Zhu Baoli, a researcher at the Institute of Subtropical Agroecology of the Chinese Academy of Sciences, and researchers from Germany and Switzerland, based on the previous findings, based on microbiomeological analysis and metabolic pathway reconstruction, assembled a genome sketch of a new anaerobic methane oxidizing bacterium, Candidatus Methylomirabilis iodofontis, from the biofilm metagenome of the cave rich in iodine spring water. It was also found that the bacterium has the potential to use iodate to drive the oxidation of anaerobic methane. On August 9, the results were published online in mLife.
Methane is an important greenhouse gas, on a 20-year scale, its greenhouse effect potential is about 85 times that of carbon dioxide, and microbial anaerobic methane oxidation (AOM) is an important methane sink. More than a decade ago, the first Methylomirabilota bacterium using nitrite-driven AOM: Methylomirabilis oxyfera was reported. Although M. Oxyfera is an anaerobic bacterium, but it produces oxygen through the process of “oxygen-producing denitrification” and uses the oxygen produced to complete the oxidation of aerobic methane. At present, there is still very limited understanding of the metabolic diversity of Methylomirabilota methane oxidizing bacteria.
The team found a cave rich in iodine (>20 mg l-1) spring water accumulation with air methane concentrations of up to 3000 ppm, forming a large biofilm at the top of the cave, on the side walls, and on the side walls under the water surface. 16S rRNA amplicon sequencing revealed that the biofilm contained a variety of aerobic methane oxidizing bacteria, and there were also high-abundance Methylomirabilota bacteria in the subsurface sidewall biofilm.
At the same time, transmission electron microscopy photographs show the presence of “star-shaped” cells in the biofilm under the surface of the water, similar to M. Oxyfera cells are morphologically similar. The team performed metagenomic sequencing of the underwater biofilm and successfully assembled a methylomirabilota bacterial genome sketch (bin48) with greater than 70% completeness. Based on the number of reads of 16S rRNA in the metagenomic, the relative abundance of the Methylomirabilota bacteria was as high as 14.3%, and the 16S rRNA fragments of all The Methylomirabilota bacteria were spliced together to form a complete 16S rRNA sequence. The 16S rRNA sequence is associated with M. Limnetica’s 16S rRNA was highly similar (>99%), but not similar to the bin48 and M.limnetica genomes (AAI, 85.8%; ANI, 91.3%), hence the bacterium Methylomirabilota was provisionally named Ca. Methylomirabilis iodofontis。
Although the cave air had a high concentration of methane, nitrite was not detectable in the spring water, and the nitrate concentration was also very low (< 0.2 mg L-1), so the team had a good understanding of M. The main metabolic pathways of iodofontis were analyzed. Surprisingly, in addition to aerobic methane oxidation and the “oxygen-producing denitrification” pathway, the M.iodofontis genome also has clusters of iodate reductase (IdrA and IdrB) encoding genes. The order of the genes in the gene cluster and the gene sequence of the catalytic subunit are consistent with the known iodate reductase and have a high degree of similarity, indicating that M. Iodofontis bacteria may have the potential for simultaneous methane oxidation, oxygen-producing denitrification, and iodate reduction. However, its activity and function of using iodate to drive AOM needs further verification.
A large biofilm formed at the top of the cave. Courtesy of respondents
“Star-type” microbial cell electron microscopy picture. Courtesy of respondents
According to the report, the results of the study expand the diversity of methylomirabilota methane oxidation bacteria metabolism and provide genomic evidence for a new potential methane oxidation process, iodolate-driven AOM. Given the widespread distribution of iodates in the marine environment, anaerobic methane oxidation with iodic acid as an electron receptor may be a neglected but important methane sink. (Source: China Science Daily Wang Haohao)
Related paper information:https://doi.org/10.1002/mlf2.12033