Identification of acid-stress-tolerant proteins from promising cyanobacterial isolates

Abstract

Cyanobacterial cultures were isolated from acidic (pH 4.9-6.2) rice grown soils in Tamil Nadu, India. The predominant genera were Anabaena (50%), Westiellopsis (17.5%), Nostoc (15%), Oscillatoria (5%) and others that were unicellulars (12.5%) viz., Microcystis, Calothrix and Phormidium. The levels of tolerance to acidity varied among these strains, which were tested and authenticated for their acid tolerance capacity under both in vitro and pot culture conditions. Westiellopsis sp. was found to predominate from pH 4.9 to pH 6.2, indicating its adaptability. Cultures tolerant to acidic conditions were characterized for growth, biomass production and biochemical constituents. Under acidic conditions, Westiellopsis sp. showed pronounced chlorophyll a content, phycobilin pigment content, ammonia excretion and nitrogenase activity compared to normal conditions. Molecular characterization, particularly isozyme and random amplified polymorphic DNA (RAPD) analysis, were also carried out. Three strains of Westielliopsis sp. strains were selected, of which two were able to grow at an acidity level of pH 4.0, while one strain was able to sustain growth at an acidity level of 5.0. These three cultures, along with acid susceptible strains of Westielliopsis sp. and Anabaena sp. PCC 7120 (standard check) were subjected to acid shock for different time intervals. Protein profiling of both the acid-tolerant and acid-susceptible strains was carried out with samples collected at different time intervals. Based on the presence/absence of protein bands in the tolerant/susceptible strains, some low- and medium-molecular weight proteins can be linked to conferring acid tolerance.