RESUMEN
Aspergillus oryzae and Aspergillus flavus are closely related fungal species. The A. flavus morphotype that produces numerous small sclerotia (S strain) and aflatoxin has a unique 1.5 kb deletion in the norB-cypA region of the aflatoxin gene cluster (i.e. the S genotype). Phylogenetic studies have indicated that an isolate of the nonaflatoxigenic A. flavus with the S genotype is the ancestor of A. oryzae. Genome sequence comparison between A. flavus NRRL3357, which produces large sclerotia (L strain), and S-strain A. flavus 70S identified a region (samA-rosA) that was highly variable in the two morphotypes. A third type of samA-rosA region was found in A. oryzae RIB40. The three samA-rosA types were later revealed to be commonly present in A. flavus L-strain populations. Of the 182 L-strain A. flavus field isolates examined, 46%, 15% and 39% had the samA-rosA type of NRRL3357, 70S and RIB40, respectively. The three types also were found in 18 S-strain A. flavus isolates with different proportions. For A. oryzae, however, the majority (80%) of the 16 strains examined had the RIB40 type and none had the NRRL3357 type. The results suggested that A. oryzae strains in the current culture collections were mostly derived from the samA-rosA/RIB40 lineage of the nonaflatoxigenic A. flavus with the S genotype.
Asunto(s)
Aspergillus oryzae/genética , Proteínas Bacterianas/genética , Variación Genética , Filogenia , Aflatoxinas/genética , Aspergillus oryzae/clasificación , Secuencia de Bases , Genotipo , Familia de MultigenesRESUMEN
A nontoxigenic Aspergillus flavus strain, K49, is currently being tested as a biological control agent in corn fields in the Mississippi Delta. However, little is known about the overall genetic diversity of A. flavus from year to year in corn fields and specifically in Mississippi. Our objective was to assess the genetic variability of A. flavus isolates from different seasons, inoculum sources, and years, from a no-till corn field. Of the 175 A. flavus isolates examined, 74 and 97 had the typical norB-cypA type I (1.5 kb) and type II (1.0 kb) deletion patterns, respectively. Variability in the sequence of the omtA gene of the majority of the field isolates (n = 118) was compared to strain K49. High levels of haplotypic diversity (24 omtA haplotypes; Hd = 0.61 ± 0.04) were found. Among the 24 haplotypes, two were predominant, H1 (n = 71), which consists of mostly toxigenic isolates, and H49 (n = 18), which consists of mostly atoxigenic isolates including K49. Toxigenic isolates were prevalent (60%) in this natural population. Nonetheless, about 15% of the population likely shared the same ancestral origin with K49. This study provides valuable information on the diversity of A. flavus. This knowledge can be further used to develop additional biological control strains.
Asunto(s)
Aspergillus flavus/genética , Variación Genética , Control Biológico de Vectores , Haplotipos , Mississippi , Zea mays/genética , Zea mays/microbiologíaRESUMEN
The floodwater mosquito Aedes vexans, a potential vector of West Nile virus, has a worldwide distribution that includes the continental United States and southern Canada. In order to determine the effect that Hurricane Katrina had on the temporal genetic variation of Ae. vexans from New Orleans, we compared genetic diversity of a portion of the mtDNA ND5 gene of mosquito specimens collected during 2005 (n = 99) with specimens from 2006 (n = 103), after the hurricane. Average haplotype diversity (Hd) was high (>0.88) in 2005 and 2006 for both the parishes studied. It does not appear that Hurricane Katrina had any impact on genetic diversity, and despite the intense efforts to control mosquitoes in New Orleans, Ae. vexans has not undergone a population bottleneck. A bottleneck effect may be lacking because this species breeds outside the city and the adults migrate into the city.