Microbial mats and physicochemistry in a saltern in the Bretagne (France) and in a laboratory scale saltern model

Abstract A saltern near La Baule (Bretagne, France) was remodeled in a programmable temperature and humidity controlled walk-in environmental chamber resembling the characteristics of the original saltern. The saltern showed different types of microbial mats predominantly composed of algae, oxy- and anoxyphotobacteria, and associated chemoorganotrophic bacteria, fungi and animals. Well-developed microbial mats were found up to a salinity of 10% during the three or four months in summer when salinity gradients and NaCl precipitation were established. The main phototrophic organisms were diatoms, the cyanobacteria Aphanothece, Microcoleus, Spirulina , and Oscillatoria , and Chromatiaceae. At higher salinity, Halobacterium sp., diatoms, and Dunaliella were dominant. Typical microbial mats and saltern-typical invertebrate, algal and bacterial species also developed in the saltern model, building up a stable community. The ionic composition of the brines and physicochemical parameters were similar to those determined for the original saltern. Different photosynthetic organisms, e.g. a filamentous purple bacterium and a hypersaline Chloroflexus -like organism, could be enriched within the microbial mats by changing the light regime.     

Sulfide fluxes in a microbial mat from the Ebro Delta, Spain

The sulfur cycle of Ebro Delta microbial mats was studied in order to determine sulfide production and sulfide consumption. Vertical distribution of two major functional groups involved in the sulfur cycle, anoxygenic phototrophic bacteria and dissimilatory sulfate-reducing bacteria (SRB), was also studied. The former reached up to 2.2×10⁸ cfu cm^–3 sediment in the purple layer, and the latter reached about 1.8×10⁵ SRB cm^–3 sediment in the black layer. From the changes in sulfide concentrations under light-dark cycles it can be inferred that the rate of H₂S production was 6.2 μmol H₂S cm^–3 day^–1 at 2.6 mm, and 7.6 μmol H₂S cm^–3 day^–1 at 6 mm. Furthermore, sulfide consumption was also assessed, determining rates of 0.04, 0.13 and 0.005 mmol l^–1 of sulfide oxidized at depths of 2.6, 3 and 6 mm, respectively. Electronic Publication     

Methanogenesis in the hypersaline Solar Lake (Sinai)

Abstract Enrichment studies on microbial mat sediments (potential stromatolites) from the hypersaline Solar Lake (Sinai) indicated high numbers of methanogenic bacteria (up to 10⁵ ml⁻¹ sediment) in spite of the high sulfate reduction rate, sulfate concentration and salinity. Among H₂/CO₂, acetate and monomethylamine, the methylated amine was the preferred substrate. The predominant species enriched was a Methanosarcina sp. The findings indicate that methanogenic bacteria play an important role in hypersaline sulfate-enriched anoxic sediments and stromatolithic microbial mats.     

Abundance and distribution of anaerobic protozoa and their contribution to methane production in Lake Cadagno (Switzerland)

Abstract In the uupermost layers of the anoxic sediment in Lake Cadagno, 9 different species of anaerobic protozoa were identified. The total number of these organisms was about 580 cells·ml⁻¹ sediment. Most pf these protozoa contained endosymbiotic methanogenic bacteria which in total amounted to 10⁶ methanogens·ml⁻¹ sediment. In addition to the methanogenic endosymbionts, cells of Metopus setosus and Caenomorpha lata also contained a non-fluorescent bacterial rod inside the cytoplasm. In some individual cells of C. lata this second type of endosymbiotic bacterium was sometimes the only endosymbiont observed. Contrary to earlier suggestions, anaerobic protozoa do not seem to play a major role in methane production at least in Lake Cadagno. No significant methane production due to the anaerobic protozoa and their methanogenic endosymbionts was found in situ. Isolated ciliates and amoebae produced methane at 12°C, but not at 6°C, probably as a result of temperature limitation. In the sediment of Lake Cadagno sulfate reduction seemed to be the dominant terminal degradation process.     

The role of phase separation and feed cycle length in leach beds coupled to methanogenic reactors for digestion of a solid substrate (Part 1): Optimisation of reactors' performance

A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first time to improve volumetric substrate degradation and methane yields from a complex substrate (maize; Zeamays). The system, which was operated for consecutive feed cycles of different durations for 120 days, was highly flexible and its performance improved by altering operational conditions. Daily substrate degradation was higher the shorter the feed cycle, reaching 8.5 g TS_destroyed d⁻¹ (7-day feed cycle) but the overall substrate degradation was higher by up to 55% when longer feed cycles (14 and 28 days) were applied. The same occurred with volumetric methane yields, reaching 0.839 m³ (m³)⁻¹ d⁻¹. The system performed better than others on specific methane yields, reaching 0.434 m³ kg⁻¹ TS_added, in the 14-day and 28-day systems. The UASB and AF designs performed similarly as second stage reactors on methane yields, SCOD and VFA removal efficiencies.     

Sulfate reduction and thiosulfate transformations in a cyanobacterial mat during a diel oxygen cycle

Abstract Bacterial sulfate reduction and transformations of thiosulfate were studied with radiotracers in a Microcoleus chthonoplastes -dominated microbial mat growing in a hypersaline pond at the Red Sea. The study showed how a diel cycle of oxygen evolution affected respiration by sulfate-reducing bacteria and the metabolism of thiosulfate through oxidative and reductive pathways. Sulfate reduction occurred in both oxic and anoxic layers of the mat and varied diurnally, apparently according to temperature rather than to oxygen. Time course experiments showed that the radiotracer method underestimated sulfate reduction in the oxic zone due to rapid reoxidation of the produced sulfide. Extremely high reduction rates of up to 10 μmol cm⁻³ d⁻¹ were measured just below the euphotic zone. Although thiosulfate was simultaneously oxidized, reduced and disproportionated by bacteria in all layers of the mat, there was a shift from predominant oxidation in the oxic zone to predominant reduction below. Concurrent disproportionation of thiosulfate to sulfate and sulfide occurred in all zones and was an important pathway of the sulfur cycle in the mat.     

Trace fossils in the Ediacaran-Cambrian transition: Behavioral diversification, ecological turnover and environmental shift

After taxonomic revision, trace fossils show a similarly explosive diversification in the Ediacaran-Cambrian transition as metazoan body fossils. In shallow-marine deposits of Ediacaran age, trace fossils are horizontal, simple and rare, and display feeding strategies related to exploitation of microbial matgrounds. Equally notable is the absence of arthropod tracks and sinusoidal nematode trails. This situation changed in the Early Cambrian, when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground-based ecology (‘‘agronomic revolution’’). On deep sea bottoms, animals have been present already in the Ediacaran, but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners. As shown by the ichnogenus Oldhamia, this life style continued to be predominant into the Early, and to a lesser extent, Middle Cambrian. Nevertheless, there was an explosive radiation of behavioral programs during the Early Cambrian. When exactly the bioturbational revolution arrived in the deep sea is uncertain. In any case, the Nereites ichnofacies was firmly established in the Early Ordovician. The rich ichnofauna in the Early Cambrian Guachos Formation of northwest Argentina probably marks a first step in this ecological onshore-offshore shift.     

Seventy-year chronology of Salinas in southern France: Coastal surfaces managed for salt production and conservation issues for abandoned sites

After World War II, twenty-nine coastal Salinas (122 km²), located in the vicinity of coastal lagoons and in deltas, were exploited along the Mediterranean coastlines in South France. Today, only five of these are still actively producing salt, currently representing 175 km². Concomitant with the abandonment of many of the smaller Salinas, the larger Salinas in the Rhône delta (Camargue) strongly increased their surfaces at the expense of natural ecosystems, of which a part has also been abandoned after 2009. This paper documents these changes in landscape use by chronological GIS mapping and describes the fate of the 91 km² of abandoned Salina surfaces. The majority of this area (88 km²) is included in the Natura 2000 network, among which most (74 km²) has been acquired by the French coastal protection agency (Conservatoire du Littoral) to be designated as Protected Areas. Only a very minor part (<1%) has been lost for industry and harbour development. Managing abandoned Salinas as Protected Areas is a challenge, because of the different landscape, biodiversity conservation, natural and cultural heritages issues at stake. In two cases, abandoned Salinas have been brought back again into exploitation by private initiative thus allowing for the protection of original hypersaline biodiversity. In other cases, the shaping of the landscape by natural processes has been privileged. This has facilitated the spontaneous recreation of temporal Mediterranean wetlands with unique aquatic vegetation, and offered opportunities for managed coastal re-alignment and the restoration of hydrobiological exchanges between land and sea. In other areas, former salt ponds continue to be filled artificially by pumping favouring opportunities for waterfowl. This has often been combined with the creation of artificial islets to provide nesting ground for bird colonies protected from terrestrial predators.     

Seasonal oscillation of microbial iron and sulfate reduction in saltmarsh sediments (Sapelo Island, GA, USA)

Seasonal variations in anaerobic respiration pathways were investigated at three saltmarsh sites using chemical data, sulfate reduction rate measurements, enumerations of culturable populations of anaerobic iron-reducing bacteria (FeRB), and quantification of in situ 16S rRNA hybridization signals targeted for sulfate-reducing bacteria (SRB). Bacterial sulfate reduction in the sediments followed seasonal changes in temperature and primary production of the saltmarsh, with activity levels lowest in winter and highest in summer. In contrast, a dramatic decrease in the FeRB population size was observed during summer at all sites. The collapse of FeRB populations during summer was ascribed to high rates of sulfide production by SRB, resulting in abiotic reduction of bioavailable Fe(III) (hydr)oxides. To test this hypothesis, sediment slurry incubations at 10, 20 and 30 °C were carried out. Increases in temperature and labile organic carbon availability (acetate or lactate additions) increased rates of sulfate reduction while decreasing the abundance of culturable anaerobic FeRB. These trends were not reversed by the addition of amorphous Fe(III) (hydr)oxides to the slurries. However, when sulfate reduction was inhibited by molybdate, no decline in FeRB growth was observed with increasing temperature. Addition of dissolved sulfide adversely impacted propagation of FeRB whether molybdate was added or not. Both field and laboratory data therefore support a sulfide-mediated limitation of microbial iron respiration by SRB. When total sediment respiration rates reach their highest levels during summer, SRB force a decline in the FeRB populations. As sulfate reduction activity slows down after the summer, the FeRB are able to recover.     

Competition between an introduced and an indigenous species: the case of Paspalum paspalodes (Michx) Schribner and Aeluropus littoralis (Gouan) in the Camargue (southern France)

Paspalum paspalodes, an introduced grass species, and Aeluropus littoralis, an indigenous species, develop abundantly in seasonally-flooded marshes in the Camargue (Rhône Delta, France). Although they occur together in many multispecies communities, neither species occurs when the other is dominat. The cultivation of cuttings of P. paspalodes and A. littoralis in a replacement series in a combination of five proportions (0/100, 25/75, 50/50, 75/25 and 100/0) and four salinities (0,2 4, and 6 g Cl^- · 1^-1) gave contrasting results for the two species: (1) strong asymmetrical competition in favour of P. paspalodes at 0 g Cl^- · 1^-1, (2) no significant effect of salinity on the mean above-ground and underground yields per plant for A. littoralis over the range tested, (3) a major decrease in the mean above-ground and belowground yields per plant for P. paspalodes with increasing salinity, (4) a reversal of the competitive balance between the species with increasing salinity. The cultivation of cuttings at high temperatures in a greenhouse in a combination of the same five proportions at two salinities (0 and 4 g Cl^- · 1^-1) refuted the hypothesis that the introduced species is better adapted to summer temperatures. Because it is not salt-tolerant, P. paspalodes cannot be considered as a potentially invasive species in the Camargue. Its abundance depends on newly created and artificially maintained habitats.     

Methanogenesis and sulfate reduction in timber and drainage water from a gold mine

Biogenesis of methane in the heartwood of diseased trees has been shown, but never in timber in service. Studies were undertaken to establish whether methan‐ogens and sulfate‐reducers were present in wooden pit props and drainage water from underground sites in a gold mine. The predominant methanogen in the mine ecosystem was tentatively identified as Methanobacterium bryantii. The sulfate‐reducers comprised Desulfovibrio desulfuricans and Desulfotomaculum antarcticum. Most probable numbers (MPN) of bacteria indicated that 3.5 × 10⁵ methanogenic and 7.9 × 10³ sulfate‐reducing bacteria were present per milliliter of stagnant drainage water. MPN values per gram of timber were lower for methanogens but comparable for sulfate‐reducers. Laboratory model systems predicted a maximum rate of methan‐ogenesis of 2.3 mL methane/g wood per day; however, rates would never attain this value because of nutrient limitations and environmental restrictions. Analysis of gas samples extracted from sealed areas of the gold mine verified the presence of methane.     

Microbial mat communities in response to recent changes in the physiochemical environment of the meltwater ponds on the McMurdo Ice Shelf,Antarctica

In spite of their dominance in meltwater environments in the Polar Regions, little is known about conditions that control community structure and production in microbial mats. Microbial mats were sampled at 13 recently separated ponds on the McMurdo Ice Shelf, Antarctica, with the aim to determine microbial mat community response to shifts in deterministic processes. Community structure in ponds of different size classes responded to different environmental variables, with conductivity as a common theme. Biomass and net oxygen exchange did not vary across the pond conditions and may reflect the very slow turnover rates characteristic of Antarctic microbial communities. Microbial mat communities on the MIS appear unresponsive to large intra-annual variability, while the long-term inter-annual physiochemical environment of the overlying appears to be influencing the community dynamics.     

Effects of seasonal flooding and grazing on the vegetation of former ricefields in the Rhône delta (Southern France)

Six management regimes were tested during 5 years in 18 abandoned ricefields in the Rh^one delta, France: two artificial floodings for 6 months (winter and summer flooding, 10 cm deep) and a control only flooded by rain, each flooding treatment either with or without grazing by cattle and horses. In the absence of artificial flooding and in presence of grazing by domestic herbivores (i.e., maintaining the initial management since the abandonment) no significant change in plant communities was recorded after 5 years. The vegetation was mainly composed of halophytes (Salicornia fruticosa and Inula crithmoides). The removal of grazing led to the dominance of a salt tolerant grass: Aeluropus littoralis. Flooding favoured the dominance of clonal plants and led to a decrease in the number of species. In the ungrazed fields, changes in plant communities were related to the height of species with Bolboschoenus maritimus and Phragmites australis becoming dominant. When grazing was combined with summer flooding, B. maritimus dominated the first two years of the experiment, but with a low cover, and was replaced in the 3rd year by Typha angustifolia. When grazing was combined with winter and early spring flooding the competitive exclusion of B. maritimus by Juncus gerardii slowed the establishment of the former. The management of former ricefields led to the establishment and dominance of emergent species common to Mediterranean wetlands. Although it is subordinate to the maintenance of artificial flooding, the project may be considered a restoration (or a rehabilitation) of seasonally flooded marshes as original functions existing before the land was put under cultivation are re-established.     

Nitrogen‐isotope fractionation in the nitrate respiration by the marine bacterium Serratia marinorubra

Abstract

The isotopic composition (δ¹⁵N) of nitrite produced during nitrate respiration by both growing and washed cells of the marine bacterium, Serratia marinorubra, was determined. In both the growing and washed cells, δ¹⁵N of the nitrite changed considerably with time. At least two reaction steps, producing different isotope effects (active transport of nitrate across membranes and reduction of nitrate to nitrite), appear to be involved. With washed cells, a fractionation factor as high as 1.039 was obtained—the highest ever reported for biologicalnitrate reduction. The physiological state of nitrate‐respiring bacteria in oxygen‐depleted subsurface waters of the sea is discussed from the viewpoint of isotope fractionation.     

Investigations into the uptake of copper,iron and selenium by a highly sulphated bacterial exopolysaccharide isolated from microbial mats

A bacterium isolated from microbial mats located on a polynesian atoll produced a high molecular weight (3,000 kDa) and highly sulphated exopolysaccharide. Previous studies showed that the chemical structure of this EPS consisted of neutral sugars, uronic acids, and high proportions of acetate and sulphate groups. The copper- and iron-binding ability of the purified pre-treated native EPS was investigated. Results showed that this EPS had a very high affinity for both copper (9.84 mmol g⁻¹ EPS) and ferrous iron (6.9 mmol g⁻¹ EPS). Amazingly, this EPS did not show any affinity for either ferric ions or selenium salts. This finding is one of the first steps in assessing the biotechnological potential of this polysaccharide.     

Physiology, phylogenetic relationships, and ecology of filamentous sulfate-reducing bacteria (genus Desulfonema)

Microscopy of organic-rich, sulfidic sediment samples of marine and freshwater origin revealed filamentous, multicellular microorganisms with gliding motility. Many of these neither contained sulfur droplets such as the Beggiatoa species nor exhibited the autofluorescence of the chlorophyll-containing cyanobacteria. A frequently observed morphological type of filamentous microorganism was enriched under anoxic conditions in the dark with isobutyrate plus sulfate. Two strains of filamentous, gliding sulfate-reducing bacteria, Tokyo 01 and Jade 02, were isolated in pure cultures. Both isolates oxidized acetate and other aliphatic acids. Enzyme assays indicated that the terminal oxidation occurs via the anaerobic C₁ pathway (carbon monoxide dehydrogenase pathway). The 16S rRNA genes of the new isolates and of the two formerly described filamentous species of sulfate-reducing bacteria, Desulfonema limicola and Desulfonema magnum, were analyzed. All four strains were closely related to each other and affiliated with the δ-subclass of Proteobacteria. Another close relative was the unicellular Desulfococcus multivorans. Based on phylogenetic relationships and physiological properties, Strains Tokyo 01 and Jade 02 are assigned to a new species, Desulfonema ishimotoi. A new, fluorescently labeled oligonucleotide probe targeted against 16S rRNA was designed so that that it hybridized specifically with whole cells of Desulfonema species. Filamentous bacteria that hybridized with the same probe were detected in sediment samples and in association with the filamentous sulfur-oxidizing bacterium Thioploca in its natural habitat. We conclude that Desulfonema species constitute an ecologically significant fraction of the sulfate-reducing bacteria in organic-rich sediments and microbial mats. Received: 30 December 1998 / Accepted: 19 July 1999     

Complete assimilation of cysteine by a newly isolated non-sulfur purple bacterium resembling Rhodovulum sulfidophilum (Rhodobacter sulfidophilus)

A rod-shaped, motile, phototrophic bacterium, strain SiCys, was enriched and isolated from a marine microbial mat, with cysteine as sole substrate. During phototrophic anaerobic growth with cysteine, sulfide was produced as an intermediate, which was subsequently oxidized to sulfate. The molar growth yield with cysteine was 103 g mol^–1, in accordance with complete assimilation of electrons from the carbon and the sulfur moiety into cell material. Growth yields with alanine and serine were proportionally lower. Thiosulfate, sulfide, hydrogen, and several organic compounds were used as electron donors in the light, whereas cystine, sulfite, or elemental sulfur did not support phototrophic anaerobic growth. Aerobic growth in the dark was possible with fructose as substrate. Cultures of strain SiCys were yellowish-brown in color and contained bacteriochlorophyll a, spheroidene, spheroidenone, and OH-spheroidene as major photosynthetic pigments. Taking the morphology, photosynthetic pigments, aerobic growth in the dark, and utilization of sulfide for phototrophic growth into account, strain SiCys was assigned to the genus Rhodovulum (formerly Rhodobacter) and tentatively classified as a strain of R. sulfidophilum. In cell-free extracts in the presence of pyridoxal phosphate, cysteine was converted to pyruvate and sulfide, which is characteristic for cysteine desulfhydrase activity (l-cystathionine γ-lyase, EC 4.4.1.1). Received: 15 December 1995 / Accepted: 1 April 1996     

New insights into the archaeal diversity of a hypersaline microbial mat obtained by a metagenomic approach

A metagenomic approach was carried out in order to study the genetic pool of a hypersaline microbial mat, paying more attention to the archaeal community and, specifically, to the putatively methanogenic members. The main aim of the work was to expand the knowledge of a likely ecologically important archaeal lineage, candidate division MSBL1, which is probably involved in methanogenesis at very high salinities.     

Dinitrogen fixation by exposed communities on the rim of Tikehau atoll (Tuamotu Archipelago, French Polynesia)

Various types of sub-aerially exposed microbial mats, including emergent mats, beach sand, beach rock and Kopara mats, are widespread on the 78 km (25 km²) of rim surrounding the Tikehau atoll lagoon. These mats form laminated accretions or diffuse microbial communities growing under high insolation and temperatures, and are therefore subject to desiccation. Both heterocystous and non-heterocystous cyanobacteria occur in these mats. Using acetylene reduction techniques, nitrogenase activity was observed at all sites over a period of 5 years and was 3–17 times higher during daylight than at night in all communities except for beach rock. ¹⁵N₂ measurements indicated a molar ratio of acetylene reduction to N₂ fixed of 1.6 for all exposed communities. Estimated N₂ fixation ranged from 1.44 to 8.0 mg N m⁻² day⁻¹ in these exposed communities (mean of 4.66 mg N m⁻² day⁻¹) with beachrock showing the highest rates. For the whole reef rim, daily N₂ fixation amounted to 98.42 kg N day⁻¹ which represents 28% of the rate of fixation in the entire lagoon (area 400 km²).