Metals in cyanobacteria: analysis of the copper, nickel, cobalt and arsenic homeostasis mechanisms

Semi-continuous cultivation of EPS-producing marine cyanobacteria: A green biotechnology to remove dissolved metals obtaining metal-organic materials

Given the necessity for bioprocesses scaling-up, the present study aims to explore the potential of three marine cyanobacteria and a consortium, cultivated in semi-continuous mode, as a green approach for i) continuous exopolysaccharide-rich biomass production and ii) removal of positively charged metals (Cu, Ni, Zn) from mono and multi-metallic solutions. To ensure the effectiveness of both cellular and released exopolysaccharides, weekly harvested whole cultures were confined in dialysis tubings. The results revealed that all the tested cyanobacteria have a stronger affinity towards Cu in mono and three-metal systems. Despite the amount of metals removed per gram of biomass decreased with higher biosorbent dosage, the more soluble carbohydrates were produced, the greater was the metal uptake, underscoring the pivotal role of released exopolysaccharides in metal biosorption. According to this, Dactylococcopsis salina 16Som2 showed the highest carbohydrate productivity (142 mg L-1 d-1) and metal uptake (84 mg Cu g-1 biomass) representing a promising candidate for further studies. The semi-continuous cultivation of marine cyanobacteria here reported assures a schedulable production of exopolysaccharide-rich biosorbents with high metal removal and recovery potential, even from multi-metallic solutions, as a step forward in the industrial application of cyanobacteria.

Leptochelins A-C, Cytotoxic Metallophores Produced by Geographically Dispersed Leptothoe Strains of Marine Cyanobacteria

Metals are important cofactors in the metabolic processes of cyanobacteria, including photosynthesis, cellular respiration, DNA replication, and the biosynthesis of primary and secondary metabolites. In adaptation to the marine environment, cyanobacteria use metallophores to acquire trace metals when necessary as well as to reduce potential toxicity from excessive metal concentrations. Leptochelins A-C were identified as structurally novel metallophores from three geographically dispersed cyanobacteria of the genus Leptothoe. Determination of the complex structures of these metabolites presented numerous challenges, but they were ultimately solved using integrated data from NMR, mass spectrometry and deductions from the biosynthetic gene cluster. The leptochelins are comprised of halogenated linear NRPS-PKS hybrid products with multiple heterocycles that have potential for hexadentate and tetradentate coordination with metal ions. The genomes of the three leptochelin producers were sequenced, and retrobiosynthetic analysis revealed one candidate biosynthetic gene cluster (BGC) consistent with the structure of leptochelin. The putative BGC is highly homologous in all three Leptothoe strains, and all possess genetic signatures associated with metallophores. Postcolumn infusion of metals using an LC-MS metabolomics workflow performed with leptochelins A and B revealed promiscuous binding of iron, copper, cobalt, and zinc, with greatest preference for copper. Iron depletion and copper toxicity experiments support the hypothesis that leptochelin metallophores may play key ecological roles in iron acquisition and in copper detoxification. In addition, the leptochelins possess significant cytotoxicity against several cancer cell lines.

Synergistic regulation of hydrogen sulfide and nitric oxide on biochemical components, exopolysaccharides, and nitrogen metabolism in nickel stressed rice field cyanobacteria

The present study examined the regulatory mechanism of hydrogen sulfide (H2S) and nitric oxide (NO) in nickel (Ni) stressed cyanobacteria viz., Nostoc muscorum and Anabaena sp. by analyzing growth, photosynthetic pigments, biochemical components (protein and carbohydrate), exopolysaccharides (EPS), inorganic nitrogen content, and activity of enzymes comprised in nitrogen metabolism and Ni accumulation. The 1 µM Ni substantially diminished growth by 18% and 22% in N. muscorum and Anabaena sp. respectively, along with declining the pigment contents (Chl a/Car ratio and phycobiliproteins), and biochemical components. It also exerted negative impacts on inorganic uptake of nitrate and nitrite contents; nitrate reductase and nitrite reductase; and ammonium assimilating enzymes (glutamine synthetase, glutamate synthase, and glutamate dehydrogenase exhibited a reverse trend) activities. Nonetheless, the adverse impact of Ni can be mitigated through the exogenous supplementation of NaHS [sodium hydrosulfide (8 µM); H2S donor] and SNP [sodium nitroprusside (10 µM); NO donor] which showed substantial improvement on growth, pigments, nitrogen metabolism, and EPS layer and noticeably occurred as a consequence of a substantial reduction in Ni accumulation content which minimized the toxicity effects. The accumulation of Ni on both the cyanobacterial cell surface (EPS layer) are confirmed by the SEM-EDX analysis. Further, the addition of NO scavenger (PTIO; 20 µM) and inhibitor of NO (L-NAME; 100 µM); and H2S scavenger (HT; 20 µM) and H2S inhibitor (PAG; 50 µM) reversed the positive responses of H2S and NO and damages were more prominent under Ni stress thereby, suggesting the downstream signaling of H2S on NO-mediated alleviation. Thus, this study concludes the crosstalk mechanism of H2S and NO in the mitigation of Ni-induced toxicity in rice field cyanobacteria.

Coupling dairy wastewaters for nutritional balancing and water recycling: sustainable heterologous 2-phenylethanol production by engineered cyanobacteria

Microalgae biotechnology is hampered by the high production costs and the massive usage of water during large-volume cultivations. These drawbacks can be softened by the production of high-value compounds and by adopting metabolic engineering strategies to improve their performances and productivity. Today, the most sustainable approach is the exploitation of industrial wastewaters for microalgae cultivation, which couples valuable biomass production with water resource recovery. Among the food processing sectors, the dairy industry generates the largest volume of wastewaters through the manufacturing process. These effluents are typically rich in dissolved organic matter and nutrients, which make it a challenging and expensive waste stream for companies to manage. Nevertheless, these rich wastewaters represent an appealing resource for microalgal biotechnology. In this study, we propose a sustainable approach for high-value compound production from dairy wastewaters through cyanobacteria. This strategy is based on a metabolically engineered strain of the model cyanobacterium Synechococcus elongatus PCC 7942 (already published elsewhere) for 2-phenylethanol (2-PE). 2-PE is a high-value aromatic compound that is widely employed as a fragrance in the food and cosmetics industry thanks to its pleasant floral scent. First, we qualitatively assessed the impact of four dairy effluents on cyanobacterial growth to identify the most promising substrates. Both tank-washing water and the liquid effluent of exhausted sludge resulted as suitable nutrient sources. Thus, we created an ideal buffer system by combining the two wastewaters while simultaneously providing balanced nutrition and completely avoiding the need for fresh water. The combination of 75% liquid effluent of exhausted sludge and 25% tank-washing water with a fine-tuning ammonium supplementation yielded 180 mg L-1 of 2-PE and a biomass concentration of 0.6 gDW L-1 within 10 days. The mixture of 90% exhausted sludge and 10% washing water produced the highest yield of 2-PE (205 mg L-1) and biomass accumulation (0.7 gDW L-1), although in 16 days. Through these treatments, the phosphates were completely consumed, and nitrogen was removed in a range of 74%-77%. Overall, our approach significantly valorized water recycling and the exploitation of valuable wastewaters to circularly produce marketable compounds via microalgae biotechnology, laying a promising groundwork for subsequent implementation and scale-up.

Polysphaeroides filiformis, a proterozoic cyanobacterial microfossil and implications for cyanobacteria evolution

Deciphering the fossil record of cyanobacteria is crucial to understand their role in the chemical and biological evolution of the early Earth. They profoundly modified the redox conditions of early ecosystems more than 2.4 Ga ago, the age of the Great Oxidation Event (GOE), and provided the ancestor of the chloroplast by endosymbiosis, leading the diversification of photosynthetic eukaryotes. Here, we analyze the morphology, ultrastructure, chemical composition, and metals distribution of Polysphaeroides filiformis from the 1040-1006 Ma Mbuji-Mayi Supergroup (DR Congo). We evidence trilaminar and bilayered ultrastructures for the sheath and the cell wall, respectively, and the preservation of Ni-tetrapyrrole moieties derived from chlorophyll in intracellular inclusions. This approach allows an unambiguous interpretation of P. filiformis as a branched and multiseriate photosynthetic cyanobacterium belonging to the family of Stigonemataceae. It also provides a possible minimum age for the emergence of multiseriate true branching nitrogen-fixing and probably heterocytous cyanobacteria.

Adaptability of sulfur-disproportionating bacteria for mine water remediation under the pressures of heavy metal ions and high sulfate content

Biological sulfide production processes mediated by sulfate/sulfur reduction have gained attention for metal removal from industrial wastewater (e.g., mine water (MW) and metallurgical wastewater) via forming insoluble metal sulfides. However, these processes often necessitate the addition of external organic compounds as electron donors, which poses a constraint on the broad application of this technology. A recent proof of concept study reported that microbial sulfur disproportionation (SD) produced sulfide with no demand for organics, which could achieve more cost-benefit MW treatment against the above-mentioned processes. However, the resistance of SD bioprocess to different metals and high sulfate content in MW remains mysterious, which may substantially affect the practical applicability of such process. In this study, the sulfur-disproportionating bacteria (SDB)-dominated consortium was enriched from a previously established SD-driven bioreactor, in which Dissulfurimicrobium sp. with a relative abundance of 39.9 % was the predominated SDB. When exposed to the real pretreated acidic MW after the pretreatment process of pH amelioration, the sulfur-disproportionating activity remained active, and metals were effectively removed from the MW. Metal tolerance assays further demonstrated that the consortium had a good tolerance to different metal ions (i.e., Pb2+, Cu2+, Ni2+, Mn2+, Zn2+), especially for Mn2+ with a concentration of approximately 20 mg/L. It suggested the robustness of Dissulfurimicrobium sp. likely due to the presence of genes encoding for the enzymes associated with metal(loid) resistance/uptake. Additionally, although high sulfate content resulted in a slight inhibition on the sulfur-disproportionating activity, the consortium still achieved sulfide production rates of 27.3 mg S/g VSS-d on average under an environmentally relevant sulfate level (i.e., 1100 mg S/L), which is comparable to those reported in sulfate reduction. Taken together, these findings imply that SDB could ensure sustainable MW treatment in a more cost-effective and organic-free way.

Protecting the invisible: Establishing guideline values for copper toxicity to marine microbiomes

Understanding the rapid responses of marine microbiomes to environmental disturbances is paramount for supporting early assessments of harm to high-value ecosystems, such as coral reefs. Yet, management guidelines aimed at protecting aquatic life from environmental pollution remain exclusively defined for organisms at higher trophic levels. In this study, 16S rRNA gene amplicon sequencing was applied in conjunction with propidium monoazide for cell-viability assessment as a sensitive tool to determine taxon- and community-level changes in a seawater microbial community under copper (Cu) exposure. Bayesian model averaging was used to establish concentration-response relationships to evaluate the effects of copper on microbial composition, diversity, and richness for the purpose of estimating microbiome Hazard Concentration (mHCx) values. Predicted mHC5 values at which a 5 % change in microbial composition, diversity, and richness occurred were 1.05, 0.72, and 0.38 μg Cu L-1, respectively. Threshold indicator taxa analysis was applied across the copper concentrations to identify taxon-specific change points for decreasing taxa. These change points were then used to generate a Prokaryotic Sensitivity Distribution (PSD), from which mHCxdec values were derived for copper, suitable for the protection of 99, 95, 90, and 80 % of the marine microbiome. The mHC5dec guideline value of 0.61 μg Cu L-1, protective of 95 % of the marine microbial community, was lower than the equivalent Australian water quality guideline value based on eukaryotic organisms at higher trophic levels. This suggests that marine microbial communities might be more vulnerable, highlighting potential insufficiencies in their protection against copper pollution. The mHCx values proposed here provide approaches to quantitatively assess the effects of contaminants on microbial communities towards the inclusion of prokaryotes in future water quality guidelines.

Trichocoleus desertorum isolated from Negev desert petroglyphs: Characterization, adaptation and bioerosion potential

The Negev petroglyphs are considered valuable cultural heritage sites, but unfortunately, they are exposed to deterioration processes caused by anthropogenic and natural forces. Despite the many studies that have already pointed to the role of cyanobacteria in biogenic rock weathering, the knowledge involved in the process is still lacking. In this study, a cyanobacterial strain was isolated from the Negev Desert petroglyphs aiming to reveal its involvement in geochemical cycles and in the weathering processes of the rock substrate. The strain was characterized using morphological, molecular, and microscopic studies. The morphological research revealed a green-bluish, bundle-forming filamentous strain characterized by trichomes embedded in a common sheath. A combination of Nanopore and Illumina sequencing technologies facilitated the assembly of a near-complete genome containing 5,458,034 base pairs. A total of 5027 coding sequences were revealed by implementing PROKKA software. Annotation of five replicas of the 16S ribosomal RNA genes revealed that the Negev cyanobacteria isolate is closely (99.73 %) related to Trichocoleus desertorum LSB90_MW403957 isolated from the Sahara Desert, Algeria. The local strain was thus named Trichocoleus desertorum NBK24 CP116619. Several gene sequences that code for possible environmental adaptation mechanisms were found. Our study also identified genes for membrane transporters involved in the exchange of chemical elements, suggesting a possible interaction with rock minerals. Microscopic observations of T. desertorum NBK24 CP116619 infected onto calcareous stone slabs under laboratory conditions demonstrated the effect of the isolated cyanobacteria on stone surface degradation. In conclusion, the findings of this study further our understanding of terrestrial cyanobacterial genomes and functions and highlight the role of T. desertorum NBK24 CP116619 in stone weathering processes. This information may contribute to the creation of efficient restoration strategies for stone monuments affected by cyanobacteria.

Comparative assessment of bacterial diversity and composition in arsenic hyperaccumulator, Pteris vittata L. and non-accumulator, Pteris ensiformis Burm

The use of arsenic (As) for various industrial and agricultural applications has led to worldwide environmental contamination. Phytoremediation using hyperaccumulators is a sustainable soil As mitigation strategy. Microbial processes play an important role in the tolerance and uptake of trace elements such as in plants. The rhizospheric and endophytic microbial communities are responsible for accelerating the mobility of trace elements around the roots and the production of plant growth-promoting compounds and enzymes. Several studies have reported that the As hyperaccumulator, Pteris vittata L. (PV) influences the microbial community in its rhizosphere and roots. Deciphering the differences in the microbiomes of hyperaccumulators and non-accumulators is crucial in understanding the mechanism of hyperaccumulation. We hypothesized that there are significant differences in the microbiome of roots, rhizospheric soil, and bulk soil between the hyperaccumulator PV and a non-accumulator of the same genus, Pteris ensiformis Burm. (PE), and that the differential recruitment of bacterial communities provides PV with an advantage in As contaminated soil. We compared root endophytic, rhizospheric, and bulk soil microbial communities between PV and PE species grown in As-contaminated soil in a greenhouse setting. There was a significant difference (p < 0.001) in the microbiome of the three compartments between the ferns. Differential abundance analysis showed 328 Amplicon Sequence Variants (ASVs) enriched in PV compared to 172 in PE. The bulk and rhizospheric soil of both ferns were abundant in As-resistant genera. However, As-tolerant root endophytic genera were present in PV but absent in PE. Our findings show that there is a difference between the bacterial composition of an As hyperaccumulator and a non-accumulator species grown in As-contaminated soil. These differences need to be further explored to develop strategies for improving the efficiency of metal uptake in plants growing in As polluted soil.

Prospects of a hot spring-originated novel cyanobacterium, Scytonema ambikapurensis, for wastewater treatment and exopolysaccharide-enriched biomass production

The present work performs the polyphasic characterization of a novel cyanobacterial species Scytonema ambikapurensis isolated from an Indian hot spring and evaluates its wastewater bioremediation potential. While the physicochemical analyses of the wastewater indicated high load of nutrients and metals, the wastewater bioremediation experiment performed using the test cyanobacterium denoted the removal of 70 and 86% phosphate, 49 and 66% sulfate, 96 and 98% nitrate, 91 and 92% nitrite, 95 and 96% ammonia, 66 and 72% chloride, 79 and 81% zinc, 68 and 80% nickel, 81 and 90% calcium, and 80 and 90% potassium from the autoclaved and un-autoclaved wastewater, respectively, after 20 days of culturing. The kinetics study of zinc and nickel removal from wastewater revealed that the cyanobacterium employed sequential biosorption (by following pseudo-second-order kinetics model) and bioaccumulation methods to remove these two metals. The quality of the autoclaved and un-autoclaved wastewater was further improved by the cyanobacterium through reduction of hardness by 74 and 81%, respectively. In wastewater, the cyanobacterium not only enhanced its biomass, chlorophyll and carbohydrate contents, but also produced small amount of released and high capsular exopolysaccharide (EPS). The FTIR and TGA analyses of capsular EPS unraveled that it was a negatively charged sulfated biomolecule having thermostability up to 240 °C, which suggested its possible use as excellent emulsifying, viscosifying, and biosorption agent. The credibility of this EPS as biosorption agent was ascertained by evaluating its metal chelating ability. Finally, the experimental data denoting the ability of S. ambikapurensis to bioremediate wastewater and simultaneously produce EPS was statistically validated by PCA1-pollutant removal model and the PCA2-cellular constituent model, respectively. Briefly, the study discloses that the cyanobacterium has huge biotechnological and industrial importance as it bioremediates wastewater and simultaneously produces thermostable exopolysaccharide.

Fluorescence Analysis of Biocide Efficiency in Antifouling Coatings against Cyanobacteria

This study focused on the antifouling effect of copper oxide (Cu₂O)- and zineb-based coatings against Cyanothece sp. ATCC 51142 by analysing photosynthetic activity using chlorophyll fluorescence. The photoautotrophically grown cyanobacterium was exposed to toxic coatings over a short-term period of 32 h. The study showed that Cyanothece cultures are particularly sensitive to biocides (i) released from antifouling paints and (ii) exhibited by contact with the coated surfaces. Changes in the maximum quantum yield of photosystem II (F_V/F_M) were observed within the first 12 h of exposure to the coatings. Partial recovery of F_V/F_M in Cyanothece was revealed 24 h post exposure to a copper- and zineb-free coating. In this research, we proposed an analysis of the evaluation of fluorescence data to study the initial response of cyanobacterial cells to copper- and non-copper-based antifouling coatings formulated with zineb. We evaluated the dynamics of coating toxicity by determining the characteristic time constants of changes in the F_V/F_M. Within the most toxic paints studied, those formulated with the highest concentration of Cu₂O and zineb, the estimated time constants were 3.9 times lower compared to the copper- and zineb-free paint. The use of zineb in copper-based antifouling coatings enhanced the toxic effect of paints and contributed to a faster decline in photosystem II activity in Cyanothece cells. The analysis we proposed, along with the fluorescence screening results, may be useful in evaluating the initial antifouling dynamic action against photosynthetic aquacultures.

The Influence of Micronutrient Trace Metals on Microcystis aeruginosa Growth and Toxin Production

Microcystis aeruginosa is a widespread cyanobacteria capable of producing hepatotoxic microcystins. Understanding the environmental factors that influence its growth and toxin production is essential to managing the negative effects on freshwater systems. Some micronutrients are important cofactors in cyanobacterial proteins and can influence cyanobacterial growth when availability is limited. However, micronutrient requirements are often species specific, and can be influenced by substitution between metals or by luxury uptake. In this study, M. aeruginosa was grown in modified growth media that individually excluded some micronutrients (cobalt, copper, iron, manganese, molybdenum) to assess the effect on growth, toxin production, cell morphology and iron accumulation. M. aeruginosa growth was limited when iron, cobalt and manganese were excluded from the growth media, whereas the exclusion of copper and molybdenum had no effect on growth. Intracellular microcystin-LR concentrations were variable and were at times elevated in treatments undergoing growth limitation by cobalt. Intracellular iron was notably higher in treatments grown in cobalt-deplete media compared to other treatments possibly due to inhibition or competition for transporters, or due to irons role in detoxifying reactive oxygen species (ROS).

Metagenomic and genomic characterization of heavy metal tolerance and resistance genes in the rhizosphere microbiome of Avicennia germinans in a semi-arid mangrove forest in the tropics

Mangroves are often exposed to heavy metals that accumulate in the food chain, generate toxicity to mangrove plants and affect microbial diversity. This study determined the abundance of genes associated with resistance and tolerance to heavy metals in the rhizosphere microbiome of Avicennia germinans from a semi-arid mangrove of La Guajira-Colombia by metagenomics and genomics approach. Twenty-eight genes associated with tolerance and 49 genes related to resistance to heavy metals were detected. Genes associated with tolerance and resistance to Cu, especially cusA and copA, were the most abundant. The highest number of genes for tolerance and resistance were for Zn and Co, respectively. The isolate Vibrio fluvialis showed the ability to tolerate Cu, Ni, Zn, and Cd. This work used a complementary approach of metagenomics and genomics to characterize the potential of mangrove microorganisms to tolerate and resist heavy metals and the influence of salinity on their abundance.

Arthrospira platensis as Bioremediator of Rhenium Mono- and Polymetallic Synthetic Effluents

Rhenium is a scarce and highly important metal for industry and technology. In the present study, the cyanobacterium Arthrospira platensis (Spirulina) was used to remove rhenium and related elements (Mo and Cu) from mono- and polymetallic synthetic effluents. Metal ions in different concentrations were added to the culture medium on the first, third, and fifth days of biomass growth, and their uptake by the biomass was traced using ICP-AES technique. The accumulation of rhenium in the biomass was dependent on the chemical composition of the effluents, and the highest uptake of 161 mg/kg was achieved in the Re-Cu system. The presence of rhenium, copper, and molybdenum affected the productivity of Spirulina biomass and its biochemical composition (proteins, carbohydrates, lipids, phycobiliproteins, the content of chlorophyll α and β-carotene). With the growth of biomass in the presence of rhenium or rhenium and molybdenum, a pronounced increase in productivity and protein content was observed. The presence of copper in systems has a negative effect on biomass productivity and biochemical composition. Arthrospira platensis may be of interest as a bioremediator of rhenium-containing effluents of various chemical compositions.

Plastic leachates impair picophytoplankton and dramatically reshape the marine microbiome

BACKGROUND

Each year, approximately 9.5 million metric tons of plastic waste enter the ocean with the potential to adversely impact all trophic levels. Until now, our understanding of the impact of plastic pollution on marine microorganisms has been largely restricted to the microbial assemblages that colonize plastic particles. However, plastic debris also leaches considerable amounts of chemical additives into the water, and this has the potential to impact key groups of planktonic marine microbes, not just those organisms attached to plastic surfaces.

RESULTS

To investigate this, we explored the population and genetic level responses of a marine microbial community following exposure to leachate from a common plastic (polyvinyl chloride) or zinc, a specific plastic additive. Both the full mix of substances leached from polyvinyl chloride (PVC) and zinc alone had profound impacts on the taxonomic and functional diversity of our natural planktonic community. Microbial primary producers, both prokaryotic and eukaryotic, which comprise the base of the marine food web, were strongly impaired by exposure to plastic leachates, showing significant declines in photosynthetic efficiency, diversity, and abundance. Key heterotrophic taxa, such as SAR11, which are the most abundant planktonic organisms in the ocean, also exhibited significant declines in relative abundance when exposed to higher levels of PVC leachate. In contrast, many copiotrophic bacteria, including members of the Alteromonadales, dramatically increased in relative abundance under both exposure treatments. Moreover, functional gene and genome analyses, derived from metagenomes, revealed that PVC leachate exposure selects for fast-adapting, motile organisms, along with enrichment in genes usually associated with pathogenicity and an increased capacity to metabolize organic compounds leached from PVC.

CONCLUSIONS

This study shows that substances leached from plastics can restructure marine microbial communities with the potential for significant impacts on trophodynamics and biogeochemical cycling. These findings substantially expand our understanding of the ways by which plastic pollution impact life in our oceans, knowledge which is particularly important given that the burden of plastic pollution in the marine environment is predicted to continue to rise. Video Abstract.

Ecotoxicological response of Spirulina platensis to coexisted copper and zinc in anaerobic digestion effluent

Copper ion (Cu²⁺) and zinc ion (Zn²⁺) are widely co-existent in anaerobic digestion effluent as typical contaminants. This work aims to explore how Cu²⁺-Zn²⁺ association affects physiological properties of S. platensis using Schlösser medium (SM) and sterilized anaerobic digestion effluent (SADE). Microalgae cells viability, biochemical properties, uptake of Cu²⁺ and Zn²⁺, and risk assessment associated with the biomass reuse as additives to pigs were comprehensively assessed. Biomass production ranged from 0.03 to 0.28 g/L in SM and 0.63 to 0.79 g/L in SADE due to the presence of Cu²⁺ and Zn²⁺. Peak value of chlorophyll-a and carotenoid content during the experiment decreased by 70-100% and 40-100% in SM, and by 70-77% and 30-55% in SADE. Crude protein level reduced by 4-41% in SM and by 65-75% in SADE. The reduction ratio of these compounds was positively related to the Cu²⁺ and Zn²⁺ concentrations. Maximum value of saturated and unsaturated fatty acids was both obtained at 0.3 Cu + 2.0 Zn (50.8% and 22.8%, respectively) and 25% SADE reactors (33.8% and 27.7%, respectively). Uptake of Cu in biomass was facilitated by Zn²⁺ concentration (> 4.0 mg/L). Risk of S. platensis biomass associated with Cu²⁺ was higher than Zn²⁺. S. platensis from SM (Cu²⁺ ≤ 0.3 mg/L and Zn²⁺ ≤ 4.0 mg/L) and diluted SADE (25% and 50% SADE) reactors could be used as feed additives without any risk (hazard index <1), which provides sufficient protein and fatty acids for pig consumption. These results revealed the promising application of using S. platensis for bioremediation of Cu²⁺ and Zn²⁺ in anaerobic digestion effluent and harvesting biomass for animal feed additives.

Assessment of Metal Accumulation by Arthrospira platensis and Its Adaptation to Iterative Action of Nickel Mono- and Polymetallic Synthetic Effluents

Cyanobacteria-mediated wastewater remediation is an economical, efficient, and eco-friendly technology. The present work deals with the bioaccumulation performance of Arthrospira platensis (Spirulina) grown for four cycles in a medium containing nickel mono- and polymetallic synthetic effluents. The metal uptake by spirulina biomass was evaluated using neutron activation analysis. The effects of effluents on biomass production, protein, and phycobiliprotein content were assessed. Metal accumulation in the biomass depended on the effluent composition and metal ion concentrations. Nickel accumulation in the biomass was directly proportional to its concentration in effluents, and maximum uptake (1310 mg/kg) was attained in the Ni/Cr/Fe system. In the same system, biomass accumulated 110 times more chromium and 4.7 times more iron than control. The highest accumulation of copper (2870 mg/kg) was achieved in the Ni/Cu/Zn/Mo system and zinc (1860 mg/kg)—in the Ni/Cu/Zn/Sr system. In biomass grown in the media loaded with nickel and also chromium, iron, copper, strontium, zinc, and molybdenum, a decrease in productivity (on average by 10%) during the first cycle of cultivation and moderate reduction of protein content (by 15–27%) was observed. The presence of metals in the cultivation media inhibited phycobiliprotein synthesis, especially of phycocyanin, and promoted the synthesis of allophycocyanin. The maximum reduction of phycocyanin content was 77%, and the increase of allophycocyanin content—by 45%. Arthrospira platensis may be deemed as bioremediation of nickel-polluted wastewaters of complex composition.

From leaves to roots: Biophysical models of transport of substances in plants

The transport processes of substances in various plant tissues are extremely diverse. However, models aimed at elucidating the mechanisms of such processes are almost absent in the literature. A unified view of all these transport processes is necessary, considering the laws of statistical physics and thermodynamics. A model of active ion transport was constructed based on the laws of statistical physics. Using this model, we traced the entire pathway of substances and energy in a plant. The pathway included aspects of the production of energy in the process of photosynthesis, consumption of energy to obtain nutrients from the soil, transport of such substances to the main organelles of all types of plant cells, the rise of water with dissolved substances along the trunk to the leaves, and the evaporation of water, accompanied by a change in the percentage of isotopes caused by different rates of evaporation. Models of ion transport in the chloroplasts and mitochondria of plant cells have been constructed. A generalized model comprising plant cells and their vacuoles was analyzed. A model of the transport of substances in the roots of plants was also developed. Based on this model, the problem of transport of substances in tall trees has been considered. The calculated concentrations of ions in the vacuoles of cells and resting potentials agreed well with the experimental data.

Peculiarities of the Edaphic Cyanobacterium Nostoc linckia Culture Response and Heavy Metal Accumulation from Copper-Containing Multimetal Systems

Soil and water pollution is a major problem that has a negative impact on ecosystems and human health in particular. In the bioremediation processes, the application of photosynthetic microorganisms, including cyanobacteria, is a direction of action addressed with increasing frequency in the context of further development and improvement of environmentally friendly techniques needed for detoxification of soils and waters polluted with low concentrations of toxic elements, since they pose a challenge for traditional treatment methods. In the present study, the removal of copper and other metal ions from multielement systems by three generations of Nostoc linckia is discussed. Changes in the biochemical composition of the nostoc biomass, which accumulates metal ions, were monitored. Neutron activation analysis was applied to assess Cu, Fe, Ni, and Zn accumulation by biomass, as well as to determine the biochemical composition of biomass after specific biochemical methods were used. The capacity of the accumulation of copper and other metal ions from multi-elemental systems by cyanobacteria Nostoc linckia was high and increased over two cycles of biomass growth in the systems Cu-Fe-Ni and Cu-Fe-Zn and over three cycles in Cu-Fe and Cu-Fe-Ni-Zn systems. It constituted 1720–10,600 µg metal/g depending on the system and cycle of cultivation. The accumulation of Fe, Ni, and Zn also increased over the generations of nostoc. The process of metal accumulation was demonstrated by a significant change in the biomass biochemical composition. Cyanobacteria Nostoc linckia possess a pronounced capacity of copper and other metal ion accumulation from multimetal systems and showed an increased resistance in environments polluted with heavy metals.

The Evaluation of Bacterial Abundance and Functional Potentials in the Three Major Watersheds, Located in the Hot Spring Zone of the Tatun Volcano Group Basin, Taiwan

The Tatun Volcanic Group (TVG), located in northern Taiwan, is characterized by acidic hot springs where the outflow of the hot springs may affect the properties of the associated lotic water bodies. We investigated the bacterial diversity and functional profiles of the Peihuang (PHC), HuangGang (HGC), and Nanhuang Creeks (NHC) located in the TVG basin using 16S rRNA gene sequencing coupled with statistical analyses. Water samples were collected from various streams of the creeks for two months of the year. The NHC showed the highest diversity, richness, and a unique number of phyla, which was followed by the HGC. A reduced number of phyla and a lower diversity was noticed in the PHC. The NHC was found to be abundant in the genera Armatimonas, Prosthecobacter, Pirellula, and Bdellovibrio, whereas the HGC was rich in Thiomonas, Acidiphilium, Prevotella, Acidocella, Acidithiobacillus, and Metallibacterium. The PHC was abundant in Thiomonsa, Legionella, Acidocella, and Sulfuriferula. The samples did not show any strong seasonal variations with the bacterial diversity and abundance; however, the relative abundance of each sampling site varied within the sampling months. The iron transport protein- and the sulfur metabolism-related pathways were predicted to be the key functions in all the creeks, whereas the heavy metal-related functions, such as the cobalt/nickel transport protein and the cobalt-zinc-cadmium efflux system were found to be abundant in the HGC and PHC, respectively. The abundance of Bdellovibrio in the NHC, Diplorickettsia in the HGC, and Legionella in the PHC samples indicated a higher anthropogenic impact over the creek water quality. This study provides the data to understand the distinct bacterial community structure, as well as the functional potentials of the three major watersheds, and helps the knowledge of the impact of the physicochemical properties of the TVG hot springs upon the watersheds.

Interactions between antibiotics and heavy metals determine their combined toxicity to Synechocystis sp

Co-pollution of antibiotics and metals is prevailing in aquatic environments. However, risks of coexisted antibiotics and metals on aquatic organisms is unclear. This study investigated the combined toxicity of antibiotics and metals towards Synechocystis sp. PCC 6803, a cyanobacterium. We found that the joint toxicity of antibiotics and metals is dependent on their interplays. The complexation between chlortetracycline (CTC) and copper/cadmium (Cu(II)/Cd(II)) resulted in their antagonistic toxicity. Contrarily, an additive toxicity was found between florfenicol (FLO) and Cu(II)/Cd(II) due to lack of interactions between them. CTC facilitated the intracellular uptake of Cu(II) and Cd(II) by increasing the membrane permeability. However, FLO had no obvious effects on the internalization of metals in Synechocystis sp. Proteomic analysis revealed that the photosynthetic proteins was down-regulated by CTC and FLO, and ribosome was the primary target of FLO. These results were verified by parallel reaction monitoring (PRM). Cu(II) induced the up-regulation of iron-sulfur assembly, while Cd(II) disturbed the cyclic electron transport in Synechocystis sp. The co-exposure of CTC and metals markedly alleviated the dysregulation of proteins, while the co-exposure of FLO and metals down-regulated biological functions such as ATP synthesis, photosynthesis, and carbon fixation of Synechocystis sp., compared with their individuals. This supports their joint toxicity effects. Our findings provide better understanding of combined toxicity between multiple pollutants in aquatic environments.

Assessing the importance of cobalt as a micronutrient for freshwater cyanobacteria

Micronutrients play key roles in numerous metabolic processes in cyanobacteria. However, our understanding of whether the micronutrient cobalt influences the productivity of freshwater systems or the occurrence of cyanobacterial blooms is limited. This study aimed to quantify the concentration of Co necessary for optimal cyanobacterial growth by exposing Microcystis aeruginosa to a range of Co concentrations under culture conditions. Extended exposure to concentrations below ˜0.06 μg · L^-1 resulted in notable inhibition of M. aeruginosa growth. A clear negative relationship was observed between Co concentration in solution and intracellular Fe quota of M. aeruginosa, possibly due to decreased transport of Fe at higher Co concentrations. Cyanocobalamin and any Co within the structure of cyanocobalamin appears to be non-bioavailable to M. aeruginosa, instead they likely rely on the synthesis of a structural variant - pseudocobalamin, which may have implications for the wider algal community as the variants of cobalamin are not necessarily functionally exchangeable. To evaluate the likelihood of Co limitation of cyanobacterial growth under field conditions, a survey of 10 freshwater reservoirs in South-Eastern Australia was conducted. Four of the ten sites had dissolved Co concentrations below the 0.06 μg · L^-1 threshold value. All four of these sites rarely undergo cyanobacterial blooms, strengthening evidence of the potential for Co to limit growth, perhaps either alone or in combination with phosphorus.

Contributions of polysaccharides to arsenate resistance in Chlamydomonas reinhardtii

Polysaccharides supply energy for various metabolic processes in cells. However, their roles in the arsenate (As(V)) resistance in microalgae remain largely unknown. Here, we explored the synthesis and transformation of polysaccharides in Chlamydomonas reinhardtii upon various levels of As(V) stress, using a number of physiological indexes along with transmission electron microscopic (TEM) and proteomic analyses. When exposed to low concentration of As(V) (0-20 μg/L), C. reinhardtii accumulated starch and produced more extracellular polysaccharides. At 50 μg/L As(V) treatment, starch accumulation gradually shifted to polysaccharides decomposition in the algal cells. Under higher As(V) concentration (500 μg/L), significantly more proteins in fatty acid metabolic pathway were differentially expressed, indicating that cells redirected carbon flux and transformed lipids into polysaccharides. The findings of this study demonstrate that polysaccharides may be critically involved in the As(V) resistance of C. reinhardtii.

Quantifying Cyanothece growth under DIC limitation

The photoautotrophic, unicellular N₂-fixer, Cyanothece, is a model organism that has been widely used to study photosynthesis regulation, the structure of photosystems, and the temporal segregation of carbon (C) and nitrogen (N) fixation in light and dark phases of the diel cycle. Here, we present a simple quantitative model and experimental data that together, suggest external dissolved inorganic carbon (DIC) concentration as a major limiting factor for Cyanothece growth, due to its high C-storage requirement. Using experimental data from a parallel laboratory study as a basis, we show that after the onset of the light period, DIC was rapidly consumed by photosynthesis, leading to a sharp drop in the rate of photosynthesis and C accumulation. In N₂-fixing cultures, high rates of photosynthesis in the morning enabled rapid conversion of DIC to intracellular C storage, hastening DIC consumption to levels that limited further uptake. The N₂-fixing condition allows only a small fraction of fixed C for cellular growth since a large fraction was reserved in storage to fuel night-time N₂ fixation. Our model provides a framework for resolving DIC limitation in aquatic ecosystem simulations, where DIC as a growth-limiting factor has rarely been considered, and importantly emphasizes the effect of intracellular C allocation on growth rate that varies depending on the growth environment.

Functional characterisation of substrate-binding proteins to address nutrient uptake in marine picocyanobacteria

Marine cyanobacteria are key primary producers, contributing significantly to the microbial food web and biogeochemical cycles by releasing and importing many essential nutrients cycled through the environment. A subgroup of these, the picocyanobacteria (Synechococcus and Prochlorococcus), have colonised almost all marine ecosystems, covering a range of distinct light and temperature conditions, and nutrient profiles. The intra-clade diversities displayed by this monophyletic branch of cyanobacteria is indicative of their success across a broad range of environments. Part of this diversity is due to nutrient acquisition mechanisms, such as the use of high-affinity ATP-binding cassette (ABC) transporters to competitively acquire nutrients, particularly in oligotrophic (nutrient scarce) marine environments. The specificity of nutrient uptake in ABC transporters is primarily determined by the peripheral substrate-binding protein (SBP), a receptor protein that mediates ligand recognition and initiates translocation into the cell. The recent availability of large numbers of sequenced picocyanobacterial genomes indicates both Synechococcus and Prochlorococcus apportion >50% of their transport capacity to ABC transport systems. However, the low degree of sequence homology among the SBP family limits the reliability of functional assignments using sequence annotation and prediction tools. This review highlights the use of known SBP structural representatives for the uptake of key nutrient classes by cyanobacteria to compare with predicted SBP functionalities within sequenced marine picocyanobacteria genomes. This review shows the broad range of conserved biochemical functions of picocyanobacteria and the range of novel and hypothetical ABC transport systems that require further functional characterisation.

The Quantitative Proteome Atlas of a Model Cyanobacterium

Cyanobacteria are a group of oxygenic photosynthetic bacteria with great potentials in biotechnological applications and advantages as models for photosynthesis research. The subcellular locations of the majority of proteins in any cyanobacteria remain undetermined, representing a major challenge in using cyanobacteria for both basic and industrial researches. Here, using label free quantitative proteomics we mapped 2027 proteins of Synechocystis sp. PCC6803, a model cyanobacterium, to different subcellular compartments, and generated a proteome atlas with such information. The atlas leads to numerous unexpected but important findings, including the predominant localization of the histidine kinases Hik33 and Hik27 on the thylakoid but not the plasma membrane. Such information completely changes the concept regarding how the two kinases are activated. Together, the atlas provides subcellular localization information for nearly 60% proteome of a model cyanobacterium, and will serve as an important resource for the cyanobacterial research community.

The periodic table of photosynthetic purple non-sulfur bacteria: intact cell-metal ions interactions

Photosynthetic purple non-sulfur bacteria (PNB) have been widely utilized as model organisms to study bacterial photosynthesis. More recently, the remarkable resistance of these microorganisms to several metals ions called particular interest. As a result, several research efforts were directed toward clarifying the interactions of metal ions with PNB. The mechanisms of metal ions active uptake and bioabsorption have been studied in detail, unveiling that PNB enable harvesting and removing various toxic ions, thus fostering applications in environmental remediation. Herein, we present the most important achievements in the understanding of intact cell-metal ions interactions and the approaches utilized to study such processes. Following, the application of PNB-metal ions interactions toward metal removal from contaminated environments is presented. Finally, the possible coupling of PNB with abiotic electrodes to obtain biohybrid electrochemical systems is proposed as a sustainable pathway to tune and enhance metal removal and monitoring.

A review on plant-microbial interactions, functions, mechanisms and emerging trends in bioretention system to improve multi-contaminated stormwater treatment

Management and treatment of multi-polluted stormwater in bioretention system have gained significant attraction recently. Besides nutrients, recent source appointment studies found elevated levels of Potentially toxic metal(loid)s (PTMs) and contaminants of emerging concern (CECs) in stormwater that highlighted many limitations in conventional media adsorption-based pollutant removal bioretention strategies. The substantial new studies include biological treatment approaches to strengthen pollutants degradation and adsorption capacity of bioretention. The knowledge on characteristics of plants and their corresponding mechanisms in various functions, e.g., rainwater interception, retention, infiltration, media clogging prevention, evapotranspiration and phytoremediation, is scattered. The microorganisms' role in facilitating vegetation and media, plant-microorganism interactions and relative performance over different functions in bioretention is still unreviewed. To uncover the underneath, it was summarised plant and microbial studies and their functionality in hydrogeochemical cycles in the bioretention system in this review, contributing to finding their interconnections and developing a more efficient bioretention system. Additionally, source characteristics of stormwater and fate of associated pollutants in the environment, the potential of genetical engineered plants, algae and fungi in bioretention system as well as performance assessment of plants and microorganisms in non-bioretention studies to propose the possible solution of un-addressed problems in bioretention system have been put forward in this review. The present review can be used as an imperative reference to enlighten the advantages of adopting multidisciplinary approaches for the environment sustainability and pollution control.

Transporter engineering for the development of cyanobacteria as cell factories: A text analytics guided survey

Cyanobacteria are attractive candidates for photoautotrophic production of platform chemicals due to their inherent ability to utilize carbon dioxide as the sole carbon source. Metabolic pathways can be engineered more readily in cyanobacteria compared to higher photosynthetic organisms. Although significant progress has been made in pathway engineering, intracellular accumulation of the product is a potential bottleneck in large-scale production. Likewise, substrate uptake is known to limit growth and product formation. These limitations can potentially be addressed by targeted and controlled expression of transporter proteins in the metabolically engineered strains. This review focuses on the transporters that have been explored in cyanobacteria. To highlight the progress on characterization and application of cyanobacterial transporters, we applied text analytics to extract relevant information from over 1000 publications. We have categorized the transporters based on their source, their function and the solute they transport. Further, the review provides insights into the potential of transporters in the metabolic engineering of cyanobacteria for improved product titer.

Smart Adsorbents for Aquatic Environmental Remediation

A noticeable interest and steady rise in research studies reporting the design and assessment of smart adsorbents for sequestering aqueous metal ions and xenobiotics has occurred in the last decade. This motivates compiling and reviewing the characteristics, potentials, and performances of this new adsorbent generation's metal ion and xenobiotics sequestration. Herein, stimuli-responsive adsorbents that respond to its media (as internal triggers; e.g., pH and temperature) or external triggers (e.g., magnetic field and light) are highlighted. Readers are then introduced to selective adsorbents that selectively capture materials of interest. This is followed by a discussion of self-healing and self-cleaning adsorbents. Finally, the review ends with research gaps in material designs.

Physicochemical behavioral changes in consort with nitrogen metabolism of cyanobacterium Anabaena PCC 7120 under arsenite regimes

The present study was undertaken to investigate the arsenite (As III)-induced changes in the diazotrophic cyanobacterium Anabaena PCC 7120. It was observed that the growth of cyanobacterial decreased with increase in As (III) concentration. The cells exposed to As (III) showed morphological variation (deformity) due to the formation of deeper constrictions in vegetative cells. Strain showed increased heterocyst differentiation (1.6-fold higher) whereas decreased nitrogenase activity at the concentration of 40 ppm As (III). The activities of NR, NiR, urease and GS decreased with increase in As (III) concentrations and attained their minimum levels at 40 ppm of As (III). The Ca²⁺-dependent ATPase activity increased with increase in As (III) concentration and attained its about 2.72-fold higher level at 40 ppm of As (III). In contrast, sharp decline in Mg²⁺-dependent ATPase activity (28%) was recorded at 1 ppm of As (III) over untreated control. The rates of photosynthetic O₂ evolution and respiration decreased with increase in As (III) concentration and attained its minimal level at 40 ppm of As (III). Therefore, this study highlighted arsenite regimes efficiently correlated with behavioral changes in consort with strain.

Reciprocal Effect of Copper and Iron Regulation on the Proteome of Synechocystis sp. PCC 6803

Cyanobacteria can acclimate to changing copper and iron concentrations in the environment via metal homeostasis, but a general mechanism for interpreting their dynamic relationships is sparse. In this study, we assessed growth and chlorophyll fluorescence of Synechocystis sp. PCC 6803 and investigated proteomic responses to copper and iron deductions. Results showed that copper and iron exerted reciprocal effect on the growth and photosynthesis of Synechocystis sp. PCC 6803 at combinations of different concentrations. And some proteins involved in the uptake of copper and iron and the photosynthetic electron transport system exhibit Cu-Fe proteomic association. The protein abundance under copper and iron deduction affected the photosynthetic electronic activity of Synechocystis sp. PCC 6803 and eventually affected the growth and photosynthesis. Based on these results, we hypothesize that the Cu-Fe proteomic association of Synechocystis sp. PCC 6803 can be elucidated via the uptake system of outer membrane-periplasmic space-inner plasma membrane-thylakoid membrane, and this association is mainly required to maintain electron transfer. This study provides a broader view regarding the proteomic association between Cu and Fe in cyanobacteria, which will shed light on the role of these two metal elements in cyanobacterial energy metabolism and biomass accumulation.

Synthetic biology approaches to copper remediation: bioleaching, accumulation and recycling

One of the current aims of synthetic biology is the development of novel microorganisms that can mine economically important elements from the environment or remediate toxic waste compounds. Copper, in particular, is a high-priority target for bioremediation owing to its extensive use in the food, metal and electronic industries and its resulting common presence as an environmental pollutant. Even though microbe-aided copper biomining is a mature technology, its application to waste treatment and remediation of contaminated sites still requires further research and development. Crucially, any engineered copper-remediating chassis must survive in copper-rich environments and adapt to copper toxicity; they also require bespoke adaptations to specifically extract copper and safely accumulate it as a human-recoverable deposit to enable biorecycling. Here, we review current strategies in copper bioremediation, biomining and biorecycling, as well as strategies that extant bacteria use to enhance copper tolerance, accumulation and mineralization in the native environment. By describing the existing toolbox of copper homeostasis proteins from naturally occurring bacteria, we show how these modular systems can be exploited through synthetic biology to enhance the properties of engineered microbes for biotechnological copper recovery applications.

Special roles for efflux systems in iron homeostasis of non-siderophore-producing cyanobacteria

In oligotrophic oceans, low bioavailability of Fe is a key factor limiting primary productivity. However, excessive Fe in cells leads to the Fenton reaction, which is toxic to cells. Cyanobacteria must strictly maintain intracellular Fe homeostasis. Here, we knocked out a series of genes encoding efflux systems in Synechocystis sp. PCC 6803, and found eight genes that are required for high Fe detoxification. Unexpectedly, the HlyBD-TolC efflux system plays an important role in the adaptation of Synechocystis under Fe-deficient conditions. Mutants of HlyD and TolC grew worse than the wild-type strain under low-Fe conditions and showed significantly lower intracellular Fe contents than the wild-type strain. We excluded the possibility that the low Fe sensitivity of the HlyBD-TolC mutants was caused by a loss of the S-layer, the main extracellular protein secreted via this efflux system. Inactivation of the HlyD protein influenced type IV pili formation and direct inactivation of type IV pili related genes affected the adaptation to low-Fe conditions. HlyBD-TolC system is likely involved in the formation of type IV pili and indirectly influenced Fe acquisition. Our findings suggest that efflux system in non-siderophore-producing cyanobacteria can facilitate Fe uptake and help cells adapt to Fe-deficient conditions via novel pathways.

The Two TpsB-Like Proteins in Anabaena sp. Strain PCC 7120 Are Involved in Secretion of Selected Substrates

The outer membrane of Gram-negative bacteria acts as an initial diffusion barrier that shields the cell from the environment. It contains many membrane-embedded proteins required for functionality of this system. These proteins serve as solute and lipid transporters or as machines for membrane insertion or secretion of proteins. The genome of Anabaena sp. strain PCC 7120 codes for two outer membrane transporters termed TpsB1 and TpsB2. They belong to the family of the two-partner secretion system proteins which are characteristic of pathogenic bacteria. Because pathogenicity of Anabaena sp. strain PCC 7120 has not been reported, the function of these two cyanobacterial TpsB proteins was analyzed. TpsB1 is encoded by alr1659, while TpsB2 is encoded by all5116 The latter is part of a genomic region containing 11 genes encoding TpsA-like proteins. However, tpsB2 is transcribed independently of a tpsA gene cluster. Bioinformatics analysis revealed the presence of at least 22 genes in Anabaena sp. strain PCC 7120 putatively coding for substrates of the TpsB system, suggesting a rather global function of the two TpsB proteins. Insertion of a plasmid into each of the two genes resulted in altered outer membrane integrity and antibiotic resistance. In addition, the expression of genes coding for the Clp and Deg proteases is dysregulated in these mutants. Moreover, for two of the putative substrates, a dependence of the secretion on functional TpsB proteins could be confirmed. We confirm the existence of a two-partner secretion system in Anabaena sp. strain PCC 7120 and predict a large pool of putative substrates.IMPORTANCE Cyanobacteria are important organisms for the ecosystem, considering their contribution to carbon fixation and oxygen production, while at the same time some species produce compounds that are toxic to their environment. As a consequence, cyanobacterial overpopulation might negatively impact the diversity of natural communities. Thus, a detailed understanding of cyanobacterial interaction with the environment, including other organisms, is required to define their impact on ecosystems. While two-partner secretion systems in pathogenic bacteria are well known, we provide a first description of the cyanobacterial two-partner secretion system.

The Two-Component System CopRS Maintains Subfemtomolar Levels of Free Copper in the Periplasm of Pseudomonas aeruginosa Using a Phosphatase-Based Mechanism

Copper is a micronutrient required as cofactor in redox enzymes. When free, copper is toxic, mismetallating proteins and generating damaging free radicals.

Two-component systems control periplasmic Cu⁺ homeostasis in Gram-negative bacteria. In characterized systems such as Escherichia coli CusRS, upon Cu⁺ binding to the periplasmic sensing region of CusS, a cytoplasmic phosphotransfer domain of the sensor phosphorylates the response regulator CusR. This drives the expression of efflux transporters, chaperones, and redox enzymes to ameliorate metal toxic effects. Here, we show that the Pseudomonas aeruginosa two-component sensor histidine kinase CopS exhibits a Cu-dependent phosphatase activity that maintains CopR in a nonphosphorylated state when the periplasmic Cu levels are below the activation threshold of CopS. Upon Cu⁺ binding to the sensor, the phosphatase activity is blocked and the phosphorylated CopR activates transcription of the CopRS regulon. Supporting the model, mutagenesis experiments revealed that the ΔcopS strain exhibits maximal expression of the CopRS regulon, lower intracellular Cu⁺ levels, and increased Cu tolerance compared to wild-type cells. The invariant phosphoacceptor residue His₂₃₅ of CopS was not required for the phosphatase activity itself but was necessary for its Cu dependency. To sense the metal, the periplasmic domain of CopS binds two Cu⁺ ions at its dimeric interface. Homology modeling of CopS based on CusS structure (four Ag⁺ binding sites) clearly supports the different binding stoichiometries in the two systems. Interestingly, CopS binds Cu^+/2+ with 3 × 10⁻¹⁴ M affinity, pointing to the absence of free (hydrated) Cu^+/2+ in the periplasm.

IMPORTANCE Copper is a micronutrient required as cofactor in redox enzymes. When free, copper is toxic, mismetallating proteins and generating damaging free radicals. Consequently, copper overload is a strategy that eukaryotic cells use to combat pathogens. Bacteria have developed copper-sensing transcription factors to control copper homeostasis. The cell envelope is the first compartment that has to cope with copper stress. Dedicated two-component systems control the periplasmic response to metal overload. This paper shows that the sensor kinase of the copper-sensing two-component system present in Pseudomonadales exhibits a signal-dependent phosphatase activity controlling the activation of its cognate response regulator, distinct from previously described periplasmic Cu sensors. Importantly, the data show that the system is activated by copper levels compatible with the absence of free copper in the cell periplasm. These observations emphasize the diversity of molecular mechanisms that have evolved in bacteria to manage the copper cellular distribution.

Rapid Transcriptional Reprogramming Triggered by Alteration of the Carbon/Nitrogen Balance Has an Impact on Energy Metabolism in Nostoc sp. PCC 7120

Nostoc (Anabaena) sp. PCC 7120 is a filamentous cyanobacterial species that fixes N₂ to nitrogenous compounds using specialised heterocyst cells. Changes in the intracellular ratio of carbon to nitrogen (C/N balance) is known to trigger major transcriptional reprogramming of the cell, including initiating the differentiation of vegetative cells to heterocysts. Substantial transcriptional analysis has been performed on Nostoc sp. PCC 7120 during N stepdown (low to high C/N), but not during C stepdown (high to low C/N). In the current study, we shifted the metabolic balance of Nostoc sp. PCC 7120 cultures grown at 3% CO₂ by introducing them to atmospheric conditions containing 0.04% CO₂ for 1 h, after which the changes in gene expression were measured using RNAseq transcriptomics. This analysis revealed strong upregulation of carbon uptake, while nitrogen uptake and metabolism and early stages of heterocyst development were downregulated in response to the shift to low CO₂. Furthermore, gene expression changes revealed a decrease in photosynthetic electron transport and increased photoprotection and reactive oxygen metabolism, as well a decrease in iron uptake and metabolism. Differential gene expression was largely attributed to change in the abundances of the metabolites 2-phosphoglycolate and 2-oxoglutarate, which signal a rapid shift from fluent photoassimilation to glycolytic metabolism of carbon after transition to low CO₂. This work shows that the C/N balance in Nostoc sp. PCC 7120 rapidly adjusts the metabolic strategy through transcriptional reprogramming, enabling survival in the fluctuating environment.

Spirulina platensis as renewable accumulator for heavy metals accumulation from multi-element synthetic effluents

Metal accumulation by Spirulina platensis from synthetic effluents with the following chemical composition: Cr/Fe, Cr/Fe/Ni, Cr/Fe/Ni/Zn, and Cr/Fe/Ni/Zn/Cu during repeated cultivation cycle was investigated. Metal ions in different concentrations were added to the culture medium at the exponential and stationary phases of biomass growth and their uptake by biomass was traced using neutron activation analysis. The effect of metal ions on biomass and main biochemical components (proteins, carbohydrates, lipids, phycobilins, and β-carotene) was monitored. S. platensis keeps high metal accumulation capacity during 2-3 cultivation cycles, while the metal ions were added in the stationary phase of its growth. By adding metals in the exponential phase of growth in the following concentrations: 10 mg/L of chromium (VI), 5 mg/L of iron, 2 mg/L of zinc, nickel, and copper, Spirulina platensis acted as renewable accumulator only in Cr/Fe system. It maintained the accumulation capacity during three cultivation cycles when exposed to lower concentrations of metal ions. Its ability to accumulate metal ions during several cultivation cycles was ensured by the maintenance of the optimal level of proteins and lipid in biomass.

Geology and climate influence rhizobiome composition of the phenotypically diverse tropical tree Tabebuia heterophylla

Plant-associated microbial communities have diverse phenotypic effects on their hosts that are only beginning to be revealed. We hypothesized that morpho-physiological variations in the tropical tree Tabebuia heterophylla, observed on different geological substrates, arise in part due to microbial processes in the rhizosphere. We characterized the microbiota of the rhizosphere and soil communities associated with T. heterophylla trees in high and low altitude sites (with varying temperature and precipitation) of volcanic, karst and serpentine geologies across Puerto Rico. We sampled 6 areas across the island in three geological materials including volcanic, serpentine and karst soils. Collection was done in 2 elevations (>450m and 0-300m high), that included 3 trees for each site and 4 replicate soil samples per tree of both bulk and rhizosphere. Genomic DNA was extracted from 144 samples, and 16S rRNA V4 sequencing was performed on the Illumina MiSeq platform. Proteobacteria, Actinobacteria, and Verrucomicrobia were the most dominant phyla, and microbiomes clustered by geological substrate and elevation. Volcanic samples were enriched in Verrucomicrobia; karst was dominated by nitrogen-fixing Proteobacteria, and serpentine sites harbored the most diverse communities, with dominant Cyanobacteria. Sites with similar climates but differing geologies showed significant differences on rhizobiota diversity and composition demonstrating the importance of geology in shaping the rhizosphere microbiota, with implications for the plant's phenotype. Our study sheds light on the combined role of geology and climate in the rhizosphere microbial consortia, likely contributing to the phenotypic plasticity of the trees.

Selective metal removal from chromium-containing synthetic effluents using Shewanella xiamenensis biofilm supported on zeolite

A scheme of selective removal of metal ions from chromium-containing synthetic solutions with the following chemical composition, Cr (VI)-Fe (III), Cr (VI)-Fe (III)-Ni (II), Cr (VI)-Fe (III)-Ni (II)-Zn (II), and Cr (VI)-Fe (III)-Ni (II)-Zn (II)-Cu (II)) by Shewanella xiamenensis biofilm immobilized on a zeolite support, was proposed. Three biological processes, biosorption, bioaccumulation, and longtime bioreduction, were applied for metal removal. The process of Zn (II), Ni (II), and Cu (II) showed to be pH dependent. The maximum removal of Ni (II) was achieved during a 1-hour biosorption process at pH 5.0-6.0, of Zn (II) at pH 5.0, and of Cu (II) at pH 3.0. Chromium (VI) and Fe (III) ions were more efficiently removed by bioaccumulation. Chromium (VI) removal in the studied systems varied from 16.4% to 34.8 and of iron from 55.8 to 94.6%. In a long-term bioreduction experiment, it was possible to achieve complete reduction of Cr (VI) to Cr (III) ions by Shewanella xiamenensis in 42 days and by Shewanella xiamenensis biofilm on zeolite in 35 days. Shewanella oneidensis can be effectively used to remove metal ions from chemically complex effluents.

Isolation and characterization of two novel plasmids pCYM01 and pCYM02 of Cylindrospermum stagnale

Cyanobacteria play a vital role in supplying nitrogen into the soil and aquatic ecosystem. It has an extra chromosomal DNA, whose role is not yet defined well. Isolation and characterization of extra chromosomal DNA in cyanobacteria might help to understand its survival mechanism. Cylindrospermum stagnale isolated (and deposited in NRMCF 3001) from soil showed presence of four plasmids namely pCYLM01, pCYLM02, pCYLM03, and pCYLM04. The following plasmids pCYLM01 and pCYLM02 were subjected to restriction digestion using HindIII restriction enzyme and cloned into pBlueScriptSK(-) vector. The sequence of pCYLM01 contained 4 potential open reading frames (ORFs) that have amino acids in the range of 59–299. Among them, ORF1 shows high sequence homology to the bacterial replication initiator family protein as evident from BLASTP analysis. The analysis of 4359 bp plasmid pCYLM02 sequence revealed 7 ORFs which are longer than 50 amino acids in length. The ORF2 of pCYLM02 has 243 amino acids and is represented in the plasmid sequence from 3045 to 3776 bp. The ORF3 of pCYLM02 corresponds to the plasmid sequence from 2323 to 2976 and codes for a putative protein of 217 amino acids long. A number of small ORFs below 50 bp were also found in the sequence analysis.

Evolutionary insights into adaptation of Staphylococcus haemolyticus to human and non-human niches

Staphylococcus haemolyticus is a well-known member of human skin microbiome and an emerging opportunistic human pathogen. Presently, evolutionary studies are limited to human isolates even though it is reported from plants with beneficial properties and in environmental settings. In the present study, we report isolation of novel S. haemolyticus strains from surface sterilized rice seeds and compare their genome to other isolates from diverse niches available in public domain. The study showed expanding nature of pan-genome and revealed set of genes with putative functions related to its adaptability. This is seen by presence of type II lanthipeptide cluster in rice isolates, metal homeostasis genes in an isolate from copper coin and gene encoding methicillin resistance in human isolates. The present study on differential genome dynamics and role of horizontal gene transfers has provided novel insights into capability for ecological diversification of a bacterium of significance to human health.

A Review of the Effect of Trace Metals on Freshwater Cyanobacterial Growth and Toxin Production

Cyanobacterial blooms are becoming more common in freshwater systems, causing ecological degradation and human health risks through exposure to cyanotoxins. The role of phosphorus and nitrogen in cyanobacterial bloom formation is well documented and these are regularly the focus of management plans. There is also strong evidence that trace metals are required for a wide range of cellular processes, however their importance as a limiting factor of cyanobacterial growth in ecological systems is unclear. Furthermore, some studies have suggested a direct link between cyanotoxin production and some trace metals. This review synthesises current knowledge on the following: (1) the biochemical role of trace metals (particularly iron, cobalt, copper, manganese, molybdenum and zinc), (2) the growth limitation of cyanobacteria by trace metals, (3) the trace metal regulation of the phytoplankton community structure and (4) the role of trace metals in cyanotoxin production. Iron dominated the literature and regularly influenced bloom formation, with 15 of 18 studies indicating limitation or colimitation of cyanobacterial growth. A range of other trace metals were found to have a demonstrated capacity to limit cyanobacterial growth, and these metals require further study. The effect of trace metals on cyanotoxin production is equivocal and highly variable. Better understanding the role of trace metals in cyanobacterial growth and bloom formation is an essential component of freshwater management and a direction for future research.

Algae colonisation of brick pavement at the University of Venda: A potential slippery hazard

A brick pavement, tramped by humans, is exposed to atmospheric elements, thus allowing cyanobacteria and algae to colonise. In this article, we report on the factors that contribute to the slipperiness of a brick pavement at the University of Venda in the Limpopo province of the South Africa. Samples were collected from brick surfaces either colonised by green algae (treated) or not (control). The samples were acid-digested and analysed for metals by Inductively Coupled Plasma Mass Spectrometry (ICP MS) in parts per billion (ppb). The treated bricks, with green algae, had average high metal contents (ppb): Al 9456.02, Ti 731.23, V 46.44, Cr 78.85, Mn 862.93, Fe 16295.18, Co 23.57, Ni 59.36, Cu 66.31, Zn 160.57, As 7.92, Se 10.45, Mo 6.74, Cd 5.19, Sn 4.65, Sb 2.31 and Pb 19.51. In contrast, control bricks had a low average of metal content (ppb) as follows: Al 2.99, Ti 0.28, V 4.04, Cr 1.42, Mn 4.29, Fe 20.89, Co 0.36, Ni 2.74, Cu 5.64, Zn 4.21, As 0.56, Se <3.00, Mo 0.88, Cd 0.01, Sn 1.05, Sb 0.04 and Pb 0.04. Other factors that promote algae colonisation include high solar radiation, neutral pH, nutrients, low electrical conductivity and total dissolved solids. The algae colonisation of brick pavement results in an unaesthetic sighting and a slippery surface that is hazardous to humans.

Molecular Modelling of the Ni(II)-Responsive Synechocystis PCC 6803 Transcriptional Regulator InrS in the Metal Bound Form

InrS (internal nickel-responsive sensor) is a transcriptional regulator found in cyanobacteria that represses the transcription of the nickel exporter NrsD in the apo form and de-represses expression of the exporter upon Ni(II) binding. Although a crystal structure of apo-InrS from Synechocystis PCC 6803 has been reported, no structure of the protein with metal ions bound is available. Here we report the results of a computational study aimed to reconstruct the metal binding site by taking advantage of recent X-ray absorption spectroscopy (XAS) data and to envisage the structural rearrangements occurring upon Ni(II) binding. The modelled Ni(II) binding site shows a square planar geometry consistent with experimental data. The structural details of the conformational changes occurring upon metal binding are also discussed in the framework of trying to rationalize the different affinity of the apo- and holo-forms of the protein for DNA.

Species-species interactions modulate copper toxicity under different visible light conditions

Combination of biotic and abiotic factors influences the effects of naturally occurring or anthropogenic chemicals on photosynthetic microorganisms in the aquatic environment. Nonetheless, the combined effects of physical stressors and species-species interaction on chemicals' toxicity are still poorly understood. The present study examines the responses of the green alga Chlamydomonas reinhardtii and the cyanobacterium Synechocystis sp. alone and in mixtures to copper exposure under increasing visible light intensities. Cell growth, chlorophyll bleaching, oxidative stress and membrane permeability were determined by flow cytometry in both mono- and multi-species tests. The results revealed that species-species interactions influenced copper toxicity under different light regimes at 4 h and 48 h - exposure. For a given light condition, monocultures of Synechocystis sp. were more sensitive to copper than those of C. reinhardtii. In long-term incubation C. reinhardtii sensitivity to copper diminished in presence of Synechocystis sp. under low-intensity light, however it was enhanced under high-intensity light. The present results revealed the complex interplay between visible light intensity variations, species-species interaction and copper effects to phytoplankton in long- term exposure.

Metalloproteins in the Biology of Heterocysts

Cyanobacteria are photoautotrophic microorganisms present in almost all ecologically niches on Earth. They exist as single-cell or filamentous forms and the latter often contain specialized cells for N₂ fixation known as heterocysts. Heterocysts arise from photosynthetic active vegetative cells by multiple morphological and physiological rearrangements including the absence of O₂ evolution and CO₂ fixation. The key function of this cell type is carried out by the metalloprotein complex known as nitrogenase. Additionally, many other important processes in heterocysts also depend on metalloproteins. This leads to a high metal demand exceeding the one of other bacteria in content and concentration during heterocyst development and in mature heterocysts. This review provides an overview on the current knowledge of the transition metals and metalloproteins required by heterocysts in heterocyst-forming cyanobacteria. It discusses the molecular, physiological, and physicochemical properties of metalloproteins involved in N₂ fixation, H₂ metabolism, electron transport chains, oxidative stress management, storage, energy metabolism, and metabolic networks in the diazotrophic filament. This provides a detailed and comprehensive picture on the heterocyst demands for Fe, Cu, Mo, Ni, Mn, V, and Zn as cofactors for metalloproteins and highlights the importance of such metalloproteins for the biology of cyanobacterial heterocysts.