Aquatic Microbial Ecology

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ISSN / EISSN : 0948-3055 / 1616-1564
Published by: Inter-Research Science Center (10.3354)
Total articles ≅ 1,994
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Aquatic Microbial Ecology, Volume 87, pp 151-166; https://doi.org/10.3354/ame01975

Abstract:
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.
Bc Yan, G Rabbani, Nly Lee, Jls Ooi, Jn Lee, D Huang,
Aquatic Microbial Ecology, Volume 87, pp 139-150; https://doi.org/10.3354/ame01976

Abstract:
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.
, I Benyoucef, M Poulin, B Jesus, P Rosa, V Méléder, G Du, L Barillé
Aquatic Microbial Ecology, Volume 87, pp 61-77; https://doi.org/10.3354/ame01971

Abstract:
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.
V Rose, G Rollwagen-Bollens, Sm Bollens, J Zimmerman
Aquatic Microbial Ecology, Volume 87, pp 29-46; https://doi.org/10.3354/ame01967

Abstract:
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.
, A Kohzu, Vs Kuwahara, Sis Matsuzaki, M Denda, K Hirabayashi
Aquatic Microbial Ecology, Volume 87, pp 47-60; https://doi.org/10.3354/ame01968

Abstract:
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.
P Song, R Yi, S Tanabe, N Goto, K Seto, M Kagami, S Ban
Aquatic Microbial Ecology, Volume 87, pp 17-28; https://doi.org/10.3354/ame01970

Abstract:
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 µm), 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.
K Yoneya, T Miki, S Van Den Wyngaert, Hp Grossart, M Kagami
Aquatic Microbial Ecology, Volume 87, pp 1-15; https://doi.org/10.3354/ame01966

Abstract:
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.
C He, S Xu, Z Kang, S Song, C Li
Aquatic Microbial Ecology, Volume 86, pp 137-151; https://doi.org/10.3354/ame01962

Abstract:
Phaeocystis globosa blooms have become one of the major ecological issues in the Beibu Gulf, China, in recent years, resulting in a series of negative impacts on local fisheries and industry. While prokaryotes play key roles in nutrient cycling and energy flow during algal blooms, information regarding the response of the prokaryotic community during Phaeocystis blooms remains scarce. Thus, a comprehensive field study covering the onset and senescent phase of P. globosa blooms was conducted in the area from December 2016 to February 2017. The community composition was revealed with high-throughput sequencing of the 16S rRNA gene. A total of 7426 operational taxonomic units (OTUs) (97% similarity) were identified from 3132328 effective tags, with Proteobacteria, Cyanobacteria, Thaumarchaeota, Verrucomicrobia, Euryarchaeota, Actinobacteria, and Bacteroidetes being the predominant taxa. The composition and structure of particle-attached (PA) and free-living (FL) prokaryotic communities were significantly different: the PA fraction was more diverse and unstable temporally compared to the FL fraction. Variations in the composition and structure of the prokaryotic community were closely associated with major environmental variables, particularly dissolved oxygen (DO), NH4 +, PO4 3-, and dissolved organic carbon (DOC). The presence of P. globosa may result in differences in the prokaryotic community; members of Rhodobacteraceae, Alteromonadales, Porticoccaceae, Vibrio, Flavobacteriales, and Verrucomicrobiae were the key taxa in the prokaryotic communities during the outbreak and senescent phases of P. globosa blooms. This study provides primary information on the response of prokaryotic communities during P. globosa blooms and will facilitate further study on biogeochemical processes of algal-derived organic matter in the tropical gulf.
, Johnson
Aquatic Microbial Ecology, Volume 86, pp 169-184; https://doi.org/10.3354/ame01964

Abstract:
The mixotrophic ciliate Mesodinium rubrum is an ambush feeder relying on cryptophyte prey motility for prey encounter and perception; therefore, cryptophyte species-specific swimming behaviors affect M. rubrum’s prey preference. Here, a high-speed microscale imaging system was used to quantify the swimming behaviors of 3 cryptophyte species (Teleaulax amphioxeia, Storeatula major, and Guillardia theta) and to conduct quantitative microvideography of M. rubrum-T. amphioxeia predator-prey interaction. T. amphioxeia, a preferred prey of M. rubrum, swam at path-averaged speeds of 155 ± 73 µm s-1 along rather straight paths. In contrast, S. major regularly tumbled slowly downward or upward at 64 ± 16 µm s-1, while G. theta moved slowly in looped/curved trajectories at 57 ± 15 µm s-1; neither supports M. rubrum growth. Only while motionlessly sinking passively did M. rubrum detect and initiate an attack on swimming T. amphioxeia at reaction distances of 8.2 ± 8.2 µm. It seemed that M. rubrum needed to use oral tentacles to initially poke T. amphioxeia’s ventral posterior part and subsequently poke the prey multiple times in a short duration to compromise the prey’s escape ability, presumably by discharging extrusomes into the prey. T. amphioxeia also responded to nearby predators by switching to tumbling similar to S. major in normal swimming, suggesting an effective anti-predator defense behavior that prevents M. rubrum from accurately poking the prey’s ventral posterior part. T. amphioxeia swimming at significantly higher speeds leads to sufficiently high prey encounters and hydrodynamic signals for M. rubrum, thereby partially explaining M. rubrum’s ability to select T. amphioxeia prey.
, Da Lemley, Jb Adams
Aquatic Microbial Ecology, Volume 86, pp 153-167; https://doi.org/10.3354/ame01963

Abstract:
Phytoplankton bloom events result in distinct changes in the composition and availability of nutrients as well as physical conditions within aquatic ecosystems, resulting in significant effects on bacterial communities. Using a metabarcoding approach, this study investigated the effect of a harmful algal bloom (HAB) of Heterosigma akashiwo in the Sundays Estuary, South Africa, on bacterial community structures in this estuarine ecosystem over an entire bloom event. The occurrence of bacterial lineages occurring in both the oxygen-rich surface water and hypoxic bottom waters in this study reflects the respiratory flexibility and potential for both aerobic and anaerobic metabolism across a wide range of bacterial phylogenetic lineages. A close correlation between the bacterial community profiles and the physiological state of the bloom was observed, with Flavobacteria found in increased relative abundances during the H. akashiwo HAB. Flavobacteria are commonly reported in the literature associated with algal blooms, which is indicative of their central role in the degradation of algal-derived organic matter. Halieaceae were prevalent during the bloom, whilst Synechococcales, Cryomorphaceae and Sporichthyaceae were found to be positively correlated with the decay of the H. akashiwo bloom. Rhodobacteraceae correlated significantly with the H. akashiwo bloom; however, unlike the Rhodobacteraceae specific bloom-associated genera reported in literature (predominantly Roseobacter), up to 74% of the Rhodobacteraceae sequence reads in this study were assigned to the genus Litorimicrobium. The distinct bacterial community profiles recorded throughout the H. akashiwo HAB can be attributed to the influence of the bloom-forming species as well as under-representation of estuarine-occurring HABs in the literature.
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