The influence of L-ascorbic acid on the antibacterial-toxic activity of aflatoxins on adsorbent layer.

AIMS: To substantiate the role of formaldehyde (HCHO) and its reaction products in the mechanism of the antibacterial-toxic effect of aflatoxins B1 (AFB1), B2, G1 and G2. MATERIALS AND RESULTS: Toxins were separated by overpressured layer chromatography, which was followed by biological evaluation directly on the adsorbent layer (BioArena system with Pseudomonas savastanoi pv. phaseolicola indicator bacteria). HCHO formed in this system was eliminated with exogenously added capturer molecule dimedone and L-ascorbic acid (AA) and measured as the adduct of dimedone and HCHO. The amount of HCHO was higher in the toxin-containing spots, particularly in the most toxic AFB1 spot, compared to a toxinless background. 0.1 mg ml(-1)AA augmented, 0.2 mg ml(-1) dimedone or 0.5 and 1 mg ml(-1) AA reduced the antibacterial effect of all four aflatoxins. CONCLUSION: The antibacterial-toxic effect of aflatoxins may be mediated by HCHO (and/or its reaction products) generated from bound HCHO forms in the bacterial cells. Basis of antibacterial-toxic activity of the four aflatoxins appears the same. SIGNIFICANCE AND IMPACT OF THE STUDY: Involvement of HCHO as a key molecule in the effect of aflatoxins indicates a totally new mechanism of action of these dangerous molecules. The BioArena system is useful to dissect the mode of action of antimicrobial compounds from different biological matrices.

Opposite effect of Cu(II) and Se(IV) ions on the antibacterial-toxic action of mycotoxins.

The effect of Se(IV) and Cu(II) ions on the antibacterial activity of aflatoxins and ochratoxin A (mycotoxins) was studied in BioArena as a complex bioautographic system. In the presence of 0.23 and 0.46 mg/100 mL Se(IV) the inhibition zones of mycotoxins were decreased, however, lower concentration (0.046 mg/100 mL) increased the antibacterial effect of aflatoxin B1. Cu(II) (1.53 mg/100 mL) enhanced the toxicity of mycotoxins. The results supported the possible role of formaldehyde and its reaction products (e.g. 1O2, O3) in the antibacterial-toxic action of mycotoxins. Cu(II) can probably generate and mobilise the formaldehyde molecules and so it could increase the toxicity with its potential reaction products. It is possible that the enzymatic or spontaneous methylation of Se(IV) takes place through formaldehyde, which may cause partial formaldehyde depletion in the system. The enhanced antibacterial effect at low concentration Se(IV) is overlapping with the often experienced prooxidant effect in cases of natural antioxidants.

Identification of virulence-associated genes of Pseudomonas viridiflava activated during infection by use of a novel IVET promoter probing plasmid.

Analysis of virulence mechanisms of plant pathogens is often limited by the lack of genetic tools that can be used to identify genes that are preferentially expressed during their interactions with plants. In the present study, we used the newly constructed IVET (in vivo expression technique) plasmid pIviGK and the corresponding antibiotic resistance-based selection method to identify genes that encode pathogenicity factors of the soft rot-causing bacterium Pseudomonas viridiflava. These included pel, the gene encoding pectate lyase, which is responsible for the development of soft rot symptoms. We have also isolated and characterized the gene mviNpv encoding a putative novel membrane associated virulence factor of P. viridiflava. A mutation in mviNpv was shown to influence motility as well as virulence of P. viridiflava. The mviNpv gene is expressed to a moderate level in LB media and its expression increases under inducing conditions as was shown by measuring in planta expression dynamics of the fused gfp reporter gene.