No abstract

The gut microbiota is considered an organ that co-develops with the host throughout its life. The composition and metabolic activities of the gut microbiota are subject to a complex interplay between the host genetics and environmental factors, such as lifestyle, diet, stress and antimicrobials. It is evident that certain prebiotics, and antimicrobials produced by lactic acid bacteria (LAB), can shape the composition of the gut microbiota and its metabolic activities to promote host health and/or prevent diseases. In this review, we aim to give an overview of the impact of prebiotic fibres, and bacteriocins from LAB, on the gut microbiota and its activities, which affect the physiology and health of the host. These represent two different mechanisms in modulating the gut microbiota, the first involving exploitative competition by which the growth of beneficial bacteria is promoted and the latter involving interference competition by which the growth of pathogens and other unwanted bacteria is prevented. For interference competition in the gut, bacteriocins offer special advantages over traditional antibiotics, in that they can be designed to act towards specific unwanted bacteria and other pathogens, without any remarkable collateral effects on beneficial microbes sharing the same niche.

In Lactobacillus plantarum C11, bacteriocin production has previously been shown to be an inducible process, in which a secreted peptide, produced by the host itself, is involved. The inducing factor, designated plantaricin A (PlnA), is a bacteriocin-like peptide encoded by a gene (plnA) located on the same operon as the genes for a two-component regulatory system (pln-BCD). This system consists of a histidine kinase (PlnB) and two response regulators (PlnC,D), and belongs to a recently de®ned subfamily of two-component regulatory systems, which are activated by secreted peptide pheromones through a quorum-sensing mechanism. We show here that the two response regulators PlnC and PlnD bind speci®cally to imperfect direct repeats found within the adjacent promoter of the plnABCD operon, and to similar sequences found within the promoter regions of two nearby operons containing bacteriocin structural genes (plnEFI and plnJKLR). Binding of PlnC and PlnD was increased two to three fold in the presence of acetyl phosphate. The results suggest that bacteriocin synthesis in L. plantarum C11 is regulated by the DNA-binding activity of the two response regulators PlnC and PlnD.

Bacteriocins are antimicrobial peptides produced by bacteria to inhibit competitors in their natural environments. Some of these peptides have emerged as commercial food preservatives and, due to the rapid increase in antibiotic resistant bacteria, are also discussed as interesting alternatives to antibiotics for therapeutic purposes. Currently, commercial bacteriocins are produced exclusively with natural producer organisms on complex substrates and are sold as semi-purified preparations or crude fermentates. To allow clinical application, efficacy of production and purity of the product need to be improved. This can be achieved by shifting production to recombinant microorganisms. Here, we identify Corynebacterium glutamicum as a suitable production host for the bacteriocin pediocin PA-1. C. glutamicum CR099 shows resistance to high concentrations of pediocin PA-1 and the bacteriocin was not inactivated when spiked into growing cultures of this bacterium. Recombinant C. glutamicum expressing a synthetic pedACD Cgl operon releases a compound that has potent antimicrobial activity against Listeria monocytogenes and Listeria innocua and matches size and mass:charge ratio of commercial pediocin PA-1. Fermentations in shake flasks and bioreactors suggest that low levels of dissolved oxygen are favorable for production of pediocin. Under these conditions, however, reduced activity of the TCA cycle resulted in decreased availability of the important pediocin precursor l -asparagine suggesting options for further improvement. Overall, we demonstrate that C. glutamicum is a suitable host for recombinant production of bacteriocins of the pediocin family.

Bacteriocins are ribosomally synthesized antimicrobial peptides, that either kill target bacteria or inhibit their growth. Bacteriocins are used in food preservation and are of increasing interest as potential alternatives to conventional antibiotics. In the present study, we show that Lactococcus petauri B1726, a strain isolated from fermented balsam pear, produces a heat-stable and protease-sensitive compound. Following genome sequencing, a gene cluster for production of a class IId bacteriocin was identified consisting of garQ (encoding for the bacteriocin garvicin Q), garI (for a putative immunity protein), garC, and garD (putative transporter proteins). Growth conditions were optimized for increased bacteriocin activity in supernatants of L. petauri B1726 and purification and mass spectrometry identified the compound as garvicin Q. Further experiments suggest that garvicin Q adsorbs to biomass of various susceptible and insusceptible bacteria and support the hypothesis that garvicin Q requires a mannose-family phosphotransferase system (PTSMan) as receptor to kill target bacteria by disruption of membrane integrity. Heterologous expression of a synthetic garQICD operon was established in Corynebacterium glutamicum demonstrating that genes garQICD are responsible for biosynthesis and secretion of garvicin Q. Moreover, production of garvicin Q by the recombinant C. glutamicum strain was improved by using a defined medium yet product levels were still considerably lower than with the natural L. petauri B1726 producer strain.Collectively, our data identifies the genetic basis for production of the bacteriocin garvicin Q by L. petauri B1726 and provides insights into the receptor and mode of action of garvicin Q. Moreover, we successfully performed first attempts towards biotechnological production of this interesting bacteriocin using natural and heterologous hosts.