Microbial Blooms Research Articles

Redox variations and organic matter accumulation on the Yangtze carbonate platform during Late Ediacaran–Early Cambrian: Constraints from petrology and geochemistry

In order to understand redox variations and organic matter accumulation on the Yangtze carbonate platform during the Late Ediacaran–Early Cambrian, petrological and geochemical studies of several wells were carried out in this work. Our data suggest that depositional environments were dominated by oxidizing bottom water conditions during the late Ediacaran, and evolved to anoxic conditions, triggered by blooms of microbial organisms in surface waters during the earliest Cambrian. Subsequently, massive release of H2S derived from both anaerobic recycling of organic matter and, probably, hydrothermal venting promoted a sulfidic ocean. The discovery of a Ni-Mo sulfide ore layer in the basal Cambrian implies that such a sulfidic condition spread onto the Yangtze carbonate platform interior during the late Cambrian Stage 2. Further, transgressive flooding led to widespread black shale deposition and persistently anoxic conditions, as indicated by geochemical proxies. During the late Ediacaran to earliest Cambrian, local and widespread phosphogenesis indicates that organic matter accumulation was intimately associated with microbial (especially cyanobacterial) blooms driven by phosphorus cycling. The organic matter accumulations in early Cambrian black shales, however, were in connection with anoxic bottom water conditions and intermittent replenishment of recycled organic phosphorus to surface waters.

Proliferation of MISS-related microbial mats following the end-Permian mass extinction in terrestrial ecosystems: Evidence from the Lower Triassic of the Yiyang area, Henan Province, North China

Microbially induced sedimentary structures (MISSs) are commonly present in siliciclastic shallow marine settings following the end-Permian mass extinction, but have been rarely reported in the post-extinction terrestrial ecosystems. Here, we present six types of well-preserved MISSs from the upper Sunjiagou Formation and lower Liujiagou Formation of Induan (Early Triassic) age in the Yiyang area, Henan Province, North China. These MISSs include: polygonal sand cracks, worm-like structures, wrinkle structures, sponge pore fabrics, gas domes, and leveled ripple marks. Microanalysis shows that these MISSs are characterized by thin clayey laminae and filamentous mica grains arranged parallel to bedding plane as well as oriented matrix supported quartz grains, which are indicative of biogenic origin. Facies analysis suggests that the MISS-hosting sediments were deposited in a fluvial sedimentary system during the Early Triassic, including lake delta, riverbeds/point bars, and flood plain paleoenvironments. Abundant MISSs from Yiyang indicate that microbes also proliferated in terrestrial ecosystems in the aftermath of the Permian–Triassic (P–Tr) biocrisis, like they behaved in marine ecosystems. Microbial blooms, together with dramatic loss of metazoans, may reflect environmental stress and degradation of terrestrial ecosystems or arid climate immediately after the severe Permian–Triassic ecologic crisis.

From Rare to Dominant: a Fine-Tuned Soil Bacterial Bloom during Petroleum Hydrocarbon Bioremediation.

Hydrocarbons are worldwide-distributed pollutants that disturb various ecosystems. The aim of this study was to characterize the short-lapse dynamics of soil microbial communities in response to hydrocarbon pollution and different bioremediation treatments. Replicate diesel-spiked soil microcosms were inoculated with either a defined bacterial consortium or a hydrocarbonoclastic bacterial enrichment and incubated for 12 weeks. The microbial community dynamics was followed weekly in microcosms using Illumina 16S rRNA gene sequencing. Both the bacterial consortium and enrichment enhanced hydrocarbon degradation in diesel-polluted soils. A pronounced and rapid bloom of a native gammaproteobacterium was observed in all diesel-polluted soils. A unique operational taxonomic unit (OTU) related to the Alkanindiges genus represented ∼ 0.1% of the sequences in the original community but surprisingly reached >60% after 6 weeks. Despite this Alkanindiges-related bloom, inoculated strains were maintained in the community and may explain the differences in hydrocarbon degradation. This study shows the detailed dynamics of a soil bacterial bloom in response to hydrocarbon pollution, resembling microbial blooms observed in marine environments. Rare community members presumably act as a reservoir of ecological functions in high-diversity environments, such as soils. This rare-to-dominant bacterial shift illustrates the potential role of a rare biosphere facing drastic environmental disturbances. Additionally, it supports the concept of "conditionally rare taxa," in which rareness is a temporary state conditioned by environmental constraints.

Seasonal progression of microbial communities on the Faroe shelf

Microorganisms, such as phytoplankton and bacterioplankton, are affected by turnover rates of nutrients and show great fluctuations over seasons. In productive coastal areas, the biomass of bacterioplankton can be in the same range as that of phytoplankton. In these coastal areas the initiation and intensity of the spring bloom is highly variable between years. This variability is reflected in higher trophic levels and is therefore of major importance for ecosystems such as that of the Faroe Islands. However, one of the major unknown components is the bacterioplankton. We report a study on seasonal dynamics from March–September of nutrients, phytoplankton composition and their co-fluctuation with bacterial succession. For this purpose SAR11, Bacteroidetes, Roseobacter and cyanobacteria were relatively quantified using real-time PCR based on 16S DNA and total bacteria was assessed by epifluorescence microscopy. The phytoplankton species were identified using the inverted microscope technique. These data showed a pronounced diatom spring bloom and autumn bloom reflected by a corresponding decrease in nitrate and silicate (R2 = 0.72 and 0.77, respectively). The cessation of the phytoplankton bloom did not, however, seem to be explained by nutrient limitation. Roseobacter bloomed during the phytoplankton spring bloom, while the other bacterial groups increased during low phytoplankton biomass. This suggests that algal substrate availability and environmental conditions provide the opportunity for bacterial communities to develop a post-spring bloom. This study reveals how planktonic bacteria adapt with their surroundings, enhancing the microbial loop post-spring bloom and providing a potentially important food resource for higher trophic levels.

DNA as genetic material and as a nutrient in halophilic Archaea.

DNA as genetic material and as a nutrient in halophilic Archaea.

Understanding Crohn's disease through genetics

Understanding Crohn's disease through genetics

Diversity and factors controlling widespread occurrence of syn-rift Ladinian microbialites in the western Tethys (Triassic Catalan Basin, NE Spain)

The fault-block carbonate ramps of the Ladinian (Middle Triassic) Catalan Basin hosted a wide variety of microbial deposits which formed during a syn-rift stage. Stratigraphical and sedimentological analyses of these microbialites allow us to reconstruct two depositional models for such microbial deposits. Moreover new insights into the interplay between the intrinsic and extrinsic factors that controlled the widespread development of these microbialites are provided. Stromatolites, ooidal-muddy microbial laminites and thrombolites were analyzed on the basis of their geometry, lamination and textural attributes. These microbialites are distributed over two Transgressive–Regressive sequences and coexisted during the Fassanian (Early Ladinian) regressive stage. Later, stromatolites and ooidal-muddy microbial laminites developed during the Longobardian (Late Ladinian) transgressive stage. Three types of lamina couplets reflect distinct accretion processes linked to water chemistry, sediment supply and hydrodynamic conditions. Thrombolite textures were produced by accretionary, binding and encrusting processes (microbially mediated) and pervasive cementation.The widespread occurrence of microbial deposits is explained as a consequence of a biogeochemical cascade of events (e.g., anoxic/dysoxic seawater conditions, volcanic activity, upwelling of alkaline waters, nutrient concentrations, and microbial blooms), which promoted favorable conditions for microbial growth in the Tethys during the Ladinian. Furthermore, in the Catalan Basin, syn-rift fault induced subsidence and local water energy gradients exerted an essential role in the distribution of the three types of microbialites through space and time. Thrombolites were prone to grow in the hanging wall block of a half-graben (subtidal conditions), whereas stromatolites and ooidal-muddy microbial laminites flourished preferably in a foot wall block setting (intertidal–shallow subtidal conditions). However, the fact that thrombolites exhibit abundant botryoidal and isopachous fibrous marine cements, corrosion and significant microbial evidence allow us to hypothesize about the relationship between thrombolite occurrence and hydrothermal fault-controlled fluid circulation during the Triassic rifting.The two depositional models here proposed constitute a step forward the understanding of the platform-to-basin microbialite heterogeneity during the Ladinian. Furthermore this work sheds new light on the mechanisms that likely promoted microbialite development during a period of major ecological restructuration and complex oceanographic conditions.

Early Triassic stromatolites in a siliciclastic nearshore setting in northern Perth Basin, Western Australia: Geobiologic features and implications for post-extinction microbial proliferation

An Early Triassic stromatolite deposit in Gondwana is documented from the Smithian succession of the Lower Triassic Kockatea Shale Formation in the Northampton area, northern Geraldton, Western Australia. Abundant tube-like sheaths of filaments and tiny circular microspherule balls are well preserved in laminae of the Northampton stromatolites, which are characterized by finely laminated domes and digitate high-relief columns. These filament sheaths are superficially analogous to their counterparts of modern stromatolites, and thus are interpreted as putative fossilized filamentous cyanobacteria. Elemental mapping of EDS analysis shows very high contents of both Fe and Si elements as well as common presence of both S and Al elements along the laminae of the stromatolites, suggesting that the stromatolites may have been ferritized or silicified. Both ferritization and silicification may have played a crucial role in the exceptional preservation of the micro-structures in the Northampton stromatolites. The high content of Al along the laminae indicates that the stromatolites may have been influenced by terrigenous fine-grained clastics during their growth. The Northampton stromatolites show several growth modes, initiating on either pebbles/conglomerates or sandy seafloor and building laminar domes and digitate, high-relief columns during an initial transgression period. Steady increase in sea level facilitated the growth of stromatolites. The Early Triassic stromatolites ceased growth due to either rapid rise in sea level or increased clay influx probably sourced from increased weathering on land at that time, or both. The occurrence of the Northampton stromatolites in the siliciclastic succession, in comparison with published records of Early Triassic microbialites, reveals that post-extinction microbialites were widespread in the Smithian. Stromatolites show a broad geographic distribution from low-latitude to southern high-latitude regions of Gondwana and inhabited not only carbonate settings, but also siliciclastic nearshore settings. All features of these Early Triassic stromatolites indicate a microbial bloom in the aftermath of the P–Tr mass extinction.

The Dead Sea Ecosystem Influenced by Red Sea – Dead Sea Conduit Project (Peace Conduit)

ABSTRACT Recently, the rapid drying out of the Dead Sea is one of the most challenging problems facing the scientists and governments of the region. Its level has dropped more than 20 m in the past decade. Massive precipitation of halite from the water column has led to a decrease in Na+ concentration, concomitant with an increase in Mg2+, making the lake supersaturated with NaCl. This situation presents a big challenge to the microbial life of the lake. However, despite these harsh conditions in the lake, several microorganisms, including members of the groups bacteria, unicellular algae, fungi, viruses, and Archaea, have been able to survive. To understand the factors that affect the microbes in the Dead Sea and to predict the possible effects of the planned conveyance of Red Sea water to the Dead Sea, a series of experiments were performed in the field, as well as in the laboratory. The results of the laboratory experiments showed that the growth of the Dunaliella was possible only when Dead Sea water was diluted with a minimum of 10% (by volume) Red Sea water. Addition of phosphate was essential for the algae to grow and growth rates and yields increased with increasing phosphate concentration and decreasing salinity. Field experiments revealed that the growth of algae was rapidly followed by the development of dense blooms of red halophilic Archaea. Although it should be realized that the closed system formed by the shallow ponds differs from the conditions in the lake, the results suggest that a microbial bloom, once formed, can remain present in the Dead Sea for months to years. These observations are important when attempting to predict how the biological properties of the lake may change in the future and they have important implications for the planning of the Red Sea- Dead Sea conduit. The “Peace Conduit”, a water carrier between the Red Sea and the Dead Sea, has been proposed to prevent the drying out of the lake and to restore the water level to a desired elevation. The present simulation experiments were designed at the Al Hussein bin Talal University (AHU) field station atMa’an to get information on the ecological impacts of the Dead Sea when the “Peace Conduit” plans are implemented and massive quantities of Red Sea water will enter the Dead Sea and lower the salinity of the upper water layers. Preliminary analysis was carried out of Fluorescence In Situ Hybridization (FISH) and Polar lipid of Archaea and Bacteria collected from the experimental ponds containing different Dead Sea-Red Sea water ratios, in order to analyze how they affect the microbial communities of the ponds. The Archaea community changed significantly according to the water mixture, presenting the greatest diversity when 30% Red Sea water was added to Dead Sea water.

Transcriptional response of bathypelagic marine bacterioplankton to the Deepwater Horizon oil spill

The Deepwater Horizon blowout released a massive amount of oil and gas into the deep ocean between April and July 2010, stimulating microbial blooms of petroleum-degrading bacteria. To understand the metabolic response of marine microorganisms, we sequenced ≈ 66 million community transcripts that revealed the identity of metabolically active microbes and their roles in petroleum consumption. Reads were assigned to reference genes from ≈ 2700 bacterial and archaeal taxa, but most assignments (39%) were to just six genomes representing predominantly methane- and petroleum-degrading Gammaproteobacteria. Specific pathways for the degradation of alkanes, aromatic compounds and methane emerged from the metatranscriptomes, with some transcripts assigned to methane monooxygenases representing highly divergent homologs that may degrade either methane or short alkanes. The microbial community in the plume was less taxonomically and functionally diverse than the unexposed community below the plume; this was due primarily to decreased species evenness resulting from Gammaproteobacteria blooms. Surprisingly, a number of taxa (related to SAR11, Nitrosopumilus and Bacteroides, among others) contributed equal numbers of transcripts per liter in both the unexposed and plume samples, suggesting that some groups were unaffected by the petroleum inputs and blooms of degrader taxa, and may be important for re-establishing the pre-spill microbial community structure.

Fish Oil Attenuates Omega-6 Polyunsaturated Fatty Acid-Induced Dysbiosis and Infectious Colitis but Impairs LPS Dephosphorylation Activity Causing Sepsis

Clinically, excessive ω-6 polyunsaturated fatty acid (PUFA) and inadequate ω-3 PUFA have been associated with enhanced risks for developing ulcerative colitis. In rodent models, ω-3 PUFAs have been shown to either attenuate or exacerbate colitis in different studies. We hypothesized that a high ω-6: ω-3 PUFA ratio would increase colitis susceptibility through the microbe-immunity nexus. To address this, we fed post-weaned mice diets rich in ω-6 PUFA (corn oil) and diets supplemented with ω-3 PUFA (corn oil+fish oil) for 5 weeks. We evaluated the intestinal microbiota, induced colitis with Citrobacter rodentium and followed disease progression. We found that ω-6 PUFA enriched the microbiota with Enterobacteriaceae, Segmented Filamentous Bacteria and Clostridia spp., all known to induce inflammation. During infection-induced colitis, ω-6 PUFA fed mice had exacerbated intestinal damage, immune cell infiltration, prostaglandin E2 expression and C. rodentium translocation across the intestinal mucosae. Addition of ω-3 PUFA on a high ω-6 PUFA diet, reversed inflammatory-inducing microbial blooms and enriched beneficial microbes like Lactobacillus and Bifidobacteria, reduced immune cell infiltration and impaired cytokine/chemokine induction during infection. While, ω-3 PUFA supplementation protected against severe colitis, these mice suffered greater mortality associated with sepsis-related serum factors such as LPS binding protein, IL-15 and TNF-α. These mice also demonstrated decreased expression of intestinal alkaline phosphatase and an inability to dephosphorylate LPS. Thus, the colonic microbiota is altered differentially through varying PUFA composition, conferring altered susceptibility to colitis. Overall, ω-6 PUFA enriches pro-inflammatory microbes and augments colitis; but prevents infection-induced systemic inflammation. In contrast, ω-3 PUFA supplementation reverses the effects of the ω-6 PUFA diet but impairs infection-induced responses resulting in sepsis. We conclude that as an anti-inflammatory agent, ω-3 PUFA supplementation during infection may prove detrimental when host inflammatory responses are critical for survival.

Dead Sea rhodopsins revisited

The Dead Sea is a unique hypersaline ecosystem with near toxic magnesium levels (∼2 M), dominance of divalent cations and a slightly acidic pH. Previously, we reported a haloarchaeon related to Halobacterium salinarum to dominate in a microbial bloom that developed in 1992 in the upper water layers of the lake following massive freshwater runoff. Whether this clade also dominated an earlier bloom in 1980-1982 cannot be ascertained as no samples for cultivation-independent analysis were preserved. The presence of the light-driven proton pump bacteriorhodopsin was reported in the 1980-1982 bloom of prokaryotes that had developed in the Dead Sea. To test the hypothesis that bacteriorhodopsin proton pumping may play a major role in determining what type of haloarchaea may dominate in specific bloom conditions, we compared rhodopsin genes recovered from Dead Sea biomass collected in different periods with genes coding for retinal proteins in isolated haloarchaea. Novel bacteriorhodopsin and sensory rhodopsin genes were found in samples collected in 2007 and 2010. The fact that no rhodopsin genes were recovered from samples collected during the 1992 bloom, which was dominated by a single species, suggests that different clades were present in the 1980-1982 and 1992 blooms, and that bacteriorhodopsin proton pumping did not necessarily play a determinative role in the dominance of specific halophiles in the blooms.

Microbial ooids and cortoids from the Lower Triassic (Spathian) Virgin Limestone, Nevada, USA: Evidence for an Early Triassic microbial bloom in shallow depositional environments

Lower Triassic sedimentary rocks contain a variety of unusual facies and fabrics, with microbialites being a distinctive component of many carbonates deposited following the Permian–Triassic mass extinction. Coated grains are common in shallow water facies from the upper Lower Triassic (Spathian) Virgin Limestone (Moenkopi Formation) in southern Nevada, and were investigated in order to determine their origin. Petrographic analysis reveals that the majority of the coated grains found within the Virgin Limestone are micritic ooids with a concentric fabric, or with a homogenous fabric composed of dense, often cloudy micrite. In addition, asymmetric ooids, aggregate grains, and distorted ooids are also locally common in some oolitic units; low-Mg calcite ooids and bimineralic ooids composed of low-Mg calcite and dense, cloudy micrite are less commonly found, but are also documented from the Virgin Limestone. Cortoids (i.e., grains that are coated with constructive micrite envelopes) are a minor component of oolitic grainstones and packstones (typically 10–15% of the grains), although they may also comprise entire beds. The cortoids are coated with micrite similar to that which comprises the ooid cortices, and may be finely laminated or dense and cloudy in nature. The micrite ooids and constructive micrite envelopes are interpreted as microbial in origin based on the finely laminated or cloudy, dense nature of the micrite, as well as coatings that are uneven, or often of greater thickness on one side of elongate nuclei, such as bivalve shells or phylliod algae blades. The origin of the low-Mg calcite ooids and layers is less certain, but may also be microbial. The results of this study suggest that a microbial bloom occurred in shallow water environments, which was the result of 3 factors: (1) the unusual chemistry of Early Triassic oceans; (2) runoff of nutrient-rich waters, which enhanced microbialite growth; and, (3) wave agitation and warm waters that led to CO2 degassing and further supersaturation of shallow waters with respect to calcium carbonate.

Geomicrobiological perspective on the pattern and causes of the 5-million-year Permo/Triassic biotic crisis

The pattern and causes of Permo/Triassic biotic crisis were mainly documented by faunal and terrestrial plant records. We reviewed herein the geomicrobiological perspective on this issue based on the reported cyanobacterial record. Two episodic cyanobacterial blooms were observed to couple with carbon isotope excursions and faunal mass extinction at Meishan section, suggestive of the presence of at least two episodic biotic crises across the Permian-Triassic boundary (PTB). The two episodes of cyanobacterial blooms, carbon isotope excursions and faunal mass extinction were, respectively, identified in several sections of the world, inferring the presence of two global changes across the PTB. Close associations among the three records (cyanobacterial bloom, shift in carbon isotope composition, and faunal extinction) were subsequently observed in three intervals in the Early Triassic, the protracted recovery period as previously thought, inferring the occurrence of more episodes of global changes. Spatiotemporal association of cyanobacterial blooms with volcanic materials in South China, and probably in South-east Asia, infers their causal relationship. Volcanism is believed to trigger the biotic crisis in several ways and to cause the close association among microbial blooms, the carbon isotope excursions and faunal mass extinctions in four intervals from the latest Permian to the Early Triassic. The major episodes of the well-known Siberian flood eruption are proposed to be responsible for the extinctions in the Early Triassic, but their synchronicity with the end-Permian extinction awaits more precise dating data to confirm. Geomicrobial records are thus suggestive of a long-term episodic biotic crisis (at least four episodes) lasting from the latest Permian to the end of the Early Triassic, induced by the global volcanic eruptions and sea level changes during Pangea formation.

The dying Dead Sea: The microbiology of an increasingly extreme environment

The Dead Sea, on the border between Israel and Jordan, currently contains around 348 g salt L−1. Divalent cations (Mg2+, Ca2+) dominate over monovalent cations (Na+, K+), while Cl− and Br− are the main anions. The pH of the Sea is about 6. The water balance of the lake is negative, having dropped over 1 m year−1 over the past decade. The water is supersaturated with Na+, with massive quantities of halite precipitating to the bottom of the lake. Biological monitoring since 1980 has indicated that blooms of the unicellular green alga Dunaliella and halophilic Archaea of the family Halobacteriaceae only develop following significant dilution of the upper water layers in the lake after very rainy winters. Such events occurred in 1980, and even more dramatically in 1992, when up to 3.5 × 107 Archaea mL−1 in the diluted upper 5–10 m of the water column coloured the lake red. Species isolated from the lake include Haloferax volcanii, Haloarcula marismortui, Halorubrum sodomense and Halobaculum gomorrense. Dunaliella was no longer observed in the lake after 1996, with prokaryote numbers remaining low. To characterize the residual microbial community in the lake, biomass was collected in February 2007 for environmental genomic analyses. The results were compared with the metagenome of microbial bloom material collected in 1992. The 16S rRNA archaeal phylotypes recovered from the 2007 sample were diverse, with phylotypes distantly related to the genera Halorhabdus, Haloplanus, Natronomonas and others. Halorhabdus sp. also was recovered in culture. The 1992 bloom sample was very homogeneous, however, with a single cluster remotely related to Halobacterium salinarum. These results illustrate that the microbial communities are dynamic, even in one of the most extreme environments on Earth, and exhibit strong shifts in species composition as conditions for life become increasingly adverse.

Gypsum and dolomite biomineralization in endoevaporitic microbial niche, EMISAL, Fayium, Egypt

Biogenic gypsum in the form of microbialite and potential domal stromatolite as well as endoevaporitic dolomite are deposited in a perennial saline basin characterized by microbial bloom. Deposition environment, mode of occurrence, and microscopic investigation including SEM of these precipitates are discussed in conjunction with XRD, XRF, and FTIR data. Combined effects of salinity gradient and the wind action on the maturity of gypsum outcrop are evident. A characteristic multi-color vertical gypsum profile reflects steep gradient of oxi-anoxic microenvironments and encodes diverse seasonal microbial communities. Direct impact of microbial signature in gypsum crystal habit is conspicuous. Endoevaporitic authigenic dolomite is recorded in specific horizons in interstices of selenite layers.

Alkaline phosphatase activity in relation to nutrient status in the northern Adriatic Sea

During 2004 and 2006, alkaline phosphatase activity (APA) was measured in the northern Adriatic to establish, if it is an important mechanism for phosphorus recycling in this area, which is poor in orthophosphate (PO4). From May to September, in conditions of exhausted PO4, microbes in upper waters induced high APA (0.41 to 5.55 μ mol l– 1 h– 1) to obtain phosphorus from the dissolved organic pool. The highest APA was found during spring and summer freshets due to the strongly deficient PO4 versus inorganic nitrogen supply from the Po River. During the summer months, APA was lower yet still important for phosphorus recycling. In these months, the low Po River nitrogen supply resulted in lower microbial biomass and, consequently, lower APA. From October to December, APA in upper waters was low (<0.2 μ mol l– 1 h– 1), even during large microbial blooms. During autumn blooms, PO4 was probably supplied from deeper waters. In deeper waters, with an almost balanced inorganic N: P ratio for microbial requirements, APA was generally irrelevant during the entire investigation period. Our results emphasise the role of APA in meeting the seasonal microbial phosphorus requirements in the northern Adriatic.

Ecological regime shifts in salinised wetland systems. II. Factors affecting the dominance of benthic microbial communities

This paper is the second in a pair investigating potential mechanisms for ecological regime change in salinising wetlands. The first paper in this series focused on the responses of the salt-tolerant submerged macrophyte community to salinity. In this second paper, we investigated some of the environmental conditions required for initiation and dominance of benthic microbial communities using a combination of experimental and observational data. Two experiments were carried out. One investigated the importance of prior establishment of benthic microbial communities on their ability to maintain prevalence over macrophyte colonisation (‘persistence’ experiment), while the other investigated hydrology and its effect on sediment perturbation, potential nutrient release and subsequent benthic microbial community establishment (‘flooding’ experiment). The ‘persistence’ experiment measured the biomass of benthic microbial communities and emergence of macrophytes from sediments kept either wet or dry for 4 weeks then flooded at a range of salinities. Benthic microbial biomass was similar across all of the salinities tested (15, 45 and 70 ppt), with a slight increase at higher salinities, suggesting that none of these limited benthic microbial community development. Pre-wetting of sediments usually increased benthic microbial community biomass and reduced macrophyte germination, but the latter was attributed to the presence of anoxic sediments rather than the increased benthic microbial community biomass. Germinating macrophytes emerged through benthic microbial communities or dense heterotrophic bacterial blooms, demonstrating that they could become dominant even when another community was already established. Field data supported these results, suggesting that the development of benthic microbial communities is not limited by salinity alone, but includes other factors, such as the water regime. In the ‘flooding’ experiment, the largest differences in nutrient concentrations ultimately lay between the pre-wet and pre-dry treatments (due to the greater release of nutrients and development of anoxia in the latter) rather than those subjected to fast versus slow flooding. In response to this, highest benthic microbial community biomass was in treatments with pre-wet sediment, corresponding with lower phytoplankton biomass.

Neuro-apoptogenic and blood platelet targeting toxins in benthic marine cyanobacteria from the Portuguese coast

Six strains of marine cyanobacteria, of which five benthic, were isolated from an area of the Portuguese coast with no known apparent toxic microbial bloom. Five strains were lethal for mice. Four of them produced lethargy and four lead to bleeding. One of the toxic strains was from a genus ( Aphanothece) not previously associated with toxin production. Extracts from four isolates induced SH-SY5Y-neuroblastoma cell apoptosis without affecting the viability of hepatocytes, NRK kidney cells, or fibroblasts. Aqueous extract from four isolates inhibited thrombin-induced blood platelet activation, with decreased P-selectin expression, platelet aggregation and shedding of platelet-derived micro-vesicles. Curiously, platelets treated with organic extracts from two of the cyanobacterial strains formed platelet micro-vesicles, expressed P-selectin on the surface and showed a distinct phosphotyrosine protein pattern, but failed to aggregate. We conclude that low-abundance marine cyanobacteria growing at low rates may be an important source for novel toxins that may be useful to dissect mammalian signalling pathways of apoptosis and platelet function.

The Late Devonian Frasnian–Famennian (F/F) biotic crisis: Insights from δ13C carb, δ13C org and 87Sr / 86Sr isotopic systematics

A severe biotic crisis occurred during the Late Devonian Frasnian–Famennian (F/F) transition (± 367 Myr). Here we present δ 13C carb, δ 13C org and 87Sr / 86Sr isotopic systematics, from identical samples of two sections across F/F boundary in South China, which directly demonstrate large and frequent climatic fluctuations (∼200 kyr) from warming to cooling during the F/F transition. These climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing, and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land, which would have increased riverine delivery to oceans and primary bioproductivity, and subsequent burial of organic matter, thereby resulting in climate cooling. Such large and frequent climatic fluctuations, together with volcanic-induced increases in nutrient (e.g., biolimiting Fe), toxin (sulfide) and anoxic water supply, and subsequent enhanced riverine fluxes and microbial bloom, were likely responsible for the stepwise faunal demise of F/F biotic crisis.