AME prepress abstract  -  DOI:

Seasonal variation in bacterial community composition and β – glucosidase expression in a tropical monsoon-influenced estuary

Ranjith Eswaran, Lidita Khandeparker*


ABSTRACT: Tidal estuaries receive carbohydrate-rich organic matter from various sources, which are mainly broken down by enzymatic processes and β – glucosidase (β-Glu) is one of the ectoenzymes produced by heterotrophic bacteria. An investigation was carried out along a tropical monsoon-influenced Zuari estuary to examine the seasonal variability in major bacterial taxa, β-Glu gene abundance, and number of cells expressing β-Glu. The results revealed a higher number of β-Glu expressing cells, β-Glu gene, and bacterial abundance at the estuarine mouth when compared to the upstream and was coupled with high phytoplankton biomass and low transparent exopolysaccharides. A clear distinction in bacterial assemblages along with β-Glu expression levels was evident during different seasons. Likewise, a spatial pattern in major bacterial taxa was observed along the salinity gradient, with high proportions of α and γ-proteobacteria at the saline mouth and β-proteobacteria at the upstream freshwater region. During the southwest monsoon which brings high freshwater influx, Actinobacteria and Firmicutes were high at the mid-estuarine region. Bacterial production at this time was mainly fueled by allochthonous riverine sources with a significant decrease in the number of cells expressing β-Glu to gene ratio. The β-Glu gene abundance was related to diverse groups (α, γ -proteobacteria, Actinobacteria, and Firmicutes). The number of cells expressing β-Glu covaried with γ – proteobacteria abundance and was influenced by suspended load, salinity, chlorophyll a and organic pool. Future studies should assess response of marine, brackish, and freshwater bacteria to different environmental conditions to ascertain their specific role in organic matter processing.