In vitro Selection of Maize Rhizobacteria to Study Potential Biological Control of Aspergillus Section Flavi and Aflatoxin Production

Abstract

The aims of this study were to select bacterial isolates from the non-rhizophere of maize soil and to examine their antagonistic activity against Aspergillus section Flavi strains. The first selection was made through ecophysiological responses of bacterial isolates to water activity (a w ) and temperature stress. Subsequently, an Index of Dominance test (I D ), ecological similarity and inhibition of the lag phase prior to growth, growth rate and aflatoxin B 1 accumulation were used as criteria. From the first assay nine bacterial strains were selected. They grew well at 25 and 30°C, with growth optima between 0.982 and 0.955 a W using 48 h of incubation. There was ecological similarity between the bacterial strains Bacillus subtilis (RCB 3, RCB 6), Pseudomonas solanacearum RCB 5, Amphibacillus xylanus RCB 27 and aflatoxigenic Aspergillus section Flavi strains at 0.982 at 25°C. The predominant interaction between all selected bacteria and fungi in dual culture was mutual intermingling at 0.982. Mutual inhibition on contact and mutual inhibition at a distance was observed at 0.955 a w , between only four bacteria and some Aspergillus strains. Bacillus subtilis RCB 55 showed antifungal activity against Aspergillus section Flavi strains. Amphibacillus xylanus RCB 27, B. subtilis RCB 90 and Sporolactobacillus inulinus RCB 196 increased the lag phase prior to growth and decreased the growth rate of Aspergillus section Flavi strains. Bacillus subtilis strains (RCB 6, RCB 55, RCB 90) and P. solanacearum RCB 110 inhibited aflatoxin accumulation. Bacillus subtilis RCB 90 completely inhibited aflatoxin B 1 accumulation at 0.982 a W . These results show that the bacterial strains selected have potential for controlling Aspergillus section Flavi over a wide range of relevant environmental conditions in the stored maize ecosystem.

Aflatoxins Biochemistry and Molecular Biology - Biotechnological Approaches for Control in Crops

“…and Burkholderia spp., have shown the ability to inhibit fungal growth and production of aflatoxins by Aspergillus spp. in laboratory experiments , the same effect was observed in strains of B. subtilis and P. solanacearum isolated from the non-rhizophere of maize soil were also able to inhibit aflatoxin accumulation (Nesci et al, 2005). In other experiments, is showed that Bacillus subtilis prevented aflatoxin contamination in corn in field tests when ears were inoculated with the bacterium 48 hours before inoculation with A. flavus (Cuero et al, 1991).…”

Aflatoxins: A Global Concern for Food Safety, Human Health and Their Management

“…are effective at control and management of aflatoxins (Palumbo et al, 2006). Several strains of B. subtilis and P. solanacearum isolated from the non-rhizosphere of maize soil have been reported to eliminate aflatoxin (Nesci et al, 2005). Biological control of aflatoxin production in crops in the US has been approved by the Environmental Protection Agency and two commercial products based on atoxigenic A. flavus strains are being used (Afla-guard ® and AF36 ® ) for the prevention of aflatoxin in peanuts, corn, and cotton seed (Dorner, 2009).…”

Scientific information on mycotoxins and natural plant toxicants

“…The present document has been produced and adopted by the bodies identified above as author(s (Nesci et al, 2005). In most cases, although these strains were highly effective against AF production and fungal growth under laboratory conditions, they do not have good efficacy in field trials because it is difficult to bring the bacterial cells to the Aspergillus infection sites on commodities under field conditions (Dorner, 2004).…”