Distinct partitioning has been observed in the composition and diversity of bacterial communities inhabiting the surface and overlying seawater of three coral species infected with black band disease (BBD) on the southern Caribbean island of Curaçao, Netherlands Antilles. PCR amplification and sequencing of bacterial 16S rRNA genes (rDNA) with universally conserved primers have identified over 524 unique bacterial sequences affiliated with 12 bacterial divisions. The molecular sequences exhibited less than 5% similarity in bacterial community composition between seawater and the healthy, black band diseased, and dead coral surfaces. The BBD bacterial mat rapidly migrates across and kills the coral tissue. Clone libraries constructed from the BBD mat were comprised of eight bacterial divisions and 13% unknowns. Several sequences representing bacteria previously found in other marine and terrestrial organisms (including humans) were isolated from the infected coral surfaces, including Clostridium spp., Arcobacter spp., Campylobacter spp., Cytophaga fermentans, Cytophaga columnaris, and Trichodesmium tenue.Infectious disease in scleractinian corals has emerged as one of the primary causes of the accelerating global destruction of coral reef ecosystems (22,25,27,56,74). Black band disease (BBD) is one of the most widespread and destructive of these coral infections (see review in reference 50). The diagnostic symptom of BBD is the development of a narrow 0.1-to 7-cmwide ring-shaped black to red microbial mat that migrates from top to bottom across massive coral colonies, killing healthy coral tissue at rates of as much as 1 cm per day (47, 53). BBD preferentially affects corals such as Montastrea annularis, Montastrea cavernosa, and Diploria strigosa (6,15,53). These species, known as framework building corals, form large structures that become the dominant physical elements of reefs. As a result, coral mortality caused by BBD is a potent force in restructuring coral reef ecosystems (15,36).There is considerable controversy as to whether BBD is caused by physical and chemical environmental stresses or is an infectious disease or both (50, 56). However, an impediment to determining the cause of BBD has been the lack of information about the diversity and distribution of microbial populations that inhabit normal healthy coral tissue and the BBD bacterial mat. It is known from studies of infectious disease in marine and terrestrial invertebrates, fish, and mammals (including humans) that pathogens are most effectively studied within an ecological context of interactions among microbes, their hosts, and the environmental conditions in which they live (25, 54). Accurate diagnosis and eventual treatment and prevention of BBD will therefore require a basic knowledge of the composition and distribution of the microbial communities associated with healthy as well as diseased organisms. This type of community-based comparative analysis of the microorganisms associated with infectious diseases in corals has not previously been...
Petrographic and geochemical analyses of travertine-depositing hot springs at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, have been used to define five depositional facies along the spring drainage system. Spring waters are expelled in the vent facies at 71 to 73؇C and precipitate mounded travertine composed of aragonite needle botryoids. The apron and channel facies (43-72؇C) is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide-oxidizing Aquificales bacteria. The travertine of the pond facies (30-62؇C) varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures. Calcite ''ice sheets'', calcified bubbles, and aggregates of aragonite needles (''fuzzy dumbbells'') precipitate at the air-water interface and settle to pond floors. The proximal-slope facies (28-54؇C), which forms the margins of terracette pools, is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face. Finally, the distal-slope facies (28-30؇C) is composed of calcite spherules and calcite ''feather'' crystals. Despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization, the compositions of spring-water and travertine predominantly reflect abiotic physical and chemical processes. Vigorous CO 2 degassing causes a ؉2 unit increase in spring water pH, as well as Rayleigh-type covariations between the concentration of dissolved inorganic carbon and corresponding ␦ 13 C. Travertine ␦ 13 C and ␦ 18 O are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher-temperature (ϳ50-73؇C) depositional facies. Conversely, travertine precipitating in the lower-temperature (Ͻϳ50؇C) depositional facies exhibits ␦ 13 C and ␦ 18 O values that are as much as 4‰ less than predicted equilibrium values. This isotopic shift may record microbial respiration as well as downstream transport of travertine crystals. Despite the production of H 2 S and the abundance of sulfideoxidizing microbes, preliminary ␦ 34 S data do not uniquely define the microbial metabolic pathways present in the spring system. This suggests that the high extent of CO 2 degassing and large open-system solute reservoir in these thermal systems overwhelm biological controls on travertine crystal chemistry.
The Yellowstone caldera contains the most numerous and diverse geothermal systems on Earth, yielding an extensive array of unique high-temperature environments that host a variety of deeply-rooted and understudied Archaea, Bacteria and Eukarya. The combination of extreme temperature and chemical conditions encountered in geothermal environments often results in considerably less microbial diversity than other terrestrial habitats and offers a tremendous opportunity for studying the structure and function of indigenous microbial communities and for establishing linkages between putative metabolisms and element cycling. Metagenome sequence (14–15,000 Sanger reads per site) was obtained for five high-temperature (>65°C) chemotrophic microbial communities sampled from geothermal springs (or pools) in Yellowstone National Park (YNP) that exhibit a wide range in geochemistry including pH, dissolved sulfide, dissolved oxygen and ferrous iron. Metagenome data revealed significant differences in the predominant phyla associated with each of these geochemical environments. Novel members of the Sulfolobales are dominant in low pH environments, while other Crenarchaeota including distantly-related Thermoproteales and Desulfurococcales populations dominate in suboxic sulfidic sediments. Several novel archaeal groups are well represented in an acidic (pH 3) Fe-oxyhydroxide mat, where a higher O2 influx is accompanied with an increase in archaeal diversity. The presence or absence of genes and pathways important in S oxidation-reduction, H2-oxidation, and aerobic respiration (terminal oxidation) provide insight regarding the metabolic strategies of indigenous organisms present in geothermal systems. Multiple-pathway and protein-specific functional analysis of metagenome sequence data corroborated results from phylogenetic analyses and clearly demonstrate major differences in metabolic potential across sites. The distribution of functional genes involved in electron transport is consistent with the hypothesis that geochemical parameters (e.g., pH, sulfide, Fe, O2) control microbial community structure and function in YNP geothermal springs.
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