Divergent Patterns of Bacterial Community Structure and Function in Response to Estuarine Output in the Middle of the Bohai Sea

Seasonal and anthropogenic influences on bacterioplankton communities: ecological impacts in the coastal waters of Qinhuangdao, Northern China

Marine bacterioplankton play a crucial role in the cycling of carbon, nitrogen, and phosphorus in coastal waters. And the impact of environmental factors on bacterial community structure and ecological functions is a dynamic ongoing process. To systematically assess the relationship between environmental changes and bacterioplankton communities, this study delved into the spatiotemporal distribution and predicted metabolic characteristics of bacterioplankton communities at two estuarine beaches in Northern China. Coastal water samples were collected regularly in spring, summer, and autumn, and were analyzed in combination with environmental parameters and bacterioplankton community. Results indicated significant seasonal variations in bacterioplankton communities as Bacteroidetes and Actinobacteria were enriched in spring, Cyanobacteria proliferated in summer. While Pseudomonadota and microorganisms associated with organic matter decomposition prevailed in autumn, closely linked to seasonal variation of temperature, light and nutrients such as nitrogen and phosphorus. Particularly in summer, increased tourism activities and riverine inputs significantly raised nutrient levels, promoting the proliferation of specific photosynthetic microorganisms, potentially linked to the occurrence of phytoplankton blooms. Spearman correlation analysis further revealed significant correlations between bacterioplankton communities and environmental factors such as salinity, chlorophyll a, and total dissolved phosphorus (TDP). Additionally, the metabolic features of the spring bacterioplankton community were primarily characterized by enhanced activities in the prokaryotic carbon fixation pathways, reflecting rapid adaptation to increased light and temperature, as well as significant contributions to primary productivity. In summer, the bacterial communities were involved in enhanced glycolysis and biosynthetic pathways, reflecting high energy metabolism and responses to increased light and biomass. In autumn, microorganisms adapted to the accelerated decomposition of organic matter and the seasonal changes in environmental conditions through enhanced amino acid metabolism and material cycling pathways. These findings demonstrate that seasonal changes and human activities significantly influence the structure and function of bacterioplankton communities by altering nutrient dynamics and physical environmental conditions. This study provides important scientific insights into the marine biological responses under global change.

Unveiling the bioactive potential of Actinomycetota from the Tagus River estuary

The increase in global travel and the incorrect and excessive use of antibiotics has led to an unprecedented rise in antibiotic resistance in bacterial and fungal populations. To overcome these problems, novel bioactive natural products must be discovered, which may be found in underexplored environments, such as estuarine habitats. In the present work, estuarine actinomycetotal strains were isolated with conventional and iChip techniques from the Tagus estuary in Alcochete, Portugal, and analysed for different antimicrobial bioactivities. Extracts were produced from the isolated cultures and tested for bioactivity against Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, Aspergillus fumigatus ATCC 240305, Candida albicans ATCC 10231 and Trichophyton rubrum FF5. Furthermore, bioactive extracts were subjected to dereplication by high-performance liquid chromatography (HPLC) and high-resolution mass spectrometry (HRMS) to putatively identify their chemical components. In total, 105 isolates belonging to 3 genera were obtained. One which was isolated, MTZ3.1 T, represents a described novel taxon for which the name Streptomyces meridianus was proposed. Regarding the bioactivity testing, extracts from 12 strains proved to be active against S. aureus, 2 against E. coli, 4 against A. fumigatus, 3 against C. albicans and 10 against T. rubrum. Dereplication of bioactive extracts showed the presence of 28 known bioactive molecules, 35 hits have one or more possible matches in the DNP and 18 undescribed ones. These results showed that the isolated bacteria might be the source of new bioactive natural products.

Spatiotemporal Shift of T4-Like Phage Community Structure in the Three Largest Estuaries of China

Estuaries are one of the most highly productive and economically important ecosystems at the continent-ocean interface. Estuary productivity is largely determined by the microbial community structure and activity. Viruses are major agents of microbial mortality and are key drivers of global geochemical cycles. However, the taxonomic diversity of viral communities and their spatial-temporal distribution in estuarine ecosystems have been poorly studied. In this study, we investigated the T4-like viral community composition at three major Chinese estuaries in winter and in summer. Diverse T4-like viruses, which were divided into three main clusters (Clusters I to III), were revealed. The Marine Group of Cluster III, with seven identified subgroups, was the most dominant (averaging 76.5% of the total sequences) in the Chinese estuarine ecosystems. Significant variations of T4-like viral community composition were observed among estuaries and seasons, with higher diversity occurring in winter. Among various environmental variables, temperature was a main driver of the viral communities. This study demonstrates viral assemblage diversification and seasonality in Chinese estuarine ecosystems. IMPORTANCE Viruses are ubiquitous but largely uncharacterized members of aquatic environments that cause significant mortality in microbial communities. Recent large-scale oceanic projects have greatly advanced our understanding of viral ecology in marine environments, but those studies mostly focused on oceanic regions. There have yet to be spatiotemporal studies of viral communities in estuarine ecosystems, which are unique habitats that play a significant role in global ecology and biogeochemistry. This work is the first comprehensive study that provides a detailed picture of the spatial and seasonal variation of viral communities (specifically, T4-like viral communities) in three major estuarine ecosystems in China. These findings provide much-needed knowledge regarding estuarine viral ecosystems, which currently lags in oceanic ecosystem research.

Comparison of assembly process and co-occurrence pattern between planktonic and benthic microbial communities in the Bohai Sea

Unraveling the mechanisms structuring microbial community is a central goal in microbial ecology, but a detailed understanding of how community assembly processes relate to living habitats is still lacking. Here, via 16S rRNA gene amplicon sequencing, we investigated the assembly process of microbial communities in different habitats [water verse sediment, free-living (FL) verse particle-associated (PA)] and their impacts on the inter-taxa association patterns in the coastal Bohai Sea, China. The results showed clear differences in the composition and diversity of microbial communities among habitats, with greater dissimilarities between water column and sediment than between FL and PA communities. The microbial community assembly was dominated by dispersal limitation, ecological drift, and homogeneous selection, but their relative importance varied in different habitats. The planktonic communities were mainly shaped by dispersal limitation and ecological drift, whereas homogeneous selection played a more important role in structuring the benthic communities. Furthermore, the assembly mechanisms differed between FL and PA communities, especially in the bottom water with a greater effect of ecological drift and dispersal limitation on the FL and PA fractions, respectively. Linking assembly process to co-occurrence pattern showed that the relative contribution of deterministic processes (mainly homogeneous selection) increased under closer co-occurrence relationships. By contrast, stochastic processes exerted a higher effect when there were less inter-taxa connections. Overall, our findings demonstrate contrasting ecological processes underpinning microbial community distribution in different habitats including different lifestyles, which indicate complex microbial dynamic patterns in coastal systems with high anthropogenic perturbations.

Bacterial and Protistan Community Variation across the Changjiang Estuary to the Ocean with Multiple Environmental Gradients

Plankton microorganisms play central roles in the marine food web and global biogeochemical cycles, while their distribution and abundance are affected by environmental variables. The determinants of microbial community composition and diversity in estuaries and surrounding waters with multiple environmental gradients at a fine scale remain largely unclear. Here, we investigated bacterial and protistan community assembly in surface waters from 27 stations across the Changjiang Estuary to the ocean, with salinity ranging from 0 to 32.1, using 16S rRNA and 18S rRNA gene amplicon sequencing. Statistical analyses revealed that salinity is the major factor structuring both bacterial and protistan communities. Salinity also acted as a significant environmental determinant influencing alpha-diversity patterns. Alpha diversity indices for bacterial and protistan communities revealed a species minimum in higher-salinity waters (22.1–32.1). Contrary to the protistan community, the highest bacterial diversity was identified in medium-salinity waters (2.8–18.8), contrasting Remane’s Artenminimum concept. The distribution of major planktonic taxa followed the expected pattern, and the salinity boundary for Syndiniales was specifically identified. These findings revealed the significant effects of salinity on the microbial community across an estuary to ocean transect and the distinct response to salinity between bacterial and protistan communities.

Comparative analysis of fecal microbiota composition diversity in Tibetan piglets suffering from diarrheagenic Escherichia coli (DEC)

This study was ascertained to investigate the adverse effects of pathogenic E. coli on gut microbiota of Tibetan piglets with history of yellow and white dysentery. For this purpose, a total of 18 fecal samples were collected from infected and healthy Tibetan piglets for 16S rRNA gene amplification and sequencing of V3-V4 region. Results showed that Firmicutes, Bacteroidia Fusobacteriota, Proteobacteria and Actinobacteriota were the predominant bacteria in Tibetan piglets at the level of phylum classification. Results on classification at family level showed that Lactobacillus, Bacteroidota, Fusobacteriota and Enterobacteriaceae were the dominant bacteria. Results on classification of bacteria at phylum level compared with normal piglets indicated that Bacteroidota, Actinobacteriota, Euryarchaota and Spirochaetota in fecal microbial community in Tibetan piglets showing yellow dysenteric and diarrhea group were significantly decreased (P ≤ 0.05). Compared with the feces of healthy Tibetan piglets, the abundance of Escherichia-Shigella, Lactobacillus and Enterococcus increased significantly in feces of Tibetan piglets having yellow dysentery and white dysentery. Moreover, results exhibited that the Proteobacteria and Fusobacteriota were significantly increased (P ≤ 0.05) suggesting dominant microbial community. Results revealed that E. coli induced different pathological alterations in intestine including damage to intestinal epithelial cells, infiltration of inflammatory cells, presence of red blood cells in spaces of tissues, hemorrhages and necrosis of intestinal villi in piglets with history of yellow dysentery. This study for the first time reported the composition, characteristics, and differences of the fecal microflora diversity of Tibetan piglets with yellow and white dysentery in Qinghai-Tibet Plateau, which can provide a suitable support for effective control of diarrhoeal disease in these animals.