Microbial Succession and Nitrogen Cycling in Cultured Biofilms as Affected by the Inorganic Nitrogen Availability

Biofilms play important roles in nutrients and energy cycling in aquatic ecosystems. We hypothesized that as eutrophication could change phytoplankton community and decrease phytoplankton diversity, ambient inorganic nitrogen level will affect the microbial community and diversity of biofilms and the roles of biofilms in nutrient cycling. Biofilms were cultured using a flow incubator either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def). The results showed that the biomass and nitrogen and phosphorous accumulation of biofilms were limited by N deficiency; however, as expected, the N-def biofilms had significantly higher microbial diversity than that of N-rep biofilms. The microbial community of biofilms shifted in composition and abundance in response to ambient inorganic nitrogen level. For example, as compared between the N-def and the N-rep biofilms, the former consisted of more diazotrophs, while the latter consisted of more denitrifying bacteria. As a result of the shift of the functional microbial community, the N concentration of N-rep medium kept decreasing, while that of N-def medium showed an increasing trend in the late stage. This indicates that biofilms can serve as the source or the sink of nitrogen in aquatic ecosystems, and it depends on the inorganic nitrogen availability.</p

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Revegetation in the water level fluctuation zone of a reservoir: An ideal measure to reduce the input of nutrients and sediment

The Three Gorges Dam (TGD) is one of the largest dams in the world. Due to the management of the Three Gorges Reservoir (TGR), a huge water level fluctuation (WLF) zone was formed and this caused significant changes to the vegetation in this area. A local vegetation survey was conducted in the WLF zone of the Xiangxi River, one of the major tributaries of the Three Gorges Reservoir, from 2010 to 2011. Based on the survey results, a revegetation method using Cynodon dactylon was established. C. dactylon can survive after very long periods of submergence, and using local species to restore vegetation can prevent the introduction of invasive species. After long-term growth and propagation, the vegetation in our experimental plots was restored, resulting in beneficial landscape and ecology effects. According to our in situ experiments, revegetation in the WLF zone significantly reduced the flow of nutrients and sediments into the TGR. Furthermore, the C. dactylon plots produced less biomass than did the control plots, meaning that less organic matter was introduced to the water. In conclusion, C. dactylon is a suitable candidate for use in the revegetation of the WLF zone of the TGR, and revegetation of the WLF zone will be beneficial in the maintenance of water quality of the TGR. (C) 2014 Elsevier B.V. All rights reserved

Regulating Nutrients and Phytoplankton by Extending the Habitats of Periphyton in a Deep River-Type Reservoir

Eutrophication and phytoplankton blooms threaten the water quality of many reservoirs, especially deep ones. Periphyton is an important component of aquatic ecosystems that can compete with phytoplankton for light and nutrients. However, studies on the dynamics of periphyton development in deep reservoirs are rare. Here, the growth characteristics of periphyton on the artificial substrate (AS) in both open water and enclosures of the Three Gorges Reservoir (TGR) are investigated. The development and relative importance of periphyton are analyzed. The results indicate that mass growth of periphyton is observed on the AS platforms after several weeks. A potential phosphorus limitation for periphyton development in the TGR is evidenced by the relatively high TN/TP ratio in the water column. The differences of phytoplankton biomass in two enclosures suggest the existence of interactions between phytoplankton and periphyton. The results indicate that the artificially loaded AS on the water surface of the deep reservoir leads to the redistribution of nutrients and light between phytoplankton and periphyton. The results are very encouraging because the use of AS for periphyton incubation is an economical and practical way to reduce the probability of phytoplankton blooms in deep reservoirs, especially when the nutrient loads cannot be reduced effectively in a short period

Harvesting Microalgae with Different Sources of Starch-Based Cationic Flocculants

In this study, starches obtained from wheat, potato, and corn were used to synthesize cationic starches (CS), and the flocculation efficiency of these materials was tested with Chlorella pyrenoidosa and Botryococcus braunii cultures under different conditions. Our results indicated that these three CS had differing degrees of substitution following identical synthesis conditions. The various CS functioned similarly in this study, and the desired harmless flocculation efficiency was obtained at low dosages, with CS to microalgal biomass ratios of approximately 89 and 119 mg g(-1) for C. pyrenoidosa and B. braunii, respectively. Impressive harmless harvesting efficiencies were obtained at lower dosages with respect to appropriate stirring time before the settling, with ratios ranging from 58 to 78 mg g(-1) for C. pyrenoidosa cultures. The cost of microalgae harvesting can be cut dramatically by choosing cheaper starches prior to the synthetic CS and by applying suitable flocculation procedures

Nitrogen-cycling microbial community functional potential and enzyme activities in cultured biofilms with response to inorganic nitrogen availability

Biofilms mediate crucial biochemical processes in aquatic ecosystems. It was hypothesized that eutrophication may promote the growth of biofilms, resulting in larger numbers of functional genes. However, the metabolic activity and the roles of biofilms in N cycling will be affected by ambient inorganic nitrogen availability, not by the abundance of functional genes. Biofilms were cultured either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def) in a flow incubator, and the N-cycling gene abundances (nifH, N-2 fixation; amoA, ammonia oxidation, archaea and bacteria; nirS and nirK, denitrification) and enzyme activities (nitrogenase and nitrate reductase) were analyzed. The results showed that, comparing the N-def and N-rep biofilms, the former contained lower nifH gene abundance, but higher nitrogenase activity (NA), while the latter contained higher nifH gene abundance, but lower NA. Different patterns of NA diel variations corresponded to the dynamic microbial community composition and different stages of biofilm colonization. Ammonia oxidizing bacteria (AOB), detected only in N-def biofilms, were responsible for nitrification in biofilms. N-rep biofilms contained high nirS and nirK gene abundance and high denitrification enzyme activity, but N-def biofilms contained significantly lower denitrification gene abundance and activity. In general, the strong N-2 fixation in N-def biofilms and strong denitrification in N-rep biofilms assured the balance of aquatic ecosystems. The results suggested that evaluation of the functional processes of N cycling should not only focus on genetic potential, but also on the physiological activity of biofilms. (C) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V

Sediment phosphorus release in response to flood event across different land covers in a restored wetland

The phosphorus (P) fraction and its release characteristics from sediment in response to flood events across different land covers (i.e., reclaimed land with dominant vegetation of Phragmites australis and/or Typha orientalis, grassland with dominant vegetation of annual and perennial forbs, and bare land) in the lakeshore of Chaohu Lake were investigated. The results indicated that the re-flooding of a restored wetland led to P release. IP (inorganic P) was the major P fraction in the soils pre-flood and post-flood. For all the soil samples, the rank order of P fractions was Ca-P (P associated with calcium) &gt; OP (organic P) &gt; Fe/Al-P (P bound to Al, Fe, and Mn oxides and hydroxides). During flooding, Fe/Al-P contributed the most as the P release source in the soils and to the P sources for the overlying water. In reclaimed land, Fe/Al-P release correlated significantly with soil pH. In grassland, Fe/Al-P release correlated significantly with soil pH and Al content. In bare land, Fe/Al-P release correlated significantly with Al and clay content. The max TP release rates were also significantly influenced by land cover, and the values in bare land, grassland, and reclaimed land were 9.91 mg P m(-2) day(-1), 8.10 mg P m(-2) day(-1), and 5.05 mg P m(-2) day(-1), respectively. The results showed that the P release processes might be regulated by different factors across different land covers, and that the reintroduction of vegetation during wetland restoration must be taken into account prior to flood events to avoid an undesirable degradation of water quality.</p

Nitrogen limitation significantly reduces the competitive advantage of toxic Microcystis at high light conditions

Microcystis is a notorious cyanobacterial genus due to its rapid growth rate, huge biomass, and producing toxins in some eutrophic freshwater environments. To reveal the regulatory factors of interspecific competition between toxic and non-toxic Microcystis, three dominant Microcystis strains were selected, and their photosynthesis, population dynamics and microcystins (MCYST) production were measured. The results suggested that nitrogen-limitation (N-limitation) had a greater restriction for the growth of toxic Microcystis than that of non-toxic Microcystis, especially when cultured at high light or high temperature based on the weight analysis of key factors. Comparison of photosynthesis showed that low light or N-rich would favor the competitive advantage of toxic Microcystis while high light combined with N-limitation would promote the competitive advantage of non-toxic Microcystis, and these two competitive advantages could be further amplified by temperature increase. Mixed competitive experiments of toxic and non-toxic Microcystis were conducted, and the results of absorption spectrum (A(485)/A(665)) and qPCR (real-time quantitative PCR) suggested that the proportion of toxic Microcystis and the half-time of succession process were significantly reduced by 69.4% and 28.4% (p &lt; 0.01) respectively by combining N-limitation with high light intensity than that measured under N-limitation condition. N-limitation led to a significant decrease of MCYST cellular quota in Microcystis biomass, which would be further decreased to a lower level by the high light. Based on above mentioned analysis, to decrease the MCYST production of Microcystis blooms, we should control nutrient, especial nitrogen through pollutant intercepting and increase the light intensity through improving water transparency. (C) 2019 Elsevier Ltd. All rights reserved.</p