Starch hydrolysing Bacillus halodurans isolates from a Kenyan soda lake

Fourteen obligate alkaliphilic and halotolerant bacterial isolates, exhibiting extracellular amylase activity at 55 degrees C and pH 10, were isolated from hot springs around Lake Bogoria, Kenya. From 16S rDNA sequence analysis, nine isolates shared 100% identity with Bacillus halodurans strain DSM 497T, while the rest shared 99% identity with alkaliphilic Bacillus species A-59. PCR of the intergenic spacer region between 16S and 23S rRNA genes (ISR-PCR) divided the isolates into two groups, while tDNA-PCR divided them into three groups. Bacillus halodurans DSM 497T had a different ISR pattern from the isolates, while it had a tDNA-PCR profile similar to the group that shared 99% identity with alkaliphilic Bacillus species A-59. All isolates hydrolysed soluble starch as well as amylose, amylopectin and pullulan. The amylase activity (1.2-1.8 U ml(-1)) in the culture broths had an optimum temperature of 55-65 degrees C, was stimulated by 1 mm Ca2+, and was either partially (16-30%) or completely inhibited by 1 mM EDTA. Activity staining of the cell-free culture supernatant from the isolates revealed five alkaline active amylase bands.