The diversity of extremophilic bacteria in lake Magadi, Kenya

Abstract

Lake Magadi, a highly saline lake with a pH range of about 11 to13, harbors extremophilic eubacteria and archaeobacteria that are either halophilic, alkaliphilic, haloalkaliphilic or thermophilic. Water sampling was done in seven hot springs along the shoreline and one sample from along the Western causeway. Physicochemical conditions included a temperature range of 30°C to 47°C , a pH range of 10 to 10.5, hydrogen peroxide concentration ofless than 0.5 ppm and dissolved O2 concentration ranging from 1.1 mg/l to 2.9 mg/l. Morphological characterization indicated presence of gram positive and gram negative bacteria with shapes varying from rods, cocci, spirilla to coccobacilli. Biochemical characteristics of the isolates included catalase production and hydrolysis of casein and starch. The optimal temperature for growth of bacterial isolates ranges from 40°C to 45°C while optimal salt concentration ranges from 6% to 9% w/v. Successful PCR was done on genomic DNA from the bacterial isolates, using 16S primers, and verified by means of agarose gel electrophoresis. On sequencing, four of the PCR products had about 1,500 bp of 16S rRNA. When aligned to existing sequences in the NCBI database, they were found to be closely related to members of the gamma subdivision of the Proteobacteria with over 98% similarity. One of the isolates appeared to have a separate lineage from the ones in the database with only 97% similarity to its closest comparison. Two of the isolates were closely related to but not identical to members of the genus Halomonas. Phylogenetic analysis by means of a rooted tree showed that three of the isolates clustered closely with members of gamma Proteobacteria. The multialignments obtained in this study can be used for primer design and the characterized isolates can be used to obtain metabolites for biotechnological applications