Lactic Acid As Available Carbon Source For The Growth Of Bacillus Subtilis Strains In Ruminant’s PH

Lactic acid usually is metabolized by enzymes from histiocyte and microorganism and does not accumulate in many ruminants’ body. However, when a large amount of forage which contains high carbohydrate is feeded to the ruminants, the unbalance between lactic acid-producing bacteria and its-utilizing bacteria in the body often occurs, and resultantly over-accumulation of lactic acid often takes place. Over-accumulation of lactic acid in body causes metabolic disease that is ruminal acidosis. Ruminal acidosis not only affects the health of animals, but brings economic losses as well. Bacillus subtilis, as a microorganism which often is isolated in forge, has a strong adaptability to survive in rumen environment. Thus, the objectives of the present study are designed to:(1) take 7 B.subtilis strains as experimental strains to explore their growth performances in lactic acid as only available carbon source; and (2) determine various factors which affect their lactic acid utilization in ruminant’s pH. The following are main results.(1) 7 B.subtilis strains were grown in the culture media containing 1.0% lactic acid as sole carbon source which were adjusted to pH between 5.3 and 6.2. The results showed that B.subtilis strains were able to grow after incubation at 37℃ for 72h in pH range from 5.3 to 6.2 with 1.0% lactic acid. Among 7 strains, B. subttlis A and SL grew better than other strains did.(2) B. subtilis strain A and SL were grown in the culture media containing peptone as sole nitrogen source and without any carbon source for 72h at 37℃. The results showed that two B.subtilis strains were able to grow in the presence of only nitrogen source.(3) Temperature, pH and lactic acid concentrations and glucose levels in media were changed to deal with their influences on the utilization of lactic acid by two strains of B. subtilis A and SL. B. subtilis strains only grew but did not consume lactic acid when incubated below 30℃. In the range of pH from 5.4 to 7.4 at 37℃, the higher the pH the lower lactic acid was utilized by two B. subtilis strains. In the concentrations of lactic acid from 1.0 to 2.0% at 37℃, the higher lactic acid level the lower two bacteria consumed lactic acid, although they still grew when lactic acid content was below 2.0%. In the presence of glucose level from 0.1 to 1.0% at 37℃, the higher the glucose level the lower two bacteria consumed lactic acid.(4) Data from SDS-PAGE and intracellular production of pyruvic acid showed that the crude enzyme of two B.subtilis strains contained lactate dehydrogenase. The bacterium B.subtilis metabolized lactic acid to pyruvic acid via the catalytic activity of lactate dehydrogenase.In conclusion, B.subtilis strain A and SL have good ability to use lactic acid as available carbon source in ruminant’s pH. They should be promising as a biological solution to the problem of rumen acidosis.