains and 5 deep sea hydrothermal vents Marinoabcter strains over 5 days. NC, negative control without inoculum.
Figure 3. Profiles in the cells number, thiosulfate and sulfate concentrations of Marinoabcterguineae M3BT (A) in autotrophic thiosulfate oxidization liquid medium and (B) in heterotrophic thiosulfate oxidization liquid medium.
Figure 4. Scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) images of sulfur-containing complexes particles of strain Marinobacter vulgaris F01T in the autotrophic thiosulfate oxidation growth. (A) Spherical sulfur-containing complexes; (B) Irregular sulfur-containing complexes.
Figure 5. Map of the sox gene cluster of six Marinobacter strains and other sulfur oxidizing bacteria.
Figure 6. Maximum likelihood phylogenetic tree of full-length protein sequences of SoxB protein derived from Marinobacter strains and other representative species. Bootstrap values indicated at each node are based on a total of 1,000 bootstrap replicates. Branch node values below 50% are not shown. Genera of the same class are in the same color and the genus Marinobacter is indicated in black bold.
Figure 7. Phylogenomic tree of Marinobacter species (53 strains) based on 92 core proteins. The color of leaves indicated the source of these strains. The tree was generated with UBCG 3.0. Bootstrap values indicated at each node are based on a total of 1,000 bootstrap replicates. Branch node values below 50% are not shown. The heatmaps represent distribution of genes for sulfur metabolism.
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