GENETIC DIVESITY AND EXTRACELULLAR ENZYMATIC ACTIVITY OF BACILLUS LICHENIFORMIS STRAINS FROM MILK POWDER

Abstract

A total of 379 B. licheniformis strains isolated from commercial milk powder were characterized genotypically and phenotypically. RAPD analysis yielded three different profiles, which include all isolates in this study, which could be assigned to strain F (n=375) or strain G (n=4), strain F also could be divided into two groups (group 1, n = 117; group 2, n = 258). Clustering by pairwise sequence similarity and phylogenetic relationships between isolates based on comparisons of the 16S rRNA gene sequence, showed two well defined groups. Group I contains all isolates tested belonging to genotype F, and Group II consists of three G genotype isolates. A total of 32 isolates, respecting the representation of each genotype, were randomly selected for extracellular enzymatic activity plate assays. Most isolates (25 out of 32) showed extracellular proteinase, lipase and amylase activity. Hydrolytic activities tested in this study are strain-dependent and none enzymatic activity could be linked to a defined group at genetic level. Preliminar characterization of proteolytic crude enzyme extract suggests the presence of a metal-activated serine protease active at an optimun temperature of 60 ºC. The exoenzymes production and its variation against different factors such as temperature, is isolate dependent so these results indicate that not all B. licheniformis strains may mean the same risk to process or product quality.