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Despite solid, growing genomic evidence for bacteria practicing bacteriochlorophyll and rhodopsin-based dual phototrophy, direct physiological proof has been lacking for over a decade until Kopejtka et al. recently solved the puzzle in an Alpine psychrophilic bacterium. Here, I highlight conceptual developments and address an overlooked, ecologically important phototrophic byproduct – heat.

Bitter-1 is a shallow hypersaline soda lake in Kulunda Steppe (Altai region, Russia). During a study period between 2005 and 2016, the salinity in the littoral area of the lake fluctuated within the range from 85 to 400 g/L (in July of each year). Light-dependent nitrogen fixation occurred in this lake up to the salt-saturating conditions. The rates increased with a decrease in salinity, both under environmental conditions and in laboratory simulations. The salinities below 100 g/L were favorable for light-dependent nitrogen fixation, while the process was dramatically inhibited above 200 g/L salts. The analysis of nifH genes in environmental samples and in enrichment cultures of diazotrophic phototrophs suggested that anaerobic fermenting and sulfate-reducing bacteria could participate in the dark nitrogen fixation process up to soda-saturating conditions. However, we cannot exclude the possibility that haloalkaliphilic nonheterocystous cyanobacteria (Euhalothece sp. and Geitlerinema sp.) and anoxygenic purple sulfur bacteria (Ectothiorhodospira sp.) might also play a role in the process at light conditions. The heterocystous cyanobacterium Nodularia sp. develops at low salinity (below 80 g/L) that is not characteristic for Bitter-1 Lake and thus does not make a significant contribution to the nitrogen fixation in this lake., Accepted Author Manuscript, BT/Environmental Biotechnology

Six phototrophic microbial mat communities from different geothermal springs (YNP) were studied using metagenome sequencing and geochemical analyses. The primary goals of this work were to determine differences in community composition of high-temperature phototrophic mats distributed across the Yellowstone geothermal ecosystem, and to identify metabolic attributes of predominant organisms present in these communities that may correlate with environmental attributes important in niche differentiation. Random shotgun metagenome sequences from six phototrophic communities (average 53Mbp/site) were subjected to multiple taxonomic, phylogenetic, and functional analyses. All methods, including G+C content distribution, MEGAN analyses, and oligonucleotide frequency-based clustering, provided strong support for the dominant community members present in each site. Cyanobacteria were only observed in non-sulfidic sites; de novo assemblies were obtained for Synechococcus-like populations at Chocolate Pots (CP_7) and Fischerella-like populations at White Creek (WC_6). Chloroflexi-like sequences (esp. Roseiflexus and/or Chloroflexus spp.) were observed in all six samples and contained genes involved in bacteriochlorophyll biosynthesis and the 3-hydroxypropionate carbon fixation pathway. Other major sequence assemblies were obtained for a Chlorobiales population from CP_7 (proposed family Thermochlorobacteriaceae), and an anoxygenic, sulfur-oxidizing Thermochromatium-like (Gamma-proteobacteria) population from Bath Lake Vista Annex (BLVA_20). Additional sequence coverage is necessary to establish more complete assemblies of other novel bacteria in these sites (e.g., Bacteroidetes and Firmicutes); however, current assemblies suggested that several of these organisms play important roles in heterotrophic and fermentative metabolisms. Definitive linkages were established between several of the dominant phylotypes present in these habitats and important functional processes such as

This article analyzes how absorption of light by suspensions of phototrophic bacteria is modulated by changes in the biomass of the culture, the size of the culture vessel and by the presence of refractile structures within the cells. Increases in biomass and culture size result in higher rates of light absorption but in the decrease of the amount of energy available per cell. The presence of refractile structures has different consequences depending on the biomass concentration. In dense cultures, the accumulation of refractile structures increases the reflection of light, and also reduces specific light absorption. In diluted cultures, however, the effect is the opposite, and refractile structures seem to increase light absorption.

To assess how completely the diversity of anoxygenic phototrophic bacteria (APB) was sampled in natural environments.All nucleotide sequences of the APB marker gene pufM from cultures and environmental clones were retrieved from the GenBank database. A set of cutoff values (sequence distances 0.06, 0.15 and 0.48 for species, genus, and (sub)phylum levels, respectively) was established using a distance-based grouping program. Analysis of the environmental clones revealed that current efforts on APB isolation and sampling in natural environments are largely inadequate. Analysis of the average distance between each identified genus and an uncultured environmental pufM sequence indicated that the majority of cultured APB genera lack environmental representatives.The distance-based grouping method is fast and efficient for bulk functional gene sequences analysis. The results clearly show that we are at a relatively early stage in sampling the global richness of APB species. Periodical assessment will undoubtedly facilitate in-depth analysis of potential biogeographical distribution pattern of APB.This is the first attempt to assess the present understanding of APB diversity in natural environments. The method used is also useful for assessing the diversity of other functional genes.

DelftChemTech, Applied Sciences

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 s, 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 composé

The objectives of the course were to provide participants with both a perspective of, and experience in, isolating, identifying, and assessing the potential activities of the diverse bacterial populations that are present in a variety of natural habitats and the roles these organisms play in determining and maintaining those habitats. The applied (industrial, biotechnological) potential of (often) poorly studied and characterized members of natural populations was noted as was also the utility of modern molecular biological approaches for identifying non-cultured microbiota in different habitats.

Chromatiaceae are unceasing present in the sediment of Certes's lagoons. The genera isolated ares Thiocapsa (80%),Chromatium and Ectothio- rhodospira. From august to October 1977, physical-chemical and bacteriological analysis, in red water present in lagoons, show the Chromatiaceae proliferation and presence of hydrogen sulfide. In October 1977, a study of white water development display the absence of sulphurbacteria and the presence of hydrogen sulfide,carbon dioxide and carbonate. The important role of photo­trophic bacteria in the sulphur cycle are demonstrated by comparison between these waters., Des prélèvements effectués dans les sédiments des lagunes aména­gées de Certes ont mis en évidence la présence permanente de Chromatiaceae et plus précisément des genres Thiocapsa (dominant à 80 %), Chromatium et Ectothiorhodospira. Des mois d'août à octobre 1977, l'analyse physico-chimique et bac­tériologique d'une zone d"eau rouge",dans les lagunes, met en évidence la prolifération de Chromatiaceae et la présence d'hydrogène sulfuré dans l'eau. En octobre 1977, une étude réalisée sur une "eau blanche" voisine de la zone rouge, montre l'absence de bactéries sulfo-oxydantes et la présence d'hydro­gène sulfuré, de gaz carbonique et de carbonates. La comparaison entre ces deux eaux permet de mettre en évidence le rôle important des bactéries phototrophes dans l'équilibre du cycle du soufre dans les milieux eutrophes. La comparaison entre l'étang du Prévost (méditer­ranée) et les lagunes de Certes, fait apparaître une similitude quantitative et qualitative entre les bactéries phototrophes isolées des sédiments, mais par contre, une différence dans l'ampleur des phénomènes d"eaux rouges".