Chemical reaction- and particle diffusion-based kinetic modeling of metal biosorption by a Phormidium sp.-dominated cyanobacterial mat

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r² = 0.932-0.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the kinetics of metal biosorption due either to prefixed order or unjustifiable change in rate constant and reaction order with varying concentrations of metal and biomass in the solution. The diffusion-based models, namely, the intra-particle diffusion model and the external mass transfer model fitted well to the time-course metal sorption data, thus suggesting involvement of both external and intra-particle diffusion processes in sorption of test metals by mat biomass. However, the Boyd kinetic expression clearly showed that the external mass transfer is the dominant process.     

Microcystins,BMAA and BMAA isomers in 100-year-old Antarctic cyanobacterial mats collected during Captain R.F. Scott’s Discovery Expedition

Microcystins (MCN), β-N-methylamino-L-alanine (BMAA) and anatoxin-a were investigated in Antarctic cyanobacterial mats collected from Ross Island and the McMurdo Ice Shelf, East Antarctica during Captain Scott’s ‘Discovery’ National Antarctic Expedition (1901–1904). Ultra-performance liquid chromatography-photodiode array detection (UPLC-PDA) and tandem mass spectrometry (MS/MS) analysis were used to quantify the cyanotoxins in seven cyanobacterial mat samples. MCNs were identified in six of the mat samples at concentrations from 0.5 to 16.1 µg?g^–1 dry weight. BMAA was found in one sample (528 ng?g^–1 dry weight, total BMAA), as well as two BMAA isomers, 2,4-diaminobutyric acid (DAB) and N-(2-aminoethyl) glycine (AEG) in six samples up to 6.56 and 6.79 μg?g^–1 dry weight, respectively. No anatoxin-a was detected. The findings confirm that MCNs, BMAA and BMAA isomers are preserved under dry herbarium conditions. The ‘Discovery’ cyanobacterial mat samples represent the oldest polar cyanobacterial samples found to contain cyanotoxins to date and provide new baseline data for cyanotoxins in Antarctic freshwater cyanobacterial mats from prior to human activity in Antarctica, the development of the ozone hole and current levels of climatic change.     

A sulfate-reducing bacterium from the oxic layer of a microbial mat from Solar Lake (Sinai), Desulfovibrio oxyclinae sp. nov.

In an investigation on the oxygen tolerance of sulfate-reducing bacteria, a strain was isolated from a 10⁷-fold dilution of the upper 3-mm layer of a hypersaline cyanobacterial mat (transferred from Solar Lake, Sinai). The isolate, designated P1B, appeared to be well-adapted to the varying concentrations of oxygen and sulfide that occur in this environment. In the presence of oxygen strain P1B respired aerobically with the highest rates [260 nmol O₂ min^–1 (mg protein)^–1] found so far among marine sulfate-reducing bacteria. Besides H₂ and lactate, even sulfide or sulfite could be oxidized with oxygen. The sulfur compounds were completely oxidized to sulfate. Under anoxic conditions, it grew with sulfate, sulfite, or thiosulfate as the electron acceptor using H₂, lactate, pyruvate, ethanol, propanol, or butanol as the electron donor. Furthermore, in the absence of electron donors the isolate grew by disproportionation of sulfite or thiosulfate to sulfate and sulfide. The highest respiration rates with oxygen were obtained with H₂ at low oxygen concentrations. Aerobic growth of homogeneous suspensions was not obtained. Additions of 1% oxygen to the gas phase of a continuous culture resulted in the formation of cell clumps wherein the cells remained viable for at least 200 h. It is concluded that strain P1B is oxygen-tolerant but does not carry out sulfate reduction in the presence of oxygen under the conditions tested. Analysis of the 16S rDNA sequence indicated that strain P1B belongs to the genus Desulfovibrio, with Desulfovibrio halophilus as its closest relative. Based on physiological properties strain P1B could not be assigned to this species. Therefore, a new species, Desulfovibrio oxyclinae, is proposed. Received: 7 August 1996 / Accepted: 29 January 1997     

Key variables controlling the vegetation of a cool-temperate mire in northern Japan

Abstract. In the cool-temperate Bibi Mire, Hokkaido, Japan, valley fens and flood-plain fens have quite different vegetation. The main variables controlling the vegetation were all hydrological: mean water level, water level fluctuation and surface water flow. Chemical factors such as electrical conductivity, dissolved oxygen and related peat decomposition were less important. The pH was about neutral and has little effect. The flood-plain fen developed under fluctuating water table conditions. The dominant species are Calamagrostis langsdotffii and Carex pseudocuraica. When temporal inundation occurs in the rainy or typhoon seasons, the submergence stimulates bud germination of the stoloniferous C. pseudocuraica, which can rapidly elongate its stolons upward. Some large floating peat mats occurred in the flood-plain fen zone. On these mats some Alnus japonica saplings establish and patches of alder forest can arise. Here the water level was higher than in the peripheral alder forest zone. The valley fen is dominated by Carex lasiocarpa var. occultans and/or C. limosa. It is formed under stable water table conditions in the inundated parts of the mire -where the non-inundated wet areas are dominated by alder trees. In the area where the surface water is flowing, these two fen sedges grow in deeper water since the high oxygen content is considered to compensate the flooding stress.     

Differential microbial communities in hot spring mats from Western Thailand

The microbial communities of freshwater hot spring mats from Boekleung (Western Thailand) were studied. Temperatures ranged from over 50 up to 57°C. Green-, red-, and yellow colored mat layers were analyzed. In order to detect the major components of the microbial communities constituting the mat as well as the microorganisms showing significant metabolic activity, samples were analyzed using DNA- and RNA-based molecular techniques, respectively. Microbial community fingerprints, performed by denaturing gradient gel electrophoresis (DGGE), revealed clear differences among mat layers. Thermophilic phototrophic microorganisms, Cyanobacteria and Chloroflexi, constituted the major groups in these communities (on average 65 and 51% from DNA and RNA analyses, respectively). Other bacteria detected in the mat were Bacteroidetes, members of the Candidate Division OP10, Actinobacteria, and Planctomycetes. Differently colored mat layers showed characteristic bacterial communities and the major components of the metabolically active fraction of these communities have been identified.     

The Chloroplast Genome of Euglena mutabilis—Cluster Arrangement,Intron Analysis,and Intrageneric Trends

A comparative analysis of the chloroplast genome of Euglena mutabilis underlined a high diversity in the evolution of plastids in euglenids. Gene clusters in more derived Euglenales increased in complexity with only a few, but remarkable changes in the genus Euglena. Euglena mutabilis differed from other Euglena species in a mirror‐inverted arrangement of 12 from 15 identified clusters, making it very likely that the emergence at the base of the genus Euglena, which has been considered a long branch artifact, is truly a probable position. This was corroborated by many similarities in gene arrangement and orientation with Strombomonas and Monomorphina, rendering the genome organization of E. mutabilis in certain clusters as plesiomorphic feature. By RNA analysis exact exon–intron boundaries and the type of the 77 introns identified were mostly determined unambiguously. A detailed intron study of psbC pointed at two important issues: First, the number of introns varied even between species, and no trend from few to many introns could be observed. Second, mat1 was localized in Eutreptiales exclusively in intron 1, and mat2 was not identified. With the emergence of Euglenaceae in most species, a new intron containing mat2 inserted in front of the previous intron 1 and thereby became intron 2 with mat1.     

Sulfur-metabolizing bacterial populations in microbial mats of the Nakabusa hot spring, Japan

At the Nakabusa hot spring, Japan, dense olive-green microbial mats develop in regions where the slightly alkaline, sulfidic effluent has cooled to 65 °C. The microbial community of such mats was analyzed by focusing on the diversity, as well as the in situ distribution and function of bacteria involved in sulfur cycling. Analyses of 16S rRNA and functional genes (aprA, pufM) suggested the importance of three thermophilic bacterial groups: aerobic chemolithotrophic sulfide-oxidizing species of the genus Sulfurihydrogenibium (Aquificae), anaerobic sulfate-reducing species of the genera Thermodesulfobacterium/Thermodesulfatator, and filamentous anoxygenic photosynthetic species of the genus Chloroflexus. A new oligonucleotide probe specific for Sulfurihydrogenibium was designed and optimized for catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). In situ hybridizations of thin mat sections showed a heterogeneous vertical distribution of Sulfurihydrogenibium and Chloroflexus. Sulfurihydrogenibium dominated near the mat surface (50% of the total mat biovolume), while Chloroflexus dominated in deeper layers (up to 64% of the total mat biovolume). Physiological experiments monitoring in vitro changes of sulfide concentration indicated slight sulfide production by sulfate-reducing bacteria under anoxic-dark conditions, sulfide consumption by photosynthetic bacteria under anoxic-light conditions and strong sulfide oxidation by chemolithotrophic members of Aquificae under oxic-dark condition. We therefore propose that Sulfurihydrogenibium spp. act as highly efficient scavengers of oxygen from the spring water, thus creating a favorable, anoxic environment for Chloroflexus and Thermodesulfobacterium/Thermodesulfatator in deeper layers.     

Identifying the interacting roles of stressors in driving the global loss of canopy‐forming to mat‐forming algae in marine ecosystems

Identifying the type and strength of interactions between local anthropogenic and other stressors can help to set achievable management targets for degraded marine ecosystems and support their resilience by identifying local actions. We undertook a meta‐analysis, using data from 118 studies to test the hypothesis that ongoing global declines in the dominant habitat along temperate rocky coastlines, forests of canopy‐forming algae and/or their replacement by mat‐forming algae are driven by the nonadditive interactions between local anthropogenic stressors that can be addressed through management actions (fishing, heavy metal pollution, nutrient enrichment and high sediment loads) and other stressors (presence of competitors or grazers, removal of canopy algae, limiting or excessive light, low or high salinity, increasing temperature, high wave exposure and high UV or CO₂), not as easily amenable to management actions. In general, the cumulative effects of local anthropogenic and other stressors had negative effects on the growth and survival of canopy‐forming algae. Conversely, the growth or survival of mat‐forming algae was either unaffected or significantly enhanced by the same pairs of stressors. Contrary to our predictions, the majority of interactions between stressors were additive. There were however synergistic interactions between nutrient enrichment and heavy metals, the presence of competitors, low light and increasing temperature, leading to amplified negative effects on canopy‐forming algae. There were also synergistic interactions between nutrient enrichment and increasing CO₂ and temperature leading to amplified positive effects on mat‐forming algae. Our review of the current literature shows that management of nutrient levels, rather than fishing, heavy metal pollution or high sediment loads, would provide the greatest opportunity for preventing the shift from canopy to mat‐forming algae, particularly in enclosed bays or estuaries because of the higher prevalence of synergistic interactions between nutrient enrichment with other local and global stressors, and as such it should be prioritized.     

Limnology of Crater Lakes in Los Tuxtlas,Mexico

Investigations on the abundance, biomass and position of heterotrophic flagellates (HF) in the benthic microbial food web of a melt water stream on King George Island, Antarctic Peninsula, were undertaken during the Antarctic summer from 23rd December 1997 until 13th March 1998. Abundance and biomass of potential HF resources (picophotoautotrophic and non-photoautotrophic bacteria) as well as potential predators on HF (ciliates and meiofauna) were also investigated. HF abundance ranged from approximately 9 × 10³ to 81 × 10³ cells cm^–3, values which fall into the same range as those found in lower latitudes. Numerically important benthic HF were euglenids, kinetoplastids, thaumatomastigids and especially chrysomonads. Most species identified have been shown to have a worldwide distribution. Abundance of the benthic ciliates ranged from 27 to 950 cells cm^–3. Mean bacterial abundance was 1.9 × 10⁷ and 5.2 × 10⁸ cells cm^–3 for picophotoautotrophic and non-photoautotrophic benthos, respectively. The well-developed microbial community was able to support the large number of nematods, gastotrichs, tardigrads and rotifers with abundances reaching more than 1000 individuals cm^–3. The largest portion of heterotrophic biomass was formed by the meiofauna with a mean of 63 g C cm^–3, followed by that of the heterotrophic bacteria with 4.80 g C cm^–3. Picophotoautotrophic bacteria contributed a mean of 1.37 g C cm^–3. HF and ciliates mean biomass was 0.61 and 1.99 g C cm^–3, respectively, with the HF biomass comprising between <10 and 70% of the total protozoan biomass. The data obtained in this study identify the melt water stream as a hot-spot of heterotrophic microbial and meiofaunal activity during the austral summer. The HF in the melt water stream formed a diverse group in terms of taxa and potential feeding types. Chrysomonads, kinetoplastids, euglenids and thaumatomastigida were the most abundant taxa. A classification into feeding types identified an average of 34% of the total HF as bacterivorous while all others were able to utilise other, larger organisms as resources. Potential trophic interactions between HF and bacteria and higher trophic levels are discussed.