Disruption of the sole IdhL gene in Lactobacillus sakei prevents the production of both L- and D-Iactate

Abstract

Summary: A 7 kb DNA fragment was cloned from Lactobacillus sakei which contains the IdhL gene encoding the l(+)-lactate dehydrogenase (l-LDH). Analysis of the DNA sequence, Northern experiments and primer extension experiments showed that IdhL is transcribed from a single promoter, leading to a monocistronic 1·15 kb mRNA which yields the l-LDH. A stable mutant was constructed by chromosomal integration of a chloramphenicol cassette into IdhL by a double-crossover event. Both l- and d-lactate were produced by the wild-type strain whereas only residual amounts of both isomers were produced by the mutant. This demonstrates that L. sakei possesses an l-LDH producing l-lactate and a lactate racemase able to transform it to d-lactate, but is devoid of d-LDH activity. Moreover the ability to degrade l-lactate present in the medium that was observed with the mutant strain grown aerobically suggests that an l-lactate oxidase activity is also present in L. sakei.