Effects of chetomin on growth and acidic fermentation products of rumen bacteria

Chetomin, an antibiotic metabolite of Chaetomium spp., was tested in the form of its tetrathiol derivative for its effects on growth and carbohydrate metabolism by five strains of functionally important rumen bacteria. The compound was bacteriostatic for the strains tested and Gram-positive bacteria were more sensitive to inhibition than Gram-negative bacteria. In an anaerobic broth dilution assay using a medium lacking rumen fluid, the minimum inhibitory concentration (MIC) of chetomin which completely inhibited growth of Butyrivibrio fibrisolvens D1 for 18 h at 39 degrees C was 40 micrograms X mL-1. The MICs determined under the same conditions for Megasphaera elsdenii B159, Selenomonas ruminantium GA192, and Succinivibrio dextrinosolvens 24 were 160, 600, and 60 micrograms X mL-1, respectively. The MIC for cellulose hydrolysis by Ruminococcus albus 7 was 20 micrograms X mL-1. Chetomin at concentrations below the MIC appeared to inhibit the separation and division of cells in cultures of B. fibrisolvens D1. Chetomin consistently stimulated acetate production from glucose by B. fibrisolvens D1, M. elsdenii B159, and S. ruminantium GA192 at the expense of compounds which comprised major soluble end products of fermentation in cultures lacking chetomin.