Organisms living in the sea are exposed to fouling by other organisms. Many benthic marine invertebrates, including sponges and bryozoans, contain natural products with antimicrobial properties, since microbes usually constitute the first stages of fouling. Extracts from 4 Antarctic sponges (Myxilla (Myxilla) mollis, Mycale tylotornota, Rossella nuda, and Anoxycalyx (Scolymastra) joubini) and 2 bryozoan species (Cornucopina pectogemma and Nematoflustra flagellata) were tested separately for antifouling properties in field experiments. The different crude extracts from these invertebrates were incorporated into a substratum gel at natural concentrations for an ecological approach. Treatments were tested by submerging plates covered by these substratum gels under water in situ during 1 lunar cycle (28 d) at Deception Island (South Shetland Islands, Antarctica). Remarkably, the butanolic extracts of M. tylotornota and C. pectogemma showed complete growth inhibition of microscopic eukaryotic organisms, one of the succession stages involved in biofouling. Our results suggest that different chemical strategies may exist to avoid fouling, although the role of chemical defenses is often species-specific. Thus, the high specificity of the microbial community attached to the coated plates seems to be modulated by the chemical cues of the crude extracts of the invertebrates tested.

Bacterioplankton and protists fulfil key roles in marine ecosystems. Understanding the abundance and distribution of these organisms through space and time is a central focus of biological oceanographers. The role of oceanographic features, in addition to environmental conditions, in structuring bacterioplankton and protist communities has been increasingly recognised. We investigated patterns in bacterioplankton and protist diversity and community structure across the Southland Front system, a compaction of the subtropical front zone, to the east of New Zealand’s South Island. We collected 24 seawater samples across a ~65 km transect and characterised bacterioplankton and protist community composition using high-throughput sequencing of the 16S and 18S rRNA genes, respectively. We identified frontal waters as a bacterioplankton diversity hotspot relative to neighbouring subtropical and subantarctic waters, but did not find evidence of this effect in protists. Bacterioplankton showed pronounced spatial structuring across the front, with communities closely tracking water type through the region. Protist communities also tracked water type through the region, though this effect was substantially less pronounced. We used an ecological null model approach to demonstrate that protist communities are primarily assembled through stochastic processes, whilst bacterioplankton are primarily assembled through deterministic processes across the Southland Front system. We suggest that this divergence emerges from fundamental differences in the characteristics of bacterioplankton and protist communities. Our findings add to a growing body of literature highlighting the importance of oceanographic features in shaping bacterioplankton and protist communities, promoting the necessity for such features to be considered more explicitly in the future.

The northwestern Pacific Ocean and East China Sea (ECS) are frequently affected by typhoons during the summer period. To identify changes in production and consumption rates of phytoplankton (<20 and 20~200 µm) affected by Typhoon Maria (9-10 July 2018), 2 sampling periods were compared: a pre-typhoon cruise (4-9 July 2018) and a post-typhoon cruise (13-17 July 2018). Results showed that <20 and 20~200 µm phytoplankton production was 14- and 1.8-fold higher, respectively, in the post-typhoon period compared to the pre-typhoon. Accompanying this post-typhoon shift from pico- and nanophytoplankton to microphytoplankton, the consumption rate of microzooplankton on <20 µm phytoplankton was 11.6 mgC m-3 d-1 in the pre-typhoon period, and increased to 203.3 mgC m-3 d-1 after the typhoon. Furthermore, the ingestion fluxes were 4.9 and 8.0 mgC m-3 d-1 through mesozooplankton grazing on microzooplankton (ciliates and dinoflagellates) pre- and post-typhoon, respectively. Our findings show that organisms from the microbial food web (i.e. ciliates and dinoflagellates) may control the phytoplankton assemblage during the post-typhoon period of increased productivity, and thus represent an important trophic link between the classical and microbial food webs in the southern ECS.

This study was conducted in 4 Labrador fjords (Nachvak, Saglek, Okak, and Anaktalak) during the summers of 2007 and 2013, early fall 2010, and late fall 2009. Our results show that water temperature combined with the availability of nutrients and organic substrates are the main abiotic factors controlling the abundance of heterotrophic bacteria in Labrador fjords. Bacterivory also played a crucial role, with heterotrophic bacteria exerting a significant bottom-up control on the abundance of heterotrophic nanoflagellates (r = 0.35, p < 0.05) and ciliates (r = 0.70, p < 0.01). During summer 2013, the intrinsic phytoplankton growth rate varied between <0 and 0.64 d-1, with a mean value of 0.36 d-1. The herbivory rate was highly variable, ranging from 0.01 to 0.86 d-1, with a mean value of 0.31 d-1. Grazing mortality was 6-fold higher than phytoplankton growth rate. Mean phytoplankton growth and herbivory rates in Labrador fjords were comparable to the Barents and Bering seas. The intrinsic growth rate of total heterotrophic bacteria ranged between <0 and 0.68 d-1, with a mean value of 0.30 d-1. Bacterivory varied from 0.01 to 0.95 d-1, with a mean of 0.30 d-1. Mortality due to grazing was up to 2.3 times higher than total bacterial growth rate. This study improves our understanding of the factors influencing the dynamics of heterotrophic bacteria and indicates that herbivory and bacterivory exert substantial control on microbial communities in Labrador fjords.

Actinobacteria from terrestrial and marine environments produce a variety of natural products that mediate inter- and intraspecies interactions. In contrast, the potential of freshwater Actinobacteria for secondary metabolite production remains underexplored. Large lakes with a long evolutionary history might contain microflora subjected to unique environmental conditions that favor the evolution of unique metabolic capabilities. One such lake is Lake Baikal (Russia), the deepest lake on earth as well as one of the oldest. In this study, we investigated the genetically encoded secondary metabolic potential of 24 Actinobacteria strains isolated from Lake Baikal sediments. PCR-based screening for genes encoding type I and type II polyketide synthases (PKSs), nonribosomal peptide synthetases (NRPSs), and halogenases confirmed that all strains possessed at least 1 of these biosynthetic genes. Both PKSs and NRPSs were widely distributed, while halogenase-encoding genes were not detected. Phylogenetic comparison of type I PKS ketosynthase (KS) domain sequences between freshwater isolates and marine and terrestrial strains supported overlap between KSs from these 3 groups. Evaluation of antibiotic activity for chemical extracts from all isolates revealed that 75% produced metabolites inhibitory toward model bacteria and/or fungi. To our knowledge, this study is among the first evaluations of the genetically encoded secondary metabolic capabilities of freshwater sediment Actinobacteria. Our findings highlight the similarities and differences between freshwater and marine Actinobacteria secondary metabolism, suggesting the potential of freshwater Actinobacteria for the production of natural products that may play roles as mediators of interactions between organisms in freshwater habitats.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 83:203-209 (2019) - DOI: https://doi.org/10.3354/ame01917 Nutrient pollution degrades microbialites in Lough Carra, an Irish marl lake Philip Doddy*, Cilian M. Roden, Martin P. Gammell Marine & Freshwater Research Centre, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland *Corresponding author: philipdoddy@gmail.com ABSTRACT: Marl lakes often have microbialite crusts in the littoral zone, containing a community of cyanobacteria and algae. Previous work has shown that these crusts are most prevalent in oligotrophic lakes and that crust metrics, such as chlorophyll content and green algal abundance, are correlated with total phosphorus concentration (TP) in lake waters, with no intact crusts being found when mean TP > 0.02 mg l-1. Two experiments were carried out to examine how microbialite crust communities respond to nutrient pollution. A culture experiment exposed crusts to various concentrations of nutrients and measured responses over a 43 wk period. In a parallel controlled field experiment, crusts were moved between areas of different trophic state within Lough Carra, a marl lake in the west of Ireland, to see how the community responded. In both experiments, increased nutrient conditions caused a change in relative abundances of taxa in the crust community, leading to a dominance of green algae and degradation of crusts. There were significant differences in chlorophyll concentrations between crusts grown in different nutrient environments. It was concluded that these metrics offer the prospect of a useful quality assessment method for marl lakes. KEY WORDS: Marl lake · Microbialite · Eutrophication · Cyanobacteria · Conservation Full text in pdf format NextCite this article as: Doddy P, Roden CM, Gammell MP (2019) Nutrient pollution degrades microbialites in Lough Carra, an Irish marl lake. Aquat Microb Ecol 83:203-209. https://doi.org/10.3354/ame01917 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in AME Vol. 83, No. 3. Online publication date: September 19, 2019 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2019 Inter-Research.

Mixotrophic phytoplankton are an important component of the microbial communities of the open ocean surface. They can control the metabolic balance and biogeochemical cycling of biogenic materials. To identify environmental factors that control the ecological prosperity of mixotrophs over obligate autotrophs in the open ocean, we quantified potential mixotrophic picoand nanophytoplankton throughout a wide area of the North Pacific Ocean on latitudinal and longitudinal transects, using a combination of flow cytometry and the fluorescent probe LysoTracker Green. The proportions of potential mixotrophic pico- and nanophytoplankton were higher in the subtropical gyre and Bering Sea than in surrounding areas, and even higher in the western area of the subtropical gyre. When the proportion of potential mixotrophs within the surface mixed layer was regressed against various environmental parameters, soluble reactive phosphorus concentration showed a significant negative partial regression coefficient. This result reflected the east-west gradient in the subtropical gyre and is consistent with previous implications that low nutrient availability can facilitate phagotrophy by mixotrophic phytoplankton. Unexpectedly, water stability did not show a significant correlation with the proportion of potential mixotrophs, which suggests that instantaneous physical parameters do not significantly affect their nutritional mode. When the data sets from water below the mixed layer were included in the multiple regression analysis, the significant regression against soluble reactive phosphorus concentration disappeared. This result may suggest a complex response of phytoplankton in the deeper ocean environment. The present results reinforce the importance of phosphorus availability as a control factor of phytoplankton nutritional physiology in the subtropical North Pacific Ocean. © 2019 Inter-Research.

Intertidal mudflats are fluctuating environments that support highly diverse microbial communities. The highly variable physico-chemical conditions complicate the understanding of the environmental controls on diversity patterns in estuarine systems. We investigated the bacterial diversity in the surface and subsurface sediments along the salinity gradient of the Humber estuary (UK) using amplicon sequencing of the 16S rRNA gene and correlated its variations with environmental variables. The sediment depths sampled were selected based on the local resuspension patterns. In general, bacterial communities showed similar composition at the different sites and depths, with Proteobacteria being the most abundant phylum. The richness of operational taxonomic units (OTUs) was uniform along the salinity gradient. However, Hill numbers, as bacterial diversity measures, showed that the common and dominant OTUs exhibited a decreasing trend from the inner towards the outer estuary sites. Additionally, surface and subsurface bacterial communities were separated by non-metric multi-dimensional scaling (NMDS) analysis only in the mid- and outer estuary samples, where redox transitions with depth were more abrupt. Salinity, porewater ammonium concentration and acid-extractable Fe(II) in solids were the subset of environmental factors that best correlated with community dissimilarities. Analysis of regional diversity indicated that the dataset may include 2 potentially distinct communities: (1) a near-surface community that is the product of regular mixing and transport and is subjected to a wide range of salinity conditions, and (2) a bacterial community indigenous to the more reducing subsurface sediments of the mudflats of the mid- and outer estuary.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 81:137-148 (2018) - DOI: https://doi.org/10.3354/ame01870 Abundance of virus-like particles (VLPs) and microbial plankton community composition in a Mediterranean Sea coastal area Carolina Johnstone, Soluna Salles, Jesús M. Mercado*, Dolores Cortés, Lidia Yebra, Francisco Gómez-Jakobsen, Antonio Sánchez, Aitor Alonso, Nerea Valcárcel-Pérez Centro Oceanográfico de Málaga, Instituto Español de Oceanografía, 29640 Fuengirola, Malaga, Spain *Corresponding author: jesus.mercado@ieo.es ABSTRACT: In the northern coastal area of the Alboran Sea (the most western basin of the Mediterranean Sea), the distribution of plankton at the surface follows complex patterns corresponding to the variability of abiotic (environmental) and biotic factors, including virus-host interactions. To assess these interactions, we measured the abundances of virus-like particles (VLPs) and different microbial virus hosts of the plankton community, including heterotrophic bacteria (HB), cyanobacteria and autotrophic eukaryote pico-, nano- and microplankton (APP, ANP and AMP, respectively). Samplings were carried out in the euphotic zone during 2 contrasting seasonal periods (autumn and spring), in 3 coastal areas of the Alboran basin. Virioplankton abundance varied, ranging from 8.5 × 105 to 2.2 × 107 VLPs ml-1, covering almost the whole range of variability described for the Mediterranean Sea. The mean VLP to microbial ratio (VMR) was 13.6 and the median was 10.5, although the VMR varied substantially from 1.3 to 44. In autumn, the abundance of VLPs did not correlate with HB, although it correlated positively with Prochlorococcus and Synechococcus and negatively with APP and AMP. In contrast, in spring, VLPs correlated positively with HB and APP and negatively with Synechococcus. These abundance data suggest that not only bacteria but also cyanobacteria could play a relevant role as virus hosts in the Alboran Sea, at least in autumn. The changes in abiotic factors that favor the growth of cyanobacteria vs. HB or vice versa and their possible role in regulating cyanophage to bacteriophage dynamics are further discussed. KEY WORDS: Virus-like particles · Bacteria · Phytoplankton · Pelagic ecosystem · Mediterranean Sea · Phosphate Full text in pdf format PreviousNextCite this article as: Johnstone C, Salles S, Mercado JM, Cortés D and others (2018) Abundance of virus-like particles (VLPs) and microbial plankton community composition in a Mediterranean Sea coastal area. Aquat Microb Ecol 81:137-148. https://doi.org/10.3354/ame01870 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 81, No. 2. Online publication date: March 21, 2018 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2018 Inter-Research.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 80:209-222 (2017) - DOI: https://doi.org/10.3354/ame01846 Acute toxicity of the cosmopolitan bloom-forming dinoflagellate Akashiwo sanguinea to finfish, shellfish, and zooplankton Ning Xu1,*,**, Meng Wang1,**, Yingzhong Tang2,3, Qun Zhang1, Shunshan Duan1, Christopher J. Gobler2 1Department of Ecology/Key Laboratory of Eutrophication and Red Tide Prevention of Guangdong Higher Education Institutes, Jinan University, Guangzhou 510632, PR China 2School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA 3Key Laboratory of Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, Shandong, PR China *Corresponding author: txuning@jnu.edu.cn**These authors contributed equally to this work ABSTRACT: The unarmored dinoflagellate Akashiwo sanguinea is a well known cosmopolitan harmful alga; however, the toxic nature of this alga has yet to be examined using multiple clonal isolates. Here we examined the toxicity of 3 clonal cultures of A. sanguinea, including JX13 and JX14, isolated from Daya Bay, South China Sea, and AS2, isolated from Chesapeake Bay, USA, to multiple aquatic animals including species of finfish, shellfish, shrimp, and zooplankton. The whole-cell cultures of A. sanguinea exhibited acute lethal effects on the shrimp Litopenaeus vannamei, the bivalve Meretrix meretrix, and 2 species of fish (Mugil cephalus and Mugilidae sp.) with 72 h mortalities ranging from 20 to 100%. The sonicated and filtrated cultures were lethal to brine shrimp Artemia salina, while the filtrates of whole-cell cultures were not, suggesting that the toxins are intracellular. Boiling and freezing led to significant reductions in toxicity. A. sanguinea toxicity differed among the Chinese strains, and the hemolytic activity of 1 Chinese strain was 3‑fold greater than that of the US strain. Cultures in exponential phase displayed stronger toxicity, and the greatest toxicity of A. sanguinea was observed at 20°C and a salinity of 35, conditions optimal for growth of the alga. Toxicity was enhanced by increased nutrient supply, suggesting that this species could both directly (via increased growth) and indirectly (e.g. via enhanced toxin production) become more toxic in response to eutrophication. Collectively, our findings suggest that the ability to produce and release toxin(s) may promote A. sanguinea blooms by suppressing predators and competitors. KEY WORDS: Akashiwo sanguinea · Toxicity · Hemolytic activity · Algal toxin · Aquatic animal · Harmful algal bloom Full text in pdf format NextCite this article as: Xu N, Wang M, Tang Y, Zhang Q, Duan S, Gobler CJ (2017) Acute toxicity of the cosmopolitan bloom-forming dinoflagellate Akashiwo sanguinea to finfish, shellfish, and zooplankton. Aquat Microb Ecol 80:209-222. https://doi.org/10.3354/ame01846 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 80, No. 3. Online publication date: October 27, 2017 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2017 Inter-Research.