Selective grazing by protists upon enteric bacteria in an aquatic system.

Area of Science:

• Environmental Microbiology
• Aquatic Ecology
• Water Quality Monitoring

Background:

• Protozoan grazing is a key factor in controlling bacterial populations in aquatic ecosystems.
• Fecal contamination is common, and Escherichia coli (E. coli) and Enterococcus are crucial water quality indicators.
• Understanding protozoan grazing effects on these indicators is vital for accurate water quality assessment.

Purpose of the Study:

• To analyze the impact of protozoan grazing on E. coli and Enterococcus faecalis in Los Padres Lagoon.
• To determine the differential susceptibility of E. coli and E. faecalis to grazing by autochthonous protozoans.
• To investigate the influence of bacterial strain origin on grazing sensitivity.

Main Methods:

• Microcosm experiments simulating freshwater conditions were conducted.
• Autochthonous bacterivorous protozoans were co-cultured with E. coli and E. faecalis strains (autochthonous and collection).
• Bacterial survival and protozoan populations were monitored daily.

Main Results:

• A preferential grazing sequence was observed, with E. faecalis being more grazing-resistant than E. coli.
• Bacterial strain origin affected grazing sensitivity, with collection strains showing less susceptibility.
• Protozoan grazing altered the relative abundance of E. coli and E. faecalis.

Conclusions:

• Protozoan grazing can significantly modify the composition of fecal indicator bacteria communities.
• This modification can potentially skew water quality study outcomes.
• The findings highlight the importance of considering protozoan grazing dynamics in microbiological water quality assessments.