Spirochaeta sinaica sp. nov., a halophilic spirochaete isolated from a cyanobacterial mat

A strain of free-living obligately anaerobic, halophilic spirochaete, SLT, was isolated from a sample of a cyanobacterial mat of the hypersaline Solar Lake, Sinai shore. The strain had motile helical cells, 0.35–0.40 × 6–10 μm. Strain SLT exhibited high resistance to NaCl among known halophilic spirochaetes growing at NaCl concentrations from 2 to 12 % (optimum growth at 7 %). The strain grew at temperatures from 10 to 32 °C (optimum at 28 °C) and pH from 6 to 8.5 (optimum at pH 7.0–7.5). Carbohydrates, but not alcohols, organic acids or nitrogenous compounds (peptone, yeast extract and amino acids), were used as energy substrates for growth. Ethanol, acetate, lactate, H2 and CO2 were the products of glucose fermentation. Sulfide was produced in the presence of S0 or thiosulfate in the medium. The DNA G+C content was 44.7 mol%. Based on 16S rRNA gene sequence analysis, strain SLT clustered within the genus Spirochaeta, exhibiting 94.2 and 93.7 % similarity with its closest relatives, Spirochaeta bajacaliforniensis DSM 160554T and Spirochaeta smaragdinae DSM 11293T, respectively; similarity with other species did not exceed 86 %. The phenotypic and chemotaxonomic characteristics of the strain, as well as the results of phylogenetic analysis support the classification of strain SLT as representing a novel species of the genus Spirochaeta, for which the name Spirochaeta sinaica sp. nov. is proposed. The type strain is SLT ( = DSM 14994 = UNIQEM U 783).

Distribution and Diversity of Archaea Corresponding to the Limnological Cycle of a Hypersaline Stratified Lake (Solar Lake, Sinai, Egypt)

ABSTRACT The vertical and seasonal distribution and diversity of archaeal sequences was investigated in a hypersaline, stratified, monomictic lake, Solar Lake, Sinai, Egypt, during the limnological development of stratification and mixing. Archaeal sequences were studied via phylogenetic analysis of 16S rDNA sequences as well as denaturing gradient gel electrophoresis analysis. The 165 clones studied were grouped into four phylogenetically different clusters. Most of the clones isolated from both the aerobic epilimnion and the sulfide-rich hypolimnion were defined as cluster I, belonging to theHalobacteriaceae family. The three additional clusters were all isolated from the anaerobic hypolimnion. Cluster II is phylogenetically located between the generaMethanobacterium and Methanococcus. Clusters III and IV relate to two previously documented groups of uncultured euryarchaeota, remotely related to the genusThermoplasma. No crenarchaeota were found in the water column of the Solar Lake. The archaeal community in the Solar Lake under both stratified and mixed conditions was dominated by halobacteria in salinities higher than 10%. During stratification, additional clusters, some of which may possibly relate to uncultured halophilic methanogens, were found in the sulfide- and methane-rich hypolimnion.

Phytoplankton Activities in Hypersaline, Anoxic Conditions. II—Photosynthetic Activity of some Sulphide Adapted Cyanobacterial Strains Isolated from Solar Lake, Taba, Egypt

Five cyanobacterial strains namely Oscillatoria limnetica, Aphanotheca stagnina, Synechococcus aeruginosus, Spirulina tenissima and Dactylococcopsis salina were isolated from an anaerobic sulphide rich hypersaline Solar Lake, Taba- Egypt. At oxygenic conditions Spirulina was the most tolerant strain to sulphide concentrations, while Aphanotheca and Synechococcus were the most sensitive. Aphanotheca have higher anoxygenic photoassimilation activity under a broad range of sulphide concentrations. The response of the five cyanobacterial strains to sulphide under oxygenic and anoxygenic conditions depends on the organism, time of exposure, presence or absence of DCMU and also on sulphide concentration.

Phytoplankton Activities in Hypersaline, Anoxic Conditions. I—Dynamics of Phytoplankton Succession in the Solar Lake (Taba, Egypt)

The seasonal and vertical distribution of planktonic algae in the Solar Lake (Taba–Egypt) and their relation to some aquatic environmental factors were discussed through the period (Sep. 1996–Aug. 1997). Surface water analysis showed that no remarkable changes were observed in nitrate, silicate and iron, while turbidity, salinity and chloride were changed according to the season. In water column profile, H2S, temperature and salinity showed clear variations between stratification and holomixis. Maximum salinity (199‰) was recorded during stratification at 3-4 m depth. Stratification (Oct-June) appears clearly with changes in temperature (surface 16°C, thermocline up to 53.3°C and the bottom temperature around 47.7°C). Cyanobacterial mats of the Solar Lake are classified into two layers, the upper layer was dominated by coccoide forms while the lower was dominated by filamentous forms. During the period of study, 39 algal species were identified among which were 17 species of Cyanobacteria, 18 species of Bacillariophyta and 2 species of either Chlorophyta or Dinoflagellates.