Simazine Enhances Dark Fermentative H2 Production by Unicellular Halotolerant Cyanobacterium Aphanothece halophytica

The Cyanobacteria Genus Aphanothece: Bioactive Compounds and Applications in Biotechnology

Aphanothece is a genus of colonial cyanobacteria with a global distribution that is found in various aquatic and terrestrial environments. It has garnered interest because of its high content of amino acids, carbohydrates, fatty acids, and pigments, which possess bioactive and biotechnological properties. This review analyzes articles highlighting Aphanothece species in biotechnological contexts and describes their biochemical composition. Among its primary metabolites are glutamic acid, alanine, palmitic acid, chlorophyll a, echinenone, and β-carotene. The biotechnological potential of Aphanothece spans the fields of biofuel, health, agro-industry, and bioremediation. The notable bioactivities of species such us A. sacrum, A. pallida, and A. bullosa include photoprotective, immunostimulant, antimicrobial, anticancer, and biostimulant activities due to secondary metabolites such as mycosporine-like amino acids, peptides, betaines, and glycerophospholipids. The high production of hydrogen and lipids by A. halophytica supports its use in biofuels. Species such as A. microscopica are effective at treating agro-industrial and domestic effluents and water polluted by metals and hydrocarbons, alongside simultaneous CO2 capture. This review provides information that can guide the sustainable use of Aphanothece species and identifies gaps in current knowledge, particularly in the development of commercial products. Continuous exploration of this genus can significantly promote environmental sustainability and biotechnological innovation.

Dark fermentative hydrogen production and transcriptional analysis of genes involved in the unicellular halotolerant cyanobacterium Aphanothece halophytica under nitrogen and potassium deprivation

The unicellular halotolerant cyanobacterium Aphanothece halophytica is known as a potential hydrogen (H₂) producer. This study aimed to investigate the enhancement of H₂ production under nutrient deprivation. The results showed that nitrogen and potassium deprivation induced dark fermentative H₂ production by A. halophytica, while no differences in H₂ production were found under sulfur and phosphorus deprivation. In addition, deprivation of nitrogen and potassium resulted in the highest H₂ production in A. halophytica due to the stimulation of hydrogenase activity. The effect of adaptation time under nitrogen and potassium deprivation on H₂ production was investigated. The results showed that the highest H₂ accumulation of 1,261.96 ± 96.99 µmol H₂ g dry wt^-1 and maximum hydrogenase activity of 179.39 ± 8.18 µmol H₂ g dry wt^-1 min^-1 were obtained from A. halophytica cells adapted in the nitrogen- and potassium-deprived BG11 medium supplemented with Turk Island salt solution (BG11₀-K) for 48 h. An increase in hydrogenase activity was attributed to the decreased O₂ concentration in the system, due to a reduction of photosynthetic O₂ evolution rate and a promotion of dark respiration rate. Moreover, nitrogen and potassium deprivation stimulated glycogen accumulation and decreased specific activity of pyruvate kinase. Transcriptional analysis of genes involved in H₂ metabolism using RNA-seq confirmed the above results. Several genes involved in glycogen biosynthesis (glgA, glgB, and glgP) were upregulated under both nitrogen and potassium deprivation, but genes regulating enzymes in the glycolytic pathway were downregulated, especially pyk encoding pyruvate kinase. Interestingly, genes involved in the oxidative pentose phosphate pathway (OPP) were upregulated. Thus, OPP became the favored pathway for glycogen catabolism and the generation of reduced nicotinamide adenine dinucleotide phosphate (NADPH), which resulted in an increase in H₂ production under dark anaerobic condition in both nitrogen- and potassium-deprived cells.