Yoneya, KinuyoMiki, TakeshiVan den Wyngaert, SilkeGrossart, Hans-Peter...
15页
查看更多>>摘要：Host-parasite interactions between phytoplankton and fungi (chytrids) are key processes in aquatic ecosystems. However, individual-level heterogeneity in these interactions remains unexplored, although its importance in predicting the spread of diseases has been demonstrated in epidemiology. In this study, we experimentally tested whether individual-level heterogeneity could be a good indicator of phytoplankton-chytrid interactions, using a freshwater green alga Staurastrum sp., the diatoms Ulnaria sp. and Fragilaria crotonensis, and chytrid fungi. The number of attached fungi per host cell showed a non-random clumped parasite distribution on Ulnaria sp. and F. crotonensis, but a random Poisson distribution on Staurastrum sp. To explore the potential mechanisms of these patterns, we developed a mathematical model describing sequential encounters between chytrid zoospores and host cells. The statistical fits of the model explained the parasite distributions for Ulnaria sp. and F. crotonensis well, indicating that the clumped parasite distributions may result from an infection rate, increasing with the number of infections that already occurred on each host cell. Simultaneous analysis of volatile organic compounds (VOCs) from uninfected and infected host populations revealed that, among 13 VOCs detected, 6 components characterized the differences in VOC compositions between species and infection status. In particular, the level of beta-ionone, potentially acting against fungal activities, was significantly reduced in the presence of chytrid infection of Staurastrum sp. These VOCs are targets for future studies, which potentially act as chemical signals influencing chytrid zoospores' behaviors. The combination of mathematical and chemical analyses represents a promising approach to better understand the individual-level processes of phytoplankton-chytrid interactions.
查看更多>>摘要：Zoosporic fungi play an important role in aquatic environments, but their diversity, especially that of parasitic fungi of phytoplankton, has still not been fully revealed. We conducted monthly analyses of the community structure of zoosporic fungi at a pelagic site in Lake Biwa, Japan, from May to December 2016. Metabarcoding analysis, targeted to a large subunit region of ribosomal DNA in the nano-size fraction of particles (2-20 mu m), was carried out on the samples. We also counted large phytoplankton and chytrid sporangia attached to the hosts. We detected 3 zoosporic fungal phyla (Blastocladiomycota, Chytridiomycota and Cryptomycota) within 107 operational taxonomic units (OTUs), in which Chytridiomycota was the most diverse and abundant phylum. Few fungal OTUs overlapped between months, and specific communities were detected in each month. These results showed that diverse zoosporic fungi with high temporal variability inhabited the lake. Five large phytoplankton species were found to be infected by chytrids: Staurastrum dorsidentiferum, S. rotula, Closterium aciculare, Asterionella formosa and Aulacoseira granulata. Some chytrids were detected by metabarcoding analysis: Zygophlyctis asterionellae infecting A. formosa, Staurastromyces oculus infecting S. dorsidentiferum and Pendulichytrium sphaericum infecting A. granulata. One OTU detected in association with infected C. aciculare by microscopic counting might have been an obligate parasitic chytrid of C. aciculare. The results indicated that a combination of metabarcoding and microscopic analysis revealed more information on zoosporic fungi, including those that are parasitic.
Rose, VanessaRollwagen-Bollens, GretchenBollens, Stephen M.Zimmerman, Julie...
18页
查看更多>>摘要：Understanding the influence of biotic and abiotic factors on riverine phytoplankton dynamics is challenging, particularly as anthropogenic stressors such as eutrophication, invasive species, and climate change alter these relationships. We examined a 14 yr (January 2005 to December 2018) dataset of phytoplankton and water quality variables, along with zooplankton and nutrient concentrations, from the Columbia River (the largest river in the US Pacific Northwest) to identify seasonal and interannual patterns of phytoplankton assemblage structure and their environmental associations. Non-metric multidimensional scaling, cluster, and indicator species analyses revealed: (1) a diatom/flagellate cluster in spring/summer, associated with chlorophyll a, discharge, ciliates, and Sarcodina; (2) a cyanobacteria/chlorophyte cluster in late summer/early fall, associated with higher water temperatures, increased clarity, the invasive copepod Pseudodiaptomus forbesi, and veligers of the invasive Asian clam Corbicula fluminea; and (3) a mixed-taxa winter cluster of minimal abundance and biomass. Nutrients were not strongly associated with the observed structural patterns. Phytoplankton bloom duration varied interannually, between years with short springtime blooms vs. years when blooms extended across multiple months. Springtime blooms of the diatom Asterionella formosa decreased in recent years, giving way to blooms of a mixed diatom assemblage. Further, high temperature, low discharge, and more invasive zooplankton were associated with cyanobacterial blooms, suggesting that increased temperature and reduced river flows predicted due to climate change in the Pacific Northwest may lead to further impacts on the late summer/early fall Columbia River plankton community.
Tsuchiya, KenjiKohzu, AyatoKuwahara, Victor S.Matsuzaki, Shin-ichiro S....
14页
查看更多>>摘要：To clarify the governing factors of planktonic and epilithic bacterial production (BP) and to quantify their relative contributions to the carbon cycle, we investigated the seasonal variation and regulatory factors of planktonic and epilithic BP in the middle reaches of the Shinano River, Japan, ecosystem from February 2019 to May 2020. Sampling was conducted at 3 stations: upper stream riffle, upper stream pool, and lower stream riffle, where current velocity, water depth, and bed shear stress were distinct. Planktonic and biofilm BP ranged from 5.5 to 466 mgC m(-3) d(-1) and 2.9 to 132 mgC m(-2) d(-1), respectively, showing clear seasonal variation. Biofilm BP was higher in the upper stream riffle than at the other stations, where no spatial variation in planktonic BP was observed. Generalized linear models suggest that BP was primarily regulated by water temperature. Additionally, planktonic BP was significantly correlated with dissolved organic carbon, suggesting carbon limitation. Biofilm BP showed no evidence of resource limitation (nutrients and organic matter), but was significantly explained by current velocity and station. The results suggest that although seasonality is dominant in biofilm BP variation, spatial differences are significant within the seasonal variability. Moreover, current velocity and bottom shear stress related to local geomorphologies such as riffles and pools affect substrate supply rate and biofilm formation processes, regulating biofilm BP variation. This study demonstrated different regulatory factors of planktonic and biofilm BP in the middle reaches of a temperate river.
查看更多>>摘要：Diatom-dominated microphytobenthos (MPB) communities of 4 intertidal mudflats along the meso- and polyhaline reaches of the Loire Estuary, France, were investigated during a year cycle. They were analysed in terms of biomass, diversity, species composition and growth form distribution. The assemblages of the 2 upstream sites were characterised by high biomass and lower diversities and were mostly dominated by epipelon. The 2 downstream, most haline sites had lower biomass and higher diversities and were dominated by both epipelon and tychoplankton. Diversity did not exhibit a clear seasonal signal in the upstream mudflats, but it was higher during the first half of the study in the downstream sites. The coexistence of 2 growth forms seems to increase diversity of the mudflat assemblages. Species distribution was mainly linked to changes in sediment texture and salinity, both with a marked seasonal variability. MPB biomass was inversely related to MPB diversity and positively related to both mud content and the epipelon. MPB diversity was not, however, significantly correlated with mud content. Slight changes in sediment texture, even if causing variations in assemblage composition, did not change overall diversity. The existence of an important and even dominant tychoplanktonic fraction could be considered a distinctive feature of these benthic environments in the Loire, as well as in other macrotidal estuaries.
Dawson, R. A.Crombie, A. T.Pichon, P.Steinke, M....
20页
查看更多>>摘要：Isoprene (2-methyl-1,3-butadiene) is emitted in vast quantities (>500 Tg C yr(-1)). Most isoprene is emitted by trees, but there is still incomplete understanding of the diversity of isoprene sources. The reactivity of isoprene in the atmosphere has potential implications for both global warming and global cooling, with human health implications also arising from isoprene-induced ozone formation in urban areas. Isoprene emissions from terrestrial environments have been studied for many years, but our understanding of aquatic isoprene emissions is less complete. Several abundant phytoplankton taxa produced isoprene in the laboratory, and the relationship between chlorophyll a and isoprene production has been used to estimate emissions from marine environments. The aims of this review are to highlight the role of aquatic environments in the biological cycling of isoprene and to stimulate further study of isoprene metabolism in marine and freshwater environments. From a microbial ecology perspective, the isoprene metabolic gene cluster, first identified in Rhodococcus sp. AD45 (isoGHIJABCDEF) and subsequently found in every genome-sequenced isoprene-degrader, provides the ideal basis for molecular studies on the distribution and diversity of isoprene-degrading communities. Further investigations of isoprene-emitting microbes, such as the influence of environmental factors and geographical location, must also be considered when attempting to constrain estimates of the flux of isoprene in aquatic ecosystems. We also report isoprene emission by the scleractinian coral Acropora horrida and the degradation of isoprene by the same coral holobiont, which highlights the importance of better understanding the cycling of isoprene in marine environments.
查看更多>>摘要：Bacterially produced extracellular enzymes (EEs) play an important role in the cycling of organic matter in the marine environment, breaking down large compounds to those small enough to be transported across the cell membrane. EEs may play an especially important role within the brines of sea ice, as freezing concentrates both bacteria and organic materials into brine pockets, leading to higher encounter rates between EEs and their substrates. However, whether EEs are able to perform under the extreme conditions of sea-ice brines, particularly during winter, is unknown. Here, we characterized EE activity (EEA) of leucine aminopeptidase produced by the psychrophilic bacterium Colwellia psychrerythraea strain 34H and the cold-tolerant Psychrobacter strain 7E, under analogue sea-ice conditions using a standard fluorescence-based activity assay. EEs produced by the psychrophile were active at the most extreme conditions tested, i.e. temperature of -8 degrees C and salt concentration of 120 ppt, with activity enhanced if the EEs concerned were produced under subzero hypersaline conditions. EEs produced by the Psychrobacter strain were less cold- and salt-active. When high-latitude Arctic samples of sea-ice brine, under-ice water, and the sea-surface microlayer were analyzed using the same assay after a freeze-thaw cycle, EEA was highest in the sea-ice samples, with activity at -10 degrees C and salinity of 142 ppt. Overall, these results indicate that EEA can contribute to the degradation of organic material in sea ice through winter, likely sustaining microbial communities in brine pores in the process and altering the nature of organic material released at spring melt.
查看更多>>摘要：Aquatic organisms rely on microbial symbionts for coping with various challenges they encounter during stress and for defending themselves against predators, pathogens and parasites. Microbial symbionts are also often indispensable for the host's development or life cycle completion. Many aquatic ecosystems are currently under pressure due to diverse human activities that have a profound impact on ecosystem functioning. These human activities are also expected to alter interactions between aquatic hosts and their associated microbes. This can directly impact the host's health and-given the importance and widespread occurrence of microbial symbiosis in aquatic systems-the ecosystem at large. In this review, we provide an overview of the importance of microbial symbionts for aquatic organisms, and we consider how the beneficial services provided by microbial symbionts can be affected by human activities. The scarcity of available studies that assess the functional consequences of human impacts on aquatic microbial symbioses shows that our knowledge on this topic is currently limited, making it difficult to draw general conclusions and predict future changes in microbial symbiont-host relationships in a changing world. To address this important knowledge gap, we provide an overview of approaches that can be used to assess the impact of human disturbances on the functioning of aquatic microbial symbioses.
Yan, Bertrand ChengxiangRabbani, GolamLee, Nicole Li YingOoi, Jillian Lean Sim...
12页
查看更多>>摘要：Seagrass meadows are critical marine ecosystems. They are significant carbon sinks and play numerous important roles in coastal areas. They help to prevent shoreline erosion and serve as nursery grounds for many marine species. Like their terrestrial counterparts, seagrasses form symbiotic relationships with diverse communities of bacteria that help to promote and maintain host fitness. In this study, we sampled the seagrass Halophila ovalis throughout Singapore and Peninsular Malaysia to characterise the associated bacterial communities and distributions in this acknowledged seagrass biodiversity hotspot. Three different parts of the seagrass (leaves, roots and rhizomes) were collected, and a sediment sample was collected in close proximity to each host. We used high-throughput 16S rRNA amplicon sequencing to examine the bacterial communities associated with each plant part and location. Our analyses indicated that bacterial assemblages associated with H. ovalis were distinct among locations, and different plant parts harboured divergent bacterial communities. We uncovered a significant distance-decay relationship, suggesting that dispersal limitations could explain the observed bacterial community structuring. We further identified bacterial indicator amplicon sequence variants (ASVs) that were associated with degraded or healthy seagrass meadows. The identification of indicator ASVs that are indicative of anthropogenically stressed seagrass, or a declining environment, could be used to implement proactive seagrass conservation and management schemes. This study addresses a current scientific gap within the characterisation of seagrass microbiomes, specifically of those from Southeast Asia, a region of acute seagrass losses, and provides a solid foundation for future seagrass research in the region.
查看更多>>摘要：Mesoscale eddies in oxygen minimum zones profoundly affect the structure and productivity of marine planktonic communities and alter key biogeochemical cycles. The influence of a mesoscale cyclonic eddy on the spatial distribution of bacterioplankton was investigated in a semi-enclosed, oxygen-depleted basin in the Gulf of California, Mexico. Most of the bacterial taxa showed a strong vertical distribution from oxygen-rich surface waters to anoxic bottom waters, but also a horizontal distribution pattern in the upper ocean associated with the eddy presence. Synechococcocales, Flavobacteriales, SAR86, and Actinomarinales were abundant in the euphotic zone within the Gulf of California water mass, whereas SAR324, SAR406, SAR202, SUP05, Arctic97B-4, and Thioglobaceae dominated the bottom layer of this basin within the Subtropical Subsurface water mass. In contrast, bacterial taxa with a preference for mesopelagic waters (Thiomicrospirales, SAR324, SAR202, HOC36, UBA10353 marine group, and Nitrospinales) dominated surface waters of the eddy center where common surface taxa (Synechococcus, SAR86, and Actinomarinales) were scarce. These changes in community composition led to a distinct diversity of bacterioplankton between the center and edges of the eddy within the euphotic zone. These results show the strong role of oxygen and water masses in controlling the vertical distribution of bacterioplankton, whereas the eddy more strongly modifies the bacterial assemblage in the upper ocean.
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