Etude in vitro du comportement des populations microbiennes du rumen en présence de zinc sous forme de sulfate

Abstract

« In vitro » study of the influence of zinc on rumen microbial populations. The effects of different zinc sulfate levels on the metabolism of rumen microorganisms and on the growth of protozoan cultures were studied in vitro. Ciliate uptake of zinc was observed by electron microscopy and by electron microprobe microanalysis. Bacteria cellu-lolytic activity, unimproved by the addition of a small quantity of Zn, was significantly reduced by a zinc level of 10 0 ygjml in the incubation medium. Bacterial proteosynthesis, estimated by ammonia utilization, was unmodified, even at a zinc level of 25 ygjml. An inhibitory effect of high zinc levels on urease was significant only when bacterial cells were disrupted. 5 to 10 fL g/ml zinc stimulated protozoan growth of the genus Entodinium. The rate of cellular division increased after each addition of zinc. At 25 !tg/mi, zinc induced a decrease of the population after 9 days of culture, whereas « granules » were already observed in the ciliate endoplasm after 20 hours ; at 500 t i g/ml, the zinc penetrated the cells heavily. Using microanalysis, the X emission recording showed Koc, and K()(2 lines of zinc in Entodinium and Polyplastron ciliates from zinc levels of 2.5 to 25 !tg/mi ; zinc uptake was greater at the higher concentration. Under these experimental conditions, zinc affected rumen microbial populations differently. Protozoa incorporated zinc easily and were intolerant of high zinc levels. However, zinc did not seem to penetrate the bacterial cells readily, and at high concentrations inhibited metabolic activities only when the enzymes were extracellular or free in the medium after microbial lysis. Introduction.