Comparison of growth, nutritional utilisation patterns, and niche overlap indices of toxigenic and atoxigenic Aspergillus flavus strains

The effects of temperatures (20-30 °C) and water activity (0.90-0.99 aw) on the lag phase duration, mycelial growth, and nutritional utilisation patterns of two toxigenic (AFL1(+) & AFL2(+)) and three atoxigenic (AFL1(-), AFL2(-), & AFL3(-)) Aspergillus flavus strains were evaluated in vitro. Both temperature and aw and their interactions had a significant influence on the growth and nutritional utilisation patterns (p < 0.05). There were no significant differences between toxigenic and atoxigenic strains in terms of lag phase prior to growth and mycelial growth rates. Based on carbon source (CS) utilisation patterns, toxigenic and atoxigenic strains' niche size was greater at higher temperatures and in wetter conditions. Additionally, based on niche overlap indices (NOIs), regardless of temperature, when water was freely available, atoxigenic and toxigenic strains co-existed. However, under moisture stress, the nutritional competitiveness was variable. Temporal carbon utilisation sequences (TCUS) of toxigenic and atoxigenic strains were compared. At 0.99 aw most CS sources were utilised by the strains and the time to detection (TTD) of each strain was shortest on monosaccharides at the same level of aw. Conversely, under moisture stress the least number of CS was utilised. The current study has demonstrated that carbon utilisation patterns are equally important as are other determinants of competitiveness and that growth rate alone is not a key attribute which determines competitiveness.