Major role of lactate dehydrogenase D-LDH1 for the synthesis of lactic acid in Fructobacillus tropaeoli CRL 2034

BLECKWEDEL, JULIANA; RAYA, RAÚL RICARDO; MOHAMED, FLORENCIA; MOZZI, FERNANDA

APPLIED MICROBIOLOGY AND BIOTECHNOLOGY

SPRINGER

Lugar: Berlin; Año: 2020

0175-7598

The enzymes D- and L-lactate dehydrogenase are involved in the reduction of pyruvate to D(+)- and L(-)-lactate, respectively. The fig-origin strain Fructobacillus tropaeoli CRL 2034 produces D- and L-lactic acids in a 9:1 ratio. In this work, two D-ldh (ldh1 and ldh2) and one L-ldh (ldh3) genes were found in the CRL 2034 genome. ldh1 and ldh2 are homologous (79% identity) and organized as contiguous operons; each gene containing 996-base pair (bp) and encoding for a 331 amino acids (aa) protein (74% identity). In contrast, ldh3 is a 927 bp gene coding for a 308 aa protein. The identity between ldh1/ldh2 and ldh3 was lower than 48%. To elucidate the role of these genes in the synthesis of lactic acid by the Fructobacillus strain, plasmid insertion mutants in each gene were generated and characterized. The growth kinetic parameters were affected only in CRL2034 ldh1::pRV300 cells; this mutant showing the lowest total lactic acid production (4.50 ± 0.15 versus 6.36 ± 0.67 g/L of wild type strain), with a D-/L- ratio of 7.1:2.9. These results showed that the ldh1 gene is primarily responsible for lactic acid production by the studied strain. A comparative analysis among strains of the five Fructobacillus species revealed that the identity of D-LDH proteins was higher than 70%, while the identity of L-LDH was over 60%. Finally, phylogenetic analysis of D- and L-LDHs revealed that only D-LDHs phylogeny was consistent to the phylogenetic evolution among Fructobacillus and evolutionary related genera.