Effect of protective polymers and storage temperatures on shelf life of cyanobacterial liquid formulation

The aim of the study was to determine the influence of protective polymers and storage temperatures to prolong the shelf life of cyanobacterial liquid formulation of efficient bio-fertilizer strains of cyanobacteria using different protective polymers and storage conditions. In this experiment, the protective polymers used in formulations were dimethyl sulfoxide (DMSO), glycerol and polyvinyl pyrrolidone (PVP) along with gum Arabic, CMC and Tween-20. The formulation without the addition of protective polymers and no pH was maintained as control. Storage temperature of formulated liquid biofertilizers of cyanobacteria were 4⁰C, 28⁰C and 40⁰C for a period of 18 months (540 days). Most of the formulations showed cell count 2.3x10⁴to 3.2 x10⁴ cells mL⁻¹, cell dry weight 1.98 to 2.51 mg mL⁻¹, total chlorophyll 3.50 and 6.05 µg mL⁻¹ and nitrogenase activity 2.07 to 3.52 jimol C₂H₄ mg⁻¹ chl h⁻¹ at all the three stored temperatures after 18 months of incubation. The performance of developed liquid formulations was good with protective polymeric additives than without them. The liquid biofertilizer formulation using combination of protective polymers showed maximum cell count and other metabolic activities as compared to alone. At 4⁰C, liquid inoculant formulated with DMSO and glycerol provided the greatest protection to cells of cyanobacteria and surviving and other growth-promoting ability whereas at 28⁰C and 40⁰C, PVP in addition to glycerol retained maximum surviving and other metabolic activities. The combinations of protective polymers viz. DMSO (3%) and glycerol (2%) at 4⁰C and PVP (2%) and glycerol at 28⁰C and 40⁰C showed the best conditions to improve shelf life of cyanobacterial liquid biofertilizer formulations. It can be recommended to maintain the shelf life of liquid formulations for storage period of 18 months.