Submitted to: Conference on Rumen Function
Publication Type: Abstract Only
Publication Acceptance Date: November 16, 1995
Publication Date: N/A
Technical Abstract: The ruminal bacterium, Streptococcus bovis, is highly amylolytic and can convert crude starches completely to fermentation end products. During rapid, uncontrolled growth, S. bovis forms large amounts of lactic acid but under controlled growth, it will produce acetate, ethanol and formate. The uncontrolled production of lactate in the rumen can lead to lactic acidosis. Cloning and characterization of the S. bovis JB1 ldh gene may allow modifications to the organism's metabolic pathways to improve rumen function by decreasing lactate production. A genomic library of S. bovis JB1 DNA was constructed in lambda ZAPII and screened using heterologous probes derived from a S. mutans ldh gene. Several clones were isolated that contained a common 2.9 kb fragment as determined by restriction analysis. DNA sequence analysis revealed a 987 bp open reading frame with extensive homology to S. thermophilus (88%) and S. mutans (82%) ldh nucleic cacid sequences. Expression of S. bovis JB1 LDH activity in E. coli by the cloned gene was confirmed by using an in-gel activity assay. The cloned LDH activity of S. bovis JB1 was able to complement the LDH mutation of E. coli FMJ39, allowing anaerobic growth on glucose as a substrate. Attempts are being made to construct LDH mutants of S. bovis JB1 using insertional mutagenisis.