Microbial ecology of halo-alkaliphilic sulfur bacteria

The research of this thesis focussed on the investigation of the microbial diversity in soda lakes, giving a special attention to the micro-organisms involved in the sulphur cycle. The present PhD was part of a bigger project aiming to develop a biological process for the removal of hydrogen sulphide under halo-alkaliphilic conditions. In this new process, sulphide is mainly oxidized to elemental sulphur by sulphur-oxidizing bacteria (SOB). However, a small percentage of unwanted sulphate is still produced, which is reduced back to sulphide by sulphate-reducing bacteria (SRB). Since this process operates under halo-alkaliphilic conditions, which are naturally occurring in soda lakes, a better understanding of the sulphur microbial diversity in such environments was required. Soda lakes are extreme environments, characterized by an extremely high pH (up to 11.5) and moderately to extremely high salinities (up to 500 g/L). They are a specific type of saline lakes and are spread all over the world, generally confined to arid and semi-arid regions. We especially researched soda lakes from the Kulunda Steppe, which are located in the south-east of Siberia (Russia). These lakes are still less investigated, due to their difficulty to be reached. So-called halo-alkaliphilic organisms inhabit these lakes, which raise the interest of the bioindustry for their capability to stand such harsh conditions. In this research we focussed on the halo-alkaliphilic sulphur bacteria. Special attention was given to the genetic diversity and biogeography of a specific group of halo-alkaliphilic chemolithoautotrophic SOB, i.e. Thioalkalivibrio, and to the diversity, activity and dynamics of the SRB communities in different soda lakes of the Kulunda Steppe, also in relation to the increase of the salt concentration.Applied Science

Bacterial diversity and activity along a salinity gradient in soda lakes of the Kulunda Steppe (Altai, Russia)

Here we describe the diversity and activity of sulfate reducing bacteria along a salinity gradient in four different soda lakes from the Kulunda Steppe (South East Siberia, Russia). For this purpose, a combination of culture-dependent and independent techniques was applied. The general bacterial and SRB diversity were analyzed by denaturing gradient gel electrophoresis (DGGE) targeting the 16S rDNA gene. DNA was used to detect the microbial populations that were present in the soda lake sediments, whereas ribosomal RNA was used as a template to obtain information on those that were active. Individual DGGE bands were sequenced and a phylogenetic analysis was performed. In addition, the overall activity of SRB was obtained by measuring the sulfate reduction rates (SRR) and their abundance was estimated by serial dilution. Our results showed the presence of minor, but highly active microbial populations, mostly represented by members of the Proteobacteria. Remarkably high SRR were measured at hypersaline conditions (200 g L-1). A relatively high viable count indicated that sulfate reducing bacteria could be highly active in hypersaline soda lakes. Furthermore, the increase of sodium carbonate/bicarbonate seemed to affect the composition of the microbial community in soda lakes, but not the rate of sulfate reduction.BiotechnologyApplied Science