Effects of temperature and nutrients on changes in genetic diversity of bacterioplankton communities in a semi-closed bay, South Korea

Marine Bacterioplankton Community Dynamics and Potentially Pathogenic Bacteria in Seawater around Jeju Island, South Korea, via Metabarcoding

Understanding marine bacterioplankton composition and distribution is necessary for improving predictions of ecosystem responses to environmental change. Here, we used 16S rRNA metabarcoding to investigate marine bacterioplankton diversity and identify potential pathogenic bacteria in seawater samples collected in March, May, September, and December 2013 from two sites near Jeju Island, South Korea. We identified 1343 operational taxonomic units (OTUs) and observed that community diversity varied between months. Alpha- and Gamma-proteobacteria were the most abundant classes, and in all months, the predominant genera were Candidatus Pelagibacter, Leisingera, and Citromicrobium. The highest number of OTUs was observed in September, and Vibrio (7.80%), Pseudoalteromonas (6.53%), and Citromicrobium (6.16%) showed higher relative abundances or were detected only in this month. Water temperature and salinity significantly affected bacterial distribution, and these conditions, characteristic of September, were adverse for Aestuariibacter but favored Citromicrobium. Potentially pathogenic bacteria, among which Vibrio (28 OTUs) and Pseudoalteromonas (six OTUs) were the most abundant in September, were detected in 49 OTUs, and their abundances were significantly correlated with water temperature, increasing rapidly in September, the warmest month. These findings suggest that monthly temperature and salinity variations affect marine bacterioplankton diversity and potential pathogen abundance.

Selective attachment of prokaryotes and emergence of potentially pathogenic prokaryotes on four plastic surfaces: Adhesion study in a natural marine environment

This study employed 16S rRNA metabarcoding to establish the diversity of prokaryotic communities and specific characteristics of potentially pathogenic prokaryotic primary colonizers of four plastic materials (EPS, expanded polystyrene; PE, polyethylene; PP, polypropylene; and PET, polyethylene terephthalate). Bacteria inhabiting plastic and seawater differ; thus, distinct changes in the attached prokaryotic community were observed over an exposure time of 21 days, specifically on Days 3, 6, 9, and 12-21. Frist colonizers were Gammaproteobacteria and Alphaproteobacteria; Bacilli and Clostridia represented secondary colonizers. On Day 3, Pseudoalteromonas had a relative abundance >80 %; whereas, the prevalence of Vibrio spp. (potentially pathogenic prokaryotes) increased rapidly on Days 6 and 9. However, after Day 12, the prevalence of other potential pathogens, namely, Clostridium spp., steadily increased. Despite the diversity of the plastic surfaces, attached prokaryotes changed over time instead of showing similar adherent diversity in all plastic materials.

Co-variance between free-living bacteria and Cochlodinium polykrikoides (Dinophyta) harmful algal blooms, South Korea

To understand the co-variance between common free-living bacteria and Cochlodinium polykrikoides harmful algal blooms (HABs) and their metabolic functions, we investigated 110 sampling sites in the Southern Sea of South Korea. These sampling sites were divided into three groups based on environmental factors and phytoplankton data with a similarity of 85% using non-metric multidimensional scaling. One group represented high-severity C. polykrikoides blooms, while the other two represented low-severity or no blooms. In high-severity HABs, inorganic phosphorous and dissolved organic carbon concentrations were strongly correlated with C. polykrikoides density (p < 0.01). This may reflect the changes in biochemical cycling due to inorganic and organic substrates released by HAB cells (or by cell destruction). Furthermore, 88 common bacterial operational taxonomic units (OTUs, with mean relative abundance > 1%) were identified. These included Gammaproteobacteria (36 OTUs), Flavobacteriia (24), Alphaproteobacteria (18), and other taxa (11). When C. polykrikoides blooms intensified, the relative abundances of Gammaproteobacteria also increased. OTU #030 (Flavicella sp., Flavobacteria, 96%) was positively correlated with C. polykrikoides abundance (r = 0.77, p < 0.001). Functional analysis based on the dominant bacterial OTUs revealed that chemoheterotrophy-related functions were more common in high-severity sites of HABs than in other groups. Therefore, the occurrence of HABs highlighted their interactions with bacteria and affected the bacterial community structure and metabolic functions.

Determinism governs the succession of disturbed bacterioplankton communities in a coastal maricultural ecosystem

Bacterioplankton community is the major engine that drives the biogeochemical cycling of various nutrient and essential elements in the coastal ecosystem. Unraveling the mechanisms governing the succession of such complex bacterioplankton communities in dynamic environment is a challenging issue in environmental science. In this study, we investigated the diversity patterns and succession mechanisms of both free-living and particle-attached bacterioplankton communities that have been exposed to low oxygen and typhoon Lekima. The community evenness was the lowest in August when the temperature was high and dissolved oxygen was low. Similar patterns in community succession were observed for free-living and particle-attached bacterioplankton community after the passing through of typhoon Lekima. Both the free-living and particle-attached bacterioplankton communities in the surface and bottom water columns were strongly affected by geo-environmental factors, among which temperature was the common factor, suggesting that the metabolic theory of ecology also underlie the dynamic patterns of bacterioplankton communities. Although the surface and bottom bacterioplankton compositions were initially different taxonomically and shaped by different environmental conditions, they followed a similar succession pattern over the sampling months. Temperature, dissolved inorganic carbon and dissolved inorganic phosphorus were the major factors associated with the variations of surface bacterioplankton ASVs. Time-decay relationship, in which community similarity decreases with increasing time interval, was clearly observed. Such pattern shall be attributed to the combined effects of time and the changing environmental factors over the sampling months, rather than time alone. Integrating multiple lines of evidences, we demonstrated that determinism governed the succession of both free-living and particle-attached bacterioplankton communities in the coastal maricultural ecosystem, with higher stochastic ratio in habitable months (i.e. fall). This study is expected to provide valuable mechanistic insights into the succession of disturbed complex bacterioplankton communities.

Dynamics of marine bacterial biofouling communities after initial Alteromonas genovensis biofilm attachment to anti-fouling paint substrates

To determine how bacterial communities succeed after the initial attachment of the bacterial biofilm adhesion using 16S rDNA meta-barcoding in plates coated with copper-based anti-fouling (AF) and non-AF (control) coatings as well as ambient seawater, coated plates were submerged in a marine environment in situ. Alteromonas genovensis (Gammaproteobacteria) in AF coating and Pacificibacter sp. (Alphaproteobacteria) in the control plate were initially abundant. In the AF coating, the abundance of A. genovensis decreased rapidly, whereas that of genus Phaeobacter (Alphaproteobacteria), Serratia (Gammaproteobacteria) and Cupriavidus (Betaproteobacteria) increased. Bacterial community in the control plate had a strong connection to pathogenic Vibrio spp. associated with the growth of invertebrates. Therefore, in the in situ AF coating experiment, A. genovensis accumulation was initially and intensively increased, and the bacteria responded to chemical antagonism, induced the proliferation of specific biofilm bacteria and influenced the interactions and recruitment of additional bacterial communities.

Dynamic bacterial community response to Akashiwo sanguinea (Dinophyceae) bloom in indoor marine microcosms

We investigated the dynamics of the bacterial composition and metabolic function within Akashiwo sanguinea bloom using a 100-L indoor microcosm and metagenomic next-generation sequencing. We found that the bacterial community was classified into three groups at 54% similarity. Group I was associated with "during the A. sanguinea bloom stage" and mainly consisted of Alphaproteobacteria, Flavobacteriia and Gammaproteobacteria. Meanwhile, groups II and III were associated with the "late bloom/decline stage to post-bloom stage" with decreased Flavobacteriia and Gammaproteobacteria in these stages. Upon the termination of the A. sanguinea bloom, the concentrations of inorganic nutrients (particularly PO43-, NH4+ and dissolved organic carbon) increased rapidly and then decreased. From the network analysis, we found that the A. sanguinea node is associated with certain bacteria. After the bloom, the specific increases in NH4+ and PO43- nodes are associated with other bacterial taxa. The changes in the functional groups of the bacterial community from chemoheterotrophy to nitrogen association metabolisms were consistent with the environmental impacts during and after A. sanguinea bloom. Consequently, certain bacterial communities and the environments dynamically changed during and after harmful algal blooms and a rapid turnover within the bacterial community and their function can respond to ecological interactions.

Zooming on dynamics of marine microbial communities in the phycosphere of Akashiwo sanguinea (Dinophyta) blooms

Characterizing ecological relationships between viruses, bacteria and phytoplankton in the ocean is critical to understanding the ecosystem; however, these relationships are infrequently investigated together. To understand the dynamics of microbial communities and environmental factors in harmful algal blooms (HABs), we examined the environmental factors and microbial communities during Akashiwo sanguinea HABs in the Jangmok coastal waters of South Korea by metagenomics. Specific bacterial species showed complex synergistic and antagonistic relationships with the A. sanguinea bloom. The endoparasitic dinoflagellate Amoebophrya sp. 1 controlled the bloom dynamics and correlated with HAB decline. Among nucleocytoplasmic large DNA viruses (NCLDVs), two Pandoraviruses and six Phycodnaviruses were strongly and positively correlated with the HABs. Operational taxonomic units of microbial communities and environmental factors associated with A. sanguinea were visualized by network analysis: A. sanguinea-Amoebophrya sp. 1 (r = .59, time lag: 2 days) and A. sanguinea-Ectocarpus siliculosus virus 1 in Phycodnaviridae (0.50, 4 days) relationships showed close associations. The relationship between A. sanguinea and dissolved inorganic phosphorus relationship also showed a very close correlation (0.74, 0 day). Microbial communities and the environment changed dynamically during the A. sanguinea bloom, and the rapid turnover of microorganisms responded to ecological interactions. A. sanguinea bloom dramatically changes the environments by exuding dissolved carbohydrates via autotrophic processes, followed by changes in microbial communities involving host-specific viruses, bacteria and parasitoids. Thus, the microbial communities in HAB are composed of various organisms that interact in a complex manner.

Distinct Temporal Succession of Bacterial Communities in Early Marine Biofilms in a Portuguese Atlantic Port

Marine biofilms are known to influence the corrosion of metal surfaces in the marine environment. Despite some recent research, the succession of bacterial communities colonizing artificial surfaces remains uncharacterized in some temporal settings. More specifically, it is not fully known if bacterial colonizers of artificial surfaces are similar or distinct in the different seasons of the year. In particular the study of early biofilms, in which the bacterial cells communities first adhere to artificial surfaces, are crucial for the development of the subsequent biofilm communities. In this work, we used amplicon-based NGS (next-generation sequencing) and universal 16S rRNA bacterial primers to characterize the early biofilm bacterial communities growing on 316 L stainless steel surfaces in a Northern Portugal port. Sampling spanned 30-day periods in two distinct seasons (spring and winter). Biofilm communities growing in steel surfaces covered with an anti-corrosion paint and planktonic communities from the same location were also characterized. Our results demonstrated that distinct temporal patterns were observed in the sampled seasons. Specifically, a significantly higher abundance of Gammaproteobacteria and Mollicutes was found on the first days of biofilm growth in spring (day 1 to day 4) and a higher abundance of Alphaproteobacteria during the same days of biofilm growth in winter. In the last sampled day (day 30), the spring biofilms significantly shifted toward a dominance of photoautotrophic groups (mostly diatoms) and were also colonized by some macrofouling communities, something not observed during the winter sampling. Our results revealed that bacterial composition in the biofilms was particularly affected by the sampled day of the specific season, more so than the overall effect of the season or overall sampling day of both seasons. Additionally, the application of a non-fouling-release anti-corrosion paint in the steel plates resulted in a significantly lower diversity compared with plates without paint, but this was only observed during spring. We suggest that temporal succession of marine biofilm communities should be taken in consideration for future antifouling/anti-biofilm applications.

Distinct Seasonal Patterns of Bacterioplankton Abundance and Dominance of Phyla α-Proteobacteria and Cyanobacteria in Qinhuangdao Coastal Waters Off the Bohai Sea

Qinhuangdao coastal waters in northern China are heavily impacted by anthropogenic and natural activities, and we anticipate a direct influence of the impact on the bacterioplankton abundance and diversity inhabiting the adjacent coastal areas. To ascertain the anthropogenic influences, we first evaluated the seasonal abundance patterns and diversity of bacterioplankton in the coastal areas with varied levels of natural and anthropogenic activities and then analyzed the environmental factors which influenced the abundance patterns. Results indicated distinct patterns in bacterioplankton abundance across the warm and cold seasons in all stations. Total bacterial abundance in the stations ranged from 8.67 × 10⁴ to 2.08 × 10⁶ cells/mL and had significant (p < 0.01) positive correlation with total phosphorus (TP), which indicated TP as the key monitoring parameter for anthropogenic impact on nutrients cycling. Proteobacteria and Cyanobacteria were the most abundant phyla in the Qinhuangdao coastal waters. Redundancy analysis revealed significant (p < 0.01) influence of temperature, dissolved oxygen and chlorophyll a on the spatiotemporal abundance pattern of α-Proteobacteria and Cyanobacteria groups. Among the 19 identified bacterioplankton subgroups, α-Proteobacteria (phylum Proteobacteria) was the dominant one followed by Family II (phylum Cyanobacteria), representing 19.1-55.2% and 2.3-54.2% of total sequences, respectively. An inverse relationship (r = -0.82) was observed between the two dominant subgroups, α-Proteobacteria and Family II. A wide range of inverse Simpson index (10.2 to 105) revealed spatial heterogeneity of bacterioplankton diversity likely resulting from the varied anthropogenic and natural influences. Overall, our results suggested that seasonal variations impose substantial influence on shaping bacterioplankton abundance patterns. In addition, the predominance of only a few cosmopolitan species in the Qinhuangdao coastal wasters was probably an indication of their competitive advantage over other bacterioplankton groups in the degradation of anthropogenic inputs. The results provided an evidence of their ecological significance in coastal waters impacted by seasonal inputs of the natural and anthropogenic matter. In conclusion, the findings anticipate future development of effective indicators of coastal health monitoring and subsequent management strategies to control the anthropogenic inputs in the Qinhuangdao coastal waters.