UV-C LED-induced cyclobutane pyrimidine dimer formation, lesion repair and mutagenesis in the biofilm-forming diatom, Navicula incerta.

The use of ultraviolet-C (UV-C) irradiation in marine biofouling control is a relatively new and potentially disruptive technology. This study examined effects of UV-C exposure on the biofilm-forming diatom, Navicula incerta. UV-C-induced mutations were identified via Illumina HiSeq. A de novo genome was assembled from control sequences and reads from UV-C-exposed treatments were mapped to this genome, with a quantitative estimate of mutagenesis then derived from the frequency of single nucleotide polymorphisms. UV-C exposure increased cyclobutane pyrimidine dimer (CPD) abundance with a direct correlation between lesion formation and fluency. Cellular repair mechanisms gradually reduced CPDs over time, with the highest UV-C fluence treatments having the fastest repair rates. Mutation abundances were, however, negatively correlated with CPD abundance suggesting that UV-C exposure may influence lesion repair. The threshold fluence for CPD formation exceeding CPD repair was >1.27 J cm-2. Fluences >2.54 J cm-2 were predicted to inhibit repair mechanisms. While UV-C holds considerable promise for marine antifouling, diatoms are just one, albeit an important, component of marine biofouling communities. Determining fluence thresholds for other representative taxa, highlighting the most resistant, would allow UV-C treatments to be specifically tuned to target biofouling organisms, whilst limiting environmental effects and the power requirement.

Bacterial colonisation of plastic in the Rockall Trough, North-East Atlantic: An improved understanding of the deep-sea plastisphere.

Plastic pollution has now been found within multiple ecosystems across the globe. Characterisation of microbial assemblages associated with marine plastic, or the so-called 'plastisphere', has focused predominantly on plastic in the epipelagic zone. Whether this community includes taxa that are consistently enriched on plastic compared to surrounding non plastic surfaces is unresolved, as are the ecological implications. The deep sea is likely a final sink for most of the plastic entering the ocean, yet there is limited information on microbial colonisation of plastic at depth. The aim of this study was to investigate deep-sea microbial communities associated with polystyrene (PS) and polyurethane (PU) with Bath stone used as a control. The substrates (n = 15) were deployed in the Rockall Trough (Atlantic), and recovered 420 days later from a depth of 1796 m. To characterise the bacterial communities, 16S rRNA genes were sequenced using the Illumina MiSeq platform. A dominant core microbiome (taxa shared across all substrates) comprised 8% of total ASVs (amplicon sequence variant) and accounted for 92% of the total community reads. This suggests that many commonly reported members of the plastisphere are simply opportunistic which freely colonise any hard surface. Transiently associated species consisted of approximately 7% of the total community. Thirty genera were enriched on plastic (P < 0.05), representing 1% of the total community. The discovery of novel deep-sea enriched taxa included Aurantivirga, Algivirga, IheB3-7, Spirosoma, HTCC5015, Ekhidna and Calorithrix on PS and Candidatus Obscuribacter, Haloferula, Marine Methylotrophic Group 3, Aliivibrio, Tibeticola and Dethiosulfatarculus on PU. This small fraction of the microbiome include taxa with unique metabolic abilities and show how bacterial communities can be shaped by plastic pollution at depth. This study outlines a novel approach in categorising the plastisphere to elucidate the ecological implications of enriched taxa that show an affinity for colonising plastic.

Diatom-Derived Polyunsaturated Aldehydes Are Unlikely to Influence the Microbiota Composition of Laboratory-Cultured Diatoms.

Diatom-derived oxylipins, including polyunsaturated aldehydes (PUA), are considered to have infochemical, allelochemical and bacteriostatic properties, with plausible roles as grazing deterrents and regulators of inter- and intraspecific competition. However, the extent and mechanisms of how PUA influence diatom-bacteria interactions remain unresolved. In this study, impacts on the diversity of the associated bacterial communities (microbiota) of two contrasting Skeletonema marinoi strains (a PUA and a non-PUA producer) were investigated under three nitrate conditions in batch culture. Further, the response of the culture microbiota was studied when spiked with PUA at ecologically relevant concentrations (86nM octadienal and 290nM heptadienal). Of the 741 identified OTUs, Proteobacteria was the most abundant phylum (62.10%), followed by Bacteroidetes (12.33%) and Firmicutes (6.11%). Escherichia/Shigella were the most abundant genera for all treatments. Similar communities were present in both spiked and non-spiked cultures suggesting they can tolerate PUA exposure at realistic concentrations. This study suggests that PUA are not major drivers of diatom-bacteria interactions in laboratory cultures.

Co-digestion of microalgae with potato processing waste and glycerol: effect of glycerol addition on methane production and the microbial community.

The production of methane-rich biogas from the anaerobic digestion (AD) of microalgae is limited by an unfavorable biomass carbon-to-nitrogen (C/N) ratio; however, this may be ameliorated using a co-digestion strategy with carbon-rich feedstocks. For reliable plant operation, and to improve the economics of the process, secure co-feedstock supply (ideally as a waste-stream) is important. To this end, this study investigated the feasibility of co-digesting microalgae (Chlorella vulgaris) with potato processing waste (potato discarded parts, PPWdp; potato peel, PPWp) and glycerol, while monitoring the response of the methanogenic community. In this semi-continuous study, glycerol (1 and 2% v/v) added to mixtures of C. vulgaris : PPWdp enhanced the specific methane yields the most, by 53-128%, whilst co-digestion with mixtures of C. vulgaris : PPWp enhanced the methane yields by 62-74%. The microbial communities diverged markedly over operational time, and to a lesser extent in response to glycerol addition. The acetoclast Methanosaeta was abundant in all treatments but was replaced by Methanosarcina in the potato peel with glycerol treatment due to volatile fatty acid (VFA) accumulation. Our findings demonstrate that the performance of microalgae co-digestion is substantially improved by the addition of glycerol as an additional co-feedstock. This should improve the economic case for anaerobically digesting microalgae as part of wastewater treatment processes and/or the terminal step of a microalgae biorefinery.