Differential Rates of Digestion of Bacteria by Freshwater and Marine Phagotrophic Protozoa

Abstract

Differential decreases over time of two bacterial species, Escherichia coli and Enterococcus faecalis, in a freshwater and a marine ecosystem were observed and explained by a differential rate of digestion of these bacteria by phagotrophic flagellates and ciliates. For this purpose, fluorescence-labeled bacteria (FLB) were used and prepared from the two species cited above. The number of FLB was observed for 5 days in fresh and marine waters in the presence or absence (0.2-,unm-pore-size-filtered water) of natural microbiota. These experiments showed a longer persistence of Enterococcusfaecalis FLB as opposed to Escherichia coli FLB in the presence of natural microbiota. Removal of FLB was due to protozoan grazing because no decrease of FLB number was observed in the absence of natural microbiota. In short-term (about 40 min) ingestion experiments, we found similar clearance rates of Escherichia coli and Enterococcus faecalis FLB by assemblages of flagelates from the freshwater and the marine ecosystem and by cultured assemblages of ciliates from the marine ecosystem. Clearance rates of Enterococcus faecalis FLB were greater than those of Escherichia coli FLB for assemblages of ciliates from the freshwater ecosystem. Comparison of rates of ingestion and digestion of FLB by protozoa showed that Escherichia coli FLB were digested and ingested at similar rates. However, Enterococcusfaecalis FLB were digested slower than they were ingested. These results suggest that a longer persistence of Enterococcus faecalis as opposed to Escherichia coli can be explained by a differential digestion by flagellates and ciliates in aquatic ecosystems. Moreover, rates of ingestion and digestion were strongly correlated for both FLB types.

Growth rate variability in geographically diverse clones of Uronema (Ciliophora: Scuticociliatida)

“…The type of food bacterium also promoted different responses in the freshwater clone SRBM. This is consistent with reports for other protozoa [35,43]. The growth rate of SRBM was almost 1.5 times higher when fed with V. natriegens than with E. aerogenes although net stationary phase population was reduced by half.…”

Effects of environmental storage conditions on survival of indicator organisms in a blend of surface water and dual disinfected reclaimed water

“…Bitton et al (1983) found that E. coli and f2 coliphage in groundwater declined at rates of 0Á0066 and 0Á059 h À1 respectively. Other researchers have suggested that observed decreases in the concentrations of bacteria in freshwater may be a result of inhibitory substances (Klein and Alexander 1986), the activities of predatory and lytic organisms, temperature effects, aggregation, adsorption, sedimentation and sunlight induced damage (Flint 1987;Gonzalez et al 1990;Characklis et al 2005;Bertrand et al 2012;Pinon and Vialette 2018). Yet other researchers attribute observed increases in microbial concentrations to disaggregation, growth or 'regrowth' and resuscitation, the so-called bottle effect and repair of UV induced damage (Hortnagl et al 2011).…”

Differential decay of human faecal Bacteroides in marine and freshwater

“…Bacteria targeted by Entero1 experienced an earlier onset of decay, but slower decay, than targeted Bacteroides. Protozoan predators have been shown to prefer prey based on prey outer membrane characteristics (Gonzalez et al, 1990;Tarao et al, 2009), size (Simek and Chrzanowski, 1992), morphology (Justice et al, 2008) and perhaps growth rate (Pernthaler, 2005). Gram-positive Actinobacteria are notably resistant to grazing (Pernthaler et al, 2001) due to surface layer characteristics (Tarao et al, 2009).…”