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Understanding how species interaction and assembly processes structure the abundant and rare bacterial biospheres in soils is crucial for predicting how biodiversity influences ecosystem functioning. Here, we profiled the bacterial communities across a salt marsh ecosystem gradient to investigate the co-occurrence patterns across taxa and the relative influence of ecological processes mediating the assembly of the abundant and rare biospheres in soil. Our results revealed abundant taxa to be ubiquitous across all sites, whereas the distributions of the rare taxa were relatively more site specific. The α-diversity indices and β-diversity of rare subcommunities were significantly higher than those of the abundant subcommunities. Besides, both the taxonomic and functional composition of soil bacterial communities differed significantly between the two biospheres. Furthermore, the influence of stochasticity differed in each subcommunity. In particular, stochastic processes were relatively more important in constraining the assembly of rare taxa. Co-occurrence network analysis revealed that a few abundant taxa occupy central nodes within the networks, possibly indicating crucial roles as keystone taxa. Collectively, these findings suggest that abundant and rare bacterial biospheres have distinct distributions underpinned by a dynamic interplay of ecological processes and taxon co-occurrence patterns. IMPORTANCE Estuarine salt marshes are highly productive ecosystems subjected to regular disturbances by hydrodynamic exchange. However, little is known about how distinct assembly processes and co-occurrence of taxa influence the structure of the abundant and rare bacterial biospheres in these soil systems. This study aims at unravelling these intricacies by studying a typical estuarine salt marsh located in Hangzhou Bay, China. Our study provides important pieces of evidence on the diverse distribution of rare and abundant bacterial biospheres. We show that a few abundant taxa are central nodes in species co-occurrence, potentially playing important roles as keystone species in the system. In addition, we highlight a dynamic interplay of assembly processes structuring these two subcommunities.

Bacterial communities play essential roles in estuarine marsh ecosystems, but the interplay of ecological processes underlying their community assembly is poorly understood. Here, we studied the sediment bacterial communities along a linear gradient extending from the water-land junction toward a high marsh, using 16S rRNA gene amplicon sequencing. Bacterial community compositions differed significantly between sediment transects. Physicochemical properties, particularly sediment nutrient levels (i.e., total nitrogen [TN] and available phosphorus [AP]), as well as sediment physical structure and pH (P < 0.05), were strongly associated with the overall community variations. In addition, the topological properties of bacterial cooccurrence networks varied with distance to the water-land junction. Both node- and network-level topological features revealed that the bacterial network of sediments farthest from the junction was less intense in complexity and interactions than other sediments. Phylogenetic null modeling analysis showed a progressive transition from stochastic to deterministic community assembly for the water-land junction sites toward the emerging terrestrial system. Taken together, data from this study provide a detailed outline of the distribution pattern of the sediment bacterial community across an estuarine marsh and inform the mechanisms and processes mediating bacterial community assembly in marsh soils.IMPORTANCESalt marshes represent highly dynamic ecosystems where the atmosphere, continents, and the ocean interact. The bacterial distribution in this ecosystem is of great ecological concern, as it provides essential functions acting on ecosystem services. However, ecological processes mediating bacterial assembly are poorly understood for salt marshes, especially the ones located in estuaries. In this study, the distribution and assembly of bacterial communities in an estuarine marsh located in south Hangzhou Bay were investigated. The results revealed an intricate interplay between stochastic and deterministic processes mediating the assembly of bacterial communities in the studied gradient system. Collectively, our findings illustrate the main drivers of community assembly, taking into consideration changes in sediment abiotic variables and potential biotic interactions. Thus, we offer new insights into estuarine bacterial communities and illustrate the interplay of ecological processes shaping the assembly of bacterial communities in estuarine marsh ecosystems.

Increasing evidence has emerged supporting a tight link between gut bacterial community and shrimp health. However, the knowledge about the variation of gut bacterial community, especially with different disease onset time, remains elusive. Here, healthy and diseased shrimps were collected at 3 disease-outbreak times (day 70, 80 and 85) to investigate the variation of gut bacterial community and its underlying ecological process with 16S rRNA gene amplicon sequencing. The gut bacterial community of diseased shrimp was distinct from the healthy one and temporally less stable, characterized by decreased alpha-diversity and dispersive structure. And its dominant ecological process experienced a transition with disease onset time, although deterministic process mainly governed the healthy gut bacterial assembly. In addition, the core microbiota of healthy shrimp gut harbored more diverse bacterial taxa with more cooperative interactions, while the diseased core microbiota showed opposite pattern with significantly higher abundance of opportunistic pathogens as well. These findings indicate that shrimp heath is highly relevant to the homeostasis of its gut bacterial community. Preservation and restoration of the bacterial community equilibrium could represent an effective strategy for shrimp disease prevention.Electronic supplementary materialThe online version of this article (10.1186/s13568-018-0644-x) contains supplementary material, which is available to authorized users.

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The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G ؊ ) to Gram-positive (G ؉ ) bacterial PLFAs (G ؊ /G ؉ ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G ؊ /G ؉ ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.

Application of algicidal compounds secreted by bacteria is a promising and environmentally friendly strategy to control harmful algal blooms (HABs). Years ago prodigiosin was described as an efficient algicidal compound, but the details about the effect of prodigiosin on algal cells are still elusive. Prodigiosin shows high algicidal activity on Phaeocystis globosa, making it a potential algicide in HAB control. When P. globosa were treated with prodigiosin at 5 μg/mL, algae cells showed cytoplasmic hypervacuolization, chloroplast and nucleus rupture, flagella missing, and cell fracture, when observed by scanning electron microscope and transmission electron microscopy. Prodigiosin induced a reactive oxygen species (ROS) burst in P. globosa at 2 h, which could result in severe oxidative damage to algal cells. Chlorophyll a (Chl a) fluorescence decreased significantly after prodigiosin treatment; about 45.3 and 90.0% of algal cells lost Chl a fluorescence at 24 and 48 h. The Fv/Fm value, reflecting the status of the photosystem II electron flow also decreased after prodigiosin treatment. Quantitative polymerase chain reaction (PCR) analysis psbA and rbcS expression indicated that photosynthesis process was remarkably inhibited by prodigiosin. The results indicated that the inhibition of photosynthesis may produce excessive ROS causing cell necrosis. This study is the first report about algal lysis mechanism of prodigiosin on harmful algae. Our results could increase our knowledge on the interaction between algicidal compounds and harmful algae, which could lead to further studies in the microcosm.

Abstract. This research explores the rainfall-El Niño-Southern Oscillation (ENSO) and runoff-ENSO relationships and examines the potential for water resource forecasting using these relationships. The Southern Oscillation Index (SOI), Niño1.2, Niño3, Niño4, and Niño3.4 were selected as ENSO indicators for cross-correlation analyses of precipitation and runoff. There was a significant correlation (95% confidence level) between precipitation and ENSO indicators during three periods: January, March, and from September to November. In addition, monthly streamflow and monthly ENSO indictors were significantly correlated during three periods: from January to March, June, and from October to December (OND), with lag periods between one and twelve months. Because ENSO events can be accurately predicted one to two years in advance using physical modeling of the coupled ocean-atmosphere system, the lead time for forecasting runoff using ENSO indicators in the Headwaters Region of the Yellow River could extend from one to 36 months. Therefore, ENSO may have potential as a powerful forecasting tool for water resources in the headwater regions of Yellow River.