Structure and function of L-lactate dehydrogenases from thermophilic, mesophilic and psychrophilic bacteria, IX. Identification, isolation and nucleotide sequence of two L-lactate dehydrogenase genes of the psychrophilic bacterium Bacillus psychrosaccharolyticus.

Two genes encoding for L-lactate dehydrogenase (LDH) from the psychrophilic bacterium Bacillus psychrosaccharolyticus (DSM 6) were cloned and their nucleotide sequence determined using a pEMBL vector and gene hybridization probes. The deduced amino-acid sequence of the gene from clone pLDH(X), which is located on a 5.87-kb HindIII-fragment, shows an identity of 86% as compared with the sequence of the wildtype LDH(P) from B. psychrosaccharolyticus and consists of 319 amino acids. Clone pLDH(P) contained a gene on a 4-kb HindIII-EcoRI fragment, of which the amino-acid sequence is identical with the enzyme isolated from B. psychrosaccharolyticus. The nucleotide sequences of LDH(P) and LDH(X) show 77% identity. Both genes are expressed in E. coli and the proteins could be isolated as shown by enzyme activity tests and determination of the N-terminal amino-acid sequence. However no expression of LDH(X) could be detected in B. psychrosaccharolyticus itself under the conditions chosen for oxygen induction of LDH. The function of the additional, non-expressed enzyme is not known.