Spatio-temporal dynamic diversity of bacterial alkaline phosphatase phoD gene and its environmental drivers in sediments during algal blooms: A case study of shallow Lake Taihu.

Bacterial alkaline phosphatase encoded by the phoD gene is essential for phosphorus (P) cycling in ecosystems. Until now, knowledge of the phoD gene diversity in shallow lake sediments is still lacking. In this study, from early to late stage of cyanobacterial blooms, we investigated the dynamic changes of the abundance of phoD gene (hereafter phoD abundance) and phoD-harboring bacterial community composition (hereafter phoD-harboring BCC) in sediments from different ecological regions of Lake Taihu, the third-largest shallow freshwater lake in China, as well as explored their environmental driving factors. Results showed that phoD abundance in the sediments of Lake Taihu showed spatiotemporal heterogeneity. The highest abundance was found in macrophyte-dominated area (mean 3.25*106copies/g DW), where Haliangium and Aeromicrobium were identified as the major contributors. Due to the negative impact of Microcystis species, phoD abundance decreased significantly (by 40.28% on average) during cyanobacterial blooms in all other regions except the estuary area. The phoD abundance in sediment was positively correlated with total organic carbon (TOC) and total nitrogen (TN). However, the relationship between phoD abundance and alkaline phosphatase activity (APA) varied with time, showing positive correlation (R2 = 0.763, P < 0.01) in the early stage of cyanobacterial blooms, but not (R2 = -0.052, P = 0.838) in the later stage. The predominant phoD-harboring genera in sediments were Kribbella, Streptomyces and Lentzea, all of which belong to Actinobacteria. Non-metric multidimensional scaling (NMDS) analysis revealed that the spatial heterogeneity of phoD-harboring BCC in the sediments of Lake Taihu was significantly higher than the temporal heterogeneity. TP and sand were the principle environmental factors affecting the phoD-harboring BCC in the sediments of the estuary area, while DO, pH, organic phosphorus (Po) and diester phosphorus were the key driving factors for other lake regions. We concluded that the C, N, and P cycles in sediments might work in concert. This study extends the understanding of the phoD gene diversity in shallow lake sediments.

Response of extracellular and intracellular alkaline phosphatase in Microcystis aeruginosa to organic phosphorus.

Cyanobacterial blooms caused by Microcystis have become a menace to public health and water quality in the global freshwater ecosystem. Alkaline phosphatases (APases) produced by microorganisms play an important role in the mineralization of dissolved organic phosphorus (DOP) into orthophosphate (Pi) to promote cyanobacterial blooms. However, the response of extracellular and intracellular alkaline phosphatase activity (APA) of Microcystis to different DOP sources is poorly understood. In this study, we compared the growth of M. aeruginosa on two DOP substrates (ß-glycerol-phosphate (ß-GP) and lecithin (LEC)) and monitored the changes of P fractions and the extra- and intracellular APA under different P sources and concentrations. M. aeruginosa can utilize both ß-GP and LEC to sustain its growth, and the bioavailability of LEC was greater than ß-GP. For the ß-GP treatment, there was no significant difference in the algal growth at different concentrations (P > 0.05), while the algal growth in the LEC treatment groups was significantly affected by concentrations (P < 0.05). The results showed that intracellular APA of M. aeruginosa could be detected in all DOP treatment groups and generally higher than extracellular APA. In addition, the intracellular APA per cell increased first and then decreased in all DOP treatment groups. Compared with the ß-GP treatment, M. aeruginosa in the LEC groups could secret more extracellular APA.

Suspended particles phoD alkaline phosphatase gene diversity in large shallow eutrophic Lake Taihu.

The bacterial phoD gene encodes alkaline phosphatase plays an important role in the release of bioavailable inorganic phosphorus (P) from organic P in environmental systems. However, phoD gene diversity in suspended particles in shallow freshwater lakes is poorly understood. In this study, we explored the potential relationship between environmental factors and phoD phosphatase gene in suspended particles in different ecosystem types (lake zones) in Lake Taihu, a large shallow eutrophic lake in China. Quantitative PCR and high-throughput sequencing were used to analyze phoD gene abundance and the phoD-harboring bacterial community composition. Our results indicate that the distribution of phoD gene abundance in suspended particles had a high spatiotemporal heterogeneity. The phoD gene abundance in each lake zone decreased significantly from June to September. The dominant phoD-harboring phylum in all samples was Actinobacteria, followed by Proteobacteria, Cyanobacteria and Gemmatimonadetes. The first predominant phoD-harboring genera varied among samples, but most of them belonged to phylum Actinobacteria. Driven by different environmental factors, the phoD-harboring bacterial community structure varied with sampling month and ecosystem type. Nitrate and ammonia nitrogen were the main environmental drivers of phoD-harboring bacterial community in suspended particles in the river mouth zone, while water pH and dissolved oxygen were important factors for the algae-dominated, macrophyte-dominated and central lake zones.

[Influence of Submerged Plants on Microbial Community Structure in Sediment of Hongze Lake].

Phospholipid fatty acids (PLFAs) method was applied to analyze the influence of submerged plants on sediment microbial community structure, in order to investigate the changes of sediment microbial community structure for different kinds of the submerged plants in different growth periods. Particularly, Potamogeton crispus L., Potamogeton pectinatus L and the mixed group were chosen as the typical submerged plants in Hongze Lake for investigation in this paper. The results indicated that the change of total PLFAs in different periods was significant, on the contrary, the PLFA change for different groups in the same period was insignificant. The values of G⁺ PLFA/G⁻ PLFA in the submerged plant group were also highly related to the different growth periods, which demonstrated that the root function of the submerged plant had a severe impact on the microbial community in sediment. Furthermore, some environmental factors, such as Temperature, pH, TOC and DO, were correlated to characteristic phospholipid of PLFAs in sediment, which means the environmental factors could also affect the microbial community structure.

[Characteristics of Organic Phosphorus Fractions in the Sediments of the Black Water Aggregation in Lake Taihu].

Potential release of phosphorus in lake sediments depends largely on the fractions and distribution of organic phosphorus. MaoDu was chosen as the research area in the west of Lake Taihu. The chemical forms of the surface sediments were investigated by the Ivannoff extraction methods. The results showed that the main organic phosphorus form of sediments at different sampling places was humic acid-OP. It accounted for 35% of the total organic phosphorus. Horizontal distribution: Total organic phosphorus content from the shore to the middle of total showed a trend of rising after decline; vertical distribution: Total organic phosphorus content was the lowest in 2-6 cm and the highest in 4-8 cm. Various phosphorus content followed the order of humic acid-OP > residual-OP > HCl-OP > fulvic acid-OP; the relative content of NaHCO3-OP in the total organic phosphorus content showed a trend of rising followed by reduction and then rising again from the shore to the middle, cyanobacteria residue deposition increased the content of NaHCO3-OP in sediment. Contents of NaHCO3-OP and humic acid-OP both first reduced, then increased and finally reduced in the vertical distribution, the content of NaHCO3-OP was the lowest in 4-6 cm and humic acid-OP was the highest in 4-8 cm. HCl-OP and fulvic-OP decreased with increasing depth in the vertical distribution. The content of residual-OP showed stable tendency in the vertical direction and was about 45 µg·g-1. Labile OP and pH, DO, the depth of water were significantly negatively correlated, OM and NaOH-Pi were significantly correlated with total organic phosphorus, labile OP, moderately labile OP and nonlabile OP. Three components of organic phosphorus had bio-availability and played an important role in lake eutrophication. The increase of the content of labile OP might promote the black water aggregation (BWA) in cyanobacteria accumulation.

Biosorption properties of hexavalent chromium on to biomass of tobacco-leaf residues.

Equilibrium isotherms of Cr(VI) uptake by tobacco-leaf residues, under controlled solution pH and temperature, were obtained with batch uptake experiments. Batch uptake kinetics under different initial Cr(VI) concentrations was also obtained. The results showed that Cr(VI) uptake capacities of the tobacco-leaf residues were up to 113.2 mg g(-1) (dry wt). The uptake capacity was found to be dependent on solution pH and the maximum values were obtained at a pH of around 1.0. On the other hand, the effect of temperature the uptake capacity was found to be small. All equilibrium isotherms were well correlated with the standard Langmuir equation. Kinetics profiles showed that the uptake process was fast, and equilibrium was reached within 30 minutes of mixing contact. The role of polyphenols in Cr(VI) biosorption was studied and the results indicated that complex formation with Cr(VI) may be an important mechanism for Cr(VI) removal. The study indicated that abundantly available tobacco-leaf residues can be used as efficient biosorbent materials for Cr(VI) removal from wastewater.

Variations of alkaline phosphatase activity and P fractions in sediments of a shallow Chinese eutrophic lake (Lake Taihu).

The distribution of alkaline phosphatase activity (APA) and P fractions in sediment cores and the relationship between them were studied in a shallow Chinese freshwater lake (Lake Taihu). Sediment cores were collected from four sites, characterized by different degrees of eutrophication in June 2004. Sediment P was fractionated into Fe/Al-P, Ca-P, organic P (OP), inorganic P (IP) and total P (TP). The former two species made the largest contribution to the sediment P pool. Results show that trophic status and hydrological conditions have great impact on the APA of the sediments. The order of the APA in sediments was conjectured to be: macrophyte dominated lake>transitional lake>algal dominated lake. APA profiles follow a similar downcore decreasing trend. There was a positive relationship between the APA and the TP, IP. The multiple linear regression equation of the APA and P fractions is: APA=-97+0.768TP-0.985Fe/Al-P.