Surviving heatwaves:Thermal experience predicts life and death in a Southern Ocean diatom

Extreme environmental fluctuations such as marine heatwaves (MHWs) can have devastating effects on ecosystem health and functioning through rapid population declines and destabilization of trophic interactions. However, recent studies have highlighted that population tolerance to MHWs is variable, with some populations even benefitting from MHWs. A number of factors can explain variation in responses between populations including their genetic variation, previous thermal experience and the cumulative heatwave intensity (°C d) of the heatwave itself. We disentangle the contributions of these factors on population mortality and post-heatwave growth rates by experimentally simulating heatwaves (7.5 or 9.2°C, for up to 9 days) for three genotypes of the Southern Ocean diatom Actinocyclus actinochilus. The effects of simulated heatwaves on mortality and population growth rates varied with genotype, thermal experience and the cumulative intensity of the heatwave itself. Firstly, hotter and longer heatwaves increased mortality and decreased post-heatwave growth rates relative to milder, shorter heatwaves. Secondly, growth above the thermal optimum before heatwaves exacerbated heatwave-associated negative effects, leading to increased mortality during heatwaves and slower growth after heatwaves. Thirdly, hotter and longer heatwaves resulted in more pronounced changes to thermal optima (Topt) immediately following heatwaves. Finally, there is substantial intraspecific variation in post-heatwave growth rates. Our findings shed light on the potential of Southern Ocean diatoms to tolerate MHWs, which will increase both in frequency and in intensity under future climate change

Microbial weathering of shale rock in natural and historic industrial environments

The weathering of shales is a globally important process affecting both natural and built environments. Shales form roughly 70 % of worldwide sedimentary rock deposits and therefore the weathering of these rocks has substantial effects on the geochemical cycling of elements such as carbon, iron and sulfur. Microbes have been shown to play a key role in weathering shales, primarily through the oxidation of the iron and sulfur of embedded pyrite and the resultant production of sulfuric acid. Despite significant interest in the microbial weathering of shales within industrial sectors such as biohydrometallurgy and civil engineering, comparatively few studies have investigated microbial shale weathering in natural environments. Furthermore, the role of microbes in natural shale weathering processes beyond iron oxidation has largely remained unexplored. In this thesis, the weathering capabilities of microbial communities from natural weathered shale was investigated. The North Yorkshire coastline was used as a study location, due to the abundance and diversity of natural cliffs and historic, disused industrial sites. Cliff erosion and recession on the North Yorkshire coastline is a major concern for local authorities and is the focus of current research. The aim of this work has been to evaluate microbial shale weathering processes within these environments, and hypothesise the possible contribution they may have to erosive processes. Phenotypic plate assays inoculated with weathered shale material were used to obtain rock weathering bacterial isolates that tested positive for a specific weathering phenotype, such as iron oxidation or siderophore production. Subsequent 16S rRNA sequencing enabled genera level identification, revealing 15 genera with rock weathering capabilities with several being associated with multiple weathering phenotypes including Aeromonas sp., Pseudomonas sp. and Streptomyces sp.. Shale enrichment liquid cultures were incubated with shale rock chips to simulate natural biological weathering conditions, and the concentration of rock-leached elements in the fluid measured. No evidence of microbially-enhanced leaching was found consistently for any element, however the significant reduction in leachate iron concentration under biological conditions indicates that iron precipitation occurred via microbial iron oxidation. Enrichment cultures inoculated with weathered shale and containing organic matter (OM) rich rocks in water or M9 medium, both liquids lacking an organic carbon source, were grown over several months. The cultures yielded microbial isolates that could utilise rock bound OM sources and one bacterial isolate, Variovorax paradoxus, was taken forward for ecophysiological study. The shale rock that the organism was isolated from, along with other OM rich rocks (mudstones and coals), elicited complex responses from V. paradoxus including enhanced growth and motility. Finally, mineral microcosms in vitro and mesocosms in situ investigated microbial colonization and weathering of shale-comprising minerals (albite, calcite, muscovite, pyrite and quartz). Microcosms were established using iron oxidizing enrichment cultures, as based on the results of the simulated rock weathering experiments, while the in situ mesocosms were buried within weathered shale scree within a disused mine level. Levels of colonization significantly varied between minerals within the microcosms (pyrite>albite, muscovite>quartz>calcite). Although differences in mineral colonization were seen in the mesocosms, they did not match those in the microcosms and were not statistically significant. Pyrite incubated in the microcosms became significantly weathered, with extensive pit formation across the mineral surface that is consistent with microbial iron oxidation. In the mesocosms, pit formation was not identified on pyrite surfaces but dark etchings into the pyrite surface were found underneath fungi hyphal growth. The results of this thesis highlights that a range of microbial rock weathering mechanisms are abundant across weathered shale environments. Microbial iron oxidizing activity was a dominant biogeochemical process that altered rock-fluid geochemistry and weathered pyrite surfaces. However, the impact on rock or mineral weathering of other microbial mechanisms was not elucidated by this work. Given the known capabilities of these mechanisms, the conditions under which they are active may not have been met within the experimental setup used. Microbial iron oxidation in shale and shale-derived materials has previously been demonstrated to weaken rock structure through acid production and secondary mineral formation. From the results of this thesis, it is clear that microbial iron oxidation is an active process within some of the weathered shale environments studied, including cliff surfaces. Therefore, it can be hypothesised that microbial activity could play a role in structurally weakening shale rock within cliffs and accelerate their erosion. Future work should attempt to quantify the rate and extent of microbial iron oxidizing activity within shale cliff environments and investigate its contribution to erosive processes

Inferring the distribution of fitness effects of spontaneous mutations in Chlamydomonas reinhardtii

Spontaneous mutations are the source of new genetic variation and are thus central to the evolutionary process. In molecular evolution and quantitative genetics, the nature of genetic variation depends critically on the distribution of effects of mutations on fitness and other quantitative traits. Spontaneous mutation accumulation (MA) experiments have been the principal approach for investigating the overall rate of occurrence and cumulative effect of mutations but have not allowed the phenotypic effects of individual mutations to be studied directly. Here, we crossed MA lines of the green alga Chlamydomonas reinhardtii with its unmutated ancestral strain to create haploid recombinant lines, each carrying an average of 50% of the accumulated mutations in a large number of combinations. With the aid of the genome sequences of the MA lines, we inferred the genotypes of the mutations, assayed their growth rate as a measure of fitness, and inferred the distribution of fitness effects (DFE) using a Bayesian mixture model. We infer that the DFE is highly leptokurtic (L-shaped). Of mutations with absolute fitness effects exceeding 1%, about one-sixth increase fitness in the laboratory environment. The inferred distribution of effects for deleterious mutations is consistent with a strong role for nearly neutral evolution. Specifically, such a distribution predicts that nucleotide variation and genetic variation for quantitative traits will be insensitive to change in the effective population size

The UK Centre for Astrobiology:A Virtual Astrobiology Centre. Accomplishments and Lessons Learned, 2011-2016

Authors thank all those individuals, UK research councils, funding agencies, nonprofit organisations, companies and corporations and UK and non-UK government agencies, who have so generously supported our aspirations and hopes over the last 5 years and supported UKCA projects. They include the STFC, the Engineering and Physical Sciences Research Council (EPSRC), the Natural Environmental Research Council (NERC), the EU, the UK Space Agency, NASA, the European Space Agency (ESA), The Crown Estate, Cleveland Potash and others. The Astrobiology Academy has been supported by the UK Space Agency (UKSA), National Space Centre, the Science and Technology Facilities Council (STFC), Dynamic Earth, The Royal Astronomical Society, The Rotary Club (Shetlands) and the NASA Astrobiology Institute.The UK Centre for Astrobiology (UKCA) was set up in 2011 as a virtual center to contribute to astrobiology research, education, and outreach. After 5 years, we describe this center and its work in each of these areas. Its research has focused on studying life in extreme environments, the limits of life on Earth, and implications for habitability elsewhere. Among its research infrastructure projects, UKCA has assembled an underground astrobiology laboratory that has hosted a deep subsurface planetary analog program, and it has developed new flow-through systems to study extraterrestrial aqueous environments. UKCA has used this research backdrop to develop education programs in astrobiology, including a massive open online course in astrobiology that has attracted over 120,000 students, a teacher training program, and an initiative to take astrobiology into prisons. In this paper, we review these activities and others with a particular focus on providing lessons to others who may consider setting up an astrobiology center, institute, or science facility. We discuss experience in integrating astrobiology research into teaching and education activities.Publisher PDFPeer reviewe

The distribution of fitness effects of spontaneous mutations in Chlamydomonas reinhardtii inferred using frequency changes under experimental evolution

The distribution of fitness effects (DFE) for new mutations is fundamental for many aspects of population and quantitative genetics. In this study, we have inferred the DFE in the single-celled alga Chlamydomonas reinhardtii by estimating changes in the frequencies of 254 spontaneous mutations under experimental evolution and equating the frequency changes of linked mutations with their selection coefficients. We generated seven populations of recombinant haplotypes by crossing seven independently derived mutation accumulation lines carrying an average of 36 mutations in the haploid state to a mutation-free strain of the same genotype. We then allowed the populations to evolve under natural selection in the laboratory by serial transfer in liquid culture. We observed substantial and repeatable changes in the frequencies of many groups of linked mutations, and, surprisingly, as many mutations were observed to increase as decrease in frequency. Mutation frequencies were highly repeatable among replicates, suggesting that selection was the cause of the observed allele frequency changes. We developed a Bayesian Monte Carlo Markov Chain method to infer the DFE. This computes the likelihood of the observed distribution of changes of frequency, and obtains the posterior distribution of the selective effects of individual mutations, while assuming a two-sided gamma distribution of effects. We infer that the DFE is a highly leptokurtic distribution, and that approximately equal proportions of mutations have positive and negative effects on fitness. This result is consistent with what we have observed in previous work on a different C. reinhardtii strain, and suggests that a high fraction of new spontaneously arisen mutations are advantageous in a simple laboratory environment

A 500-year experiment

Charles Cockell and colleagues describe an experiment that started in 2014 and will finish in 2514. It will document how long desiccated microbes can survive, with implications for life in the planetary crust and in space