EFFECT OF MOLYBDENUM AND ENVIRONMENTAL FACTORS ON ABUNDANCE AND TAXONOMIC AFFILIATION OF GENES THAT TRANSPORT OR USE MO

The trace element molybdenum (Mo) is an important component of enzymes known as molybdoenzymes, which are involved in nitrogen, sulfur and carbon metabolisms. Despite the Mo importance in biogeochemical cycles, little information exists about microbial Mo utilization in extreme environments. Using metagenomic data from 9 hot springs in Tengchong, Yunnan Province, China, which range in temperature from 42°C to 96°C and pH from 2.34 to 9.07, the effect of pH, temperature and spring water chemistry on the abundance and taxonomic affiliations of genes that transport or use Mo as a cofactor was studied with a special emphasis on the nitrogenase enzyme protein (nifD). BLAST search using custom Mo utilizing and transport protein database followed by taxonomic and functional pathway annotation suggests a positive correlation between Mo concentration and relative abundance of Mo transporting/ utilizing genes up to 0.2 ppb of Mo. Mo transport genes were predominantly annotated within the Archaeal phylum Crenarchaeota and Thaumarchaeota in low pH and high pH, respectively. The KEGG annotations for the genes involved in Mo transport at all sites were predominantly ABC transporter proteins. Similarly genes that use Mo as a cofactor were predominantly annotated within the Archaeal phylum (genus Sulfolobus and Candidatus Caldiarchaeum in low pH and high pH, respectively). Circumneutral pH (6.3 to 7.5) sites were dominated by phyla Proteobacteria and Chloroflexi. The functional annotation of Mo utilization was mainly genes involved in nitrogen metabolism followed by glycolysis/ gluconeogenesis and nitrotoluene degradation in most sites. The nifD gene was found at most sites and was detected in six bacterial phyla (Firmicutes, Cyanobacteria, Chloroflexi, Proteobacteria, Aquificae and Nitrospirae). The results suggested that temperature, pH and spring water geochemistry work intricately to affect the taxonomy and molybdoenzyme in these high temperature environments. Mo is a trace element that microbes need to access despite physio-chemical parameters that reduce aqueous Mo concentrations.