CLONING, SEQUENCE, AND EXPRESSION OF THE L-(-DEHYDROGENASE OF STREPTOCOCCUS-BOVIS() LACTATE)

The ldh gene encoding the fructose-1,6-diphosphate-dependent L-(+) lac tate dehydrogenase from the ruminal bacterium Streptococcus bovis was cloned and sequenced. A genomic library of S. bovis JB1 DNA was constr ucted in lambda ZAP LT and screened by use of a heterologous probe der ived from the cloned Streptococcus mutans ldh gene. Several clones wer e isolated that contained a common 2.9-kb fragment as determined by re striction analysis. Nucleotide sequence analysis revealed a 987-bp ope n reading frame with extensive homology to Streptococcus thermophilus and S. mutans ldh nucleic acid and amino acid sequences. Expression of the cloned S. bovis ldh gene in Escherichia coli was confirmed by the ability to complement 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 mult icopy plasmid.