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Cyanobacteria are the most ancient lineages of the domain Bacteria and have been playing a crucial role in shaping our planet through their highly proliferating nature in harsh environmental conditions because of their adaptability to grow along with other photosynthetic and heterotrophic microbial community with varied ranges of salinity, pH, temperature, radiation, and water potential. Rise in temperature is reported to be the deciding factor in bringing down the microbial community diversity of hot springs. In the present study, for the first time, we reported the current status of the variability in community structure and predicted metabolic activity among cyanobacteria population of two sulfur hot springs, Atri at 48 °C and Taptapani at 58 °C, from the state of Odisha, Eastern India, using metagenomic approach. We further tried to establish the relationship between the differential occurrences of cyanobacteria clades with those of coexisting non-cyanobacteria clades chloroflexi from our previously published findings of hot spring microbial diversity analysis.

Algal-bacterial process biotechnology is a recent low-cost method toward toxic pollutant removal from wastewater that has received more attention in the present scenario. The pollutants are mainly categorized into inorganic, organic, radioactive, acid/base, etc. The water pollutants mainly include SO2 from power plants, chemical waste, fertilizers from agricultural use, oil spillage, silt, harmful pesticides, detergents, harmful compounds in cosmetics, pathogenic bacteria from livestock operations and food processing wastes, and chemical compounds found in cosmetics products, effluent outfalls from factories, refineries, waste treatment plants, contaminants from improper disposal of industrial wastes running through rainwater, etc. The proper pretreatment of wastewater needs to be done before disposal to the water bodies unless it would cause serious damage to our entire ecosystem. Algae, mostly behaving as water-purifying agent acting as pollution indicator, can act as a better alternative toward bioremediation through low-cost approach. Due to certain limitations in the algal cell during toxic pollutant accumulation, sometimes it can remediate contaminants up to a certain level. So another emerging concept of algal-bacterial symbiotic system, a less energy consumption technology, was developed which gained much attention toward wastewater treatment in the present scenario. Introduction of cost-effective algal-bacterial consortia treatment technology is reported to treat toxic wastewater effluents from municipal, domestic, industrial, and agricultural activities by using many special unicellular microalgae and pollutant-specific-degrading bacteria. It has been found from recent studies that two important factors such as selection of suitable strain as well as cultivation are responsible for biodegrading toxic chemicals and compounds such as polycyclic aromatic hydrocarbons, phenolics, and organic solvents. The organic compounds released after algal photosynthesis can ultimately become a food source for a variety of heterotrophic microbes. The growth-promoting substance production by bacteria can promote microalgal growth, whereas few bacteria can promote algal growth by photosynthetic oxygen tension reduction inside the algal cell, e.g., Pseudomonas diminuta and P. vesicularis. The wastewater can be treated in an open system, i.e., by the construction of artificial ponds, or closed system, i.e., using a bioreactor. From the available reports, it was found that the algal-bacterial consortium may include mainly microalgae and bacteria, e.g., Flavobacteriia, Gammaproteobacteria, Bacteroidia, and β-proteobacteria. The harmful dissolved methane in anaerobically treated wastewater can effectively be treated by the methane-oxidizing bacteria and algae. It can be concluded that the conventional algal-bacterial system treatment technology acts as a natural biological treatment method as a viable alternative and is of great importance for achieving good wastewater treatment performance as well as the reduction in energy consumption cost.

Arsenic is a gray-appearing metalloid which occurs naturally and is the 20th most prolific element in the earth’s crust. It is an integral part of more than 200 minerals. These are mostly ores containing sulfides, along with copper, nickel, lead, and other metals. In the environment, arsenic and its compounds are very mobile. Although in its organic form arsenic is nontoxic, it is highly toxic in its inorganic form (arsenite, a free form of arsenic) with arsine gas being the most fatal. The World Health Organization recommends a concentration below 20 mg/l for an individual to be considered free of arsenic poisoning. Accumulation of arsenic in the body beyond this level could adversely affect human health. An individual suffering from chronic arsenic poisoning via contaminated water could suffer from severe skin-related ailments like melanosis (pigmentation of the skin), keratosis (associated with the formation of rough, dry, and popular skin lesions), and leucomelanosis (also known as spotted melanosis) ultimately leading to arsenicosis in the long term. Other than that arsenic poisoning also may lead to other manifestations like neurological disorders, diabetes mellitus, high blood pressure, obstetric problems, disorders of the respiratory system, and cancer in the lung, skin, and bladder. The Indian subcontinent is very rich in arsenic, and countries like India and Bangladesh are a disaster waiting to happen. West Bengal, India, is a state severely affected by arsenic-contaminated water, and a case study showed an astounding 16 sites from one single village with very high concentrations of arsenic. As such, it is the need of the hour for governments to be ready with an immediate action plan to tackle such large-scale disasters. Existing solutions to this problem include phytoremediation via hyperaccumulation with plants like Pteris vittata and grasses like A. delicatula and use of phosphate-based fertilizers. However, a long-term use of phosphate-based fertilizers may ultimately lead to an algal bloom in water bodies, and phytoremediation is a time-consuming process. Planktons, however, have the potential to be a game changer in tackling arsenic-contaminated water bodies by virtue of accumulation and bioremediation. Spirulina platensis, a typical plankton, produces an enzyme called arsenite S-adenosylmethionine methyltransferase which has the ability to methylate arsenic making it nontoxic. This enzyme confers Spirulina platensis the unique ability to convert the toxic trivalent arsenic to its nontoxic pentavalent form. Spirulina platensis produces this enzyme by the virtue of arsenite S-adenosylmethionine methyltransferase (SpArsM) gene.