Response of Seagrass ‘Blue Carbon’ Stocks to Increased Water Temperatures

Seagrass meadows are globally important sinks of ‘Blue Carbon’, but warming water temperatures due to climate change may undermine their capacity to sequester and retain organic carbon (Corg). We tested the effects of warming on seagrass Corg stocks in situ by transplanting seagrass soil cores along a thermal plume generated by a coal-fired power plant in a seagrass-dominated estuary (Lake Macquarie, Australia). Transplanted cores were subjected to temperatures 2 and 4 °C above ambient temperatures and Corg content was measured after 7, 30, 90 and 180 days. We were unable to detect any significant effect of warming on Corg concentration, stocks, chemical composition (as measured by labile, recalcitrant, refractory ratios), or microbial abundance at any time point. In fact, Corg levels were temporally variable. These findings contrast those of previous studies (mostly laboratory-based) that have reported increases in microbial remineralisation (breakdown) of Corg in response to warming. To explain the lack of any detectable warming effect, we suggest that higher temperatures, longer durations of warming exposure, or additional stressors (e.g., oxygen exposure) may be needed to overcome microbial activation barriers and stimulate Corg remineralisation.</jats:p

Isolation of the Pneumocystis carinii dihydrofolate synthase gene and functional complementation in Saccharomyces cerevisiae

The Pneumocystis carinii gene encoding the enzyme dihydrofolate synthase (DHFS), which is involved in the essential biosynthesis of folates, was isolated from clones of the Pneumocystis genome project, and sequenced. The deduced P. carinii DHFS protein shares 38% and 35% identity with DHFS of Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. P. carinii DHFS expressed from a plasmid functionally complemented a S. cerevisiae mutant with no DHFS. Comparison of available DHFSs with highly similar folylpolyglutamate synthases allowed the identification of potential signatures responsible for the specificities of these two classes of enzymes. The results open the way to experimentally analyse the structure and function of P. carinii mono-functional enzyme DHFS, to investigate a possible role of DHFS in the resistance to antifolates of P. jirovecii, the species infecting specifically humans, and to develop a new class of antifolates

Comment on 'Geoengineering with seagrasses: Is credit due where credit is given?'

Over the past decade scientists around the world have sought to estimate the capacity of seagrass meadows to sequester carbon, and thereby understand their role in climate change mitigation. The number of studies reporting on seagrass carbon accumulation rates is still limited, but growing scientific evidence supports the hypothesis that seagrasses have been efficiently locking away CO2 for decades to millennia (e.g. Macreadie et al 2014, Mateo et al 1997, Serrano et al 2012). Johannessen and Macdonald (2016), however, challenge the role of seagrasses as carbon traps, claiming that gains in carbon storage by seagrasses may be \u27illusionary\u27 and that \u27their contribution to the global burial of carbon has not yet been established\u27. The authors warn that misunderstandings of how sediments receive, process and store carbon have led to an overestimation of carbon burial by seagrasses. Here we would like to clarify some of the questions raised by Johannessen and Macdonald (2016), with the aim to promote discussion within the scientific community about the evidence for carbon sequestration by seagrasses with a view to awarding carbon credits

Inhibition of 3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase and Application of Statins as a Novel Effective Therapeutic Approach against Acanthamoeba Infections

Acanthamoeba is an opportunistic pathogen in humans, whose infections most commonly manifest as Acanthamoeba keratitis or, more rarely, granulomatous amoebic encephalitis. Although there are many therapeutic options for the treatment of Acanthamoeba, they are generally lengthy and/or have limited efficacy. Therefore, there is a requirement for the identification, validation, and development of novel therapeutic targets against these pathogens. Recently, RNA interference (RNAi) has been widely used for these validation purposes and has proven to be a powerful tool for Acanthamoeba therapeutics. Ergosterol is one of the major sterols in the membrane of Acanthamoeba. 3-Hydroxy-3-methylglutaryl–coenzyme A (HMG-CoA) reductase is an enzyme that catalyzes the conversion of HMG-CoA to mevalonate, one of the precursors for the production of cholesterol in humans and ergosterol in plants, fungi, and protozoa. Statins are compounds which inhibit this enzyme and so are promising as chemotherapeutics. In order to validate whether this enzyme could be an interesting therapeutic target in Acanthamoeba, small interfering RNAs (siRNAs) against HMG-CoA were developed and used to evaluate the effects induced by the inhibition of Acanthamoeba HMG-CoA. It was found that HMG-CoA is a potential drug target in these pathogenic free-living amoebae, and various statins were evaluated in vitro against three clinical strains of Acanthamoeba by using a colorimetric assay, showing important activities against the tested strains. We conclude that the targeting of HMG-CoA and Acanthamoeba treatment using statins is a novel powerful treatment option against Acanthamoeba species in human disease

Connectivity of larval stages of sedentary marine communities between hard substrates and offshore structures in the North Sea

Man-made structures including rigs, pipelines, cables, renewable energy devices, and ship wrecks, offer hard substrate in the largely soft-sediment environment of the North Sea. These structures become colonised by sedentary organisms and non-migratory reef fish, and form local ecosystems that attract larger predators including seals, birds, and fish. It is possible that these structures form a system of interconnected reef environments through the planktonic dispersal of the pelagic stages of organisms by ocean currents. Changes to the overall arrangement of hard substrate areas through removal or addition of individual man-made structures will affect the interconnectivity and could impact on the ecosystem. Here, we assessed the connectivity of sectors with oil and gas structures, wind farms, wrecks, and natural hard substrate, using a model that simulates the drift of planktonic stages of seven organisms with sedentary adult stages associated with hard substrate, applied to the period 2001–2010. Connectivity was assessed using a classification system designed to address the function of sectors in the network. Results showed a relatively stable overall spatial distribution of sector function but with distinct variations between species and years. The results are discussed in the context of decommissioning of oil and gas infrastructure in the North Sea

Can mud (silt and clay) concentration be used to predict soil organic carbon content within seagrass ecosystems?

The emerging field of blue carbon science is seeking cost-effective ways to estimate the organic carbon content of soils that are bound by coastal vegetated ecosystems. Organic carbon (Corg) content in terrestrial soils and marine sediments has been correlated with mud content (i.e., silt and clay, particle sizes \u3c 63 µm), however, empirical tests of this theory are lacking for coastal vegetated ecosystems. Here, we compiled data (n =  1345) on the relationship between Corg and mud contents in seagrass ecosystems (79 cores) and adjacent bare sediments (21 cores) to address whether mud can be used to predict soil Corg content. We also combined these data with the δ13C signatures of the soil Corg to understand the sources of Corg stores. The results showed that mud is positively correlated with soil Corg content only when the contribution of seagrass-derived Corg to the sedimentary Corg pool is relatively low, such as in small and fast-growing meadows of the genera Zostera, Halodule and Halophila, and in bare sediments adjacent to seagrass ecosystems. In large and long-living seagrass meadows of the genera Posidonia and Amphibolis there was a lack of, or poor relationship between mud and soil Corg content, related to a higher contribution of seagrass-derived Corg to the sedimentary Corg pool in these meadows. The relatively high soil Corg contents with relatively low mud contents (e.g., mud-Corg saturation) in bare sediments and Zostera, Halodule and Halophila meadows was related to significant allochthonous inputs of terrestrial organic matter, while higher contribution of seagrass detritus in Amphibolis and Posidonia meadows disrupted the correlation expected between soil Corg and mud contents. This study shows that mud is not a universal proxy for blue carbon content in seagrass ecosystems, and therefore should not be applied generally across all seagrass habitats. Mud content can only be used as a proxy to estimate soil Corg content for scaling up purposes when opportunistic and/or low biomass seagrass species (i.e., Zostera, Halodule and Halophila) are present (explaining 34 to 91 % of variability), and in bare sediments (explaining 78 % of the variability). The results obtained could enable robust scaling up exercises at a low cost as part of blue carbon stock assessments