Novel and Unexpected Prokaryotic Diversity in Water and Sediments of the Alkaline, Hypersaline Lakes of the Wadi An Natrun, Egypt

Abstract

The phylogenetic diversity of the bacterial and archaeal community in the water and sediments of three large lakes of the Wadi An Natrun was investigated using 16S rRNA clone libraries. The bacterial community was diverse: 769 clones formed 345 operational taxonomic units (OTUs) defined at 99% 16S rRNA sequence identity. The bacterial community in both the water and sediments of the lakes was dominated by clones affiliated with the low G + C Gram-type-positive group, alpha-proteobacteria, and Bacteroidetes, (11-39, 11-30, and 10-37% of OTUs observed, respectively), patterns that have been observed in previously described alkaline, athalassohaline systems. However, a relatively high proportion of Firmicutess-related clones in the water of the lakes and alpha-proteobacteria in the sediments was observed. The bacterial community composition of the water and sediment of the same lake and of different lakes was significantly different (p < 0.05). Operational taxonomic units related to the gamma-proteobacteria were more abundant in the sediment of Lake Fazda, whereas the sediment of Lake UmRisha was dominated by members of the delta-proteobacteria. The proportion of gamma-proteobacterial and Bacteroidetes-affiliated OTUs were predominant in the water of Lake UmRisha and differed significantly from other lake waters (chi-squared analysis, p < or = 0.01). The more oxygenated and dilute nature of Lake Hamra was reflected in its microbial community composition, with the abundance of Bacillales sequences in the water, the absence of Halanaerobiales, Clostridiales, and Archaea in the water, and the presence of representatives of more phyla such as the Actinobacteria, Spirochaetes, and Verrucomicrobia. The archaeal community composition appeared less diverse: 589 clones resulted in 198 OTUs defined at 99% 16S rRNA sequence identity, and all sequences fell into the phylum Euryarchaeota. Phylogenetic analysis showed that many of the sequences were distantly related (83-90% 16S rRNA sequence identity) to cultured and uncultured archaea, with many clones forming clusters that branched deeply within the Euryarchaeota. Forty-two and 53% of the bacterial and archaeal clones had less than 90% 16S rRNA sequence identity to previously described sequences. This indicates that the water and sediments of the Wadi An Natrun harbor a unique and novel prokaryotic diversity that is different from what has been described among other alkaline, athalassohaline lakes.

Planktonic bacterial community composition of an extremely shallow soda pond during a phytoplankton bloom revealed by cultivation and molecular cloning

“…Sequences related to the species Aquiflexum balticum were also found by cultivation. The detection of phylotypes related to Bacteroidetes as one of the predominant groups is in agreement with the previous cultivation independent studies performed on the bacterial communities inhabiting soda lakes (Humayoun et al 2003;Mesbah et al 2007;Rees et al 2004). …”

“…However, many Böddi-szék clones showed the highest sequence similarities to uncultured environmental clones originating from similar saline and alkaline aquatic environments (Dimitru et al 2008;Humayoun et al 2003;Mesbah et al 2007). In accordance with our results, studying the prokaryotic communities inhabiting the water and sediment of Wadi an Natrun lakes (Egypt), Mesbah et al (2007) also revealed an unexpected phylogenetic diversity and found that none of their rarefaction curves obtained from the analysis of clone libraries reached plateaus.…”

“…Recently, the cultivation dependent and independent analyses of planktonic and sediment microbial communities include, among others, studying the soda lakes of South-East Siberia, Russia (Foti et al 2007(Foti et al , 2008, North-East Mongolia (Sorokin et al 2004), Inner Mongolia, China (Zhang et al 2001;Ma et al 2004a), Lonar Lake, India (Wani et al 2006;Joshi et al 2008), the East African Rift Valley, Kenya and Tanzania (Rees et al 2004;Mwirichia et al 2010Mwirichia et al , 2011, Wadi An Natrun, Egypt (Mesbah et al 2007), as well as Mono Lake, California, USA (Hollibaugh et al 2001;Humayoun et al 2003) and Soap Lake, Washington, USA (Dimitru et al 2008).…”

“…Besides the oxygen-producing cyanobacteria, the dominant presence of sulfide in the water and the anoxic circumstances can provide favorable conditions for mass production of haloalkaliphilic phototrophic purple sulfur and non-sulfur bacteria, which may play a role in the development of the reddish-brown discoloration of these lakes (Jones et al 1998;Mesbah et al 2007;Milford et al 2000;Mwirichia et al 2011). …”

“…Sequences related to thiosulfate-reducing species of Dethiosulfatibacter aminovorans and Fusibacter paucivorans as well as the sulfate-reducing species Desulfobotulus sapovorans and Desulfonatronum lacustre were also found among the Böddi-szék clones. In previous studies, the presence of sulfate-reducing phylotypes was reported mainly from the sediment of saline and soda lakes (Foti et al 2007(Foti et al , 2008Mesbah et al 2007). …”