Persistence of fecal indicator bacteria associated with zooplankton in a tropical estuary-west coast of India
Abstract
In a study carried out during 2014, bacteria associated with zooplankton in the Zuari estuary were 3–
4 orders of magnitude higher in abundance than in seawater. The live zooplankton carried much
more bacterial load compared to the carcasses and the fecal pellets harbored the highest density of
bacteria ie. 8 x 1013 CFU cm–3
. The diversity of bacteria was higher in live zooplankton and also in
seawater. But the activity of the zooplankton-associated bacteria was much higher compared to the
free-living ones. Most of the associated bacteria belonged to the genus Enterobacter, Pseudomonas,
Aeromonas and Bacillus. In growth experiments, Aeromonas and Bacillus were found to have lower
salinity optima than Enterobacter (20 psu ) and Vibrio and Pseudomonas (normal seawater salinity).
Better growth of bacteria was observed in the medium containing the diatom Chaetoceros sp. than
Navicula sp. Bacterial isolates were also able to survive in oligotrophic conditions and produce
optimum biomass in two days at salinity 5 psu but in freshwater, the bacteria took a week’s time to
attain the optima. At salinities 0– 35, the bacteria survived even for 3 months without nutrient
addition, indicating resilience in these bacteria and mechanisms to persist in the estuaries even in
adverse conditions.
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