3.7. Biogeochemical potentials of CAB
3.7.1. Potential methanogenesis by CAB: Evidence of interlinking methanogenesis, DMSP degradation and phosphate utilisation
The genes responsible for the reduction of methyl phosphonate into methane (MPn genes -phnL, phnM, phnJ, phnI, phnH and phnG) were relatively high in the CAB of Pleuromamma spp. and Calanusspp. (Figure S2). Also, based on the present analysis, the CAB of theCentropages sp. had a high proportion of mttB genes followed byAcartia spp. and Calanus spp. One should note that these mttB genes involved in the oxidation of Trimethylamine (TMA) to Methyl-CoM (Figure S2).
CAB of Pleuromamma spp. and Calanus spp. contained some proportion of dmd-tmd (Tri/Demethylation to methylamine) genes, whereas there was no or low proportion of this gene in the CAB of Temoraspp., Centropages sp. and Acartia spp. (Figure. S2). The proportion of DmmD gene was high in the CAB of Centropages sp. followed by Acartia spp. and Temora spp., while the CAB ofPleuromamma spp. had the minimum proportion. The proportion of dmdA (DMSP to 3-(Methylthio)-propanote) gene was found to be high in the CAB of Acartia spp. followed by Centropages sp. andCalanus spp., whereas, the proportion was minimum in the CAB ofTemora spp..
Also, the dddL gene (DMSP to Methyl thioether) was found to be high in the CAB of Centropages sp. and Acartia spp. and low in the CAB of Temora spp. But the dmsA gene that converts the DMSO to Methyl thioether was found to be high in the CAB of Pleuromammaspp. followed by Centropages sp., whereas the genes (dmsB-K00184 and dmsC -K00185) responsible for aerobic conversion of DMSO to Methyl thioether were higher in proportion than the anaerobic genes (dmsA-K07306, dmaB-k07307 and dmsC-K07308), which converts the DMSO to Methyl thioether. The genes dmsB and dmsC (aerobic pathway) were high in CAB of Temora spp. followed by Acartia spp. whereas, the dmsB and dmsC (anaerobic pathway) gene were high in the CAB of Pleuromamma spp. followed by Centropages sp.
Besides, the dmoA gene that converts Methyl thioether to Methanethiol was found only in the Pleuromamma spp., but at low proportion. Most importantly, mtsA and mtsB genes (converts Methanethiol to Methyl-CoM) were found to be high in the CAB of Pleuromamma spp. when compared to the other copepod genera. Furthermore, the gene responsible for methanogenesis, i.e., the mcrA gene that converts Methyl-CoM to CH4, was found to be high in number within the CAB ofPleuromammaspp., but at low proportion (Figure S2).