Cyanobacteria are rich source of array of bioactive compounds. The present study reports a novel antibacterial bioactive compound purified from cyanobacterium Nostoc sp. MGL001 using various chromatographic techniques viz. thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Further characterization was done using electrospray ionization mass spectroscopy (ESIMS) and nuclear magnetic resonance (NMR) and predicted structure of bioactive compound was 9-Ethyliminomethyl-12-(morpholin - 4 - ylmethoxy) -5, 8, 13, 16–tetraaza–hexacene - 2, 3 dicarboxylic acid (EMTAHDCA). Structure of EMTAHDCA clearly indicated that it is a novel compound that was not reported in literature or natural product database. The compound exhibited growth inhibiting effects mainly against the gram negative bacterial strains and produced maximum zone of inhibition at 150 μg/mL concentration. The compound was evaluated through in silico studies for its ability to bind 30S ribosomal fragment (PDB ID: 1YRJ, 1MWL, 1J7T, and 1LC4) and OmpF porin protein (4GCP, 4GCQ, and 4GCS) which are the common targets of various antibiotic drugs. Comparative molecular docking study revealed that EMTAHDCA has strong binding affinity for these selected targets in comparison to a number of most commonly used antibiotics. The ability of EMTAHDCA to bind the active sites on the proteins and 30S ribosomal fragments where the antibiotic drugs generally bind indicated that it is functionally similar to the commercially available drugs.

Influence of various levels of CaCl (0, 1, 10 and 100 mM) on exopolysaccharide production has been investigated in the cyanobacterium 7120. At the concentration of 1 mM CaCl, growth was found to be stimulatory while 100 mM was sub lethal for the cyanobacterial cells. Estimation of EPS content revealed that EPS production depends on the concentration of calcium ions in the immediate environment with maximum being at10 mM CaCl. A possible involvement of gene in the process of EPS production was also revealed through qRT-PCR. Further, FTIR-spectra marked the presence of aliphatic alkyl-group, primary amine-group, and polysaccharides along with shift in major absorption peaks suggesting that calcium levels in the external environment regulate the composition of EPS produced by 7120. Thus, both quantity and composition of EPS is affected under different calcium chloride concentrations presenting possibilities of EPS with novel unexplored features that may offer biotechnological applications.

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The cyanobacterium Anabaena sp. PCC 7120 was grown in presence and absence of iron to decipher the role of manganese in protection against the oxidative stress under iron starvation and growth, manganese uptake kinetics, antioxidative enzymes, lipid peroxidation, electrolyte leakage, thiol content, total peroxide, proline and NADH content was investigated. Manganese supported the growth of cyanobacterium Anabaena 7120 under iron deprived conditions where maximum uptake rate of manganese was observed with lower K(m) and higher V(max) values. Antioxidative enzymes were also found to be elevated in iron-starved conditions. Estimation of lipid peroxidation and electrolyte leakage depicted the role of manganese in stabilizing the integrity of the membrane which was considered as the prime target of oxygen free radicals in oxidative stress. The levels of total peroxide, thiol, proline and NADH content, which are the representative of oxidative stress response in Anabaena 7120, were also showed increasing trends in iron starvation. Hence, the results discerned, clearly suggested the role of manganese in protection against the oxidative stress in cyanobacterium Anabaena 7120 under iron starvation either due to its antioxidative properties or involvement as cofactor in a number of antioxidative enzymes.

The present study was undertaken to examine the salinity stress-induced physiological and biochemical alterations in the cyanobacterium Synechococcus sp. PCC 7942. Cyanobacterial cultures supplemented with different concentrations of NaCl were evaluated for growth, carbohydrate, total lipid, ROS generation, and stress biomarkers to evaluate the ROS-mediated lipid production in Synechococcus 7942. Salt concentration of 500 mM induced a five-and threefold increase in the production of carbohydrates and lipids, respectively. The fatty acids composition in terms of total quantity and oleic acid content of the investigated species was also improved as the salinity level increased from 0 to 500 mM NaCl. The data showed maximum MUFA production at 10 mM NaCl with dominance of palmitoleic acid (88.3%) and oleic acid (0.31%), whereas PUFA was found to be maximally produced at 250 mM NaCl with dominance of linoleic acid. Salt stress enhanced the accumulation of carbohydrate and total lipids and antioxidative enzymes, and modulates the fatty acids and hydrocarbon composition of cyanobacterium. Production of fatty acid and hydrocarbon under saline conditions indicates that salinity can be used as a factor to modulate the biochemical pathways of cyanobacteria toward efficient biofuel production.