Obligately phototrophic Chloroflexus: primary production in anaerobic hot spring microbial mats

Microbial mats which lack cyanobacteria occur at 50° to 65° C in the sulfide-containing Mammoth Springs of Yellowstone National Park. The principal organisms within these mats are filamentous bacteria which resemble Chloroflexus aurantiacus. The incorporation of [¹⁴C]-HCO ₃ ^- into mat material depended upon both light and sulfide, and was not inhibited when complete natural light was replaced with far-red and infra-red radiation. [¹⁴C]-acetate was incorporated in a light-dependent reaction which was stimulated by, but did not require, sulfide. In situ experiments with microelectrodes demonstrated net sulfide uptake by the mat in the light, and net sulfide production by the mat in the dark, suggesting the operation of a sulfur cycle.Filamentous phototrophic bacteria isolated from the mat were incapable of sustained growth in the presence of O₂.Simultaneous exposure of cultures to light and O₂ caused degradation of bacteriochlorophyll c. The stimulation of light-dependent [¹⁴C]-HCO ₃ ^- -uptake by sulfide was more pronounced in these isolates than in strains of Chloroflexus aurantiacus.     

Comparison of methods of repelling mosquitoes

Comparisons were made with human subjects of repellency of free flying Anopheles gambiae using soaps containing deet and permethrin or permethrin alone. The reduction in biting did not differ statistically significantly between these two forms of repellent soap. Some mosquitoes which touched the permethrin soap layer without biting died within the next day. The soap with deet was compared with the same amount of deet in a commercially available stick or as a liquid. Only in the latter form did the repellent show resistance to being washed off by cold water.Electrically heated vaporizing mats containing bio-allethrin were shown to be more effective than smouldering coils containing natural pyrethrins, in that there was more complete prevention of biting, and more rapid knock-down and kill. Operation of the vaporizing mat caused deposition of insecticide on the room surfaces.     

Uptake and transformation of metals and metalloids by microbial mats and their use in bioremediation

Summary Constructed microbial mats, used for studies on the removal and transformation of metals and metalloids, are made by combining cyanobacteria inoculum with a sediment inoculum from a metal-contaminated site. These mats are a heterotrophic and autotrophic community dominated by cyanobacteria and held together by slimy secretions produced by various microbial groups. When contaminated water containing high concentrations of metals is passed over microbial mats immobilized on glass wool, there is rapid removal of the metals from the water. The mats are tolerant of high concentrations of toxic metals and metalloids, such as cadmium, lead, chromium, selenium and arsenic (up to 350 mg L^–1). This tolerance may be due to a number of mechanisms at the molecular, cellular and community levels. Management of toxic metals by the mats is related to deposition of metal compounds outside the cell surfaces as well as chemical modification of the aqueous environment surrounding the mats. The location of metal deposition is determined by factors such as redox gradients, cell surface micro-environments and secretion of extra-cellular bioflocculents. Metal-binding flocculents (polyanionic polysaccharides) are produced in large quantities by the cyanobacterial component of the mat. Steep gradients of redox and oxygen exist from the surface through the laminated strata of microbes. These are produced by photosynthetic oxygen production at the surface and heterotrophic consumption in the deeper regions. Additionally, sulfur-reducing bacteria colonize the lower strata, removing and utilizing the reducing H₂S, rather than water, for photosynthesis. Thus, depending on the chemical character of the microzone of the mat, the sequestered metals or metalloids can be oxidized, reduced and precipitated as sulfides or oxides. For example precipitates of red amorphous elemental selenium were identified in mats exposed to selenate (Se-VI) and insoluble precipitates of manganese, chromium, cadmium, cobalt, and lead were found in mats exposed to soluble salts of these metals. Constructed microbial mats offer several advantages for use in the bioremediation of metal-contaminated sites. These include low cost, durability, ability to function in both fresh and salt water, tolerance to high concentrations of metals and metalloids and the unique capacity of mats to form associations with new microbial species. Thus one or several desired microbial species might be integrated into mats in order to design the community for specific bioremediation applications.     

Sporulation ofEnteromorpha spp. (Chlorophyta) and overwintering of spores in sediments of the Wadden Sea,Island Sylt,North Sea

For the last two decades dense mats of species of the filamentous green algaeEnteromorpha spp. have regulary occurred on tidal flats of Köningshafen Bay (island Sylt, North Sea, FRG). In calm areas overwintering of adult plants or plant fragments is a common process to guarantee the mass development during the next season. In contrast, the distribution ofEnteromorpha on exposed sandy tidal flats depends on recruitment by juvenile stages. In 1993Enteromorpha spore settlement was recorded regularly in the field. Polyethylene dishes were placed in the field and left for a period of seven days and lateron cultivated in the laboratory to checkEnteromorpha germling development. During summer 1993 — at a minimum distance of 200 m to the nearest adultEnteromorpha populations — a total of at least 82×10⁶ spores m^–2 settled. During winter the number of spores attached to the collecting dishes was close to zero and the adjacent sand flats were free of any visibleEnteromorpha plants. In further experiments it was shown that the development ofEnteromorpha juveniles in the next spring depended on the overwintering capacity of spores. More than 2×10⁶ spores m^–2 attached to large sand grains and other substrata (e.g. Hydrobia ulvae) survived the winter. In a laboratory experiment several species ofEnteromorpha were able to survive in total darkness for at least 10 months.     

Chloroflexus-like organisms from marine and hypersaline environments: Distribution and diversity

We report the presence of a diverse number ofChloroflexus-like organisms in intertidal marine and submerged hypersaline microbial mats using light, infrared fluorescence, and electron microscopy. The intertidal organisms appear morphologically very similar to thermophilicC. aurantiacus while the 2 hypersaline strains are larger and have a more complex ultrastructure composed of chlorosome-bearing internal membranes that appear to arise as invaginations of the cell membrane. By comparing spectroradiometry of microbial mat layers with microscopic observations, we have confirmed that theChloroflexus-like organisms are major constituents of the hypersaline microbial mat communities. In situ studies on mat layers dominated byChloroflexus-like organisms showed that sulfide-dependent photoautotrophic activity sustained by near infrared radiation prevailed. Autoradiographic analyses revealed that autotrophy was sustained in the filaments by 750 nm radiation. Three morphologically distinct strains are now maintained in mixed culture. One of these appears to be growing photoautotrophically.     

Physico-chemical characteristics of a permanent Spanish hypersaline lake: La Salada de Chiprana (NE Spain)

La Salada de Chiprana Lake, located in the Ebro River basin, northeastern Spain, is the only permanent and deep water hypersaline ecosystem in all of western Europe. With a total surface of 31 ha and a maximum depth of 5.6 m, it has several basins bounded by elongated sandstone-bodies or ribbons which are paleochannels of Miocene age. Its salinity varied from 30 to 73 g 1^–1 during the 1989 hydrological cycle and the most abundant ions were magnesium and sulphate. Depth-time distributions of major physico-chemical variables demonstrated that the lake was stratified in two distinctive layers during most of the year. The chemocline disappeared only in October, with the complete overturn of the water column. In the deep water, three conditions occurred which allowed development of green sulphur bacteria populations: (1) oxygen depletion, (2) presence of hydrogen sulphide and (3) presence of light. Benthic microbial mats covered the sediments of shallow shores of moderate slope.     

Morphology,distribution, and preservation potential of microbial mats in the hydromagnesite-magnesite playas of the Cariboo Plateau,British Columbia,Canada

Benthic microbial mats are common in the alkaline hydromagnesite-magnesite playa lakes of Interior British Columbia. Four main zones are recognized based on mat morphology that can be related to the type and duration of wetting. From the basin margin toward the playa centre they are: (i) vegetated hummocky ground; (ii) polygonal hummocky ground; (iii) low-domal and stratiform mats, and (iv) laterally continuous and pustular mats. Mats in peripheral mudflats are commonly mineralized by hydromagnesite, mostly precipitated by capillary evaporation of shallow groundwaters. Mats forming in the ephemeral lake tend to have lower carbonate content.Although widespread, the mats are poorly preserved in the Holocene sedimentary record. Underlying sediments are commonly weakly bedded, disturbed or massive. Desiccation, dehydration, wetting-drying cycles, and grazing by invertebrates cause fragmentation of mats at the surface, facilitating erosion. Cryogranulation, interstitial mineral precipitation, vesiculation, bioturbation, compaction, and volume changes associated with diagenesis, disrupt and destroy lamination in the upper few centimetres. Most surviving organic matter is lost by early microbial degradation.     

CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN,A CYANOBACTERIAL SHEATH PIGMENT1

Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near-ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near-ultraviolet-blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m^?2· S^?1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV-A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short-wavelength solar irradiance.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.