EFFECTS OF LAIDLOMYCIN PROPIONATE AND MONENSIN ON GLUCOSE-UTILIZATIONAND NUTRIENT TRANSPORT BY STREPTOCOCCUS-BOVIS AND SELENOMONAS-RUMINANTIUM

The objective of this study was to compare the effects of laidlomycin propionate and monensin on cell growth, glucose fermentation, and gluc ose uptake in Streptococcus bovis strain JB1 and Selenomonas ruminanti um strain HD4. Experiments were also conducted to compare the effects of both ionophores on sodium-dependent serine transport and cell yield in S. bovis. Batch cultures (500 mt) of each bacterium were grown on 3.6 g/L D-glucose in semidefined medium and treated with either 5 ppm monensin or 2 ppm laidlomycin propionate (n = 2). Cell growth was moni tored by measuring optical density at 600 nm (OD600) Glucose and L-lac tate concentrations were measured using coupled enzyme assays. In S. b ovis, both monensin and laidlomycin propionate decreased OD600, glucos e utilization, and L-lactate production. Neither ionophore had any eff ect on glucose utilization by S. ruminantium. [C-14]Glucose uptake bet ween 5 and 30 min by both bacteria was not altered by either ionophore . Sodium-dependent [C-14]serine uptake by S. bovis was inhibited by mo nensin but not; laidlomycin propionate. When S. bovis was grown in glu cose-limited continuous culture (dilution rate = .10 h(-1)) at extrace llular pH 6.7, increasing concentrations of both ionophores decreased bacterial yield, and both ionophores were more potent at an extracellu lar pH of 5.7. However, monensin was a more potent inhibitor than laid lomycin propionate at pH 6.7 and 5.7. Collectively, these results sugg est that the ionophore laidlomycin propionate inhibits the Gram-positi ve bacterium S. bovis in a manner similar to that of monensin, but, at the concentrations used in this study, laidlomycin propionate seems t o be less potent than monensin in inhibiting serine uptake and cell yi eld.