Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/1996
Publication Date: N/A
Citation: Interpretive Summary: Lactic acidosis is a digestive disorder in cattle caused by excess lactic acid production by rumen bacteria and occurs when starchy grains are increased suddenly in the diet. This condition has been estimated to cost the U.S. beef industry $40-100 million per year due to liver abscesses and loss of weight gain. One organism thought to be responsible for this acid production is the bacterium Streptococcus bovis. This research describes the isolation and characterization of the gene responsible for lactic acid production by this organism. Understanding the mechanisms of acid production by this bacteria may lead to methods to control lactic acidosis in cattle.
Technical Abstract: The ldh gene encoding the fructose-1,6-diphosphate dependent L-(+) lactate dehydrogenase from the ruminal bacterium Streptococcus bovis was cloned and sequenced. A genomic library of S. bovis JB1 DNA was constructed in lambda ZAP II and screened using a heterologous probe derived from the cloned S. mutans ldh gene. Several clones were isolated that contained a common 2.9 kb fragment as determined by restriction analysis. Nucleotide sequence analysis revealed a 987 bp open reading frame with extensive homology to S. thermophilus and S. mutans ldh nucleic acid and amino acid sequences. Expression of the cloned S. bovis ldh gene in E. coli was confirmed by the ability to compliment the ldh mutation of E. coli FMJ39, by using an in-gel activity screen and by enzymatic assay. Increased LDH activity was observed in S. bovis JB1 containing the cloned ldh genes on a multicopy plasmid.