RESUMO
Quorum quenching (QQ), the obstruction of quorum sensing, is the most attractive way to break down the N-acyl-homoserine lactones (AHL) molecules. This work was focused at isolating AHL degrading bacteria from gastrointestinal tract of Oreochromis niloticus, with abilities appropriate for use as probiotic in aquaculture. The presence of an autoinducer inactivation (aiiA) homolog gene and AHL inactivation assay showed that Enterococcus faecium QQ12, which was one among the 20 isolates, could rapidly degrade synthetic C6-HSL in vitro and hampered violacein production by Chromobacterium violaceum. It had excellent biodegrading ability of natural N-AHL produced by Aeromonas hydrophila, suggesting that it can be used as a potential quencher bacterium for disrupting the virulence of A. hydrophila. It was susceptible to all the five antibiotics tried out. The isolate grew well at pH 3.0-7.0, was resistant to high level of bile salts (0-0.9%) and 0.5% of phenol. QQ12 also exhibited high degree of auto-aggregation and co-aggregation, confirming that it possessed good probiotic attributes. Goldfish fed diet incorporated with 108 and 1010 CFU g-1 of the QQ12 for 30 days showed 76.66-86.66% survival when challenged with A. hydrophila. The study indicates that Enterococcus faecium QQ12 could be used as a non-antibiotic feed additive in aquaculture to control bacterial diseases.
Assuntos
Aeromonas hydrophila/efeitos dos fármacos , Ciclídeos/microbiologia , Enterococcus faecium/fisiologia , Doenças dos Peixes/microbiologia , Trato Gastrointestinal/microbiologia , Infecções por Bactérias Gram-Negativas/veterinária , Probióticos/farmacologia , Percepção de Quorum , Aeromonas hydrophila/fisiologia , Animais , Enterococcus faecium/genética , Enterococcus faecium/isolamento & purificação , Doenças dos Peixes/tratamento farmacológico , Carpa Dourada/microbiologia , Infecções por Bactérias Gram-Negativas/tratamento farmacológico , Infecções por Bactérias Gram-Negativas/microbiologiaRESUMO
Azospirillum brasilense is an important plant-growth promoting bacterium (PGPB) that requires several critical steps for root colonization, including biofilm and exopolysaccharide (EPS) synthesis and cell motility. In several bacteria these mechanisms are mediated by quorum sensing (QS) systems that regulate the expression of specific genes mediated by the autoinducers N-acyl-homoserine lactones (AHLs). We investigated QS mechanisms in strains Ab-V5 and Ab-V6 of A. brasilense, which are broadly used in commercial inoculants in Brazil. Neither of these strains carries a luxI gene, but there are several luxR solos that might perceive AHL molecules. By adding external AHLs we verified that biofilm and EPS production and cell motility (swimming and swarming) were regulated via QS in Ab-V5, but not in Ab-V6. Differences were observed not only between strains, but also in the specificity of LuxR-type receptors to AHL molecules. However, Ab-V6 was outstanding in indole acetic acid (IAA) synthesis and this molecule might mimic AHL signals. We also applied the quorum quenching (QQ) strategy, obtaining transconjugants of Ab-V5 and Ab-V6 carrying a plasmid with acyl-homoserine lactonase. When maize (Zea mays L.) was inoculated with the wild-type and transconjugant strains, plant growth was decreased with the transconjugant of Ab-V5-confirming the importance of an AHL-mediated QS system-but did not affect plant growth promotion by Ab-V6.