Characterization of Sporohalobacter salinus sp. nov., an anaerobic, halophilic, fermentative bacterium isolated from a hypersaline lake.

Abstract

Halophilic, obligately anaerobic, Gram-stain-negative bacterial strains were isolated from a sediment sample taken from under the salt crust of El-Jerid hypersaline lake in southern Tunisia by using tryptone or glucose as the substrate. One strain, CEJFT1B(T), was characterized phenotypically and phylogenetically. Cells were non-motile, non-spore-forming, short rods. Strain CEJFT1B(T) was able to grow in the presence of 5-30 % (w/v) NaCl (optimum 20 %) and at 30-60 °C (optimum 45 °C). It grew at pH 5.5-7.8 and the optimum pH for growth was 6.8. The isolate required yeast extract for growth. Substrates utilized by strain CEJFT1B(T) as the sole carbon source included glucose, fructose, sucrose, pyruvate, Casamino acids and starch. Individual amino acids such as glutamate, lysine, methionine, serine, tyrosine, and amino acid mixtures formed by the Stickland reaction such as alanine-glycine, valine-proline, leucine-proline, isoleucine-proline were also utilized. Products of glucose fermentation were acetate (major product), butyrate, H2 and CO2. The genomic DNA G+C content of strain CEJFT1B(T) was 32.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CEJFT1B(T) should be assigned to the genus Sporohalobacter. The sequence similarity between strain CEJFT1B(T) and Sporohalobacter lortetii was 98.5 %, but DNA-DNA hybridization between the two strains revealed a relatedness value of 56.4 %, indicating that they are not related at the species level. The combination of phylogenetic analysis, DNA-DNA hybridization data, and differences in substrate utilization support the view that strain CEJFT1B(T) represents a novel species of the genus Sporohalobacter, for which the name Sporohalobacter salinus sp. nov. is proposed. The type strain is CEJFT1B(T) ( = DSM 26781(T) = JCM 19279(T)).