Bacteria, archaea and viruses of Soda Lakes

Abstract

The soda lake environment presents microorganisms with many combinations of physical and chemical extremes, amongst them extremes of alkaline pH, salinity (NaCl), temperature and incident radiation and water and oxygen availability. Despite this harsh regime, soda lakes are fertile habitats for an enormous diversity of alkaliphilic prokaryotic microbiota, which in turn is a host to a range of alkaliphilic viruses. The main driver for these ecosystems is the prodigious rate of photosynthetic primary production provided by alkaliphilic Cyanobacteria and anoxygenic phototrophic Bacteria, which deliver fixed carbon for a vast array of aerobic and anaerobic chemoorganotrophic Bacteria and Archaea. Many of these microbes are unique to soda lakes although the soda lake microorganisms are found within all the main prokaryotic evolutionary divisions and amongst all the major trophic groups and often have relatives or counterparts in freshwater and salt lake ecosystems. Due mainly to their often difficult accessibility and a general lack of familiarity with soda lakes, they were little explored by microbiologists until the 1980s, when systematic studies began on the alkaline lakes of the East African Rift System (EARS) in Kenya. The investigations in East Africa stimulated and inspired examination of other soda lakes around the globe. Accordingly, as of today (June 2015), around 200 Bacteria and Archaea, many of them novel or unique to soda lakes, have been reported. Based on analyses in the EARS soda lakes, the microorganisms involved in the cycling of carbon, together with nitrogen and sulphur, in soda lakes worldwide can now be construed with some confidence, revealing a complex trophic web of microbial interactions. This chapter provides a reference for the microbiota of the EARS soda lakes, as determined by culture-dependent and culture-independent methods, in relation to that in soda lakes around the world.