In vitro growth and starch digestion by Entodinium exiguum as influenced by the presence or absence of live bacteria

In a preliminary study, the addition of antibiotics was shown to reduce bac terial concentrations in Entodinium exiguum cultures by more than 99% in 4 h, whereas the protozoal population was apparently unaffected. Using this p rocedure, the growth and amylolytic capability of Entodinium exiguum, in th e presence or absence of live bacteria, was studied in vitro. Treatments fo r Trial 1 were protozoa plus antibiotics (PA), PA plus autoclaved bacteria (PAB), protozoa plus living bacteria (PLB), and only bacteria (BAC). Autocl aved or non-autoclaved cornstarch was used as an energy source. Treatment m ain effects were as follows: higher concentration of E. exiguum in PLB than in PA or PAB at 24 and 48 h (P < 0.01); PA and PAB were not different (P > 0.05); concentrations of E. exiguum higher in autoclaved cornstarch at 12 h (P < 0.05) but lower than in non-autoclaved cornstarch at 24 and 48 h (P < 0.01); and starch digestion in PLB was higher than in PA and PAB at all t ime periods, but only greater than BAC up to 24 h (P < 0.01). In Trial 2, o nly treatments PA, PLB, and BAC were tested. Rice starch and cornstarch wer e used as substrates. With rice starch, growth was higher in PLB than in PA at 24 and 48 h (P < 0.05). Starch digestion started earlier in PLB with ri ce starch T < 0.05) but was complete for both substrates after 24 h. Up to 12 h (autoclaved cornstarch and rice starch) and 24 h (non-autoclaved corns tarch and cornstarch), the sum of digestion by bacteria and protozoa did no t equal the extent of digestion in PLB, suggesting some kind of synergism. Total extent of digestion with protozoa was similar between the two sources ; however, bacteria digested rice starch faster and to a greater extent tha n cornstarch. Approximate lag times with rice starch, autoclaved cornstarch , and non-autoclaved cornstarch were 6, 3, and 12 h for bacteria and < 6, 3 , and 9 h for protozoa, respectively. Rate of digestion for non-autoclaved cornstarch was similar for bacteria and protozoa, whereas the rate of bacte rial digestion was much faster with the other two substrates autoclaved cor nstarch and rice starch).