Mechanisms of microbial coexistence in a patchy ecosystem: Differences in ecological niche overlap and species fitness between rhythmic and non-rhythmic species.

Resource patchiness caused by external events breaks the continuity and homogeneity of resource distribution in the original ecosystem. For local organisms, this leads to drastic changes in the availability of resources, breaks down the co-existence of species, and reshuffles the local ecosystem. West Lake is a freshwater lake with resource patchiness caused by multiple exogenous disturbances that has strong environmental heterogeneity that prevents clear observation of seasonal changes in the microbial communities. Despite this, the emergence of rhythmic species in response to irregular changes in the environment has been helpful for observing microbial communities dynamics in patchy ecosystems. We investigated the ecological mechanisms of seasonal changes in microbial communities in West Lake by screening rhythmic species based on the ecological niche and modern coexistence theories. The results showed that rhythmic species were the dominant factors in microbial community changes and the effects of most environmental factors on the microbial community were indirectly realised through the rhythmic species. Random forest analyses showed that seasonal changes in the microbial community were similarly predicted by the rhythmic species. In addition, we incorporated species interactions and community phylogenetic patterns into stepwise multiple regression analyses, the results of which indicate that ecological niches and species fitness may drive the coexistence of these subcommunities. Thus, this study extends our understanding of seasonal changes in microbial communities and provides new ways for observing seasonal changes in microbial communities, especially in ecosystems with resource patches. Our study also show that combining community phylogenies with co-occurrence networks based on ecological niches and modern coexistence theory can further help us understand the ecological mechanisms of interspecies coexistence.

Microalgae Inoculation Significantly Shapes the Structure, Alters the Assembly Process, and Enhances the Stability of Bacterial Communities in Shrimp-Rearing Water.

Intensive shrimp farming may lead to adverse environmental consequences due to discharged water effluent. Inoculation of microalgae can moderate the adverse effect of shrimp-farming water. However, how bacterial communities with different lifestyles (free-living (FL) and particle-attached (PA)) respond to microalgal inoculation is unclear. In the present study, we investigated the effects of two microalgae (Nannochloropsis oculata and Thalassiosira weissflogii) alone or in combination in regulating microbial communities in shrimp-farmed water and their potential applications. PERMANOVA revealed significant differences among treatments in terms of time and lifestyle. Community diversity analysis showed that PA bacteria responded more sensitively to different microalgal treatments than FL bacteria. Redundancy analysis (RDA) indicated that the bacterial community was majorly influenced by environmental factors, compared to microalgal direct influence. Moreover, the neutral model analysis and the average variation degree (AVD) index indicated that the addition of microalgae affected the bacterial community structure and stability during the stochastic process, and the PA bacterial community was the most stable with the addition of T. weissflogii. Therefore, the present study revealed the effects of microalgae and nutrient salts on bacterial communities in shrimp aquaculture water by adding microalgae to control the process of community change. This study is important for understanding the microbial community assembly and interpreting complex interactions among zoo-, phyto-, and bacterioplankton in shrimp aquaculture ecosystems. Additionally, these findings may contribute to the sustainable development of shrimp aquaculture and ecosystem conservation.

The Assembly Process of Free-Living and Particle-Attached Bacterial Communities in Shrimp-Rearing Waters: The Overwhelming Influence of Nutrient Factors Relative to Microalgal Inoculation.

The ecological functions of bacterial communities vary between particle-attached (PA) lifestyles and free-living (FL) lifestyles, and separately exploring their community assembly helps to elucidate the microecological mechanisms of shrimp rearing. Microalgal inoculation and nutrient enrichment during shrimp rearing are two important driving factors that affect rearing-water bacterial communities, but their relative contributions to the bacterial community assembly have not been evaluated. Here, we inoculated two microalgae, Nannochloropsis oculata and Thalassiosira weissflogii, into shrimp-rearing waters to investigate the distinct effects of various environmental factors on PA and FL bacterial communities. Our study showed that the composition and representative bacteria of different microalgal treatments were significantly different between the PA and FL bacterial communities. Regression analyses and Mantel tests revealed that nutrients were vital factors that constrained the diversity, structure, and co-occurrence patterns of both the PA and FL bacterial communities. Partial least squares path modeling (PLS-PM) analysis indicated that microalgae could directly or indirectly affect the PA bacterial community through nutrient interactions. Moreover, a significant interaction was detected between PA and FL bacterial communities. Our study reveals the unequal effects of microalgae and nutrients on bacterial community assembly and helps explore microbial community assembly in shrimp-rearing ecosystems.

Toxic cyanobacteria induce coupled changes in gut microbiota and co-metabolite of freshwater gastropods.

Frequent outbreaks of harmful cyanobacterial blooms and the microcystins (MCs) they produce seriously affect the survival of aquatic organisms. Interactions between gut microbiota and hosts often play crucial roles in driving the adaptation of aquatic organisms to environmental changes. In this study, we investigated the phenotypic indicators of the freshwater gastropod Bellamya aeruginosa, after uptake of Microcystis aeruginosa and explored its gut microbial composition and gut metabolites in response to toxic cyanobacterial stress. Results showed that the MCs concentration in the hepatopancreas of snails fed with toxic cyanobacteria decreased from 2.64 ± 0.14 µg·g-1 on day 7 to 1.16 ± 0.10 µg·g-1 on day 14. The compositions of the intestinal microbiota of snails fed with different algae significantly differed, and the relative abundance of gut microbes such as Lactobacillus and Sphingobium significantly increased after feeding toxic cyanobacteria. Significant differences also existed in intestinal metabolites, the relative abundance of the following metabolites significantly increased: l-proline, 5,6-DHET, stachyose, raffinose, and 3-isopropylmalate. Sankey network diagrams showing links between gut microbes and gut metabolites. The association of Lactobacillus and Sphingobium with amino acids may be related to host tolerance to toxicity, and the linkages of gut microbes with metabolites such as levan, imidazolepropionic acid, and eicosanoids may be associated with involvement in host immune responses. The association of microbes with stachyose and raffinose can help the host to regulate energy homeostasis. These results reveal the underlying mechanisms of gut microbes in the snail adaptation to toxic cyanobacterial stress. This study could be great important for gaining new insights into toxic cyanobacteria-induced changes in snail gut microbes and metabolites and their roles in snail adaptation to toxic cyanobacterial stress, and may provide important insights into the use of freshwater gastropods for the prevention and control of cyanobacterial blooms.

Adsorption performance of tetracycline by the biomass ash derived from the pyrolysis of FeCl3-activated municipal sludge without gas protection.

The municipal sludge activated by FeCl3 solution was pyrolyzed at 500 °C without gas protection, and the pyrolysis products, named as biomass ash, could effectively adsorb tetracycline (TC) from aqueous solution. Different FeCl3 concentrations could directly affect the physicochemical properties of the biomass ash, so that the biomass ash as adsorbent showed different adsorption efficiency toward TC. The activation of FeCl3 increased the oxygen-containing functional groups and surface polarities of the biomass ash. When the concentration of FeCl3 solution was 0.5 mol/L, the biomass ash behaved the maximum specific surface area (37.74 m2/g) and the best adsorption efficiency. The pseudo-second-order kinetics model and the Freundlich multi-molecule model could fully explain the TC adsorption process by the biomass ash pyrolyzed from municipal sludge activated by FeCl3. Moreover, the adsorption mechanism was mainly attributed to the chemical adsorption.

Biomass ash pyrolyzed from municipal sludge and its adsorption performance toward tetracycline: effect of pyrolysis temperature and KOH activation.

Large amount of municipal sludge is difficult to handle; its resource utilization is an effective measure. In this study, the municipal sludge from sewage treatment plant was pyrolyzed without gas protection at different temperatures and potassium hydroxide (KOH) concentrations for activation. The pyrolysis products, named biomass ash, with higher surface area and enriched pore structures could be obtained at the pyrolysis temperature of 773 K. Moreover, the KOH activation for raw municipal sludge could further increase the surface area of the pyrolysis biomass ash. The maximum specific surface area was 44.71 m2/g, which was obtained under 2 mol/L KOH activation before pyrolysis at 773 K. And in this situation, the obtained pyrolysis biomass ash as adsorbent showed the maximum adsorption capacity of 50.75 mg/g toward tetracycline (TC). Moreover, the TC adsorption onto pyrolysis biomass ash obtained under various conditions followed the pseudo-second-order kinetic model. Adsorption thermodynamics analysis suggested the TC adsorption onto the pyrolysis biomass ash with no pre-activation was mainly due to the multi-molecule heterogeneous adsorption, while the TC adsorption onto pyrolysis biomass ash pretreated through the activation of KOH followed the monomer adsorption mechanism. This different adsorption mechanism was largely related to the pore structure, polarity, and aromaticity of the adsorbent.

Nonsmooth Continuous-Time Distributed Algorithms for Seeking Generalized Nash Equilibria of Noncooperative Games via Digraphs.

In this article, the problem of distributed generalized Nash equilibrium (GNE) seeking in noncooperative games is investigated via multiagent networks, where each player aims to minimize his or her own cost function with a nonsmooth term. Each player's cost function and feasible action set in the noncooperative game are both determined by actions of others who may not be neighbors, as well as his/her own action. Particularly, feasible action sets are constrained by private convex inequalities and shared linear equations. Each player can only have access to his or her own cost function, private constraint, and a local block of shared constraints, and can only communicate with his or her neighbours via a digraph. To address this problem, a novel continuous-time distributed primal-dual algorithm involving Clarke's generalized gradient is proposed based on consensus algorithms and the primal-dual algorithm. Under mild assumptions on cost functions and graph, we prove that players' actions asymptotically converge to a GNE. Finally, a simulation is presented to demonstrate the effectiveness of our theoretical results.

Distributed Algorithms Involving Fixed Step Size for Mixed Equilibrium Problems With Multiple Set Constraints.

In this brief, the problem of distributively solving a mixed equilibrium problem (EP) with multiple sets is investigated. A network of agents is employed to cooperatively find a point in the intersection of multiple convex sets ensuring that the sum of multiple bifunctions with a free variable is nonnegative. Each agent can only access information associated with its own bifunction and a local convex set. To solve this problem, a distributed algorithm involving a fixed step size is proposed by combining the mirror descent algorithm, the primal-dual algorithm, and the consensus algorithm. Under mild conditions on bifunctions and the graph, we prove that all agents' states asymptotically converge to a solution of the mixed EP. A numerical simulation example is provided for demonstrating the effectiveness of theoretical results.

Distributed Algorithms for Searching Generalized Nash Equilibrium of Noncooperative Games.

In this paper, the distributed Nash equilibrium (NE) searching problem is investigated, where the feasible action sets are constrained by nonlinear inequalities and linear equations. Different from most of the existing investigations on distributed NE searching problems, we consider the case where both cost functions and feasible action sets depend on actions of all players, and each player can only have access to the information of its neighbors. To address this problem, a continuous-time distributed gradient-based projected algorithm is proposed, where a leader-following consensus algorithm is employed for each player to estimate actions of others. Under mild assumptions on cost functions and graphs, it is shown that players' actions asymptotically converge to a generalized NE. Simulation examples are presented to demonstrate the effectiveness of the theoretical results.

[Seasonal Succession of Phytoplankton Functional Groups and Their Driving Factors in the Siminghu Reservoir].

The succession of phytoplankton communities is affected by pure environmental factors as well as the interaction of various factors. Phytoplankton communities with eleven aquatic abiotic factors and four biotic factors were investigated in the Siminghu Reservoir, and the seasonal succession of phytoplankton FGs related to the biotic and abiotic factors was analyzed. The results suggested that a total of 22 phytoplankton functional groups were identified across the samples, and they were all affiliated with Chlorophyta and Bacillariophyta. An obvious seasonal succession was discovered by NMDS, which were present as D+Lo in summer, D+P+Lo in autumn and winter, and X2+P+MP in spring. In particular, we screened 10 functional groups with biomass significantly associated with the seasonal change in the phytoplankton community. A variance partitioning analysis (VPA) revealed that water temperature-zooplankton covariation and water temperature explained the variation in the phytoplankton functional groups throughout the year. A canonical correspondence analysis (CCA) showed that water temperature, transparency, nitrate nitrogen, and the biomass of zooplankton were the most critical factors determining the community dynamics of phytoplankton.

Nutrient enrichment during shrimp cultivation alters bacterioplankton assemblies and destroys community stability.

Intensive shrimp farming is generally accompanied by nutrient enrichment and gradual eutrophication, which impose major threats to shrimp culture ecosystems. However, little is known about how the bacterioplankton community in a rearing environment responds to increased eutrophication during shrimp culture processes. In this study, we used the MiSeq sequencing technique to explore the impacts of nutrient enrichment on the assembly and stability of the bacterioplankton community. Our results showed that magnitudes of the changes in the bacterioplankton community compositions (BCCs) and diversity were closely associated with eutrophication level. Moreover, a phylogenetic-based mean nearest taxon distance (MNTD) analysis revealed that increased eutrophication significantly (P < 0.01) changed the bacterioplankton ecological processes from deterministic to stochastic. A structural equation model showed that eutrophication indicators affected the BCCs either directly by controlling resources or indirectly by modifying other environmental variables of the shrimp ponds in complex pathways. Furthermore, association network comparisons revealed that nutrient enrichment increased the complexity of interspecies interactions and the proportion of cooperative interactions and decreased the proportion of generalists, which suggest that nutrient enrichment destroyed the community stability. These findings suggest that minimizing nutrient pollution, especially at the end of cultivation, could be an important management tool for establishing a microbially mature water system.

Temporal variations in a phytoplankton community in a subtropical reservoir: An interplay of extrinsic and intrinsic community effects.

The phytoplankton community structure is potentially influenced by both extrinsic effects originating from the surrounding environment and intrinsic effects relying on interspecific interactions between two species. However, few studies have simultaneously considered both types of effects and assessed the relative importance of these factors. In this study, we used data collected over nine months (August 2012-May 2013) from a typical subtropical reservoir in southeast China to analyze the temporal variation of its phytoplankton community structure and develop a quantitative understanding of the extrinsic and intrinsic effects on phytoplankton community dynamics. Significant temporal variations were observed in environmental variables as well as the phytoplankton and zooplankton communities, whereas their variational trajectories and directions were entirely different. Variance partitioning analysis showed that extrinsic factors significantly explained only 31% of the variation in the phytoplankton community, thus suggesting that these factors were incomplete predictors of the community structure. Random forest-based models showed that 48% of qualified responsible phytoplankton species were more accurately predicted by phytoplankton-only models, which revealed clear effects of interspecific species-to-species interactions. Furthermore, we used association networks to model the interactions among phytoplankton, zooplankton and the environment. Network comparisons indicated that interspecific interactions were widely present in the phytoplankton community and dominated the network rather than those between phytoplankton and extrinsic factors. These findings expand the current understanding of the underlying mechanisms that govern phytoplankton community dynamics.

[Community Dynamics of Phytoplankton and Related Affecting Factors in a Eutrophicated Small Pond].

The high-density sampling of eutrophic water can help to reveal the general rules of phytoplankton community succession and the relationship with environmental factors. The species and abundance of plankton and the physical-chemical factors were tracked for 30 weeks from March to October in a eutrophicated small pond. The relationships between the phytoplankton community dynamic change and the physical-chemical factors as well as the zooplankton in the water body community were studied by the multivariate statistical analysis with PRIMER. A total of 54 phytoplankton and 55 zooplankton species were identified, and the abundances of plankton varied from 0.28 x 10(8) - 6.11 x 10(8) cells x L(-1) for phytoplankton and 26-2.5 x 10(5) ind x L(-1) for zooplankton. The dominant species of phytoplankton were Cyanophyta and Chlorophyta, and an obvious succession process was showed with the seasonal change, which could be roughly divided into three stages: Chlorophyta-Cryptophyta type, Chlorophyta-Cyanophyta type and Cyanophyta type. BIO-ENV showed that pH, water temperature, transparency, total phosphorus and the abundances of Rotifera and Copepoda were the most critical influencing factors on the community dynamics of phytoplankton, and compared to zooplankton, the physical-chemical factors might have a greater influence.

[The establishment, development and application of classification approach of freshwater phytoplankton based on the functional group: a review].

Appropriate schemes for classification of freshwater phytoplankton are prerequisites and important tools for revealing phytoplanktonic succession and studying freshwater ecosystems. An alternative approach, functional group of freshwater phytoplankton, has been proposed and developed due to the deficiencies of Linnaean and molecular identification in ecological applications. The functional group of phytoplankton is a classification scheme based on autoecology. In this study, the theoretical basis and classification criterion of functional group (FG), morpho-functional group (MFG) and morphology-based functional group (MBFG) were summarized, as well as their merits and demerits. FG was considered as the optimal classification approach for the aquatic ecology research and aquatic environment evaluation. The application status of FG was introduced, with the evaluation standards and problems of two approaches to assess water quality on the basis of FG, index methods of Q and QR, being briefly discussed.

Characterizing the structural diversity of a bacterial community associated with filter materials in recirculating aquaculture systems of Scortum barcoo.

The bacterial community structure associated with filter materials in the recirculating aquaculture system of Scortum barcoo was investigated using the 16S rRNA gene clone library method. Preliminary results showed that the clone library constructed from the initial operation condition was characterized by 31 taxa of bacteria belonging to eight phyla including Proteobacteria, Acidobacteria, Firmicutes, Fusobacteria, Sphingobacteria, Bacteroidetes, Verrucomicrobiae, and Actinobacteria. There were 14 taxa of bacteria belonging to four phyla including Proteobacteria, Acidobacteria, Planctomycetacia, and Nitrospirae from the stable operation condition where the water quality was well maintained. Nitrospirae was only found under the stable operation condition in this study. Our results further indicated that Nitrospira was dominated by members of the Nitrospira sp. lineages, with a minor fraction related to Nitrospira moscoviensis and an unknown Nitrospira cluster. These great differences of both diversity and composition between two operation conditions suggested that the composition of the microbial community varied with the degree of water quality in the recirculating aquaculture system of S. barcoo.

Biochemical and ultrastructural changes in the hepatopancreas of Bellamya aeruginosa (Gastropoda) fed with toxic cyanobacteria.

This study was conducted to investigate ultrastructural alterations and biochemical responses in the hepatopancreas of the freshwater snail Bellamya aeruginosa after exposure to two treatments: toxic cyanobacterium (Microcystis aeruginosa) and toxic cyanobacterial cells mixed with a non-toxic green alga (Scendesmus quadricauda) for a period of 15 days of intoxication, followed by a 15-day detoxification period. The toxic algal suspension induced a very pronounced increase of the activities of acid phosphatases, alkaline phosphatases and glutathione S-transferases (ACP, ALP and GST) in the liver at the later stage of intoxication. During the depuration, enzymatic activity tended to return to the levels close to those in the control. The activity of GST displayed the most pronounced response among different algal suspensions. Severe cytoplasmic vacuolization, condensation and deformation of nucleus, dilation and myeloid-like in mitochondria, disruption of rough endoplasmic reticulum, proliferation of lysosome, telolysosomes and apoptotic body were observed in the tissues. All cellular organelles began recovery after the snails were transferred to the S. quadricauda. The occurrence of a large amount of activated lysosomes and heterolysosomes and augment in activity of detoxification enzyme GST might be an adaptive mechanism to eliminate or lessen cell damage caused by hepatotoxicity to B. aeruginosa.

[Comparing the primer specificity for betaproteobacterial ammonia-oxidizing bacteria in recirculation aquaculture systems].

OBJECTIVE: To analyze the difference of specificity of four primers for betaproteobacterial ammonia-oxidizing bacteria (beta-AOB) 16S rDNA gene from the biofilm of closed recirculation aquaculture systems. METHODS: We used 16S rDNA clone libraries to describe the beta-AOB diversity. RESULTS: CTO189f/CTO654r produced the highest frequency of beta-AOB-like sequences (67.3%). The amplification performance of primer was noticeably influenced by the biofilm samples. Hereinto, the biofilm of closed recirculation aquaculture systems of Tilapia nilotica resulted in the higher amplification performance of primers. CONCLUSION: CTO189f/CTO654r exhibited the highest specific for beta-AOB 16S rDNA gene from the biofilm of closed recirculation aquaculture systems.