Arsenic Accumulation and Biotransformation Affected by Nutrients (N and P) in Common Blooming-Forming Microcystis wesenbergii (Komárek) Komárek ex Komárek (Cyanobacteria)

Arsenic accumulation and biotransformation in algae was mostly carried out in a medium that contained far higher nutrient concentrations than that in natural freshwaters. The obtained results might have limited environmental validity and result in a failure to describe authentic arsenic biogeochemical cycles in natural freshwater systems. To validate the assumption, arsenic accumulation, and biotransformation in common bloom forming Microcystis wesenbergii was performed under a high nutrient concentration in BG11 medium (N = 250 mg/L, P = 7.13 mg/L), and adjusted low nutrients that mimicked values in natural freshwaters (N = 1.5 mg/L, P = 0.3 mg/L). The growth rate and maximum M. wesenbergii cell density were much lower in the high nutrient set, but more inhibition was shown with increasing ambient iAs(V) concentrations both in the high and low nutrient sets. The proportion of intracellular contents in total arsenicals decreased with increasing iAs(V) concentrations in both high and low nutrient sets but increased with incubation time. Intracellular iAs(III) was not found in the high nutrient set, while it formed high concentrations that could be comparable to that of an extracellular level in the low nutrient set. M. wesenbergii could methylate arsenic, and a higher proportion of organoarsenicals was formed in the low nutrient set. Lower intracellular MMA(V) and DMA(V) concentrations were found in the high nutrient set; contrarily, they presented a higher concentration that could be comparable to the extracellular ones in the low nutrient set. The results demonstrated that different nutrient regimes could affect arsenic accumulation and biotransformation in M. wesenbergii, and low nutrient concentrations could inhibit the excretion of iAs(III), MMA(V) and DMA(V) out of cells. Further investigations should be based on natural freshwater systems to obtain an authentic arsenic accumulation and biotransformation in cyanobacteria.

Manifestations and environmental implications of microbially-induced calcium carbonate precipitation (MICP) by the cyanobacterium Dolichospermum flosaquae

The aim of this work is to explore the ability and magnitude of the temperate cyanobacterium Dolichospermum flosaquae in microbially-induced calcium carbonate precipitation (MICP). Environmentally, MICP controls the availability of calcium, carbon and phosphorus in freshwater lakes and simultaneously controls carbon exchange with the atmosphere. Cultures of flosaquae were grown in BG11 medium containing 0, 1, 1.5, 2 and 4 mg Ca2+ L−1, as cardinal concentrations previously reported in freshwater lakes, in addition to a control culture (BG11 containing 13 mg Ca2+ L−1). Growth (cell number, chlorophyll a, and protein content) of D. flosaquae was generally reduced by elevating calcium concentrations of the different salts used (chloride, acetate, or citrate). D. flosaquae exhibited its ability to perform MICP as carbonate alkalinity was sharply increased up to its highest level (six times that of the control) at a citrate concentration of 4 mg Ca2+ L−1. Calcium carbonate was formed at a pre-precipitation stage as the minimum pH necessary for precipitation (8.7) has been scarcely approached under such conditions. In this work, MICP took place mostly empowered by photosynthesis and respiration. Residual calcium exhibited its lowest value at 4 mg Ca2+ citrate L−1, coinciding with the highest alkalinity level. Precipitated calcium was increased with chlorophyll a content, but not with increasing cell numbers.

Influence of Light Intensity and Photoperiod on the Photoautotrophic Growth and Lipid Content of the Microalgae Verrucodesmus verrucosus in a Photobioreactor

Microalgal biomass has the capacity to accumulate relatively large quantities of triacylglycerides (TAG) for the conversion of methyl esters of fatty acids (FAME) which has made microalgae a desirable alternative for the production of biofuels. In the present work Verrucodesmus verrucosus was evaluated under autotrophic growth conditions as a suitable source of oil for biodiesel production. For this purpose BG11 media were evaluated in three different light:dark photoperiods (L:D; 16:08; 12:12; 24:0) and light intensities (1000, 2000 and 3000 Lux) in a photobioreactor with a capacity of three liters; the evaluation of the microalgal biomass was carried out through the cell count with the use of the Neubauer chamber followed by the evaluation of the kinetic growth parameters. So, the lipid accumulation was determined through the lipid extraction with a Soxhlet system. Finally, the fatty acid profile of the total pooled lipids was determined using gas chromatography-mass spectroscopy (GC-MS). The results demonstrate that the best conditions are a photoperiod of 12 light hours and 12 dark hours with BG11 medium in a 3 L tubular photobioreactor with 0.3% CO2, 25 °C and 2000 Lux, allowing a lipid accumulation of 50.42%. Palmitic acid is identified as the most abundant fatty acid at 44.90%.

An Aerobic Anoxygenic Phototrophic Bacterium Fixes CO2 via the Calvin-Benson-Bassham Cycle

Aerobic anoxygenic phototrophic bacteria (AAnPB) are photoheterotrophs, which use light as auxiliary energy and require organic carbon (OC) for growth. Herein, we report the unusual strain B3, which is a true AAnPB because it requires oxygen for growth, harbours genes for cbb3- and bd-type cytochromes and acsF, and produces bacteriochlorophyll. The B3 genome encodes the complete metabolic pathways for AAnPB light utilization, CO2 fixation via Calvin-Benson-Bassham (CBB) cycle and oxidation of sulfite and H2, and the transcriptome indicated that all components of these pathways were fully transcribed. Expression of the marker genes related to photosynthesis, including pufM for light harnessing and rbcL for CO2 fixation, and the activity of RubisCO, the key enzyme in the Calvin-Benson-Bassham (CBB) cycle, increased in response to decreased OC supply. Large amounts of cell biomass were obtained in liquid BG11 medium under illumination. The strain thus likely photoautotrophically grows using sulfite or H2 as an electron donor. Similar GC contents between photosynthesis, the CBB cycle and 16S rRNA genes and the consistency of their phylogenetic topologies implied that light harnessing and carbon fixation genes evolved vertically from an anaerobic phototrophic ancestor of Rhodospirillaceae in Alphaproteobacteria. In conclusion, strain B3 represents a novel AAnPB characterized by photoautotrophy using the CBB cycle. This kind of AAnPB may be ecologically significant in the global carbon cycle.

Optimization and qualitative comparison of two vinasse pre-treatments aiming at microalgae cultivation

ABSTRACT The cultivation of microalgae is a possible destination for vinasse, a residue from the sugar and alcohol industry. This use can help reduce the costs of microalgae production and remediate this residue rich in nutrients. However, the physicochemical characteristics of vinasse limit its use for microalgae growth at low concentrations, except when the residue is pretreated. This work aimed at optimizing the vinasse pretreatments of centrifugation and adsorption by smectite clay and activated charcoal on laboratory scale in terms of amounts of materials used and time spent, making them more viable on larger scales. The optimized processes were then compared in productive, economic, and environmental terms. The dilution of treated vinasse with distilled water resulted in similar growth of Chlorella vulgaris to those obtained with the dilution in BG11 medium, indicating that the addition of nutrients in culture media is not necessary. Although microalgae growth occurs in higher concentrations of vinasse treated by adsorption, the results show that centrifugation required less processing time, has cheaper processing costs, and generated much less residue. Centrifugation treatment has greater economic and environmental viabilities and was more sustainable than the adsorption, even though the algae did not grow in the centrifuged residue in concentrations as high as it did after the adsorption treatment. Therefore, this article brings a new view about the economic and environmental aspects on the use of pretreated vinasse for microalgal growth, giving a lucrative destination for a highly polluting waste.

Phytoremediation of CYN, MC-LR and ANTX-a from Water by the Submerged Macrophyte Lemna trisulca

Cyanotoxins are harmful to aquatic and water-related organisms. In this study, Lemna trisulca was tested as a phytoremediation agent for three common cyanotoxins produced by bloom-forming cyanobacteria. Cocultivation of L. trisulca with Dolichospermum flos-aquae in BG11 medium caused a release of the intracellular pool of anatoxin-a into the medium and the adsorption of 92% of the toxin by the plant—after 14 days, the total amount of toxin decreased 3.17 times. Cocultivation with Raphidopsis raciborskii caused a 2.77-time reduction in the concentration of cylindrospermopsin (CYN) in comparison to the control (62% of the total pool of CYN was associated with the plant). The greatest toxin limitation was noted for cocultivation with Microcystis aeruginosa. After two weeks, the microcystin-LR (MC-LR) concentration decreased more than 310 times. The macrophyte also influenced the growth and development of cyanobacteria cells. Overall, 14 days of cocultivation reduced the biomass of D. flos-aquae, M. aeruginosa, and R. raciborskii by 8, 12, and 3 times, and chlorophyll a concentration in comparison to the control decreased by 17.5, 4.3, and 32.6 times, respectively. Additionally, the macrophyte stabilized the electrical conductivity (EC) and pH values of the water and affected the even uptake of cations and anions from the medium. The obtained results indicate the biotechnological potential of L. trisulca for limiting the development of harmful cyanobacterial blooms and their toxicity.

Mixotrophic Growth of Astaxanthin-Rich Alga Haematococcus pluvialis using Refined Crude Glycerol as Carbon Substrate: Batch and Fed-Batch Cultivations

Due to a current overabundance of crude glycerol produced from the biodiesel industry, the compound has the potential to be used as an inexpensive carbon source for growing the green microalga Haematococcus pluvialis (H. pluvialis), the richest source of natural astaxanthin (ATX). In order to investigate the practical use of crude glycerol, microalgal cultures were grown mixotrophically and heterotrophically in BG11 medium with the supplementation of refined crude glycerol, a mixture of glycerol and ethanol, under 2, 5 and 7 g L-1, using photoautotrophic cultivation as a control. H. pluvialis green-stage growth and red-stage ATX accumulation were effectively facilitated by mixotrophic conditions, with the highest µ of 0.27 ± 0.03 day-1 and the highest ATX content of (3.5 ± 0.4 % wt) (both observed under 7 g glycerol L-1). In contrast, growth was completely inhibited under heterotrophic conditions. Under repeated fed-batch operation, the exponential growth phase, during green-stage mixotrophic cultivation, was significantly extended from 5 days (in batch) to 24 days, making biomass yield of 1.86 ± 0.06 g DCW L-1 (around 2.6-fold higher). Monitoring of substrates (glycerol, ethanol and nitrate) in the broth was carried out and subsequently suggested that further optimization of media could be made.

Extracellular Vesicles: A Novel Messenger of Unicellular Microalgae Communication?

Background Extracellular vesicles (EVs) are nanoparticles with membrane structures secreted by cells that play a role in the transfer of proteins, lipids, small RNAs, lncRNAs and DNA. Thus, EVs mediate mammalian cell-to-cell communication and have potential applications in the diagnosis and treatment of diseases. However, these studies have been primarily focused on the microenvironmental fluids between mammalian cells. Microalgae are single-celled organisms living in natural and dynamic aquatic environments. Whether microalgae can secrete EVs and adapt to changing environments via EV-mediated communication between cells is still unclear. ResultsWe demonstrated that EVs are widely present in microalgae and have surprisingly rich contents of miRNAs and proteins. The differential expression of miRNAs and proteins was correlated with different cell growth stages and abiotic stressors. Our preliminary data suggested that Chlamydomonas EVs significantly affected the growth of the cyanobacterium Synechocystis in full BG11 medium. However, incubating EVs isolated from Chlamydomonas with Synechocystis cells showed that EVs themselves did not promote cell growth in nitrogen depleted BG11 medium. In this case, EVs appear to function primarily via information sensing and message delivery between cells under nutrient stress conditions. More detailed studies need to be conducted to revise our current perspective on the distribution of nutrients in aquatic environments and how EVs may affect microbial communications and interactions.Conculsions These findings suggest that EVs may play a critically important role in information exchange between microalgal cells and, in turn, adaptation to changing aquatic environments.

Light regulating metabolic responses of Cyanobium sp. (Cyanobacteria)

Cyanobacteria are an important group of microorganisms of significant economic interest due to, for ex- ample, the antioxidant capacity of their metabolites. Cyanobium sp. LEGE 06113 is a marine cyanobacterium poorly studied, but with promising future applications. The aim of this study was to optimize the light conditions (both source and irradiance) and nutrient (N and P) concentration for Cyanobium sp. production as a source of high-valued com- pounds. The optimization of the processing parameters was performed using two different light sources (fluorescent and low-pressure sodium lamp), four irradiances (50, 100, 200 and 300 μmol photons m–2 s–1) and two variations of BG11 medium (BG11 and BG11+, with the second containing double amounts of phosphates and nitrates). The effects of the three factors were evaluated on the biomass production, photosynthetic activity, biochemical composition and antioxidant capacity. A synergistic effect between the light source, light intensity, and medium was observed for all measured parameters, with the greatest impact of light irradiance on the metabolism of Cyanobium sp. The combination of the SOX lamp, BG11+ medium, and a light irradiance of 200 μmol photons m–2 s–1 was optimal for the cultivation of Cyanobium sp. This work reports the tools for the production of Cyanobium sp. as a source of high-value products, thus increasing its biotechnological potentials.

Cultivation of Chlorella vulgaris in a Light-Receiving-Plate (LRP)-Enhanced Raceway Pond for Ammonium and Phosphorus Removal from Pretreated Pig Urine

Fresh pig urine is unsuitable for microalgae cultivation due to its high concentrations of NH4+-N, high pH and insufficient magnesium. In this study, fresh pig urine was pretreated by dilution, pH adjustment, and magnesium addition in order to polish wastewater and produce microalgae biomass. Chlorella vulgaris was cultured in an in-house-designed light-receiving-plate (LRP)-enhanced raceway pond to treat the pretreated pig urine in both batch and continuous mode under outdoor conditions. NH4+-N and TP in wastewater were detected, and the growth of C. vulgaris was evaluated by chlorophyll fluorescence activity as well as biomass production. Results indicated that an 8-fold dilution, pH adjusted to 6.0 and MgSO4·7H2O dosage of 0.1 mg·L−1 would be optimal for the pig urine pretreatment. C. vulgaris could stably accumulate biomass in the LRP-enhanced raceway pond when cultured by both BG11 medium and the pretreated pig urine. About 1.72 g·m−2·day−1 of microalgal biomass could be produced and 98.20% of NH4+-N and 68.48% of TP could be removed during batch treatment. Hydraulic retention time of 7-9d would be optimal for both efficient nutrient removal and microalgal biomass production during continuous treatment.