Phytohormone up-regulates the biochemical constituent, exopolysaccharide and nitrogen metabolism in paddy-field cyanobacteria exposed to chromium stress.

BACKGROUND: Cyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; however, increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields. Plant growth regulators play beneficial role in combating the negative effects induced by heavy metals in photoautotroph. Current study evaluates the potential role of indole acetic acid (IAA; 290 nm) and kinetin (KN; 10 nm) on growth, nitrogen metabolism and biochemical constituents of two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 exposed to two concentrations of chromium (CrVI; 100 µM and 150 µM). RESULTS: Both the tested doses of CrVI declined the growth, ratio of chlorophyll a to carotenoids (Chl a/Car), contents of phycobiliproteins; phycocyanin (PC), allophycocyanin (APC), and phycoerythrin (PE), protein and carbohydrate associated with decrease in the inorganic nitrogen (nitrate; NO3- and nitrite; NO2-) uptake rate that results in the decrease in nitrate and ammonia assimilating enzymes; nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT) except glutamate dehydrogenase (GDH). However, exogenous supplementation of IAA and KN exhibited alleviating effects on growth, nitrogen metabolism and exopolysaccharide (EPS) (first protective barrier against metal toxicity) contents in both the cyanobacteria, which probably occurred as a result of a substantial decrease in the Cr uptake that lowers the damaging effects. CONCLUSION: Overall result of the present study signifies affirmative role of the phytohormone in minimizing the toxic effects induced by chromium by stimulating the growth of cyanobacteria thereby enhancing its ability as bio-fertilizer that improved fertility and productivity of soil even in metal contaminated condition.

Proteomic mechanisms for the stimulatory effects of antibiotics on Microcystis aeruginosa during hydrogen peroxide treatment.

Application of low dosage of H2O2 at early stage of cyanobacterial life cycle is a promising route for cyanobacterial bloom mitigation, which could minimize adverse effects on non-target organisms. Besides, influence of co-existing contaminants on cyanobacterial bloom mitigation under combined pollution conditions remains unclear. This study assessed the influence of a mixture of four frequently detected antibiotics (tetracycline, sulfamethoxazole, ciprofloxacin and amoxicillin) during H2O2 treatment of Microcystis aeruginosa at early growth stage. H2O2 significantly (p < 0.05) inhibited growth rate, chlorophyll a content, Fv/Fm and rETRmax in a dose-dependent manner at low doses of 0.25-1 mg L-1, through downregulating proteins involved in cell division, cellular component organization, gene expression and photosynthesis. Although H2O2 increased microcystin content in each cyanobacterial cell through the upregulation of microcystin synthetases (mcyC and mcyF), total microcystin concentration in H2O2 treated groups was significantly (p < 0.05) reduced due to the decrease of cell density. Existence of 80 and 200 ng L-1 mixed antibiotics during H2O2 treatment facilitated the scavenging of ROS by antioxidant enzymes and significantly (p < 0.05) stimulated growth, photosynthesis, microcystin synthesis and microcystin release in H2O2 treated cells, through the upregulation of proteins involved in photosynthesis, oxidation-reduction process, biosynthesis, gene expression and transport. Mixed antibiotics increased the hazard of M. aeruginosa during H2O2 treatment, through the stimulation of microcystin synthesis and release at the proteomic level. Each target antibiotic should be controlled below 5 ng L-1 before the application of H2O2 for eliminating the interference of antibiotics on cyanobacterial bloom mitigation.

Phosphorus deficiency induced by aluminum in a marine nitrogen-fixing cyanobacterium Crocosphaera watsonii WH0003.

Large amounts of aluminum (Al) enter the ocean through atmospheric dust deposition and river runoffs. However, few studies have reported the effects of Al on marine phytoplankton, especially nitrogen-fixing cyanobacteria. By using the isotope tracer method and quantitative reverse transcription PCR (RT-qPCR), we examined the physiological effect of Al (0.2, 2 and 20 µM) on the unicellular marine nitrogen-fixing cyanobacterium Crocosphaera watsonii in Aquil* medium. We show that Al has an inhibitory physiological effect on C. watsonii, including changes in growth rate, nitrogen fixation rate, carbon fixation rate, cell size, fast rise chlorophyll fluorescence kinetics, cellular photosynthetic pigment and C/N/P content, the same as that of the phosphorus deficient treatment. The ratio of cellular elements C:N:P showed that phosphorus was deficient in the cell of C. watsonii after Al treatment (2 and 20 µM). In addition, Al stimulated the expression of phosphorus-related genes pstS, phoH, phoU, ppK and ppX in C. watsonii. All these results suggest that Al-treated C. watsonii is phosphorus-limited, and that the phosphorus deficiency induced by Al may be one mechanism behind aluminum's toxicity.

Amentoflavone, a novel cyanobacterial killing agent from Selaginella tamariscina.

Harmful cyanobacterial bloom (HCB) by Microcystis aeruginosa is increasingly becoming a serious concern to the environment and human health alike. Currently, many physical, chemical, and biological controls are underway to eliminate HCB, but natural chemicals are rarely used. To find a control agent with low environmental toxicity and high potential for practical use, 60 plant extracts were screened. Only Selaginella tamariscina extract killed all four Microcystis aeruginosa strains, but not the other tested bacteria. Chloroform fraction of S. tamariscina extract (CSE) showed the highest killing activity. The effects of CSE on M. aeruginosa were monitored using differential interference contrast microscopy and flow-cytometry analysis, scanning electron microscopy, and transmission electron microscopy. The images showed that CSE-treated cells were abnormally altered, with damaged cell membranes, peptidoglycan layers, and cytoplasm. Quadrupole time-of-flight liquid chromatography-mass spectrometry was used to identify amentoflavone as a major active compound. Pure amentoflavone, even at low concentrations showed a powerful killing effect on M. aeruginosa, but not on other non-cyanobacteria. Overall, in this study, we have highlighted the potentials of S. tamariscina extracts and amentoflavone as selective HCB control agents.

Effects of an aluminum-based chemical remediator on the cyanobacteria population: a study in the northeast of Brazil.

Water sources destined to human supply are increasingly threatened worldwide due to various sources of pollution, either point or diffuse. In this sense, the objective of this work was to evaluate the efficiency of an aluminum-based chemical remediator in the Joanes River. An statistical analysis of physical, chemical, biological, and hydraulic monitoring data was performed relying on a 2013-2018 recording period, provided by the local sanitation service provider and the environmental agency. The results showed that even with the use of aluminum-based chemical remediators, the key parameters for controlling flowering events remained high with mean values of 0.18 mg P L-1, 176.155 cells mL-1 of cyanobacteria and peaks of 1.56 µg L-1 and 4.02 µg L-1 for microcystin and saxitoxin, respectively. At the end of this study, it was verified that the aluminum-based chemical remediator showed low effectiveness in the reduction of phosphorus and cyanobacteria, opposing to expectations of the sanitation provider.

Effects of scrubber washwater discharge on microplankton in the Baltic Sea.

In 2020, the global cap of maximum allowable sulphur content in marine fuel will be reduced from the current 3.5% to 0.5%. Another way to reduce the sulphur emissions is to install a seawater scrubber that cleans exhausts but instead release acidic water containing nutrients and contaminants back to the marine environment. In the current study, scrubber washwater was tested on a Baltic Sea microplankton community. A significant increase in chlorophyll a, particulate organic phosphorus (POP), carbon (POC) and nitrogen (PON) were observed when the community was exposed to 10% scrubber washwater for 13 days as compared to the control. A laboratory experiment with the filamentous cyanobacteria Nodularia spumigena and the chain-forming diatom Melosira cf. arctica showed negative responses in photosynthetic activity (EC10 = 8.6% for N. spumigena) and increased primary productivity (EC10 = 5.5% for M. cf. arctica), implying species-specific responses to scrubber washwater discharge.

Active nitrogen fixation by Crocosphaera expands their niche despite the presence of ammonium - A case study.

Unicellular nitrogen fixer Crocosphaera contributes substantially to nitrogen fixation in oligotrophic subtropical gyres. They fix nitrogen even when significant amounts of ammonium are available. This has been puzzling since fixing nitrogen is energetically inefficient compared with using available ammonium. Here we show that by fixing nitrogen, Crocosphaera can increase their population and expand their niche despite the presence of ammonium. We have developed a simple but mechanistic model of Crocosphaera based on their growth in steady state culture. The model shows that the growth of Crocosphaera can become nitrogen limited despite their capability to fix nitrogen. When they fix nitrogen, the population increases by up to 78% relative to the case without nitrogen fixation. When we simulate a simple ecological situation where Crocosphaera exists with non-nitrogen-fixing phytoplankton, the relative abundance of Crocosphaera increases with nitrogen fixation, while the population of non-nitrogen-fixing phytoplankton decreases since a larger fraction of fixed nitrogen is consumed by Crocosphaera. Our study quantitatively supports the benefit of nitrogen fixation despite the high electron/energy costs, even when an energetically efficient alternative is available. It demonstrates a competitive aspect of Crocosphaera, permitting them to be regionally significant nitrogen fixers.

Toxicity mechanisms of ZnO UV-filters used in sunscreens toward the model cyanobacteria Synechococcus elongatus PCC 7942.

Zinc oxide (ZnO) nanoparticles are commonly used in sunscreens for their UV-filtering properties. Their growing use can lead to their release into ecosystems, raising question about their toxicity. Effects of these engineered nanomaterials (ENMs) on cyanobacteria, which are important primary producers involved in many biogeochemical cycles, are unknown. In this study, we investigated by several complementary approaches the toxicological effects of two marketed ZnO-ENMs (coated and uncoated) on the model cyanobacteria Synechococcus elongatus PCC 7942. It was shown that despite the rapid adsorption of ENMs on cell surface, toxicity is mainly due to labile Zn released by ENMs. Zn dissipates cell membrane potential necessary for both photosynthesis and respiration, and induces oxidative stress leading to lipid peroxidation and DNA damages. It leads to global downregulation of photosystems, oxidative phosphorylation, and transcription/translation machineries. This also translates into significant decrease of intracellular ATP content and cell growth inhibition. However, there is no major loss of pigments and even rather an increase in exposed cells compared to controls. A proposed way to reduce the environmental impact of Zn would be the improvement of the coating stability to prevent solubility of ZnO-ENMs.

The concentration thresholds establishment of nitrogen and phosphorus considering the effects of extracellular substrate-to-biomass ratio on cyanobacterial growth kinetics.

Harmful cyanobacterial blooms have caused serious threat to the sustainable development of freshwater ecosystems due to eutrophication, but there is no consensus on nutrients threshold for controlling cyanobacterial bloom. A Monod-based ratio-dependent model was originally developed to investigate the effects of the extracellular substrate-to-biomass (Chlorophyll a) ratio (Sex/X) on the growth kinetics of Cyanobacteria and to determine the concentration thresholds of nitrogen (N) and phosphorus (P) in the form of Sex/X. The results indicated that biomass growth was completely suppressed at Sex/X ≤ 0.21 µg µg-1 for P and Sex/X ≤ 2.82 µg µg-1 for N, which are far lower than the values of most of the eutrophic freshwater lakes. This indicates that in addition to curbing N and P nutrients of eutrophic water, to conduct some biologically mediated changes and to find a suitable environmental fate or a suitable position for excessive N and P nutrients is also of great significance in controlling HABs.

The Impact of Warming and Nutrients on Algae Production and Microcystins in Seston from the Iconic Lake Lesser Prespa, Greece.

Lake Lesser Prespa and its adjacent pond, Vromolimni in Greece, is a shallow freshwater system and a highly protected area hosting an exceptional biodiversity. The occurrence of microcystins (MCs) producing cyanobacterial blooms in these waters during recent years can be harmful to the wildlife. We tested the hypothesis that both cyanobacterial biomass and MCs are strongly influenced by nutrients (eutrophication) and warming (climate change). Lake and pond water was collected from two sites in each water body in 2013 and incubated at three temperatures (20 °C, 25 °C, 30 °C) with or without additional nutrients (nitrogen +N, phosphorus +P and both +N and +P). Based on both biovolume and chlorophyll-a concentrations, cyanobacteria in water from Lesser Prespa were promoted primarily by combined N and P additions and to a lesser extent by N alone. Warming seemed to yield more cyanobacteria biomass in these treatments. In water from Vromolimni, both N alone and N+P additions increased cyanobacteria and a warming effect was hardly discernible. MC concentrations were strongly increased by N and N+P additions in water from all four sites, which also promoted the more toxic variant MC-LR. Hence, both water bodies seem particularly vulnerable to further N-loading enhancing MC related risks.

Beneficial effects of aluminum enrichment on nitrogen-fixing cyanobacteria in the South China Sea.

Few studies focus on the effects of aluminum (Al) on marine nitrogen-fixing cyanobacteria, which play important roles in the ocean nitrogen cycling. To examine the effects of Al on the nitrogen-fixing cyanobacteria, bioassay experiments in the oligotrophic South China Sea (SCS) and culture of Crocosphaera watsonii in the laboratory were conducted. Field data showed that 200 nM Al stimulated the growth and the nitrogenase gene expression of Trichodesmium and unicellular diazotrophic cyanobacterium group A, and the nitrogen fixation rates of the whole community. Laboratory experiments demonstrated that Al stimulated the growth and nitrogen fixation of C. watsonii under phosphorus limited conditions. Both field and laboratory results indicated that Al could stimulate the growth of diazotrophs and nitrogen fixation in oligotrophic oceans such as the SCS, which is likely related to the utilization of phosphorus, implying that Al plays an important role in the ocean nitrogen and carbon cycles by influencing nitrogen fixation.

Methods for enhancing cyanobacterial stress tolerance to enable improved production of biofuels and industrially relevant chemicals.

Cyanobacteria are photosynthetic prokaryotes that can fix atmospheric CO2 and can be engineered to produce industrially important compounds such as alcohols, free fatty acids, alkanes used in next-generation biofuels, and commodity chemicals such as ethylene or farnesene. They can be easily genetically manipulated, have minimal nutrient requirements, and are quite tolerant to abiotic stress making them an appealing alternative to other biofuel-producing microbes which require additional carbon sources and plants which compete with food crops for arable land. Many of the compounds produced in cyanobacteria are toxic as titers increase which can slow growth, reduce production, and decrease overall biomass. Additionally, many factors associated with outdoor culturing of cyanobacteria such as UV exposure and fluctuations in temperature can also limit the production potential of cyanobacteria. For cyanobacteria to be utilized successfully as biofactories, tolerance to these stressors must be increased and ameliorating stress responses must be enhanced. Genetic manipulation, directed evolution, and supplementation of culture media with antioxidants are all viable strategies for designing more robust cyanobacterial strains that have the potential to meet industrial production goals.

Influence of Phoslock® on legacy phosphorus, nutrient ratios, and algal assemblage composition in hypereutrophic water resources.

Acceleration of eutrophication in freshwater resources can result in prolific growth of nuisance algae, notably cyanobacteria. In this research, we evaluated the ability of an in situ P binding technology (Phoslock®) to alter available water column and sediment P, and the subsequent impact on nutrient ratios and algal assemblage composition. Two golf course irrigation ponds with legacy nutrient loads and chronic cyanobacterial blooms were treated with Phoslock and monitored for 2 years post-treatment. Phoslock significantly (P < 0.05) decreased water column total P levels and shifted mobile sediment P fractions (i.e., labile, reductant-soluble, organic) to the residual fraction. Total N/P ratios (by mass) significantly increased and were sustained at over 30:1 in the Hickory Meadows irrigation pond and 100:1 in the Chockyotte irrigation pond throughout the study. Consequent changes in the algal assemblage included decreases in dominance and overall density of cyanobacteria as well as a shift away from scum-forming genera (e.g., Microcystis spp. and Anabaena [Dolichospermum] sp.) to planktonic forms (e.g., Pseudanabaena sp. and Planktolyngbya sp.). This research provides information regarding mitigation of in situ water and sediment P toward shifting nutrient ratios and altering algal assemblage composition.

Response of the phytoplankton community to water quality in a local alpine glacial lake of Xinjiang Tianchi, China: potential drivers and management implications.

Eutrophication has become one of the most serious threats to aquatic ecosystems in the world. With the combined drivers of climate change and human activities, eutrophication has expanded from warm shallow lakes to cold-water lakes in relatively high latitude regions and has raised greater concerns over lake aquatic ecosystem health. A two-year field study was carried out to investigate water quality, phytoplankton characteristics and eutrophication status in a typical alpine glacial lake of Tianchi, a scenic area and an important drinking water source in the Xinjiang Autonomous Region of China, in 2014 and 2015. Clear seasonal and annual variations of nutrients and organic pollutants were found especially during rainy seasons. For the phytoplankton community, Bacillariophyta held the dominant position in terms of both species and biomass throughout the year, suggesting the dominant characteristics of diatoms in the phytoplankton structure in such a high-altitude cold-water lake. This was quite different from plain and warm lakes troubled with cyanobacterial blooming. Moreover, the dominant abundance of Cyclotella sp. in Tianchi might suggest regional warming caused by climate change, which might have profound effects on the local ecosystems and hydrological cycle. Based on water quality parameters, a comprehensive trophic level index TLI (Σ) was calculated to estimate the current status of eutrophication, and the results inferred emerging eutrophication in Tianchi. Results from Canonical Correspondence Analysis (CCA) and correlation analysis of phytoplankton genera and physico-chemical variables of water indicated that abiotic factors significantly influenced the phytoplankton community and its succession in Tianchi Lake. These abiotic factors could explain 77.82% of the total variance, and ammonium was identified as the most discriminant variable, which could explain 41% of the total variance followed by TP (29%). An estimation of annual nutrient loadings to Tianchi was made, and the results indicated that about 212.97 t of total nitrogen and 32.14 t of total phosphorus were transported into Tianchi Lake annually. Human socio-economic activities (runoff caused by historical overgrazing and increasing tourism) were identified as the most important contributors to Tianchi nutrient loadings.

Controlling cyanobacterial harmful blooms in freshwater ecosystems.

Cyanobacteria's long evolutionary history has enabled them to adapt to geochemical and climatic changes, and more recent human and climatic modifications of aquatic ecosystems, including nutrient over-enrichment, hydrologic modifications, and global warming. Harmful (toxic, hypoxia-generating, food web altering) cyanobacterial bloom (CyanoHAB) genera are controlled by the synergistic effects of nutrient (nitrogen and phosphorus) supplies, light, temperature, water residence/flushing times, and biotic interactions. Accordingly, mitigation strategies are focused on manipulating these dynamic factors. Strategies based on physical, chemical (algaecide) and biological manipulations can be effective in reducing CyanoHABs. However, these strategies should invariably be accompanied by nutrient (both nitrogen and phosphorus in most cases) input reductions to ensure long-term success and sustainability. While the applicability and feasibility of various controls and management approaches is focused on freshwater ecosystems, they will also be applicable to estuarine and coastal ecosystems. In order to ensure long-term control of CyanoHABs, these strategies should be adaptive to climatic variability and change, because nutrient-CyanoHAB thresholds will likely be altered in a climatically more-extreme world.

Molybdenum and phosphorus limitation of moss-associated nitrogen fixation in boreal ecosystems.

Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both. BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a 15 N2 tracer technique to assess the ARA to N2 fixation conversion ratios at our subarctic site. BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA : 15 N2 ratios increased with increasing Mo additions. These findings show that N2 fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited by Mo availability.

Phytoestrogens and sterols in waters with cyanobacterial blooms - Analytical methods and estrogenic potencies.

Compounds with estrogenic potencies and their adverse effects in surface waters have received much attention. Both anthropogenic and natural compounds contribute to overall estrogenic activity in freshwaters. Recently, estrogenic potencies were also found to be associated with cyanobacteria and their blooms in surface waters. The present study developed and compared the solid phase extraction and LC-MS/MS analytical approaches for determination of phytoestrogens (8 flavonoids - biochanin A, coumestrol, daidzein, equol, formononetin, genistein, naringenin, apigenin - and 5 sterols - ergosterol, ß-sitosterol, stigmasterol, campesterol, brassicasterol) and cholesterol in water. The method was used for analyses of samples collected in stagnant water bodies dominated by different cyanobacterial species. Concentrations of individual flavonoids ranged from below the limit of detection to 3.58 ng/L. Sterols were present in higher amounts up to 2.25 µg/L. Biological potencies of these phytoestrogens in vitro were characterized using the hERα-HeLa-9903 cell line. The relative estrogenic potencies (compared to model estrogen - 17ß-estradiol) of flavonoids ranged from 2.25E-05 to 1.26E-03 with coumestrol being the most potent. None of the sterols elicited estrogenic response in the used bioassay. Estrogenic activity was detected in collected field water samples (maximum effect corresponding to 2.07 ng/L of 17ß-estradiol equivalents, transcriptional assay). At maximum phytoestrogens accounted for only 1.56 pg/L of 17ß-estradiol equivalents, contributing maximally 8.5% of the total estrogenicity of the water samples. Other compounds therefore, most likely of anthropogenic origin such as steroid estrogens, are probably the major drivers of total estrogenic effects in these surface waters.

Experimental iron amendment suppresses toxic cyanobacteria in a hypereutrophic lake.

The effects of reducing nutrient inputs to lakes and reservoirs are often delayed by hysteresis resulting from internal phosphorus (P) loading from sediments. Consequently, controlling harmful algal blooms (HABs) in many eutrophic ecosystems requires additional management to improve water quality. We manipulated iron (Fe) concentrations in a hypereutrophic lake to determine if Fe amendment would suppress HABs by inhibiting P release from sediments. Our experiment consisted of 15 in situ mesocosms, 12 of which each received a different dose of Fe (ranging from 2 to 225 g/m2 ); the remaining three were unmanipulated to serve as controls. Iron amendment decreased P accumulation in porewaters and the flux of P from sediments, which significantly lowered P concentrations in the water column. Iron exerted significant dose-dependent negative effects on the biomass of phytoplankton and periphyton, and reduced the dominance of cyanobacteria. Even at the lowest doses, Fe appeared to reduce the toxicity of cyanobacterial blooms, as measured by concentrations of hepatotoxic microcystins. Overall, our findings highlight the potential for Fe treatment as an effective strategy for minimizing HABs in eutrophic lakes and reservoirs. More broadly, our study reinforces the importance of Fe in regulating the trophic state of freshwaters, and the sensitivity of certain ecosystems to changes in Fe supply. Finally, we hypothesize that decreases in natural Fe supplies to lakes associated with anthropogenic activities may worsen outbreaks of toxic cyanobacteria.

Assessing the impacts of phosphorus inactive clay on phosphorus release control and phytoplankton community structure in eutrophic lakes.

Addressing the challenge that phosphorus is the key factor and cause for eutrophication, we evaluated the phosphorus release control performance of a new phosphorus inactive clay (PIC) and compared with Phoslock®. Meanwhile, the impacts of PIC and Phoslock® on phytoplankton abundance and community structure in eutrophic water were also discussed. With the dosage of 40 mg/L, PIC effectively removed 97.7% of total phosphorus (TP) and 98.3% of soluble reactive phosphorus (SRP) in eutrophic waters. In sediments, Fe/Al-phosphorus and organic phosphorus remained stable whereas Ca-phosphorus had a significant increase of 13.1%. The results indicated that PIC may form the active overlay at water-sediment interface and decrease the bioavailability of phosphorus. The phytoplankton abundance was significantly reduced by PIC and decreased from (1.0-2.4) × 107 cells/L to (1.3-4.3) × 106 cells/L after 15 d simultaneous experiment. The phytoplankton community structure was also altered, where Cyanobacteria and Bacillariophyceae were the most inhibited and less dominant due to their sensitivity to phosphorus. After PIC treatment, the residual lanthanum concentration in water was 1.44-3.79 µg/L, and the residual aluminium concentration was low as 101.26-103.72 µg/L, which was much less than the recommended concentration of 200 µg/L. This study suggests that PIC is an appropriate material for phosphorus inactivation and algal bloom control, meaning its huge potential application in eutrophication restoration and management.

Molecular markers define progressing stages of phosphorus limitation in the nitrogen-fixing cyanobacterium, Crocosphaera.

Crocosphaera watsonii is a marine cyanobacterium that frequently inhabits low phosphate environments in oligotrophic oceans. While C. watsonii has the ability to fix atmospheric nitrogen, its growth may be limited by availability of phosphorus. Biomarkers that indicate cellular phosphorus status give insight into how P-limitation can affect the distribution of nitrogen-fixing cyanobacterial populations. However, adaptation to phosphorus stress is complex and one marker may not be sufficient to determine when an organism is P-limited. In this study, we characterized the transcription of key genes, activated during phosphorus stress in C. watsonii WH8501, to determine how transcription changed during the phosphorus stress response. Transcription of pstS, which encodes a high-affinity phosphate binding protein, was discovered to be quickly up-regulated in phosphorus-depleted cells as an immediate stress response; however, its transcription declined after a period of phosphorus starvation. In addition, diel regulation of pstS in C. watsonii WH8501 complicates the interpretation of this marker in field applications. Transcription of the gene coding for the arsenite efflux protein, arsB, was upregulated after pstS in phosphorus limited cells, but it remained upregulated at later stages of phosphorus limitation. These results demonstrate that a single molecular marker does not adequately represent the entire phosphorus stress response in C. watsonii WH8501. Using both markers, the variations in transcriptional response over a range of degrees of phosphorus limitation may be a better approach for defining cellular phosphorus status.