Long-term acclimation might enhance the growth and competitive ability of Microcystis aeruginosa in warm environments

1. The positive effect of global warming on the growth of cyanobacteria has been widely predicted, but long-term studies targeting their adaptive potential to higher temperature have not been carried out so far. Predicting the magnitude and impact of cyanobacterial blooms in the future as a response to global warming requires an understanding of how cyanobacteria might change in the long term due to climate change. 2. Here we examined the effect of exposing three Microcystis aeruginosa strains isolated in Romania to ambient (22°C) and high (26°C) temperature for 6 months. Then, the competitive ability of the strains after heat acclimation was evaluated, by analysing their impact on plankton community composition. 3. One of the three strains displayed significantly higher growth rates after 6 months of cultivation at higher temperatures. Following inoculation into a natural plankton community, the overall cyanobacterial abundance significantly increased in the cultures inoculated with this heat-acclimated strain of M. aeruginosa as compared to the ambient-acclimated version. The structure of eukaryotic communities was impacted by both inoculated cyanobacteria and temperature during the experiments. 4. The results of this study emphasise the high potential of cyanobacteria to respond to stressors, and highlight the fact that previous acclimation to warming is a critical factor in shaping the overall structure of plankton communities. 5. Our study strongly advocates for including a step of culture acclimation to future experimental conditions in research programmes aiming to better understand the long-term impact of climate change on aquatic ecosystems

The combined impact of low temperatures and shifting phosphorus availability on the competitive ability of cyanobacteria

In freshwater systems, cyanobacteria are strong competitors under enhanced temperature and eutrophic conditions. Understanding their adaptive and evolutionary potential to multiple environmental states allows us to accurately predict their response to future conditions. To better understand if the combined impacts of temperature and nutrient limitation could suppress the cyanobacterial blooms, a single strain of Microcystis aeruginosa was inoculated into natural phytoplankton communities with different nutrient conditions: oligotrophic, eutrophic and eutrophic with the addition of bentophos. We found that the use of the bentophos treatment causes significant differences in prokaryotic and eukaryotic communities. This resulted in reduced biodiversity among the eukaryotes and a decline in cyanobacterial abundance suggesting phosphorus limitation had a strong impact on the community structure. The low temperature during the experiment lead to the disappearance of M. aeruginosa in all treatments and gave other phytoplankton groups a competitive advantage leading to the dominance of the eukaryotic families that have diverse morphologies and nutritional modes. These results show cyanobacteria have a reduced competitive advantage under certain temperature and nutrient limiting conditions and therefore, controlling phosphorus concentrations could be a possible mitigation strategy for managing harmful cyanobacterial blooms in a future warmer climate

PEGylation of surfacted magnetite core–shell nanoparticles for biomedical application

The surface of oleate double layer coated (surfacted) magnetite nanoparticles (OA@MNPs) was coated by PEG (poly(ethylene glycol) of Mw=1000, 4000 or 20,000Da, respectively, to get core-shell structured nanomagnets. The oleate bilayers were prepared in two different ways; (i) oleic acid was added directly into the magnetite co-precipitation mixture containing the MNPs to obtain OA@s-MNP samples - s-MNP standing for "as-synthesized MNP" and (ii) sodium oleate (oleate anion, OA) was added to the purified MNPs to obtain OA@p-MNP samples - p-MNP standing for "purified MNP". The effect of the surfactant addition method on the pH- and ionic strength-dependent stability (dynamic laser light scattering and laser-Doppler electrophoresis experiments), the biomedical applicability (MRI measurements) and the biocompatibility (blood sedimentation and blood smear tests) of the core-shell MNPs was studied. Different mechanisms of oleate adsorption were found in ATR FT-IR experiments (inner sphere surface complexation via ligand exchange for the s-MNPs and additional H-bonding for the p-MNPs), suggesting different behaviour. The colloidal stability and salt tolerance of the two kinds of OA@MNPs were similar, but the hydrodynamic diameter of the OA@s-MNP was considerably larger than that of OA@p-MNP. In accordance with this, the r2 relaxation was also higher for the s-MNP samples (~400 and ~200mM-1s-1, respectively). The physico-chemical tests indicate that the OA-coated MNPs form clusters and the degree of clustering of OA@s-MNPs is significantly greater than that of OA@p-MPNs. PEGylation does not appear to affect colloidal stability and salt tolerance meaningfully. The adsorption of PEG was proved experimentally. We have found that the PEG top layer decreases the electrostatic contribution, nevertheless increases the steric contribution of the original electrosteric stabilization caused by the OA double layer. However, an increase in the molecular weight above 1000Da and the amount of added PEG above 5mmol/g gradually reduces the salt tolerance of the samples. The results indicate strong potential for biomedical application and biocompatibility of the PEGylated MNPs

The impact of cation concentration on Microcystis (cyanobacteria) scum formation

Cyanobacterial scums at the surface of the lakes are potentially harmful phenomena with increasing occurrence in the last decades, and the causes that lead to their formation are still an unresolved issue. In order to better understand what triggers the scums, we investigated the effect of several Mg²⁺ and Ca²⁺ ion concentrations in promoting them in eight Microcystis aeruginosa strains. The possibility to prevent scum formation by using the ion chelator EDTA was also explored. We found that in some strains the cell aggregation takes place under lower ion source concentrations (20 mM MgSO₄ or CaCl₂), while in others this phenomenon does not occur even at 60 mM concentration. The scum formation correlated to the amount of extracellular polymeric substances (between 234 and 351 µg/cell). EDTA failed to prevent the scum formation in most strains, and in turn it caused cell lysis followed by the release of cellular content into the culture medium. We emphasize the relevance of these results for cyanobacterial scum formation in the environment and we also suggest that controlling the salinity of the medium (by manipulating the ion concentration) is a potentially efficient method for biomass harvesting in large ponds/tanks

Spatio-temporal insights into microbiology of the freshwater-to-hypersaline, oxic-hypoxic-euxinic waters of Ursu Lake

Ursu Lake is located in the Middle Miocene salt deposit of Central Romania. It is stratified, and the water column has three distinct water masses: an upper freshwater-to-moderately saline stratum (0–3 m), an intermediate stratum exhibiting a steep halocline (3–3.5 m), and a lower hypersaline stratum (4 m and below) that is euxinic (i.e. anoxic and sulphidic). Recent studies have characterized the lake's microbial taxonomy and given rise to intriguing ecological questions. Here, we explore whether the communities are dynamic or stable in relation to taxonomic composition, geochemistry, biophysics, and ecophysiological functions during the annual cycle. We found: (i) seasonally fluctuating, light-dependent communities in the upper layer (≥0.987–0.990 water-activity), a stable but phylogenetically diverse population of heterotrophs in the hypersaline stratum (water activities down to 0.762) and a persistent plate of green sulphur bacteria that connects these two (0.958–0.956 water activity) at 3–3.5 to 4 m; (ii) communities that might be involved in carbon- and sulphur-cycling between and within the lake's three main water masses; (iii) uncultured lineages including Acetothermia (OP1), Cloacimonetes (WWE1), Marinimicrobia (SAR406), Omnitrophicaeota (OP3), Parcubacteria (OD1) and other Candidate Phyla Radiation bacteria, and SR1 in the hypersaline stratum (likely involved in the anaerobic steps of carbon- and sulphur-cycling); and (iv) that species richness and habitat stability are associated with high redox-potentials. Ursu Lake has a unique and complex ecology, at the same time exhibiting dynamic fluctuations and stability, and can be used as a modern analogue for ancient euxinic water bodies and comparator system for other stratified hypersaline systems

Comparison Evaluation of the Biological Effects of Sterigmatocystin and Aflatoxin B1 Utilizing SOS-Chromotest and a Novel Zebrafish (Danio rerio) Embryo Microinjection Method

Aflatoxin B1 (AFB1) is a potent mycotoxin and natural carcinogen. The primary producers of AFB1 are Aspergillus flavus and A. parasiticus. Sterigmatocystin (STC), another mycotoxin, shares its biosynthetic pathway with aflatoxins. While there are abundant data on the biological effects of AFB1, STC is not well characterised. According to published data, AFB1 is more harmful to biological systems than STC. It has been suggested that STC is about one-tenth as potent a mutagen as AFB1 as measured by the Ames test. In this research, the biological effects of S9 rat liver homogenate-activated and non-activated STC and AFB1 were compared using two different biomonitoring systems, SOS-Chromotest and a recently developed microinjection zebrafish embryo method. When comparing the treatments, activated STC caused the highest mortality and number of DNA strand breaks across all injected volumes. Based on the E. coli SOS-Chromotest, the two toxins exerted the same genotoxicities. Moreover, according to the newly developed zebrafish microinjection method, STC appeared more toxic than AFB1. The scarce information correlating AFB1 and STC toxicity suggests that AFB1 is a more potent genotoxin than STC. Our findings contradict this assumption and illustrate the need for more complex biomonitoring systems for mycotoxin risk assessment

Sources and mechanisms of combined heavy-metal and antibiotic resistance traits in bacteria

Nowadays, antibiotic resistance poses a great threat to the health of the individuals worldwide. In this context, scientific interest on how bacteria adapt in stress-related environmental conditions like those enriched in heavy metals and how the heavy-metal adaptive mechanism influence the antibiotic resistance is increasing. It was noted that the simultaneous use of heavy metals and antibiotics in agriculture and aquaculture might positively impact the dissemination of the antibiotic resistance genes in the environment. Current knowledge on the sources of simultaneous pollution with heavy metals and antibiotics, the co-occurrence of heavy-metal and antibiotic resistance traits in bacteria altogether with physiological mechanism underlying this phenomenon are overviewed. Tugui et al (PDF

Drinking water quality assessment in the Danube Delta Biosphere Reserve

This research is aimed mainly at the assessment of water quality of several drinking water treatment plants and groundwater wells, from the Danube Delta Biosphere Reserve and the habits of the local population in terms of water consumption and use. Thus, the study highlights the presence and distribution of prokaryotic and eukaryotic assemblages, specifically the algal communities which emerged as a dominant group in the investigated drinking water sources. The spatial variation of the pH, EC, turbidity, dissolved oxygen (DO), temperature, algae species and biomass was measured in five drinking water treatment plants (DWTP) and three groundwater wells from villages located in the Danube Delta Biosphere Reserve. No PCR product was present for either genes coding anatoxin, microcystin and saxitoxin. The bbe- Moldaenke technique identified the presence of sligthly more algal groups, than the light microscopic technique; both methods show clear results: the water treated in the drinking water treatment plants has significant algal biomass. The water quality indicated by the algal communities shows oligo-β-mesosaprobic conditions, despite the high number of taxa and individuals from Sf. Gheorghe and C. A. Rosseti samples, they reflect oligotrophic conditions. Torok et al (PDF

Genome-wide transcriptional response to silver stress in extremely halophilic archaeon Haloferax alexandrinus DSM 27206 T

Abstract Background The extremely halophilic archaeon Haloferax (Hfx.) alexandrinus DSM 27206 T was previously documented for the ability to biosynthesize silver nanoparticles while mechanisms underlying its silver tolerance were overlooked. In the current study, we aimed to assess the transcriptional response of this haloarchaeon to varying concentrations of silver, seeking a comprehensive understanding of the molecular determinants underpinning its heavy metal tolerance. Results The growth curves confirmed the capacity of Hfx. alexandrinus to surmount silver stress, while the SEM–EDS analysis illustrated the presence of silver nanoparticles in cultures exposed to 0.5 mM silver nitrate. The RNA-Seq based transcriptomic analysis of Hfx. alexandrinus cells exposed to 0.1, 0.25, and 0.5 mM silver nitrate revealed the differential expression of multiple sets of genes potentially employed in heavy-metal stress response, genes mostly related to metal transporters, basic metabolism, oxidative stress response and cellular motility. The RT-qPCR analysis of selected transcripts was conducted to verify and validate the generated RNA-Seq data. Conclusions Our results indicated that copA, encoding the copper ATPase, is essential for the survival of Hfx. alexandrinus cells in silver-containing saline media. The silver-exposed cultures underwent several metabolic adjustments that enabled the activation of enzymes involved in the oxidative stress response and impairment of the cellular movement capacity. To our knowledge, this study represents the first comprehensive analysis of gene expression in halophillic archaea facing increased levels of heavy metals