Isolation and characterization of spirilloid purple phototrophic bacteria forming red layers in microbial mats of Mediterranean salterns: description of Halorhodospira neutriphila sp. nov. and emendation of the genus Halorhodospira

Abstract

Microbial mats developing in the hypersaline lagoons of a commercial saltern in the Salin-de-Giraud (Rhô ne delta) were found to contain a red layer fully dominated by spirilloid phototrophic purple bacteria underlying a cyanobacterial layer. From this layer four strains of spirilloid purple bacteria were isolated, all of which were extremely halophilic. All strains were isolated by using the same medium under halophilic photolithoheterotrophic conditions. One of them, strain SG 3105 was a purple non-sulfur bacterial strain closely related to Rhodovibrio sodomensis with a 16S rDNA sequence similarity of 98?8 %. The three other isolated strains, SG 3301 T , SG 3302 and SG 3304, were purple sulfur bacteria and were found to be very similar. The cells were motile by a polar tuft of flagella. Photosynthetic intracytoplasmic membranes of the lamellar stack type contained BChl a and spirilloxanthin as the major carotenoid. Phototrophic growth with sulfide as electron donor was poor; globules of elemental sulfur were present outside the cells. In the presence of sulfide and CO 2 good growth occurred with organic substrates. Optimum growth occurred in the presence of 9-12 % (w/v) NaCl at neutral pH (optimal pH 6?8-7) and at 30-35˚C. The DNA base composition of strains SG 3301 T and SG 3304 were 74?5 and 74?1 mol% G+C, respectively.According to the 16S rDNA sequences, strains SG 3301 T and SG 3304 belonged to the genus Halorhodospira, but they were sufficiently separated morphologically, physiologically and genetically from other recognized Halorhodospira species to be described as a new species of the genus. They are, therefore, described as Halorhodospira neutriphila sp. nov. with strain SG 3301 T as the type strain (=DSM 15116 T ).

Characterization of Phototrophic Purple Nonsulfur Bacteria Forming Colored Microbial Mats in a Swine Wastewater Ditch

“…Although PPNS bacteria were occasionally found in a laminated microbial mat dominated by cyanobacteria (27,36), there has been no definite information about the development of microbial mats or biofilms fully dominated by PPNS bacteria. To our knowledge, this is the first report describing colored microbial mats mainly composed of PPNS bacteria.…”

“…Since the pioneer work by Miyoshi in 1897 (37), geothermal hot springs have received much attention as the habitats allowing these bacteria to form colored microbial mats and blooms (for reviews, see references 7, 16, and 33). The massive growth by the phototrophic sulfur bacteria have also been found in tidal seawater pools (45), hypersaline environments (27,30,38,44,47), and stabilization lagoons (9,42,50). On the other hand, phototrophic purple nonsulfur (PPNS) bacteria have been considered to rarely appear in massive development in nature, although the metabolic diversity of these bacteria allows them to occupy a broad range of environments (28,33).…”

Life at high salt concentrations, intracellular KCl concentrations, and acidic proteomes

“…With respect to salt requirement and tolerance they are quite similar, and all tolerate NaCl at concentrations up to 25% or higher. They can be divided into two groups, phylogenetically separated on the basis of 16S rRNA gene sequences: H. halophila and H. neutriphila contain bacteriochlorophyll a and carotenoids of the spirilloxanthin group, while H. halochloris and H. abdelmalekii contain bacteriochlorophyll b and rhopdopin carotenoids (Imhoff and Süling, 1996; Hirschler-Réa et al, 2003; Oren, 2013e). With respect to their mode of osmotic adaptation they were always considered to be a prime example of organisms that use organic compatible solutes.…”

Molecular sequence analysis of prokaryotic diversity in the anoxic sediments underlying cyanobacterial mats of two hypersaline ponds in Mediterranean salterns

“…Station A is characterized by a lower salinity (150^200x) and a thick gypsum crust (CaSO 4 ) that completely covers the sediment surface. These bacteria morphologically resemble Ectothiorhodospira-or Halorhodospira-like cells, due to the presence of extracellular sulfur globules, but some spirilloid purple non-sulfur bacteria may also be present in this layer [7]. This mat is composed of three colored layers of photosynthetic organisms visible and characterized under microscopic observation.…”

“…In the present study, we have used the 16S rDNA approach to improve our knowledge of Bacteria and Archaea diversity in the anoxic sediments beneath the microbial mats in two hypersaline ponds of the Salin-de-Giraud salterns [7]. In these two ponds of di¡ering salinity, the microbial mats have been observed to be very di¡erent.…”