Electron transport chains of lactic acid bacteria - walking on crutches is part of their lifestyle

A variety of lactic acid bacteria contain rudimentary electron transport chains that can be reconstituted by the addition of heme and menaquinone to the growth medium. These activated electron transport chains lead to higher biomass production and increased robustness, which is beneficial for industrial applications, but a major concern when dealing with pathogenic lactic acid bacteria

Heme and menaquinone induced electron transport in lactic acid bacteria

<p>Abstract</p> <p>Background</p> <p>For some lactic acid bacteria higher biomass production as a result of aerobic respiration has been reported upon supplementation with heme and menaquinone. In this report, we have studied a large number of species among lactic acid bacteria for the existence of this trait.</p> <p>Results</p> <p>Heme- (and menaquinone) stimulated aerobic growth was observed for several species and genera of lactic acid bacteria. These include <it>Lactobacillus plantarum, Lactobacillus rhamnosus, Lactobacilllus brevis, Lactobacillus paralimentarius, Streptococcus entericus </it>and <it>Lactococcus garviae</it>. The increased biomass production without further acidification, which are respiration associated traits, are suitable for high-throughput screening as demonstrated by the screening of 8000 <it>Lactococcus lactis </it>insertion mutants. Respiration-negative insertion-mutants were found with <it>noxA</it>, <it>bd</it>-type cytochrome and menaquinol biosynthesis gene-disruptions. Phenotypic screening and <it>in silico </it>genome analysis suggest that respiration can be considered characteristic for certain species.</p> <p>Conclusion</p> <p>We propose that the <it>cyd</it>-genes were present in the common ancestor of lactic acid bacteria, and that multiple gene-loss events best explains the observed distribution of these genes among the species.</p

Functional identification in Lactobacillus reuteri of a PocR-like transcription factor regulating glycerol utilization and vitamin B12 synthesis

<p>Abstract</p> <p>Background</p> <p><it>Lactobacillus reuteri </it>harbors the genes responsible for glycerol utilization and vitamin B₁₂synthesis within a genetic island phylogenetically related to gamma-Proteobacteria. Within this island, resides a gene (<it>lreu_1750</it>) that based on its genomic context has been suggested to encode the regulatory protein PocR and presumably control the expression of the neighboring loci. However, this functional assignment is not fully supported by sequence homology, and hitherto, completely lacks experimental confirmation.</p> <p>Results</p> <p>In this contribution, we have overexpressed and inactivated the gene encoding the putative PocR in <it>L. reuteri</it>. The comparison of these strains provided metabolic and transcriptional evidence that this regulatory protein controls the expression of the operons encoding glycerol utilization and vitamin B₁₂synthesis.</p> <p>Conclusions</p> <p>We provide clear experimental evidence for assigning Lreu_1750 as PocR in <it>Lactobacillus reuteri</it>. Our genome-wide transcriptional analysis further identifies the loci contained in the PocR regulon. The findings reported here could be used to improve the production-yield of vitamin B₁₂, 1,3-propanediol and reuterin, all industrially relevant compounds.</p