Treatment of Cr(VI)-containing wastewaters with exopolysaccharide-producing cyanobacteria in pilot flow through and batch systems

Cyanobacterial and microalgae polymers: antiviral activity and applications

At the end of 2019, the world witnessed the beginning of the COVID-19 pandemic. As an aggressive viral infection, the entire world remained attentive to new discoveries about the SARS-CoV-2 virus and its effects in the human body. The search for new antivirals capable of preventing and/or controlling the infection became one of the main goals of research during this time. New biocompounds from marine sources, especially microalgae and cyanobacteria, with pharmacological benefits, such as anticoagulant, anti-inflammatory and antiviral attracted particular interest. Polysaccharides (PS) and extracellular polymeric substances (EPS), especially those containing sulfated groups in their structure, have potential antiviral activity against several types of viruses including HIV-1, herpes simplex virus type 1, and SARS-CoV-2. We review the main characteristics of PS and EPS with antiviral activity, the mechanisms of action, and the different extraction methodologies from microalgae and cyanobacteria biomass.

Cyanobacteria as a Valuable Natural Resource for Improved Agriculture, Environment, and Plant Protection

Taking into consideration, the challenges faced by the environment and agro-ecosystem make increased for suggestions more reliable methods to help increase food security and deal with difficult environmental problems. Environmental factors play a critical role in the growth, development, and productivity of crop plants. Unfavorable changes in these factors, such as abiotic stresses, can result in plant growth deficiencies, yield reductions, long-lasting damage, and even death of the plants. In reflection of this, cyanobacteria are now considered important microorganisms that can improve the fertility of soils and the productivity of crop plants due to their different features like photosynthesis, great biomass yield, ability to fix the atmospheric N2, capability to grow on non-arable lands, and varied water sources. Furthermore, numerous cyanobacteria consist of biologically active substances like pigments, amino acids, polysaccharides, phytohormones, and vitamins that support plant growth enhancement. Many studies have exposed the probable role of these compounds in the alleviation of abiotic stress in crop plants and have concluded with evidence of physiological, biochemical, and molecular mechanisms that confirm that cyanobacteria can decrease the stress and induce plant growth. This review discussed the promising effects of cyanobacteria and their possible mode of action to control the growth and development of crop plants as an effective method to overcome different stresses.

Graphical Abstract

The Role of Microbial Mats in the Removal of Hexavalent Chromium and Associated Shifts in Their Bacterial Community Composition

Microbial mats are rarely reported for chromium-polluted ecosystems, hence information on their bacterial diversity and role in chromium removal are very scarce. We investigated the role of nine microbial mats, collected from three quarry sumps of chromium mining sites, in the removal of hexavalent chromium [Cr(VI)]. Bacterial diversity in these mats and community shifts after incubation with Cr(VI) have been investigated using MiSeq sequencing. In nature, a chromium content of 1,911 ± 100 mg kg^–1 was measured in the microbial mats, constituting the third highest source of environmentally available chromium. The mats were able to remove 1 mg l^–1 of Cr(VI) in 7 days under aerobic conditions. MiSeq sequencing of the original mats yielded 46–99% of the sequences affiliated to Proteobacteria, Firmicutes and Actinobacteria. When the mats were incubated with Cr(VI), the bacterial community shifted in the favor of Alphaproteobacteria and Verrucomicrobiae. We conclude that microbial mats in the quarry sumps harbor diverse microorganisms with the ability to remove toxic Cr(VI), hence these mats can be potentially used to remove chromium from polluted waters.

Potential of higher plants, algae, and cyanobacteria for remediation of radioactively contaminated waters

The potential of photosynthetic organisms to remediate radioactively contaminated water was evaluated for scenarios related to nuclear installations and included the following radionuclides: ¹³⁷Cs, ¹³⁴Cs, ¹³⁶Cs, ⁹⁰Sr, ¹³¹I, ²³⁹Pu, ²⁴¹Am, ¹³²Te/¹³²I, ⁵⁸Co, ⁶⁰Co, ⁵¹Cr, ^110mAg, ⁵⁴Mn, ¹²⁴Sb, ⁵⁹Fe, ⁶⁵Zn, ⁹⁵Zr, and ⁹⁵Nb. An extensive literature review was undertaken leading to the creation of a database including more than 20,000 entries from over 100 references in which terrestrial and aquatic plants, macro- and microalgae, cyanobacteria and biosorbents derived from these organisms were used to clean water from these specific radionuclides or their stable isotopes. In a first phase, the remediation potential of the organisms and biosorbents was evaluated for the individual elements based on parameters such as plant uptake, removal percentage, and bioconcentration factor, and for two radionuclide mixtures based on the ability of the organisms/biosorbents to work under mixture conditions. As the experimental and environmental conditions will influence the performance of the organisms and biosorbents, a literature-based evaluation of the most influencing or restricting parameters was made and water pH, competing ions, and the chemical modification of biosorbents showed to be of major importance. Finally, the most promising organisms and biosorbents were identified using a specifically developed selection procedure taking into account their performance and robustness. Ranking was done based on clear criteria with a distinct weight and scoring scheme. As such, 20 organisms/biosorbents were identified that showed high potential to clean waters contaminated with (mixtures of) radionuclides related to nuclear installations and which can be used for further experimental investigations.

Cyanobacteria: Photoautotrophic Microbial Factories for the Sustainable Synthesis of Industrial Products

Cyanobacteria are widely distributed Gram-negative bacteria with a long evolutionary history and the only prokaryotes that perform plant-like oxygenic photosynthesis. Cyanobacteria possess several advantages as hosts for biotechnological applications, including simple growth requirements, ease of genetic manipulation, and attractive platforms for carbon neutral production process. The use of photosynthetic cyanobacteria to directly convert carbon dioxide to biofuels is an emerging area of interest. Equipped with the ability to degrade environmental pollutants and remove heavy metals, cyanobacteria are promising tools for bioremediation and wastewater treatment. Cyanobacteria are characterized by the ability to produce a spectrum of bioactive compounds with antibacterial, antifungal, antiviral, and antialgal properties that are of pharmaceutical and agricultural significance. Several strains of cyanobacteria are also sources of high-value chemicals, for example, pigments, vitamins, and enzymes. Recent advances in biotechnological approaches have facilitated researches directed towards maximizing the production of desired products in cyanobacteria and realizing the potential of these bacteria for various industrial applications. In this review, the potential of cyanobacteria as sources of energy, bioactive compounds, high-value chemicals, and tools for aquatic bioremediation and recent progress in engineering cyanobacteria for these bioindustrial applications are discussed.

Protective effect of vanilloids against chemical stress on the white-rot fungus Ganoderma lucidum

Bioremediation of contaminated sites by biosorption of pollutants onto a wide range of materials has emerged as a promising treatment for recalcitrant aromatic compounds or heavy metals. When adsorption occurs on living white-rot fungi mycelia, the pollutants may be degraded by ligninolytic enzymes. However, the survival of mycelia in harsh conditions is one of the drawbacks of those methodologies. In this study, it was demonstrated that culture media supplemented with several guaiacol derivatives (vanilloids) increased the resistance of Ganoderma lucidum E47 cultures to chemical stress by enhancing the adsorptive capacity of the extracellular mucilaginous material (ECMM). The toxicity of the fungicides gentian violet (GV), malachite green (MG) and clotrimazole, and the heavy metal Cadmium was noticeably diminished in fungal cultures supplemented with the guaiacol derivative vanillic acid (VA). No degradation of the tested compounds was detected. The activity of the oxidative enzymatic systems like laccase, a well-known oxidase associated to dye degradation, was only detectable after complete growth on plates. Extremely low concentrations of VA caused a significant protective effect, radial extension of the growth halo in plates supplemented with 0.0001 mM of VA plus GV was up to 20% to that obtained in control plates (without addition of GV and VA). Therefore, the protective effect could not be attributable to VA per se. ECMM separated from the mycelium exhibited a much higher increase in the adsorptive capacity when isolated from liquid cultures containing VA, while that obtained from unsupplemented cultures showed an almost null adsorptive capacity.

Gold biosorption by exopolysaccharide producing cyanobacteria and purple nonsulphur bacteria

AIMS

This study was aimed at investigating the possible exploitation of phototrophic micro-organisms for the removal and the recovery of Au from Au-containing wastewaters deriving from a plating industry.

METHODS AND RESULTS

A screening among ten phototrophic micro-organisms was carried out with pure solutions of Au to select the best strain in terms of metal uptake and selectivity. The direct use of the selected micro-organism on the Au-containing industrial wastewater was then carried out with the aim of assessing the potential of its use for the removal and the recovery of the precious metal from industrial wastewaters.

CONCLUSIONS

This study showed the good potential of some exopolysaccharide-producing cyanobacteria as biosorbents for the recovery of Au from wastewaters of plating industries but also pointed out the need to design an efficient technology for the recovery of the metal from the biomass.

SIGNIFICANCE AND IMPACT OF THE STUDY

The selection of good biosorbents for the recovery of gold from industrial wastewaters may open new perspectives to a green biotechnology so far considered too expensive for the mere treatment of wastewaters containing low valuable metals.