Abstract
Microarray-based comparative genome hybridization (CGH) analysis was used to obtain information regarding chromosomal changes that occurred during successive rounds of mutagenesis in a pedigree of Aspergillus niger glucoamylase production strains. This analysis revealed both deletions and amplifications of discrete DNA segments ranging in size from less than one kb to as much as 400 kb. Most importantly, we observed repeated amplification of a 216 kb region that included the glaA (glucoamylase) gene. CHEF (Contour-clamped Homogeneous Electric Field) gel analyses indicated that the amplified DNA segment was translocated nonreciprocally and several chromosomes were rearranged in successive strains of the lineage. The number of glaA gene copies increased from 2 in the original parent strain to approximately 10 in the final strain of the pedigree. Quantitative real-time PCR analyses confirmed the CGH results, leading us to hypothesize that at least some of the incremental improvements in glucoamylase titers obtained from mutants derived by successive rounds of mutagenesis and screening may be associated with increases in the number of chromosomal glaA gene copies. Furthermore, the genomic region that encompasses the glaA gene might be particularly susceptible to duplication and translocation by virtue of its telomereproximal location.
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