Variations in bacterial community at Chlorophyll Maximum (C-Max) depths along the west coast of India due to seasonal changes in the primary productivity

Abstract

An increase in primary productivity is recorded annually during the southwest monsoon season along the west coast of India, an important upwelling zone. The influence of the seasonal variations in the in situ primary productivity on the bacterial dynamics and community structure was explored during the non-monsoon and productive monsoon seasons. In the monsoon season, shallower mixed layer depth, increased nutrient concentration and a significant, positive correlation of bacterial carbon (p < 0.01) with primary productivity was observed. Bacterial diversity was assessed in the chlorophyll maxima depths during both seasons based on next-generation, metagenomic analysis. In the non-monsoon season, genera such as Idiomarina, Salinimonas, Marinobacter of Proteobacteria and Bacillus and Lactobacillus of Firmicutes were dominant. These major bacterial genera are shown through canonical correspondence analysis to play an important ecological role. They could be responsible for the increased heterotrophic activity recorded through predicted functional gene profiles in this season. In the monsoon season, increased abundance in the autotrophic Cyanobacteria community and its photosynthetic activity was recorded in the gene profiles. Higher diversity of heterotrophic phyla such as Bacteroidetes, Actinobacteria and a few Candidatus phyla and changes in the diversity of Proteobacteria with a representation of Alteromonas, SAR86 clade and OM60 (NOR5) was observed. These results highlight the bacterial dynamics associated with seasonal variations in primary productivity along the west coast of India.