A volatile relationship: profiling an inter-kingdom dialogue between two plant pathogens, Ralstonia Solanacearum and Aspergillus Flavus.

Microbes in the rhizosphere have a suite of extracellular compounds, both primary and secondary, that communicate with other organisms in their immediate environment. Here, we describe a two-way volatile interaction between two widespread and economically important soil-borne pathogens of peanut, Aspergillus flavus and Ralstonia solanacearum, a fungus and bacterium, respectively. In response to A. flavus volatiles, R. solanacearum reduced production of the major virulence factor extracellular polysaccharide (EPS). In parallel, A. flavus responded to R. solanacearum volatiles by reducing conidia production, both on plates and on peanut seeds and by increasing aflatoxin production on peanut. Volatile profiling of these organisms using solid-phase micro-extraction gas chromatography mass spectroscopy (SPME-GCMS) provided a first glimpse at the compounds that may drive these interactions.

Antifungal activity of 2 lactic acid bacteria of the Weissella genus isolated from food.

UNLABELLED: In the present study, a total of 116 lactic acid bacteria (LAB) strains isolated from Mill flour and fermented cassava were screened for their antifungal activity. Three strains among 116 were selected for their strongest inhibitory activity against food molds. These 3 strains were Lactobacillus plantarum VE56, Weissella cibaria FMF4B16, and W. paramesenteroides LC11. The compounds responsible for the antifungal activity were investigated. The strains displayed an inhibitory activity against targeted molds at acidic pH. However, the influence of organic acids was rejected according to the calculated minimal inhibitory concentration (MIC). Antifungal compounds were investigated in the cell-free supernatants and phenyllactic acid (PLA) was detected in different amounts with a maximal concentration for Lb. plantarum VE56 (0.56 mM). Hydroxy fatty acid, such as 2-hydroxy-4-methylpentanoic acid, was also produced and involved in the inhibitory activity of Lb. plantarum VE56 and W. paramesenteroides LC11. Antifungal LAB are known to produce PLA and 3-hydroxy fatty acids and other organic acids with antifungal activity. This short communication focuses on antifungal activity from Weissella genus. The antifungal activity was attributed to antifungal compounds identified such as PLA, 2-hydroxy-4-methylpentanoic acid, and other organic acids. Nevertheless, the concentration produced in the cell-free supernatant was too low to compare to their MIC, suggesting that the inhibitory activity was caused by a synergy of these different compounds. PRACTICAL APPLICATION: Antifungal LAB are interesting to prevent food spoilage in fermented food and prolong their shelf life. In this way, chemical preservatives could be avoided and replaced by natural preservatives.

Characterisation of an Antilisterial Bacteriocin Produced by Lactobacillus sakei CWBI-B1365 Isolated from Raw Poultry Meat and Determination of Factors Controlling its Production.

Amongst 101 lactic acid bacteria isolated from meat and fish samples, strain CWBI-B1365, identified as Lactobacillus sakei, was found to produce the subclass IIa bacteriocin sakacin G. Partial sequencing of the gene involved in the biosynthetic pathways revealed an unusual gene organisation in that the accessory gene associated with bacteriocin transport did not occur immediately downstream of the gene encoding an ABC transporter, but upstream of the putative immunity gene and encoded on the opposite DNA strand. Sakacin G production was strongly regulated by pH, temperature and the carbon sources used in the growth medium, as well as the concentration of carbon and nitrogen sources. The condition of pH 5.5 and the temperature of 25°C appeared to be optimal for bacteriocin production. The use of sucrose during culturing and the fed batch addition of sucrose and meat extract greatly enhanced bacteriocin production.