Note: purification and characterization of the bacteriocin PsVP-10 produced by Pseudomonas sp

Outer Membrane Channel Protein TolC Regulates Escherichia coli K12 Sensitivity to Plantaricin BM-1 via the CpxR/CpxA Two-Component Regulatory System

Plantaricin BM-1, a class IIa bacteriocin produced by Lactobacillus plantarum BM-1, has significant antibacterial activity against Gram-positive and Gram-negative bacteria. This study aimed to explore the role of the Escherichia coli K12 outer membrane (OM) channel protein TolC in the response to plantaricin BM-1. The tolC null mutant (E. coli K12^∆tolC) was constructed by Red homologous recombination. The mechanism of tolC regulating the sensitivity of E. coli K12 under plantaricin BM-1 was investigated. tolC null mutation significantly increased the E. coli K12 sensitivity to plantaricin BM-1 and inhibited biofilm formation, and cells ruptured and shrunk. Proteomic analysis showed that the AcrAB-TolC and EmrAB-TolC efflux pumps were significantly (p < 0.05) upregulated in E. coli K12^∆tolC. Based on the results of real-time PCR, we concluded that under plantaricin BM-1, the CpxR/CpxA two-component regulatory system of E. coli K12 responded with envelope damage, followed by activation of the transcription of marA and expression of AcrAB-TolC efflux pump. Moreover, tolC null mutation weakened the AcrAB-TolC efflux pump and then increased the sensitivity of E. coli K12 to plantaricin BM-1. These will contribute exploring the action mechanism of class IIa bacteriocins against Gram-negative bacteria.

Inhibition of food-related bacteria by antibacterial substances produced by Pseudomonas sp. strains isolated from pasteurized milk

In this work, the production of antimicrobial substances by strains of Pseudomonas sp. isolated from pasteurized milk and their potential action against food-related bacteria were investigated. Samples of pasteurized milk were purchased from arbitrarily chosen commercial establishments in the city of Rio de Janeiro, Brazil. Of the four samples analyzed, three presented several typical colonies of Pseudomonas. About 100 colonies were chosen and subjected to biochemical tests for confirmation of their identity. Eighteen strains of the Pseudomonas genus were identified and submitted to tests for the production of antimicrobial substances. Twelve strains (66.7%) were identified as Pseudomonas fluorescens, four (22.2%) as P. aeruginosa, one (5.5%) as P. mendocina and one (5.5%) as P. pseudoalcaligenes. Only two P. fluorescens strains were unable to produce any antimicrobial substance against any of the indicator strains tested. Most of the strains presented a broad spectrum of action, inhibiting reference and food-related strains such as Proteus vulgaris, Proteus mirabilis, Hafnia alvei, Yersinia enterocolitica, Escherichia coli and Salmonella typhi. Five antimicrobial substance-producing strains, which presented the broadest spectrum of action, were also tested against Staphylococcus aureus reference strains and 26 Staphylococcus sp. strains isolated from foods, some of which were resistant to antibiotics. The producer strains 8.1 and 8.3, both P. aeruginosa, were able to inhibit all the staphylococcal strains tested. The antimicrobial substances produced by strains 8.1 and 8.3 did not seem to be typical bacteriocins, since they were resistant to the three proteolytic enzymes tested. Experiments involving the characterization of these substances are being carried out in order to evaluate their biotechnological application.

Plant lectin-like bacteriocin from a rhizosphere-colonizing Pseudomonas isolate

Rhizosphere isolate Pseudomonas sp. strain BW11M1, which belongs to the Pseudomonas putida cluster, secretes a heat- and protease-sensitive bacteriocin which kills P. putida GR12-2R3. The production of this bacteriocin is enhanced by DNA-damaging treatment of producer cells. We isolated a TnMod mutant of strain BW11M1 that had lost the capacity to inhibit the growth of strain GR12-2R3. A wild-type genomic fragment encompassing the transposon insertion site was shown to confer the bacteriocin phenotype when it was introduced into Escherichia coli cells. The bacteriocin structural gene was identified by defining the minimal region required for expression in E. coli. This gene was designated llpA (lectin-like putidacin) on the basis of significant homology of its 276-amino-acid product with mannose-binding lectins from monocotyledonous plants. LlpA is composed of two monocot mannose-binding lectin (MMBL) domains. Several uncharacterized bacterial genes encoding diverse proteins containing one or two MMBL domains were identified. A phylogenetic analysis of the MMBL domains present in eukaryotic and prokaryotic proteins assigned the putidacin domains to a new bacterial clade within the MMBL-containing protein family. Heterologous expression of the llpA gene also conveyed bacteriocin production to several Pseudomonas fluorescens strains. In addition, we demonstrated that strain BW11M1 and heterologous hosts secrete LlpA into the growth medium without requiring a cleavable signal sequence. Most likely, the mode of action of this lectin-like bacteriocin is different from the modes of action of previously described Pseudomonas bacteriocins.