Zhongbo Yu

Temperature Responses of Ammonia-Oxidizing Prokaryotes in Freshwater Sediment Microcosms

In order to investigate the effects of temperature on the abundances and community compositions of ammonia-oxidizing archaea (AOA) and bacteria (AOB), lake microcosms were constructed and incubated at 15°C, 25°C and 35°C for 40 days, respectively. Temperature exhibited different effects on the abundance and diversity of archaeal and bacterial amoA gene. The elevated temperature increased the abundance of archaeal amoA gene, whereas the abundance of bacterial amoA gene decreased. The highest diversity of bacterial amoA gene was found in the 25°C treatment sample. However, the 25°C treatment sample maintained the lowest diversity of archaeal amoA gene. Most of the archaeal amoA sequences obtained in this study affiliated with the Nitrosopumilus cluster. Two sequences obtained from the 15°C treatment samples were affiliated with the Nitrosotalea cluster. N. oligotropha lineage was the most dominant bacterial amoA gene group. Several sequences affiliated to Nitrosospira and undefined N. europaea/NC. mobilis like lineage were found in the pre-incubation and 25°C treatment groups.

Effects of benthic macrofauna bioturbation on the bacterial community composition in lake sediments

Benthic macrofauna are considered to be an important part of the lacustrine ecosystem, and bioturbation may greatly affect the biogeochemical processes and microbial activities in sediments. In the present study, the bacterial community composition in sediments inhabited by 3 different types of benthic macrofauna (Corbicula fluminea, Chironomidae larvae, and tubificid worms) in the shallow and eutrophic Lake Taihu was studied to investigate the different effects of bioturbation on the composition of these communities. Microcosms were constructed, and culture-independent methods, including terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis, were performed to evaluate the bacterial communities. Analysis of similarities (ANOSIM) and multidimensional scaling (MDS) analysis of T-RFLP patterns demonstrated that differences in the bacterial community composition between the control and the macrofauna-inhabited sediments were not as great as expected, although the chemical properties of the sediments changed remarkably. Nevertheless, the dominant bacterial group in each type of macrofauna-inhabited sediment was different. Acidobacteria, Betaproteobacteria, and Deltaproteobacteria were the dominant bacterial groups in sediments inhabited by C. fluminea, tubificid worms, and Chironomidae larvae, respectively. The data obtained in this study are helpful for understanding the effects of bioturbation in a shallow, eutrophic lake.

Network analysis reveals seasonal variation of co-occurrence correlations between Cyanobacteria and other bacterioplankton

Association network approaches have recently been proposed as a means for exploring the associations between bacterial communities. In the present study, high-throughput sequencing was employed to investigate the seasonal variations in the composition of bacterioplankton communities in six eutrophic urban lakes of Nanjing City, China. Over 150,000 16S rRNA sequences were derived from 52 water samples, and correlation-based network analyses were conducted. Our results demonstrated that the architecture of the co-occurrence networks varied in different seasons. Cyanobacteria played various roles in the ecological networks during different seasons. Co-occurrence patterns revealed that members of Cyanobacteria shared a very similar niche and they had weak positive correlations with other phyla in summer. To explore the effect of environmental factors on species-species co-occurrence networks and to determine the most influential environmental factors, the original positive network was simplified by module partitioning and by calculating module eigengenes. Module eigengene analysis indicated that temperature only affected some Cyanobacteria; the rest were mainly affected by nitrogen associated factors throughout the year. Cyanobacteria were dominant in summer which may result from strong co-occurrence patterns and suitable living conditions. Overall, this study has improved our understanding of the roles of Cyanobacteria and other bacterioplankton in ecological networks.

Community composition and assembly processes of the free-living and particle-attached bacteria in Taihu Lake

ABSTRACT Although previous studies have compared the diversity and community composition of free‐living (FL) and particle‐attached (PA) bacterial groups in marine ecosystems, few studies have focused on the FL and PA bacterial communities in large and shallow eutrophic lakes. Furthermore, the assembly processes of the FL and PA bacterial communities have not been investigated. To illustrate the differences between PA (≥5.0 &mgr;m) and FL (0.22‐5.0 &mgr;m) bacterial communities, samples were collected from 13 different sites in Taihu Lake, China. A higher diversity of the PA bacterial group than that of the FL group was observed, and significant differences in bacterial community composition between FL and PA groups were found (analysis of similarity, R = 0.2425, P < 0.001). Moreover, the two groups exhibited different relationships with environmental factors and geographic distance. Environmental factors played more important roles in affecting the FL bacterial community. A deterministic process was found as the primary factor driving the community of FL bacteria in Taihu Lake. However, the PA bacterial group was characterized by insignificant results of partial Mantel tests, which indicated that the community assembly was controlled by unknown processes. &NA; Graphical Abstract Figure. Comparisons between free‐living and particle‐attached bacterial communities in diversity, their relationships with environmental factors and the assembly processes were investigated in this paper.

Contrasting Network Features between Free-Living and Particle-Attached Bacterial Communities in Taihu Lake

Free-living (FL) and particle-attached (PA) bacterial communities play critical roles in nutrient cycles, metabolite production, and as a food source in aquatic systems, and while their community composition, diversity, and functions have been well studied, we know little about their community interactions, co-occurrence patterns, and niche occupancy. In the present study, 13 sites in Taihu Lake were selected to study the differences of co-occurrence patterns and niches occupied between the FL and PA bacterial communities using correlation-based network analysis. The results show that both FL and PA bacterial community networks were non-random and significant differences of the network indexes (average path length, clustering coefficient, modularity) were found between the two groups. Furthermore, the PA bacterial community network consisted of more correlations between fewer OTUs, as well as higher average degree, making it more complex. The results of observed (O) to random (R) ratios of intra- or inter-phyla connections indicate more relationships such as cross-feeding, syntrophic, mutualistic, or competitive relationships in the PA bacterial community network. We also found that four OTUs (OTU00074, OTU00755, OTU00079, and OTU00454), which all had important influences on the nutrients cyclings, played different roles in the two networks as connectors or module hubs. Analysis of the relationships between the module eigengenes and environmental variables demonstrated that bacterial groups of the two networks favored quite different environmental conditions. These findings further confirmed the different ecological functions and niches occupied by the FL and PA bacterial communities in the aquatic ecosystem.

Diversity and composition of bacterial community in the rhizosphere sediments of submerged macrophytes revealed by 454 pyrosequencing

Freshwater lake sediments support a variety of submerged macrophytes that may host groups of bacteria exerting important ecological functions. We collected three kinds of commonly found submerged macrophyte species (Ceratophyllum demersum, Vallisneria spiralis and Elodea nuttallii) to investigate the bacterial community associated with their rhizosphere sediments. High-throughput 454 pyrosequencing and bioinformatics analyses were performed to examine the diversity and composition of the bacterial community. The results obtained indicated that the diversity of the bacterial community associated with the rhizosphere sediments of submerged macrophytes was significantly lower than that of the bulk sediment. Remarkable differences in the bacterial community composition between the rhizosphere and bulk sediments were also observed.

Abundance and community composition of ammonia oxidizers in rhizosphere sediment of two submerged macrophytes

ABSTRACT Ammonium oxidation is both the first and a rate-limiting step in the nitrification process that can be catalysed by ammonia-oxidizing archaea (AOA) or ammonia-oxidizing bacteria (AOB). In this study, the abundance and community composition of AOA and AOB in the rhizosphere sediments of two submerged macrophytes (Ceratophyllum demersum and Potamogeton malainus) were investigated. Physicochemical parameters, including pH, total nitrogen, total phosphorus, ammonia nitrogen, nitrate and organic matter, were measured. The number of copies of both the archaeal and bacterial amoA gene was quantified by real-time PCR and clone libraries were constructed for both AOA and AOB. The abundance of archaeal amoA gene ranged from 3.83 × 106 to 4.23 × 106 copies per gram of dry sediment and no significant difference was found among the three treatment groups (one control group and two submerged macrophyte groups). The abundance of bacterial amoA gene ranged from 2.68 × 106 to 8.05 × 107 copies per gram of dry sediment. Bulk sediment maintained significantly higher copy numbers of bacterial amoA gene than those of C. demersum rhizosphere sediment. The diversity of archaeal amoA gene was higher in the rhizosphere sediment of C. demersum; however, the diversity of bacterial amoA gene was relatively lower in rhizosphere sediment of both macrophytes.

Heterogeneity of interactions of microbial communities in regions of Taihu Lake with different nutrient loadings: A network analysis

To investigate the differences in the interactions of microbial communities in two regions in Taihu Lake with different nutrient loadings [Meiliang Bay (MLB) and Xukou Bay (XKB)], water samples were collected and both intra- and inter-kingdom microbial community interactions were examined with network analysis. It is demonstrated that all of the bacterioplankton, microeukaryotes and inter-kingdom communities networks in Taihu Lake were non-random. For the networks of bacterioplankton and inter-kingdom community in XKB, higher clustering coefficient and average degree but lower average path length indexes were observed, indicating the nodes in XKB were more clustered and closely connected with plenty edges than those of MLB. The bacterioplankton and inter-kingdom networks were considerably larger and more complex with more module hubs and connectors in XKB compared with those of MLB, whereas the microeukaryotes networks were comparable and had no module hubs or connectors in the two lake zones. The phyla of Acidobacteria, Cyanobacteria and Planctomycetes maintained greater cooperation with other phyla in XKB, rather than competition. The relationships between microbial communities and environmental factors in MLB were weaker. Compared with the microbial community networks of XKB, less modules in networks of MLB were significantly correlated with total phosphorous and total nitrogen.

Effects of macrobenthic bioturbation on the abundance and community composition of ammonia-oxidizing prokaryotes under different temperatures

ABSTRACT In order to investigate the effects of macrobenthos on the abundance and community composition of ammonia-oxidizing prokaryotes under different temperature conditions, laboratory microcosms containing two kinds of macrobenthos (Corbicula fluminea and Tubificid worms) were constructed. Real-time polymerase chain reaction (PCR) and clone libraries were applied to analyze the ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities in the surface sediments. The lowest abundances of the archaeal and bacterial amoA gene were found in the samples cultured under 28 °C (archaeal amoA gene abundance, 2.71 × 106 copies/g dry sediment; bacterial amoA gene abundance, 1.17 × 107 copies/g dry sediment) of the C. fluminea group. However, there was no significant difference in terms of the abundance of archaeal amoA gene in all Tubificid worms treatment groups. Compared to the community composition of AOB, greater variations in the community composition of AOA were observed among the three different temperature groups.

Emergent macrophytes modify the abundance and community composition of ammonia oxidizers in their rhizosphere sediments

Ammonia oxidation is a crucial process in global nitrogen cycling, which is catalyzed by the ammonia oxidizers. Emergent plants play important roles in the freshwater ecosystem. Therefore, it is meaningful to investigate the effects of emergent macrophytes on the abundance and community composition of ammonia oxidizers. In the present study, two commonly found emergent macrophytes (Zizania caduciflora and Phragmitas communis) were obtained from freshwater lakes and the abundance and community composition of the ammonia‐oxidizing prokaryotes in the rhizosphere sediments of these emergent macrophytes were investigated. The abundance of the bacterial amoA gene was higher in the rhizosphere sediments of the emergent macrophytes than those of bulk sediments. Significant positive correlation was found between the potential nitrification rates (PNRs) and the abundance of bacterial amoA gene, suggesting that ammonia‐oxidizing bacteria (AOB) might play an important role in the nitrification process of the rhizosphere sediments of emergent macrophytes. The Nitrosotalea cluster is the dominant ammonia‐oxidizing archaea (AOA) group in all the sediment samples. Analysis of AOB group showed that the N. europaeal cluster dominated the rhizosphere sediments of Z. caduciflora and the bulk sediments, whereas the Nitrosospira cluster was the dominant AOB group in the rhizosphere sediments of P. communis.