Taxonomic rearrangements of the genera Thiocapsa and Amoebobacter on the basis of 16S rDNA sequence analyses and description of Thiolamprovum gen. nov.

Complete nucleotide sequences of the 16S rDNAs were determined from Thiocapsa and Amoebobacter species, including all available type strains and some additional isolates. The distance-matrix analysis and the dendrogram for estimating the genetic relationships revealed that the investigated strains were found in two major clusters within the Chromatiaceae. One cluster comprises all Amoebobacter species, Thiocapsa roseopersicina and several isolates related to Thiocapsa roseopersicina. Representatives of the species Amoebobacter roseus, Amoebobacter pendens and Thiocapsa roseopersicina, the so called ‘Thiocapsa roseopersicina group’, are very closely related, justifying their inclusion into one genus, Thiocapsa, for which an emended description is presented. Amoebobacter purpureus and Amoebobacter pedioformis formed two separate lines of descent with less than 93% (89·6–92·9%) similarity to strains of the ‘Thiocapsa roseopersicina group’. Therefore, they will be considered as two separate genera. As a consequence, an emended description is presented for the genus Amoebobacter, with Amoebobacter purpureus as the new type species and A. pedioformis is transferred to Thiolamprovum pedioforme gen. nov., comb. nov. Two species, Thiocapsa pfennigii and Thiocapsa halophila, which have been classified with the genus Thiocapsa because of their morphological properties, were found within another major cluster of the Chromatiaceae and are only distantly phylogenetically related to the first cluster with 88·4–90·6% and 90·4–92·2% sequence similarity, respectively

Utilization of the compatible solutes sucrose and trehalose by purple sulfur and nonsulfur bacteria

International audienceOwing to their ubiquity as compatible solutes, sucrose and trehalose and their constituent monosaccharides, glucose and fructose, may represent a significant source of carbon for the growth of other bacteria. We investigated sugar utilization by 34 strains of purple sulfur and nonsulfur bacteria isolated from coastal lagoons. Amongst the purple nonsulfur bacteria, sugar utilization was common with almost all strains utilizing the tested monosaccharides and 70 and 50% of strains utilizing sucrose and trehalose, respectively. Sugar utilization was rarer amongst the purple sulfur bacteria, with none of the strains using glucose or trehalose. Fructose, was utilized by 50% of isolates and sucrose was utilized only by strains of Thiorhodococcus. Surprisingly, although unable to use glucose directly, Thiorhodococcus strains used both the glucose and fructose moieties of sucrose and utilized glucose slowly in the presence of fructose, indicating that these strains may be impaired in glucose transport, rather than glucose metabolism per se. Disaccharide metabolism was dependent on sugar uptake and none of the strains produced trehalases or sucrases. Efficacy of sugar utilization varied widely with specific growth yield between 0.09 and 0.78 g dry weight·g sugar-1, and was dependent upon both the sugar and the strain. Similarly, specific growth rates were highly variable with strain and the sugar present and ranged between 5.4 and 0.5 x 10-2·h-1. Overall, data indicate that in natural high salinity ecosystems, purple sulfur and particularly purple nonsulfur bacteria may be able to efficiently exploit compatible solutes released to the environment by other members of the bacterial community

Impact of macroalgal dredging on dystrophic crises and phototrophic bacterial blooms (red waters) in a brackish coastal lagoon

The Prevost lagoon (Mediterranean coast, France), was subject to annual dystrophic crises caused by the biodegradation of opportunistic macroalgae (Ulva lactuca) in the past. These crises result in anoxic waters with subsequent blooms of Purple Sulphur Bacteria (red waters) which, by oxidizing sulphide, contribute to the reestablishment of oxic conditions in the water column. Mechanical dredging of the macroalgal biomass has been carried out in the lagoon since 1991 with the aim of preventing the ecological and economic disturbances caused by such crises. Dredging began just before the phototrophic bloom when the water was already hypoxic (O-2 = 0.7 mg . L-1) and contained sulphilde (H2S = 7.3 mg . L-1) and purple patches of phototrophic bacteria (Thiocapsa sp.) that were beginning to develop on decaying macroalgae at the sediment surface. The dredging prevented red water formation and drastically modified both phototrophic community structure and activity and biogeochemical sulphur cycling. The dredging permitted the reestablishment of oxic conditions for a short period only (1-13 August). Resuspension of the superficial sediment layers disturbed the phototrophic bacterial community, whose numbers decreased by one order of magnitude (from 2 x 10(6) to 3.9 x 10(5) CFU.mL(-1)). The phototrophic community was no longer effective in reoxidizing the reduced sulphur compounds remaining its the sediments, as shown by a drastic sulphate depletion in the superficial sediment layers. Moreover, the increase in the specific bacteriochlorophyll a concentration of the phototrophic purple bacteria and the rapid development of Green Sulphur Bacteria (Prosthecochloris-like microorganisms) indicated that the phototrophic community was growing under severe light-limiting conditions due to the resuspension of sediment particles in the water. These conditions did not allow the phototrophic bacterial community to efficiently reoxidize the reduced sulphur compounds originating from the sediments. In consequence, hypoxic conditions (O-2 = 4.7 to 4.8 mg . L-1) and low sulphide concentrations (H2S = 0.4 to 0.7 mg . L-1) were detected in the water column until September. The ecological balance in the lagoon was reestablished only in October, whereas, in previous years it had been restored in August.L'étang du Prévost (côte méditerranéenne française) a été soumis périodiquement à des crises dystrophiques estivales provoquées par la biodégradation de grandes quantités de macroalgues (Ulva lactuca). Ces crises se traduisent par l'anoxie des eaux et la formation d'eaux rouges (malaïgues) dues au développement des bactéries phototrophes sulfureuses rouges ; par leur activité de réoxydation des composés soufrés toxiques, ces microorganismes contribuent à la restauration de conditions oxiques. Depuis 1991, afin d'éviter les nuisances écologiques et économiques causées par ces phénomènes, un programme de dragage des macroalgues a été mis en place dans l'étang. Le ramassage des algues est entrepris juste avant le développement de l'eau rouge, lorsque les eaux sont déjà hypoxiques (O2 = 0.4 to 0.7 mg·L−1) et contiennent du sulfure (H2S = 7,3 mg·L−1). Les bactéries phototrophes (Thiocapsa sp.) forment déjà des biofilms sur les macroalgues en décomposition à la surface des sédiments. Le dragage évite la formation de l'eau rouge et influe largement sur la communauté de bactéries phototrophes et donc sur le cycle du soufre. Le dragage ne restaure des conditions oxiques dans les eaux de l'étang que pour une courte durée. La mise en suspension des sédiments superficiels affecte la communauté de bactéries phototrophes dont les nombres ont chuté d'un facteur 10 (de 2 × 106 à 3,9 × 105 CFU.mL−1). Le déficit en sulfate des sédiments superficiels montre que cette communauté n'est plus capable de réoxyder les composés soufrés issus des sédiments. De plus, l'augmentation du contenu spécifique en Bchl.a des bactéries phototrophes rouges ainsi que le développement rapide des bactéries phototrophes vertes sulfureuses (Prosthecochloris sp.) indiquent que la lumière constitue un facteur limitant l'activité de ces microorganismes, facteur limitant par suite de la mise en suspension de particules sédimentaires. Cette communauté ne pouvant plus jouer son rôle dans la réoxydation des composés soufrés, les eaux redeviennent hypoxiques (O2 = 4,7 à 4,8 mg·L−1) alors que de faibles concentrations en sulfures y sont détectées (H2S = 0,4 à 0,7 mg·L−1). Les conditions normales ne sont rétablies dans l'étang du Prévost qu'en octobre alors que les années précédentes elles étaient atteintes plus tôt en été

Comparison of cultivation-dependent and molecular methods for studying the diversity of anoxygenic purple phototrophs in sediments of an eutrophic brackish lagoon

International audiencePhototrophic anoxygenic purple bacteria play a key role in many aquatic ecosystems by oxidizing sulfur compounds and low-molecular-weight organic compounds using light as energy source. In this study, molecular methods based upon pufM gene (photosynthetic unit forming gene) were compared with culture-dependent methods to investigate anoxygenic purple phototrophic communities in sediments of an eutrophic brackish lagoon. Thirteen strains, belonging to eight different genera of purple phototrophic bacteria were isolated with a large dominance of the metabolically versatile purple non-sulfur bacteria (eight strains), some purple sulfur bacteria (three strains) and two strains belonging to the Roseobacter clade (aerobic phototrophs). The pufM genes amplified from the isolated strains were not detected by the molecular methods [terminal-restriction fragment length polymorphism (T-RFLP)] applied on in situ communities. An environmental clone library of the pufM gene was thus constructed from sediment samples. The results showed that most of the clones probably corresponded to aerobic phototrophic bacteria. Our results demonstrate that the culture-dependent techniques remain the best experimental approach for determining the diversity of phototrophic purple non-sulfur bacteria whereas the molecular approach clearly illustrated the abundance of organisms related to the Roseobacter clade in these eutrophic sediment

Hopanoid production by Desulfovibrio bastinii isolated from oilfield formation water

cited By 28International audienceHopanoids are important lipid components of many bacterial groups and are therefore ubiquitous in soils, sediments, and rocks. Until recently, it was believed that the synthesis of hopanoids is restricted to at least microaerophilic bacteria and consequently geological findings of hopanoids were used as an indication for oxygenated settings. Recent studies, however, demonstrated the biosynthesis of hopanoids under strictly anoxic conditions by a few bacterial groups, although their relevance is still unclear. We therefore extended our previous work studying hopanoid production among members of the genus Desulfovibrio, a group of sulphate-reducing bacteria (SRB) widely distributed in marine sediments, water-logged soils, and oil reservoirs. We found three species (Desulfovibrio halophilus, Desulfovibrio vulgaris Hildenborough, and Desulfovibrio africanus) to be devoid of hopanoids. In contrast, Desulfovibrio bastinii contains high amounts of nonextended hopanoids and bacteriohopanepolyols, with diploptene, 17β(H),21β(H)- bacteriohopane-32,33,34,35-tetrol, and 17β(H),21β(H)-35- aminobacteriohopane-32,33,34-triol being the major compounds. Because the moderately halophilic D. bastinii was isolated from a deep subsurface oil formation water, a contribution of hopanoids by SRB to the intrinsic oil hopanoid inventory is feasible, which would influence hopanoidal compositions often used for organic-geochemical characterization purposes. Nevertheless, our data indicate that hopanoid production might be common, but not obligate in the genus Desulfovibrio. © 2009 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved

Anoxygenic phototrophic bacteria in eutrophic coastal lagoons of the French Mediterranean and Atlantic coasts (Prévost Lagoon, Arcachon Bay, Certes fishponds)

cited By 25International audienceSediment samples collected from coastal lagoons on the French Mediterranean (Prévost Lagoon) and Atlantic coasts (Arcachon Bay and Certes fishponds) have been studied in order to determine the population densities and the species diversity of the different groups of anoxygenic phototrophic bacteria (purple sulfur bacteria, purple nonsulfur bacteria and green sulfur bacteria) present in these ecosystems. Several strains of each group were isolated in pure culture and characterized by their physiological properties. The occurrence of purple nonsulfur bacteria in organic rich sediments of the Arcachon Bay and the dominance of purple sulfur bacteria in the Prévost lagoon and Certes fishponds are discussed with respect to their community structure and abundance. The diversity differences of the phototrophic bacterial strains isolated from both environments are also discussed. ©1996 Kluwer Academic Publishers

Simultaneous determination of mercury methylation and demethylation capacities of various sulfate-reducing bacteria using species-specific isotopic tracers

International audienceThe use of species-specific isotopic tracers for inorganic and methyl mercury has allowed the simultaneous determination of the methylation and demethylation potentials of pure culture of isolated sulfate-reducing (SR) bacterial strains using low Hg species concentration levels (7 μg/L 199Hg(II), 1 μg/L Me 201Hg). A major advantage of the method reported here is that it can be used to follow simultaneously both the degradation of the species added but also the formation of their degradation products and thus the determination during the same incubation of the specific methylation/demethylation yields and rate constants. Methylation/demethylation capacities and extents have been found to differ between the tested strains and the tested conditions. The methylating/demethylating capacities of bacteria appear to be strain specific. All the methylating strains were found to demethylate methylmercury (MeHg). The active mechanism responsible for Hg methylation appears directly dependent on the bacterial activity but is not dependent on the metabolism used by the tested bacteria (sulfate reduction, fermentation, or nitrate respiration). The results provide confirmation that SR strains contribute to MeHg demethylation under anoxic conditions, leading to Hg(II) as the end product, consistent with the oxidative degradation pathway. Kinetic experiments have allowed specific transformation rate constants to be addressed for the two reversible processes and the reactivity of each isotopic tracer to be compared. The differential reactivity highlighted the different steps involved in the two apparent processes (i.e., uptake plus internal transformation of mercury species). Methylation appears as the slowest process, mainly controlled by the assimilation of Hg(II), whereas demethylation is faster and not dependent on the MeHg concentration

Green sulfur bacteria from hypersaline Chiprana Lake (Monegros, Spain): Habitat description and phylogenetic relationship of isolated strains

International audienceThe 'Salada de Chiprana' (Chiprana Lake) is a hypersaline (30-73‰), permanent and shallow lake of endorheic origin in a semi-arid region of the Ebro depression (Aragon, Spain). Magnesium sulfate and sodium chloride represent the main salts of this athalassohaline environment. Anoxic conditions occurred periodically in the bottom layers of the lake during the study period. When stratified, high sulfide concentrations (up to 7 mM) were measured in the hypolimnion. Physical and chemical conditions gave rise to the development of very dense green sulfur bacteria blooms (10.7 mg 1-1 of BChl c and 16.7 mg 1-1 of BChl d) at 0.5-1 m from the bottom. Microscopic observations revealed that cells morphologically similar to Chlorobium vibrioforme were dominant in the phototrophic bacterial community, but Prosthecochloris aestuarii was also found sometimes at lower concentrations, as revealed by both microscopic observation and flow cytometric analyses. Deep agar dilution series allowed to obtain several axenic cultures of phototrophic bacteria. They were identified according to their morphology, pigment composition and phylogenetic relationships (16S rDNA sequence analysis). Two of the sequenced strains (CHP3401 and CHP3402) belonged to the green sulfur bacteria and were related to Prosthecochloris aestuarii SK413T and Chlorobium vibrioforme DSM260T, respectively. HPLC analyses of both natural samples and Chlorobium vibrioforme isolates indicated that these strains contained both BChl c and BChl d. Phylogenetic results suggested that Chlorobium vibrioforme strains DSM260T and CHP3402, all sequenced strains of Prosthecochloris aestuarii and strain CIB2401 constitute a separate cluster of green sulfur bacteria, all of them isolated from marine to hypersaline habitats