Jiangyu Dai

Comparing sediment bacterial communities in the macrophyte-dominated and algae-dominated areas of eutrophic Lake Taihu, China.

Bacterial community structure and the effects of several environmental factors on bacterial community distribution were investigated in the sediment of the macrophyte-dominated and algae-dominated areas in a large, shallow, eutrophic freshwater lake (Lake Taihu, China). Surface sediment samples were collected at 6 sampling sites (3 sites from each of the 2 areas) on 15 February and 15 August 2009. Based on cluster analysis of the DGGE banding patterns, there were significant seasonal variations in the structure of the sediment bacterial community in the macrophyte- and algae-dominated areas, and site-specific variation within an area and between 2 areas. However, there were no significant between-area variations due to the large within-area variation. Analysis of DNA sequences showed that there were differences in the species composition of the sediment bacteria between the macrophyte- and algae-dominated area clone libraries. In the macrophyte-dominated area library, the bacterial community was dominated by Deltaproteobacteria, Verrucomicrobia, Acidobacteria, Bacteroidetes, Gammaproteobacteria, and Betaproteobacteria. OP10 was found in the library of this area but not in the algae-dominated area library. The algae-dominated area library was dominated by Betaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, and Acidobacteria. Cyanobacteria, Alphaproteobacteria, and Planctomycetes were found in this area library but not in the macrophyte-dominated area library. Canonical correspondence analysis demonstrated that total phosphorus and water temperature were the dominant environmental factors affecting bacterial community composition in the sediment.

Decomposition of Microcystis blooms: implications for the structure of the sediment bacterial community, as assessed by a mesocosm experiment in Lake Taihu, China.

The effect of decomposition of Microcystis blooms on the sediment bacterial communities was investigated in a 14‐day mesocosm experiments under dark and anoxic condition with three differing levels of Microcystis spp. biomass (from 20 to 2000 µg L−1) as measured by chlorophyll‐a (Chl‐a) concentration in the water column. Sediment samples were collected on days 0 and 14 for bacterial community composition (BCC) analysis, based on rapid decreases in the Chl‐a concentration of water column. The BCC was determined by denaturing gradient gel electrophoresis and sequencing of predominant bands. The results showed that after Microcystis decomposition (day 14), the bacterial phylotype diversity in the sediment increased in enclosures with added Microcystis, and the relative abundance of bacteria affiliated with Bacteroidetes and Verrucomicrobia strongly increased. Canonical correspondence analysis showed that organic matter and Chl‐a contributed significantly to the changes in sediment bacterial communities during Microcystis decomposition. The present results demonstrate Microcystis decomposition may directly and indirectly influence the BCC of the sediment.

Recovery of novel alkaline phosphatase-encoding genes (phoX) from eutrophic Lake Taihu.

To expand current knowledge on the molecular aspects of alkaline phosphatase PhoX in shallow eutrophic freshwaters, we investigated the genetic diversity and abundance of the PhoX-encoding gene (phoX) in 4 ecological regions in Lake Taihu, China, following a gradient in total phosphorus concentrations ranging from hypereutrophic to mesotrophic. Bacterial phoX was heterogeneously distributed with the highest diversity in the eutrophic regions and the highest abundance in the mesotrophic Xukou Bay. The concentrations of total phosphorus and enzymatically hydrolyzable phosphorus determined the distribution of bacterial phoX in Lake Taihu. Most (70.8%) of the phoX-translated proteins had <90% similarity to the PhoX proteins in the GenBank database, suggesting the presence of novel phoX genotypes in Lake Taihu. The low overlap in phoX genotypes (15.8%) between Lake Taihu and some marine ecosystems, and the dominance of the translated proteins most similar to the Alphaproteobacteria-affiliated PhoX, demonstrate the uniqueness of PhoX in eutrophic freshwaters.

The response of epiphytic microbes to habitat and growth status of Potamogeton malaianus Miq. in Lake Taihu.

To investigate the effects of different habitats and plant growth status on abundance, biomass and community structure of epiphytic microbes, Potamogeton malaianus Miq. at two different habitats (Gonghu Bay and East Taihu) in Lake Taihu were collected in June, August and November (corresponding to the period of development of submerged macrophytes). The relative abundance of major epiphytic algae groups was determined with high performance liquid chromatography (HPLC), and the structures and dynamics of epiphytic bacteria were assessed by terminal restriction fragment length polymorphism (T‐RFLP) analysis. Results showed that the biomass of epiphytic microbes was not significant difference between the two sites, and the analysis of similarity found no significant intra‐lake heterogeneity in community structure, but the temporal heterogeneity of epiphytic microbes was significant, which linked to the growth state of submerged macrophytes and water temperature. The difference in community structure between June and August was larger than that between August and November at each site, indicating that the growth status of submerged macrophytes has a greater impact on the community structure of epiphytic microbes than the seasonal variation of environmental conditions.

Bacterial community changes along a salinity gradient in a Chinese wetland

We analyzed the composition and diversity of a bacterial community to determine its response to increasing salinity in the Xiangsi Lake wetland in the arid region of northwest China. We studied 12 sites, ranging from freshwater to saltwater habitats, using polymerase chain reaction (PCR)-based terminal restriction fragment length polymorphism (T-RFLP) and sequencing of the 16S rRNA genes of 5 selected samples. Cluster analysis and phylogenetic analysis revealed that the bacterial community changed significantly in response to increased salinity within the small-scale wetland (50.8 km(2)). Detailed analysis showed that (i) Betaproteobacteria can maintain balanced growth over a salinity range (from 0.34 to 6.86 g/L) through intergenus changes in community structure, followed by a sharp decrease in relative abundance (from 62.2% to 16.0%) when salinity reaches 26.18 g/L; (ii) salt-sensitive and halophobic taxa were progressively replaced by halotolerant and halophilic taxa with increasing salinity; (iii) bacterial diversity was lowest at intermediate salinity levels (6.86 g/L); and (iv) an increasing percentage of unclassified bacterial taxa were found with increasing salinity. This study has implications to improve understanding of bacterial community response to water salinization.

Comparative analysis of alkaline phosphatase-encoding genes (phoX) in two contrasting zones of Lake Taihu.

Limnetic habitats that are dominated by either algae or macrophytes represent the 2 dominant ecosystems in shallow lakes. We assessed seasonal variations in the diversity and abundance of alkaline phosphate-encoding genes (phoX) in these 2 zones of Lake Taihu, which is a large, shallow, eutrophic lake in China. There was no significant difference in seasonal mean phoX diversity between the 2 zones, whereas the seasonal mean phoX abundance in the macrophyte-dominated region was higher than that in the algae-dominated region. The bulk of the genotypes in the 2 regions were most similar to the alphaproteobacterial and betaproteobacterial phoX. Genotypes most similar to phoX affiliated with Betaproteobacteria were present with greater diversity in the macrophyte-dominated zone than in the algae-dominated zone. In the algae-dominated zone, the relative proportion of genotypes most similar to cyanobacterial phoX was highest (38.8%) in summer. In addition to the different genotype structures and environmental factors between the 2 stable states, the lower gene abundances and higher alkaline phosphatase activities in Meiliang Bay in summer than those in Xukou Bay reveals different organophosphate-mineralizing modes in these 2 contrasting habitats.

Bacterial Community Composition in Oligosaline Lake Bosten: Low Overlap of Betaproteobacteria and Bacteroidetes with Freshwater Ecosystems.

Oligosaline lakes in arid regions provide indispensable water resources for humans; however, information on the bacterial community composition (BCC) of this ecosystem is limited. In the present study, we explored seasonal and vertical variations in BCC in Lake Bosten, a unique oligosaline lake (1.2‰ salinity) in arid, northwestern China, using denaturing gradient gel electrophoresis and 16S rRNA gene sequencing. We obtained 544 clones and 98 operational taxonomic units (OTUs) from six clone libraries. The top 10 OTUs represented 59.4% of the entire bacterial community. Betaproteobacteria (22.1%), Gammaproteobacteria (19.9%), Bacteroidetes (18.8%), and Firmicutes (11.4%) dominated in Lake Bosten. Although seasonal variations were recorded in BCC, the vertical changes observed were not significant. Water temperature and salinity were the most important factors shaping the dynamics of BCC. A low degree of overlap was observed in BCC between Lake Bosten and freshwater ecosystems, especially for Betaproteobacteria and Bacteroidetes. An RDP seqmatch analysis showed that 169 sequences (31%) were novel bacterial sequences (<97% similarity to the closest sequences in GenBank), which suggested that specific indigenous bacteria inhabit this oligosaline environment. Our results support bacterial endemicity being more common than previously considered, particularly in oligosaline lakes. An analysis of these communities may reveal how bacteria respond to increases in salinity and nutrients in the early stage of salinization and eutrophication.

Effects of Trophic Status and Temperature on Communities of Sedimentary Ammonia Oxidizers in Lake Taihu

To probe the responsiveness of ammonia oxidizers to environmental factors along different seasons in eutrophic lakes, we investigated the seasonal distribution of community structure and abundance of ammonia oxidizers in relation to the environmental factors in sediments within eutrophic Lake Taihu. We used terminal restriction fragment length polymorphism and real-time PCR to target the molecular biomarker gene of ammonia monooxygenase subunit A. Both phylogenetic analyses and the dominant terminal restriction fragments showed that archaeal ammonia oxidizers belonged to the Crenarchaeota Group I.1a and Crenarchaeota Group I.1b, while bacterial ammonia oxidizers included both Nitrosomonas-like and Nitrosospira-like species. The bacterial ammonia oxidizers were more diverse but less abundant than the ammonia-oxidizing archaea. Significant spatial differences in the ammonia-oxidizing archaeal community structure and abundance were found between the algae-dominated and the macrophyte-dominated regions, which suggest sedimentary trophic status is an important influence. In contrast, there was no significant correlation between bacterial ammonia oxidizer communities and sedimentary trophic status. There were pronounced seasonal variations in ammonia-oxidizing bacterial community structures, reflected by the absence of the Nitrosospira-like species in August and their presence in other months. Both the abundances of archaeal and bacterial ammonia oxidizers were highest in February. The correlation analyses between prokaryotic ammonia oxidizer communities and the investigated physicochemical variables demonstrated that the overlying water temperature was the dominant factor influencing the seasonal variations in ammonia oxidizer community structure and abundance. Supplemental materials are available for this article. Go to the publishers online edition of Geomicrobiology Journal to view the supplemental file.

Photosynthetic response of Vallisneria natans (Lour.) Hara (Hydrocharitaceae) to increasing nutrient loadings

To explore the effects of water column nutrient loading on photosynthesis of the submerged macrophyte Vallisneria natans (Lour.) Hara during the growth season (June to October), we determined the diurnal and seasonal variation in rapid light curves of plants cultivated under 4 different nutrient concentrations (N-P [mg L−1]: (1) 0.5, 0.05; (2) 1.0, 0.1; (3) 5.0, 0.5; (4) 10.0, 1.0). Nutrient concentration significantly affected the magnitude of the rapid light curves of V. natans, but not the direction of their diurnal variations. At low nutrient conditions (N-P 1 [mg L−1]: 0.5, 0.05), the maximum relative electron transport rate (rETRmax) and minimum saturating irradiance (Ek) derived from rapid light curves were significantly lower than those of other treatments, and their seasonal variations were suppressed. These results indicated that photosynthesis of V. natans was inhibited by the lack of nutrients in water column. At high nutrient conditions (N-P 4, [mg L−1]: 10.0, 1.0), there was an increase in photosynthetic rate in the light-limited region of rapid light curve (α), and a decrease in rETRmax and Ek, relative to moderate nutrient conditions (N-P 2, [mg L−1]: 1.0, 0.1). In addition, at high nutrient concentrations, the rapid light curves of V. natans reached a plateau, and then markedly declined compared with those at the lower nutrient levels, especially in July and August. These results suggested that V. natans were adapted to low-light environments in the high-nutrient loading treatment.

An ultrasonic method for separation of epiphytic microbes from freshwater submerged macrophytes

Epiphytic microbes are common inhabitants of freshwater submerged macrophytes, which play an important role in aquatic ecosystems. An important precondition for studying the epiphytic microbes is having an effective method of separating the attached microbes from the host macrophytes. We developed an ultrasound‐based method for separating epiphytic microbes from freshwater submerged macrophytes, optimized the conditions of ultrasonic separation with an orthogonal experimental design, and compared the optimized ultrasonic method with manual separation. This method can be particularly useful for freshwater submerged macrophytes having a complex morphology.