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Phosphorus (P) fractionation and sorption behavior as well as the abundance and community composition of phosphorus-solubilizing bacteria (PSB) in sediments, including inorganic phosphate-solubilizing bacteria (IPB) and organic phosphate-mineralizing bacteria (OPB), were investigated in 27 sampling sites of five sections in the Three Gorges Reservoir (TGR) in December 2012. The calcium-bound phosphorus (CaCO 3 ∼P) accounted for the largest part for P fractions in the sediment of TGR, which was paralleled with IPB outnumbering OPB. Furthermore, some PSB isolates, such as Micromonospora sp., Aminobacter sp., and Arthrobacter sp., were shared by the IPB and OPB. Thus, some IPB species functioned as OPB and vise versa, which could be further reflected by a negative and significant relationship between PSB (IPB + OPB) number and content of CaCO 3 ∼P together with acid-soluble organic phosphorus (ASOP). Spatially, the highest ASOP content in the section Mudong and the highest CaCO 3 ∼P plus iron-bound phosphorus (Fe(OOH)∼P) as well as equilibrium phosphorus concentration (EPC 0 ) in the sections of Yunyang and Zigui due to sediment sequestration by the dam, as well as the positive relationship between EPC 0 and the ratios of different phosphorus species and phosphorus sorption maximum (Q max ), jointly indicated pathway diversification and potential risk of phosphorus release mediated by PSB in TGR.

The coupled nitrification-denitrification process plays a pivotal role in cycling and removal of nitrogen in aquatic ecosystems. In the present study, the communities of ammonia oxidizers and denitrifiers in the sediments of 2 basins (Guozhenghu Basin and Tuanhu Basin) of a large urban eutrophic lake (Lake Donghu) were determined using the ammonia monooxygenase subunit A (amoA) gene and the nitrite reductase gene. At all sites of this study, the archaeal amoA gene predominated over the bacterial amoA gene, whereas the functional gene for denitrification nirK gene far outnumbered the nirS gene. Spatially, compared with the Tuanhu Basin, the Guozhenghu Basin showed a significantly greater abundance of the archaeal amoA gene but less abundance of the nirK and nirS genes, while there was no significant difference of bacterial amoA gene copy numbers between the 2 basins. Unlike the archaeal amoA gene, the nirK gene showed a significant difference in community structure between the 2 basins. Archaeal amoA diversity was limited to the water-sediment cluster of Crenarchaeota, in sharp contrast with nirK for which 22 distinct operational taxonomic units were found. Accumulation of organic substances were found to be positively related to nirK and nirS gene copy numbers but negatively related to archaeal amoA gene copy numbers, whereas the abundance of the bacterial amoA gene was related to ammonia concentration.

Ammonia oxidation plays a pivotal role in the cycling and removal of nitrogen in aquatic ecosystems. Recent findings have expanded the known ammonia-oxidizing prokaryotes from Bacteria to Archaea. However, the relative importance of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in nitrification is still debated. Here we showed that, in two large eutrophic lakes in China (Lake Taihu and Lake Chaohu), the abundance of AOA and AOB varied in opposite patterns according to the trophic state, although both AOA and AOB were abundant. In detail, from mesotrophic to eutrophic sites, the AOA abundance decreased, while the AOB increased in abundance and outnumbered the AOA at hypertrophic sites. In parallel, the nitrification rate increased along these trophic gradients and was significantly correlated with both the AOB abundance and the numerical ratio of AOB to AOA. Phylogenetic analysis of bacterial amoA sequences showed that Nitrosomonas oligotropha- and Nitrosospira-affiliated AOB dominated in both lakes, while Nitrosomonas communis-related AOB were only detected at the eutrophic sites. The diversity of AOB increased from mesotrophic to eutrophic sites and was positively correlated with the nitrification rate. Overall, this study enhances our understanding of the ecology of ammonia-oxidizing prokaryotes by elucidating conditions that AOB may numerically predominated over AOA, and indicated that AOA may play a less important role than AOB in the nitrification process of eutrophic lakes., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The impacts of different nutrient additions (N + P, N + P + C, 4N + P, 4N + P + C, N + 2P) on the growth of algae and bacteria were studied in a microcosm experiment. Since alkaline phosphatase activity (APA) provides an indication of phosphorus deficiency, the higher value for algal APA in the treatments with excess nitrogen and for bacterial APA in the treatments with excess carbon suggested that, algal and bacterial phosphorus-limited status were induced by abundant nitrogen and carbon input, respectively. Bacterial phosphorus-limited status was weakened due to higher bacterial competition for phosphorus, compared to algae. In comparison with the bacterial and specific bacterial APA, higher values of algal and specific algal APA were found, which showed a gradual increase that coincided with the increase of chlorophyll a concentration. This fact indicated not only a stronger phosphorus demand by algae than by bacteria, but also a complementary relationship for phosphorus demand between algae and bacteria. However, this commensalism could be interfered by glucose input resulting in the decline of chlorophyll a concentration. Furthermore, the correlation between bacterial numbers and chlorophyll a concentration was positive in treatments without carbon and blurry in treatments with carbon. These observations validate a hypothesis that carbon addition can stimulate bacterial growth justifying bacterial nutrient demand, which decreases the availability of nutrients to algae and affects nutrient relationship between algae and bacteria. However, this interference would terminate after algal and bacterial adaption to carbon input., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

Purpose: Dissimilatory nitrate (NO3−) reduction to ammonium (DNRA) is a significant nitrogen (N) transformation process in estuarine ecosystem. The objectives of this study were to clarify the key biotic and abiotic factors influencing DNRA potential rates in Xiamen Bay. Methods: We characterized DNRA, anammox, and denitrification rates through 15 N isotope tracer experiments. Then quantitative real-time PCR and high-throughput sequencing analysis were conducted to analyze the abundance and community of DNRA bacteria. Spearman correlation analysis was used to understand the relationships of DNRA rate, nrfA abundance, and community with environmental characteristics. Results: Denitrification was dominated in dissimilatory NO3− reduction processes in sediments of Xiamen Bay. Bacteroidetes and Proteobacteria were the main phyla of DNRA bacteria and Pelobacter was the dominant genus. Spearman correlation analysis showed that DNRA rate was significantly positively correlated with nitrite (NO2−) and NO3− in interstitial water, total organic carbon (TOC), acid volatile sulfide (AVS), and total nitrogen (TN) in sediment. Besides, nrfA abundance showed positive correlations with DNRA rate, NO2−, TOC, AVS, and TN. Furthermore, AVS and nrfA abundance were positively correlated with Pelobacter. Conclusion: DNRA rates were limited by sulfide, organic carbon, abundances of nrfA gene, and DNRA bacteria. Sulfide and organic carbon shaped DNRA bacterial community thereby controlled DNRA rate. Heterotrophic sulfide-producing genus (Pelobacter) prevailed among DNRA bacteria, which might support autotrophic DNRA bacteria. In this way, heterotrophic and autotrophic DNRA bacteria were connected through sulfide-producing genus and acted as a whole functional community. [ABSTRACT FROM AUTHOR]

The shift of mutualistic nutrient relationship among algae, free-living and attached bacteria as well as the effects on algal growth were conducted in experimental mesocosm in which three nutrient addition treatments, including excessive phosphorus (P), excessive carbon (C) and nitrogen (N) to P as 16:1, were designed. The algal community composition did not change greatly in all treatments. The mutualism between algae and its attached bacteria was confirmed in treatments with excessive P and N:P as 16:1, in terms of the significantly higher dissolved organic nutrients derived from algae, extracellular enzyme activities produced by attached bacteria with high abundance and production. Interestingly, compared to treatment with excessive P, this mutualism was even more pronounced in treatment with N:P as 16:1, and resulted in stronger ecological function expressed as higher chlorophyll a content, indicating the importance of nutrient addition with stoichiometric equilibrium. On the contrary, excessive organic C input led to the nutrients competition between algae and free-living bacteria due to the latter's growth in biomass and luxury uptake of inorganic nutrients, which finally limited algal growth. Our results indicated that mutualistic relationship among algae, free-living and attached bacteria could be shifted by nutrient equilibrium (N:P ratio) and dissolved organic C availability. [ABSTRACT FROM AUTHOR]

The impacts of nutrient amendment termination on the growth strategies of algae and bacteria were conducted in experimentally designed mesocosm in which two different phosphorus (P) dosages were treated. The algal community composition did not change greatly in Group A (low phosphorus) and Group B (high phosphorus). In Group A, the secretion of bacterial alkaline phosphatase (AP) after nutrient termination stimulated bacterial phosphorus acquisition, which caused the decrease in algal phosphorus levels, in terms of the increase of bacterial abundance and bacterial production, as well as the decrease in chlorophyllaand particulate organic carbon. The algal collapse resulted in dissolved organic carbon secretion, further fuelling bacterial growth. In Group B, excess phosphorus input urged algae to store phosphorus as poly-phosphate. When phosphorus input ceased, in order to maintain their used high phosphorus demand, algae strengthened to gain phosphorus through the hydrolysis of dissolved organic phosphorus in water column and ploy-phosphate inside the cells by AP, evidenced by high algal alkaline phosphatase activity, algal growth continuation, and bacterial growth decline. These facts indicated that phosphorus content should reduce to a lower level than expected, so that algal bloom can be effectively controlled in eutrophic water bodies. [ABSTRACT FROM AUTHOR]

Sediment phosphorus (P) release accelerates lake eutrophication, while retention capacity and release potential of different P fractions, calcium-bound P (CaCO3∼P) in particular, still remains unclear. Fractionation and sorption behaviors of phosphorus were studied in sediment of a Chinese shallow lake (Lake Wabu) and two inflowing rivers from December 2011 to December 2012. Abundance of P releasing bacteria was analyzed, and their main species were isolated using a culture-dependent method and identified by their 16S rDNA sequences. CaCO3∼P release abilities of these bacteria were also tested. In sediments of both the lake and rivers studied, the rank order of the different P extracts was CaCO3∼P > iron-bound P > acid-soluble organic P > hot NaOH-extractable organic P. At the same time, CaCO3∼P content and equilibrium P concentration (EPC0) values in river sediments were significantly higher than those in the lake. Additionally, EPC0changes non-monotonically with increasing CaCO3∼P content, forming a V-shaped curve, with the lowest EPC0at an intermediate CaCO3∼P content (around 180 mg kg−1). Below this threshold, CaCO3∼P was a component strengthening P retention; moreover, CaCO3∼P became an active species responsible for P release. Noticeably, between the two parts divided by this threshold, the differences in abundance of inorganic phosphorus solubilizing bacteria (IPB) and organic phosphorus mineralizing bacteria (OPB) were insignificant and the dominant IPB species clustered together. By contrast, OPB was distinguished from each other, whose dominant species isolated from the part with higher CaCO3∼P content, namelyNovosphingobium sp., exhibited a stronger ability to solubilize CaCO3∼P. Shortly, with lower content, CaCO3∼P tends to stabilize P in sediment; while with higher content or under eutrophic condition, it shifted into P source, with some OPB species becoming the main factors to drive its release. [ABSTRACT FROM AUTHOR]

Bacterial and phytoplankton communities are known to be in close relationships, but how natural and anthropogenic stressors can affect their dynamics is not fully understood. To study the response of microbial communities to environmental and human-induced perturbations, phytoplankton and bacterial communities were seasonally monitored in a Mediterranean coastal ecosystem, Syracuse Bay, where multiple conflicts co-exist. Quali-quantitative, seasonal surveys of the phytoplankton communities (diatoms, dinoflagellates and other taxa), the potential microbial enzymatic activity rates (leucine aminopeptidase, beta-glucosidase and alkaline phosphatase) and heterotrophic culturable bacterial abundance, together with the thermohaline structure and trophic status in terms of nutrient concentrations, phytoplankton biomass (as Chlorophyll-a), and total suspended and particulate organic matter, were carried out. The aim was to integrate microbial community dynamics in the context of the environmental characterization and disentangle microbial patterns related to natural changes from those driven by the anthropic impact on this ecosystem. In spite of the complex relationships between the habitat characteristics, microbial community abundance and metabolic potential, in Syracuse Bay, the availability of organic substrates differently originated by the local conditions appeared to drive the distribution and activity of microbial assemblage. A seasonal pattern of microbial abundances was observed, with the highest concentrations of phytoplankton in spring and low values in winter, whereas heterotrophic bacteria were more abundant during the autumn period. The autumn peaks of the rates of enzymatic activities suggested that not only phytoplankton-derived but also allochthonous organic polymers strongly stimulated microbial metabolism. Increased microbial response in terms of abundance and metabolic activities was detected especially at the sites directly affected by organic matter inputs related to agriculture or aquaculture activities. Nitrogen salts such as nitrate, rather than orthophosphate, were primary drivers of phytoplankton growth. This study also provides insights on the different seasonal scenarios of water quality in Syracuse Bay, which could be helpful for management plans of this Mediterranean coastal environment. [ABSTRACT FROM AUTHOR]

The organic phosphorus mineralizing bacteria (OPB) play an important role in phosphorus cycling in lake sediment, to which less attention has been paid. Monthly sediment samples in 2009 ending in October, together with the samples from different seasons (May, July, October, and December) in 2008, were collected at 6 sites in a Chinese large shallow eutrophic lake (Lake Taihu). The sediment OPB numbers ranged from 2.2 × 106 to 1.79 × 108 cells g−1 (dry weight) at different sampling sites and in different seasons, with the average being 3.88 × 107 cells g−1 (dry weight). Its number was highest at the most polluted site and peaked in spring and summer, which can be explained by the enrichment of organic matter in sediment. Furthermore, there existed a significant positive relationship between the OPB numbers and alkaline phosphatase activities in the sediment. The 6 OPB strains isolated from the sediment were distinct in terms of their colony morphology on the yolk agar, biochemical characteristics and phosphorus release abilities. According to the 16S rDNA sequences, these OPB belong to Bacillus cereus, Stenotrophomonas maltophilia, Stenotrophomonas sp., Bacillus cereus, Xanthomonas sp., Pseudomonas sp. They were distinguished from the OPB species recorded in a Chinese small shallow eutrophic lake whose sediment organic content was remarkably higher. Taken together, organic matter shaped the OPB community not only quantitatively but also qualitatively, which in concert facilitated the enzymatic hydrolysis of organic phosphorus in lake sediment. [ABSTRACT FROM PUBLISHER]

Nitrification is a process in which ammonia is oxidized to nitrite (NO) that is further oxidized to nitrate (NO). The relations between these two steps and ambient ammonia concentrations were studied in surface water of Chinese shallow lakes with different trophic status. For the oxidations of both ammonia and NO, more eutrophic lakes generally showed significantly higher potential and actual rates, which was linked with excessive ammonia concentrations. Additionally, both potential and actual rates for ammonia oxidation were higher than those for NO oxidation in the more eutrophic lakes, while in the lakes with lower trophic status, both potential and actual rates for ammonia oxidation were almost equivalent to those for NO oxidation. This can be explained by the excessive unionized ammonia (NH3) concentration that inhibits nitrite-oxidizing bacteria in the more eutrophic lakes. The laboratory experiment with different ammonia concentrations, using the surface water in a eutrophic lake, showed that ammonia oxidation rates were proportional to the ammonia concentrations, but NO oxidation rates did not increase in parallel. Furthermore, NO oxidation was less associated with particles in natural water of the studied lakes. Without effective protection, it would be selectively inhibited by the excessive ammonia in hypereutrophic lakes, resulting in NO accumulation. Shortly, the increased concentrations of ammonia cause a misbalance between the NO-producing and the NO-consuming processes, thereby exacerbating the lake eutrophication. [ABSTRACT FROM AUTHOR]

The relationship between chlorophyll a and fractionation of sediment phosphorus, inorganic phosphate-solubilizing bacteria (IPB), and organic phosphate-mineralizing bacteria (OPB) was evaluated in a large Chinese shallow eutrophic lake (Lake Taihu) and its embayment (Wuli Bay). At the three study sites, the increase of chlorophyll a concentrations in April paralleled those of the iron bound phosphate accounting for major portion of sediment inorganic phosphate, and in June significantly higher OPB and IPB numbers (especially OPB) in sediment were main contributors to the peaks of chlorophyll a concentration. Even though IPB peaked from February to June, it should serve as an unimportant P source due to the irrelevancy with chlorophyll a and soluble reactive phosphorus (SRP). By contrast, at the other site in the embayment, the calcium-bound phosphate was predominant and solid, which was difficult to be released, and neither IPB nor OPB were detectable in the sediment, indicating weak potential for phosphorus release from the sediment, which was reflected in the small seasonal variation in SRP concentration in water column. Hence, the extents to which the three general mechanisms behind phosphate release from sediment (desorption of iron bound phosphate, solubilization by IPB and enzymatic hydrolysis by OPB) operated were different depending on seasons and sites in Lake Taihu, they may jointly drive phosphate release and accelerate the eutrophication processes. [ABSTRACT FROM AUTHOR]