Growth at the limits: comparing trace metal limitation of a freshwater cyanobacterium (Dolichospermum lemmermannii) and a freshwater diatom (Fragilaria crotonensis)

Freshwater phytoplankton blooms are increasing in prevalence and there are conflicting views on whether trace metals limit growth of key species and thus bloom formation. The Taupō Volcanic Zone (TVZ), New Zealand, was formed by multiple eruptions of a super-volcano which emitted rhyolitic tephra leaving lakes depleted in trace metals. This provides an opportunity to test the potential of trace metal limitation on freshwater phytoplankton growth under nanomolar concentrations. Growth responses of two algal species isolated from Lake Taupō, Dolichospermum lemmermannii (cyanobacteria) and Fragilaria crotonensis (diatom), to six biologically important trace metals (manganese, iron, zinc, cobalt, copper and molybdenum) were examined in culture experiments. These were conducted at three trace metal concentrations: (1) ambient, (2) two-times ambient, and (3) ten-times ambient concentrations in Lake Taupō. Elevated concentrations of iron significantly increased growth rates and maximum cell densities in D. lemmermannii, whereas no significant concentration dependence was observed for other trace metals. Fragilaria crotonensis showed no significant growth response to elevated concentrations of trace metals. These results highlight the importance of iron as a growth limiting nutrient for cyanobacteria and indicate that even small (twofold) increases in Fe concentrations could enhance cyanobacteria growth rates in Lake Taupō, potentially causing cyanobacterial blooms.

Winter diet of Japanese macaques from Chubu Sangaku National Park, Japan incorporates freshwater biota

The Japanese macaque (Macaca fuscata) is native to the main islands of Japan, except Hokkaido, and is the most northerly living non-human primate. In the Chubu Sangaku National Park of the Japanese Alps, macaques live in one of the coldest areas of the world, with snow cover limiting the availability of preferred food sources. Winter is typically a bottleneck for food availability potentially resulting in marked energy deficits, and mortality may result from famine. However, streams with groundwater upwelling flow during the winter with a constant water temperature of about 5 °C are easily accessible for Japanese macaques to search for riverine biota. We used metabarcoding (Cytochrome c oxidase I) of fecal samples from Japanese macaques to determine their wintertime diet. Here we provide the first robust evidence that Japanese macaques feed on freshwater biota, including brown trout, riverine insects and molluscs, in Chubu Sangaku National Park. These additional food sources likely aid their winter survival.

Metabarcoding Reveals Lacustrine Picocyanobacteria Respond to Environmental Change Through Adaptive Community Structuring

Picocyanobacteria (Pcy) are important yet understudied components of lake foodwebs. While phylogenetic studies of isolated strains reveal a high diversity of freshwater genotypes, little is known about abiotic drivers associated with Pcy in different lakes. Due to methodological limitations, most previous studies assess potential drivers using total cell abundances as a response, with often conflicting and inconsistent results. In the present study, we explored how picocyanobacterial communities respond to environmental change using a combination of epifluorescence microscopy and community data determined using 16S rRNA gene metabarcoding. Temporal shifts in picocyanobacterial abundance, diversity and community dynamics were assessed in relation to potential environmental drivers in five contrasting lakes over 1year. Cell abundances alone were not consistently related to environmental variables across lakes. However, the addition of metabarcoding data revealed diverse picocyanobacterial communities that differed significantly between lakes, driven by environmental variables related to trophic state. Within each lake, communities were temporally dynamic and certain amplicon sequence variants (ASVs) were strongly associated with specific environmental drivers. Rapid shifts in community structure and composition were often related to environmental changes, indicating that lacustrine Pcy can persist at high abundances through collective community adaptation. These results demonstrate that a combination of microscopy and metabarcoding enables an in-depth characterisation of picocyanobacterial communities and reveals strain-specific drivers. We recommend that future studies cease referring to picocyanobacterial as one functional group and take strain specific variability into consideration.

Genome Streamlining, Plasticity, and Metabolic Versatility Distinguish Co-occurring Toxic and Nontoxic Cyanobacterial Strains of Microcoleus

Harmful cyanobacterial bloom occurrences have increased worldwide due to climate change and eutrophication, causing nuisance and animal deaths. Species from the benthic cyanobacterial genus Microcoleus are ubiquitous and form thick mats in freshwater systems, such as rivers, that are sometimes toxic due to the production of potent neurotoxins (anatoxins). Anatoxin-producing (toxic) strains typically coexist with non-anatoxin-producing (nontoxic) strains in mats, although the reason for this is unclear. To determine the genetic mechanisms differentiating toxic and nontoxic Microcoleus, we sequenced and assembled genomes from 11 cultures and compared these to another 31 Microcoleus genomes. Average nucleotide identities (ANI) indicate that toxic and nontoxic strains are distinct species (ANI, <95%), and only 6% of genes are shared across all 42 genomes, suggesting a high level of genetic divergence among Microcoleus strains. Comparative genomics showed substantial genome streamlining in toxic strains and a potential dependency on external sources for thiamine and sucrose. Toxic and nontoxic strains are further differentiated by an additional set of putative nitrate transporter (nitrogen uptake) and cyanophycin (carbon and nitrogen storage) genes, respectively. These genes likely confer distinct competitive advantages based on nutrient availability and suggest nontoxic strains are more robust to nutrient fluctuations. Nontoxic strains also possess twice as many transposable elements, potentially facilitating greater genetic adaptation to environmental changes. Our results offer insights into the divergent evolution of Microcoleus strains and the potential for cooperative and competitive interactions that contribute to the co-occurrence of toxic and nontoxic species within mats. IMPORTANCE Microcoleus autumnalis, and closely related Microcoleus species, compose a geographically widespread group of freshwater benthic cyanobacteria. Canine deaths due to anatoxin-a poisoning, following exposure to toxic proliferations, have been reported globally. While Microcoleus proliferations are on the rise, the mechanisms underpinning competition between, or coexistence of, toxic and nontoxic strains are unknown. This study identifies substantial genetic differences between anatoxin-producing and non-anatoxin-producing strains, pointing to reduced metabolic flexibility in toxic strains, and potential dependence on cohabiting nontoxic strains. Results provide insights into the metabolic and evolutionary differences between toxic and nontoxic Microcoleus, which may assist in predicting and managing aquatic proliferations.

Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide

Nearshore (littoral) habitats of clear lakes with high water quality are increasingly experiencing unexplained proliferations of filamentous algae that grow on submerged surfaces. These filamentous algal blooms (FABs) are sometimes associated with nutrient pollution in groundwater, but complex changes in climate, nutrient transport, lake hydrodynamics, and food web structure may also facilitate this emerging threat to clear lakes. A coordinated effort among members of the public, managers, and scientists is needed to document the occurrence of FABs, to standardize methods for measuring their severity, to adapt existing data collection networks to include nearshore habitats, and to mitigate and reverse this profound structural change in lake ecosystems. Current models of lake eutrophication do not explain this littoral greening. However, a cohesive response to it is essential for protecting some of the world's most valued lakes and the flora, fauna, and ecosystem services they sustain.

Development of droplet digital Polymerase Chain Reaction assays for the detection of long-finned (Anguilla dieffenbachii) and short-finned (Anguilla australis) eels in environmental samples

Freshwater eels are ecologically, and culturally important worldwide. The New Zealand long-finned eel (Anguilla dieffenbachii) and short-finned eel (Anguilla australis) are apex predators, playing an important role in ecosystem functioning of rivers and lakes. Recently, there has been a national decline in their populations due to habitat destruction and commercial harvest. The emergence of targeted environmental DNA detection methodologies provides an opportunity to enhance information about their past and present distributions. In this study we successfully developed species-specific droplet digital Polymerase Chain Reaction (ddPCR) assays to detect A. dieffenbachii and A. australis DNA in water and sediment samples. Assays utilized primers and probes designed for regions of the mitochondrial cytochrome b and 16S ribosomal RNA genes in A. dieffenbachii and A. australis, respectively. River water samples (n = 27) were analyzed using metabarcoding of fish taxa and were compared with the ddPCR assays. The presence of A. dieffenbachii and A. australis DNA was detected in a greater number of water samples using ddPCR in comparison to metabarcoding. There was a strong and positive correlation between gene copies (ddPCR analyses) and relative eel sequence reads (metabarcoding analyses) when compared to eel biomass. These ddPCR assays provide a new method for assessing spatial distributions of A. dieffenbachii and A. australis in a range of environments and sample types.

Deciphering the molecular signal from past and alive bacterial communities in aquatic sedimentary archives

Lake sediments accumulate information on biological communities thus acting as natural archives. Traditionally paleolimnology has focussed on fossilized remains of organisms, however, many organisms do not leave fossil evidence, meaning major ecosystem components are missing from environmental reconstructions. Many paleolimnology studies now incorporate molecular methods, including investigating microbial communities using environmental DNA (eDNA), but there is uncertainty about the contribution of living organisms to molecular inventories. In the present study, we obtained DNA and RNA inventories from sediment spanning 700 years to investigate the contribution of past and active communities to the molecular signal from sedimentary archives. Additionally, a droplet digital PCR (ddPCR) targeting the 16S ribosomal RNA (16S rRNA) gene of the photosynthetic cyanobacterial genera Microcystis was used to explore if RNA signals were from legacy RNA. We posit that the RNA signal is a mixture of legacy RNA, dormant cells, living bacteria and modern-day trace level contaminants that were introduced during sampling and preferentially amplified. The presence of legacy RNA was confirmed by the detection of Microcystis in sediments aged to ~200 years ago. Recent comparisons between 16S rRNA gene metabarcoding and traditional paleo proxies showed that past changes in bacterial communities can be reconstructed from sedimentary archives. The recovery of RNA in the present study has provided new insights into the origin of these signals. However, caution is required during analysis and interpretation of 16S rRNA gene metabarcoding data especially in recent sediments were there are potentially active bacteria.

Towards reproducible metabarcoding data: Lessons from an international cross-laboratory experiment

Advances in high-throughput sequencing (HTS) are revolutionizing monitoring in marine environments by enabling rapid, accurate and holistic detection of species within complex biological samples. Research institutions worldwide increasingly employ HTS methods for biodiversity assessments. However, variance in laboratory procedures, analytical workflows and bioinformatic pipelines impede the transferability and comparability of results across research groups. An international experiment was conducted to assess the consistency of metabarcoding results derived from identical samples and primer sets using varying laboratory procedures. Homogenized biofouling samples collected from four coastal locations (Australia, Canada, New Zealand and the USA) were distributed to 12 independent laboratories. Participants were asked to follow one of two HTS library preparation workflows. While DNA extraction, primers and bioinformatic analyses were purposefully standardized to allow comparison, many other technical variables were allowed to vary among laboratories (amplification protocols, type of instrument used, etc.). Despite substantial variation observed in raw results, the primary signal in the data was consistent, with the samples grouping strongly by geographical origin for all data sets. Simple post hoc data clean-up by removing low-quality samples gave the best improvement in sample classification for nuclear 18S rRNA gene data, with an overall 92.81% correct group attribution. For mitochondrial COI gene data, the best classification result (95.58%) was achieved after correction for contamination errors. The identified critical methodological factors that introduced the greatest variability (preservation buffer, sample defrosting, template concentration, DNA polymerase, PCR enhancer) should be of great assistance in standardizing future biodiversity studies using metabarcoding.

Lake microbial communities are not resistant or resilient to repeated large-scale natural pulse disturbances

Opportunities to study community level responses to extreme natural pulse disturbances in unaltered ecosystems are rare. Lake sediment records that span thousands of years can contain well resolved sediment pulses, triggered by earthquakes. These paleo-records provide a means to study repeated pulse disturbance and processes of resistance (insensitivity to disturbance) and ecological resilience (capacity to regain structure, function and process). In this study, sedimentary DNA was extracted from a sediment core from Lake Paringa (New Zealand) that is situated in a near natural catchment. Metabarcoding and inferred functions were used to assess the lake microbial community over the past 1,100 years - a period that included four major earthquakes. Microbial community composition and function differed significantly between highly perturbed (postseismic, c. 50 yrs) phases directly after the earthquakes and more stable (interseismic, c. 250 yr) phases, indicating a lack of community resistance. Although community structure differed significantly in successive postseismic phases, function did not, suggesting potential functional redundancy. Significant differences in composition and function in successive interseismic phases demonstrates communities are not resilient to large-scale natural pulse disturbances. The clear difference in structure and function, and high number of indicator taxa (responsible for driving differences in communities between phases) in the fourth interseismic phase likely represents a regime shift, possibly due to the two-fold increase in sediment and terrestrial biospheric organic carbon fluxes recorded following the fourth earthquake. Large pulse disturbances that enhance sediment inputs into lake systems may produce an underappreciated mechanism that destabilises lake ecosystem processes.

Variability in microcystin quotas during a Microcystis bloom in a eutrophic lake

Microcystis is a bloom-forming genus of cyanobacteria with some genotypes that produce highly toxic microcystin hepatotoxins. In waterbodies where biological and physical factors are relatively homogenous, toxin quotas (the average amount of toxin per cell), at a single point in time, are expected to be relatively constant. In this study we challenged this assumption by investigating the spatial distribution of microcystin quotas at a single point in time on two separate occasions in a lake with a major Microcystis bloom. Microcystis cell concentrations varied widely across the lake on both sampling occasions (730- and 137-fold) together with microcystin quotas (148- and 362-fold). Cell concentrations and microcystin quotas were strongly positively correlated (R2 = 0.89, P < 0.001, n = 28; R2 = 0.67, P < 0.001, n = 25). Analysis of Microcystis strains using high-throughput sequencing of the 16S-23S rRNA intergenic spacer region showed no relationship between microcystin quota and the relative abundance of specific sequences. Collectively, the results of this study indicate an association between microcystin production and cell density that magnifies the potential for bloom toxicity at elevated cell concentrations.

Spatial abundance and distribution of picocyanobacterial communities in two contrasting lakes revealed using environmental DNA metabarcoding

Freshwater picocyanobacteria (Pcy) are important yet understudied components of lake ecosystems. Most previous studies have relied on cell abundances to assess Pcy dynamics in largely oligotrophic lakes, while little is known about spatial diversity and dynamics across different lake types. In the present study we assessed the horizontal-spatial abundance and community structure of Pcy in two contrasting (oligotrophic and hypertrophic) New Zealand lakes using epifluorescence microscopy and 16S rRNA metabarcoding. Pcy abundance and community composition differed significantly both between and within the oligotrophic and hypertrophic lakes. While spatial variability was observed in both study lakes, these differences were particularly pronounced in the oligotrophic, morphometrically complex Lake Wanaka where cell abundances were typically higher in bays than open-water sites and community structure differed significantly between sites. Community structuring appeared to be driven by localised environmental conditions, with different factors influencing each lake. These results suggest that single spot-samples are insufficient to gain an understanding of Pcy dynamics and consequently, phytoplankton dynamics in lakes.

Phospholipid fatty acid (PLFA) analysis as a tool to estimate absolute abundances from compositional 16S rRNA bacterial metabarcoding data

Microbial biodiversity monitoring through the analysis of DNA extracted from environmental samples is increasingly popular because it is perceived as being rapid, cost-effective, and flexible concerning the sample types studied. DNA can be extracted from diverse media before high-throughput sequencing of the prokaryotic 16S rRNA gene is used to characterize the taxonomic diversity and composition of the sample (known as metabarcoding). While sources of bias in metabarcoding methodologies are widely acknowledged, previous studies have focused mainly on the effects of these biases within a single substrate type, and relatively little is known of how these vary across substrates. We investigated the effect of substrate type (water, microbial mats, lake sediments, stream sediments, soil and a mock microbial community) on the relative performance of DNA metabarcoding in parallel with phospholipid fatty acid (PLFA) analysis. Quantitative estimates of the biomass of different taxonomic groups in samples were made through the analysis of PLFAs, and these were compared to the relative abundances of microbial taxa estimated from metabarcoding. Furthermore, we used the PLFA-based quantitative estimates of the biomass to adjust relative abundances of microbial groups determined by metabarcoding to provide insight into how the biomass of microbial taxa from PLFA analysis can improve understanding of microbial communities from environmental DNA samples. We used two sets of PLFA biomarkers that differed in their number of PLFAs to evaluate how PLFA biomarker selection influences biomass estimates. Metabarcoding and PLFA analysis provided significantly different views of bacterial composition, and these differences varied among substrates. We observed the most notable differences for the Gram-negative bacteria, which were overrepresented by metabarcoding in comparison to PLFA analysis. In contrast, the relative biomass and relative sequence abundances aligned reasonably well for Cyanobacteria across the tested freshwater substrates. Adjusting relative abundances of microbial taxa estimated by metabarcoding with PLFA-based quantification estimates of the microbial biomass led to significant changes in the microbial community compositions in all substrates. We recommend including independent estimates of the biomass of microbial groups to increase comparability among metabarcoding libraries from environmental samples, especially when comparing communities associated with different substrates.

Beyond taxonomy: Validating functional inference approaches in the context of fish-farm impact assessments

Characterization of microbial assemblages via environmental DNA metabarcoding is increasingly being used in routine monitoring programs due to its sensitivity and cost-effectiveness. Several programs have recently been developed which infer functional profiles from 16S rRNA gene data using hidden-state prediction (HSP) algorithms. These might offer an economic and scalable alternative to shotgun metagenomics. To date, HSP-based methods have seen limited use for benthic marine surveys and their performance in these environments remains unevaluated. In this study, 16S rRNA metabarcoding was applied to sediment samples collected at 0 and ≥1,200 m from Norwegian salmon farms, and three metabolic inference approaches (Paprica, Picrust2 and Tax4Fun2) evaluated against metagenomics and environmental data. While metabarcoding and metagenomics recovered a comparable functional diversity, the taxonomic composition differed between approaches, with genera richness up to 20× higher for metabarcoding. Comparisons between the sensitivity (highest true positive rates) and specificity (lowest true negative rates) of HSP-based programs in detecting functions found in metagenomic data ranged from 0.52 and 0.60 to 0.76 and 0.79, respectively. However, little correlation was observed between the relative abundance of their specific functions. Functional beta-diversity of HSP-based data was strongly associated with that of metagenomics (r ≥ 0.86 for Paprica and Tax4Fun2) and responded similarly to the impact of fish farm activities. Our results demonstrate that although HSP-based metabarcoding approaches provide a slightly different functional profile than metagenomics, partly due to recovering a distinct community, they represent a cost-effective and valuable tool for characterizing and assessing the effects of fish farming on benthic ecosystems.

Investigating variability in microbial community composition in replicate environmental DNA samples down lake sediment cores

Lake sediments are natural archives that accumulate information on biological communities and their surrounding catchments. Paleolimnology has traditionally focussed on identifying fossilized organisms to reconstruct past environments. In the last decade, the application of molecular methodologies has increased in paleolimnological studies, but further research investigating factors such as sample heterogeneity and DNA degradation are required. In the present study we investigated bacterial community heterogeneity (16S rRNA metabarcoding) within depth slices (1-cm width). Sediment cores were collected from three lakes with differing sediment compositions. Samples were collected from a variety of depths which represent a period of time of approximately 1,200 years. Triplicate samples were collected from each depth slice and bacterial 16S rRNA metabarcoding was undertaken on each sample. Accumulation curves demonstrated that except for the deepest (oldest) slices, the combination of three replicate samples were insufficient to characterise the entire bacterial diversity. However, shared Amplicon Sequence Variants (ASVs) accounted for the majority of the reads in each depth slice (max. shared proportional read abundance 96%, 86%, 65% in the three lakes). Replicates within a depth slice generally clustered together in the Non-metric multidimensional scaling analysis. There was high community dissimilarity in older sediment in one of the cores, which was likely due to the laminae in the sediment core not being horizontal. Given that most paleolimnology studies explore broad scale shifts in community structure rather than seeking to identify rare species, this study demonstrates that a single sample is adequate to characterise shifts in dominant bacterial ASVs.

Potential applications of CRISPR/Cas for next-generation biomonitoring of harmful algae blooms: A review

Research on harmful algal and cyanobacterial blooms (HABs and CHABs) has risen dramatically due to their increasing global distribution, frequency, and intensity. These blooms jeopardize public health, ecosystem function, sustainability and can have negative economic impacts. Numerous monitoring programs have been established using light microscopy, liquid chromatography coupled to mass spectrometry (LC-MS), ELISA, and spectrophotometry to monitor HABs/CHABs outbreaks. Recently, DNA/RNA-based molecular methods have been integrated into these programs to replace or complement traditional methods through analyzing environmental DNA and RNA (eDNA/eRNA) with techniques such as quantitative polymerase chain reaction (qPCR), fluorescent in situ hybridization (FISH), sandwich hybridization assay (SHA), isothermal amplification methods, and microarrays. These have enabled the detection of rare or cryptic species, enhanced sample throughput, and reduced costs and the need for visual taxonomic expertise. However, these methods have limitations, such as the need for high capital investment in equipment or detection uncertainties, including determining whether organisms are viable. In this review, we discuss the potential of newly developed molecular diagnosis technology based on Clustered Regularly Interspaced Short Palindromic Repeats/Cas proteins (CRISPR/Cas), which utilizes the prokaryotic adaptative immune systems of bacteria and archaea. Cas12 and Cas13-based platforms can detect both DNA and RNA with attomolar sensitivity within an hour. CRISPR/Cas diagnostic is a rapid, inexpensive, specific, and ultrasensitive technology that, with some further development, will provide many new platforms that can be used for HABs/CHABs biomonitoring and research.

Ruling out Color Transparency in Quasielastic ^{12}C(e,e^{'}p) up to Q^{2} of 14.2 (GeV/c)^{2}

Quasielastic ^{12}C(e,e^{'}p) scattering was measured at spacelike 4-momentum transfer squared Q^{2}=8, 9.4, 11.4, and 14.2  (GeV/c)^{2}, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no Q^{2} dependence, up to proton momenta of 8.5  GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured Q^{2} scales in exclusive (e,e^{'}p) reactions. These results impose strict constraints on models of color transparency for protons.

Biosecurity implications of drifting marine plastic debris: Current knowledge and future research

The introduction and spread of marine non-indigenous species (NIS) and pathogens into new habitats are a major threat to biodiversity, ecosystem services, human health, and can have substantial economic consequences. Shipping is considered the main vector for marine biological invasions; less well understood is the increased spread of marine NIS and pathogens rafting on marine plastic debris (MPD). Despite an increasing research interest and recent progress in characterizing the plastisphere, this manuscript highlights critical knowledge gaps and research priorities towards a better understanding of the biosecurity implications of MPD. We advocate for future research to (i) investigate plastisphere community succession and the factors influencing NIS propagules and pathogens recruitment through robust experimental investigations; (ii) combine microscopy and molecular approaches to effectively assess the presence of specific taxa; (iii) include additional genetic markers to thoroughly characterize the biodiversity associated with MPD and explore the presence of specific marine pests.

Acute toxicity of dihydroanatoxin-a from Microcoleus autumnalis in comparison to anatoxin-a

The cyanobacterium Microcoleus autumnalis grows as thick benthic mats in rivers and is becoming increasingly prevalent around the world. M. autumnalis can produce high concentrations of anatoxins and ingestion of benthic mats has led to multiple dog deaths over the past two decades. M. autumnalis produces a suite of different anatoxin congeners including anatoxin-a (ATX), dihydroanatoxin-a, (dhATX), homoanatoxin-a and dihydrohomoanatoxin-a. Benthic mat samples often contain high levels of dhATX, but there is little toxicology information on this congener. In the present study, natural versions of dhATX and ATX were purified from cyanobacteria to determine the acute toxicity by different routes of administration using mice. Nuclear magnetic resonance spectroscopy was used to confirm the putative structure of dhATX. By intraperitoneal (ip) injection, the median lethal dose (LD₅₀) for dhATX was 0.73 mg/kg, indicating a reduced toxicity compared to ATX (LD₅₀ of 0.23 mg/kg). However, by oral administration (both gavage and feeding), dhATX was more toxic than ATX (gavage LD₅₀ of 2.5 mg/kg for dhATX and 10.6 mg/kg for ATX; feeding LD₅₀ of 8 mg/kg for dhATX and 25 mg/kg for ATX). The relative nicotinic acetylcholine receptor-binding affinities of ATX and dhATX were determined using the Torpedo electroplaque assay which showed consistency with the relative toxicity determined by ip injection. This work highlights that toxicity studies based solely on ip injection may not yield LD₅₀ values that are relevant to those derived via oral administration, and hence, do not provide a good estimate of the risk posed to human and animal health in situations where oral ingestion is the likely route of exposure. The high acute oral toxicity of dhATX, and its abundance in M. autumnalis proliferations, demonstrates that it is an important environmental contaminant that warrants further investigation.

Probing the Deuteron at Very Large Internal Momenta

We measure ^{2}H(e,e^{'}p)n cross sections at 4-momentum transfers of Q^{2}=4.5±0.5  (GeV/c)^{2} over a range of neutron recoil momenta p_{r}, reaching up to ∼1.0  GeV/c. We obtain data at fixed neutron recoil angles θ_{nq}=35°, 45°, and 75° with respect to the 3-momentum transfer q[over →]. The new data agree well with previous data, which reached p_{r}∼500  MeV/c. At θ_{nq}=35° and 45°, final state interactions, meson exchange currents, and isobar currents are suppressed and the plane wave impulse approximation provides the dominant cross section contribution. We compare the new data to recent theoretical calculations, where we observe a significant discrepancy for recoil momenta p_{r}>700  MeV/c.

Local factors drive bacterial and microeukaryotic community composition in lake surface sediment collected across an altitudinal gradient

Lake surface sediments are dominated by microorganisms that play significant roles in biogeochemical cycling within lakes. There is limited knowledge on the relative importance of local environmental factors and altitude on bacterial and microeukaryotic community richness and composition in lake sediments. In the present study, surface sediment samples were collected from 40 lakes along an altitude gradient (2-1215 m). Microbial communities were characterized using 16S (bacteria) and 18S (microeukaryotes) rRNA gene metabarcoding. Bacterial and microeukaryotic richness were not correlated with altitude but instead to environmental variables (e.g. area of water in the catchment (bacteria: R = -0.43). For both bacteria and microeukaryotes, dissimilarity in the community structure had a higher correlation to combined environmental variables (without altitude) (bacteria: R = 0.53; microeukaryotes: R = 0.55) than altitude alone (bacteria: R = 0.34; microeukaryotes: R = 0.47). Sediment sulfur and productive grassland were important variables in determining the relative abundance of sulfate reducing bacteria. Nitrospira, was positively related to altitude but negatively to water column total organic carbon and the proportion of productive grassland in the catchment. Little overlap in amplicon sequence variants was shown amongst lakes. This has important considerations for management decisions, suggesting that to protect biodiversity, conservation of numerous lakes and lake types is required.

Comparing sediment DNA extraction methods for assessing organic enrichment associated with marine aquaculture

Marine sediments contain a high diversity of micro- and macro-organisms which are important in the functioning of biogeochemical cycles. Traditionally, anthropogenic perturbation has been investigated by identifying macro-organism responses along gradients. Environmental DNA (eDNA) analyses have recently been advocated as a rapid and cost-effective approach to measuring ecological impacts and efforts are underway to incorporate eDNA tools into monitoring. Before these methods can replace or complement existing methods, robustness and repeatability of each analytical step has to be demonstrated. One area that requires further investigation is the selection of sediment DNA extraction method. Environmental DNA sediment samples were obtained along a disturbance gradient adjacent to a Chinook (Oncorhynchus tshawytscha) salmon farm in Otanerau Bay, New Zealand. DNA was extracted using four extraction kits (Qiagen DNeasy PowerSoil, Qiagen DNeasy PowerSoil Pro, Qiagen RNeasy PowerSoil Total RNA/DNA extraction/elution and Favorgen FavorPrep Soil DNA Isolation Midi Kit) and three sediment volumes (0.25, 2, and 5 g). Prokaryotic and eukaryotic communities were amplified using primers targeting the 16S and 18S ribosomal RNA genes, respectively, and were sequenced on an Illumina MiSeq. Diversity and community composition estimates were obtained from each extraction kit, as well as their relative performance in established metabarcoding biotic indices. Differences were observed in the quality and quantity of the extracted DNA amongst kits with the two Qiagen DNeasy PowerSoil kits performing best. Significant differences were observed in both prokaryotes and eukaryotes (p < 0.001) richness among kits. A small proportion of amplicon sequence variants (ASVs) were shared amongst the kits (~3%) although these shared ASVs accounted for the majority of sequence reads (prokaryotes: 59.9%, eukaryotes: 67.2%). Differences were observed in the richness and relative abundance of taxonomic classes revealed with each kit. Multivariate analysis showed that there was a significant interaction between "distance" from the farm and "kit" in explaining the composition of the communities, with the distance from the farm being a stronger determinant of community composition. Comparison of the kits against the bacterial and eukaryotic metabarcoding biotic index suggested that all kits showed similar patterns along the environmental gradient. Overall, we advocate for the use of Qiagen DNeasy PowerSoil kits for use when characterizing prokaryotic and eukaryotic eDNA from marine farm sediments. We base this conclusion on the higher DNA quality values and richness achieved with these kits compared to the other kits/amounts investigated in this study. The additional advantage of the PowerSoil Kits is that DNA extractions can be performed using an extractor robot, offering additional standardization and reproducibility of results.

Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation

1. This review summarises knowledge on the ecology, toxin production, and impacts of toxic freshwater benthic cyanobacterial proliferations. It documents monitoring, management, and sampling strategies, and explores mitigation options. 2. Toxic proliferations of freshwater benthic cyanobacteria (taxa that grow attached to substrates) occur in streams, rivers, lakes, and thermal and meltwater ponds, and have been reported in 19 countries. Anatoxin- and microcystin-containing mats are most commonly reported (eight and 10 countries, respectively). 3. Studies exploring factors that promote toxic benthic cyanobacterial proliferations are limited to a few species and habitats. There is a hierarchy of importance in environmental and biological factors that regulate proliferations with variables such as flow (rivers), fine sediment deposition, nutrients, associated microbes, and grazing identified as key drivers. Regulating factors differ among colonisation, expansion, and dispersal phases. 4. New -omics-based approaches are providing novel insights into the physiological attributes of benthic cyanobacteria and the role of associated microorganisms in facilitating their proliferation. 5. Proliferations are commonly comprised of both toxic and non-toxic strains, and the relative proportion of these is the key factor contributing to the overall toxin content of each mat. 6. While these events are becoming more commonly reported globally, we currently lack standardised approaches to detect, monitor, and manage this emerging health issue. To solve these critical gaps, global collaborations are needed to facilitate the rapid transfer of knowledge and promote the development of standardised techniques that can be applied to diverse habitats and species, and ultimately lead to improved management.

Precision Measurement of the Beam-Normal Single-Spin Asymmetry in Forward-Angle Elastic Electron-Proton Scattering

A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to the imaginary part of the two-photon exchange process. We report a 2% precision measurement of the beam-normal single-spin asymmetry in elastic electron-proton scattering with a mean scattering angle of θ_{lab}=7.9° and a mean energy of 1.149 GeV. The asymmetry result is B_{n}=-5.194±0.067(stat)±0.082 (syst) ppm. This is the most precise measurement of this quantity available to date and therefore provides a stringent test of two-photon exchange models at far-forward scattering angles (θ_{lab}→0) where they should be most reliable.

Seasonal and Spatial Variations in Bacterial Communities From Tetrodotoxin-Bearing and Non-tetrodotoxin-Bearing Clams

Tetrodotoxin (TTX) is one of the most potent naturally occurring compounds and is responsible for many human intoxications worldwide. Paphies australis are endemic clams to New Zealand which contain varying concentrations of TTX. Research suggests that P. australis accumulate the toxin exogenously, but the source remains uncertain. The aim of this study was to identify potential bacterial TTX-producers by exploring differences in bacterial communities in two organs of P. australis: the siphon and digestive gland. Samples from the digestive glands of a non-toxic bivalve Austrovenus stutchburyi that lives amongst toxic P. australis populations were also analyzed. Bacterial communities were characterized using 16S ribosomal RNA gene metabarcoding in P. australis sourced monthly from the Hokianga Harbor, a site known to have TTX-bearing clams, for 1 year, from ten sites with varying TTX concentrations around New Zealand, and in A. stutchburyi from the Hokianga Harbor. Tetrodotoxin was detected in P. australis from sites all around New Zealand and in all P. australis collected monthly from the Hokianga Harbor. The toxin averaged 150 μg kg^-1 over the year of sampling in the Hokianga Harbor but no TTX was detected in the A. stutchburyi samples from the same site. Bacterial species diversity differed amongst sites (p < 0.001, F = 5.9) and the diversity in siphon samples was significantly higher than in digestive glands (p < 0.001, F = 65.8). Spirochaetaceae (4-60%) and Mycoplasmataceae (16-78%) were the most abundant families in the siphons and the digestive glands, respectively. The bacterial communities were compared between sites with the lowest TTX concentrations and the Hokianga Harbor (site with the highest TTX concentrations), and the core bacterial communities from TTX-bearing individuals were analyzed. The results from both spatial and temporal studies corroborate with previous hypotheses that Vibrio and Bacillus could be responsible for the source of TTX in bivalves. The results from this study also indicate that marine cyanobacteria, in particular picocyanobacteria (e.g., Cyanobium, Synechococcus, Pleurocapsa, and Prochlorococcus), should be investigated further as potential TTX producers.

Elucidating Biodiversity Shifts in Ballast Water Tanks during a Cross-Latitudinal Transfer: Complementary Insights from Molecular Analyses

In this study, the evolution of ballast water (BW) assemblages across different trophic levels was characterized over a 21 day cross-latitudinal vessel transit using a combination of molecular methods. Triplicate BW samples were collected every second day and size-fractionated (<2.7, 10, >50 μm). Measurements of adenosine triphosphate (ATP) and metabarcoding of environmental nucleic acid (DNA and RNA) analyses, complemented by microscopy and flow cytometry, were performed on each sample. Measured ATP concentrations exhibited high variance between replicates and a strong negative trend in the large (≥50 μm) fraction over the voyage. In concert with microscopy, the metabarcoding data indicated a die-off of larger metazoans during the first week of study and gradual reductions in dinoflagellates and ochrophytes. The ATP and metabarcoding data signaled persistent or increased cellular activity of heterotrophic bacteria and protists in the BW, which was supported by flow cytometry. The metabarcoding showed the presence of active bacteria in all size fractions, suggesting that the sequential filtration approach does not ensure taxonomical differentiation, which has implications for BW quality assessment. Although our data show that ATP and metabarcoding have potential for indicative BW screening for BW compliance monitoring, further research and technological development is needed to improve representativeness of sampling and deliver the unequivocal response criteria required by the international Ballast Water Management Convention.