Assessment of alkaliphilic haloarchaeal diversity in Sua pan evaporator ponds in Botswana

Abstract

Cultivation-dependent and molecular-based culture-independent methods were used to assess alkaliphilic haloarchaeal diversity at Sua pan evaporator ponds in Botswana. Isolates belonging to the genera Natrialba, Natronococcus and Natronorubrum were recovered from brine samples by enrichment and identified through a series of biochemical tests as well as sequencing of 16S rRNA fragments. In addition, an environmental 16S rRNA library was constructed from brine samples of two evaporator ponds. The library comprised members of the genera Halorubrum (65%), Natrialba (14%), Natronorubrum (7%) and new phylotypes (14%). The new phylotypes consisted of two clones that exhibited low 16S rRNA similarity (95 – 97%) with known species and could potentially represent new species in the genus Halorubrum, one clone with 91% similarity to Natronolimnobius which could represent a new genus, as well as an unidentifiable phylotype which exhibited 79% similarity to Methanotorris formicicus. Two major differences were observed between cultivation- and molecularbased methods; firstly, Halorubrum species were largely represented in the environmental clone library but no isolates were obtained, and secondly, Natronococcus species were isolated but not detected in the clone library. An overlap between the archaeal isolates and the ribosomal library clones was apparent although the novel phylotypes detected in this study were not recovered through cultivation