Variability among strains of Aspergillus section Nigri with capacity to degrade tannic acid isolated from extreme environments.

Tannins are polyphenolic compounds that cause astringent flavor and turbidity in food. Tannase is an enzyme that catalyzes the hydrolysis of tannins and is used in food industry. This study was conducted to determine the genetic variability and the tannase alleles variation in fungal strains isolated from soil and plants at five extreme areas of Coahuila, México. Two screening assays under 1 and 20 % of tannic acid were performed, with the isolations. In these assays, it was possible to identify 756 and 128 fungal strains, respectively. The major fungal variability was observed in "Cuatro Ciénegas" with 26 strains. The microorganisms were distributed in 11 groups, which correspond to Aspergillus section Nigri. AN7 and AN1 groups showed the major number of isolates from "Paila" and "Cuatro Ciénegas" locations, respectively. In the last location, the major diversity and specific richness were found. But in "Ojo Caliente," tannase allele conservations were observed.

Nucleotide and amino acid variations of tannase gene from different Aspergillus strains.

Tannase is an enzyme that catalyses the hydrolysis of ester bonds present in tannins. Most of the scientific reports about this biocatalysis focus on aspects related to tannase production and its recovery; on the other hand, reports assessing the molecular aspects of the tannase gene or protein are scarce. In the present study, a tannase gene fragment from several Aspergillus strains isolated from the Mexican semidesert was sequenced and compared with tannase amino acid sequences reported in NCBI database using bioinformatics tools. The genetic relationship among the different tannase sequences was also determined. A conserved region of 7 amino acids was found with the conserved motif GXSXG common to esterases, in which the active-site serine residue is located. In addition, in Aspergillus niger strains GH1 and PSH, we found an extra codon in the tannase sequences encoding glycine. The tannase gene belonging to semidesert fungal strains followed a neutral evolution path with the formation of 10 haplotypes, of which A. niger GH1 and PSH haplotypes are the oldest.