The use of bacterial alginates to prepare biocontrol formulations

Summary Formulations which are economical and which can deliver a viable organism are critical to developing successful biocontrol products for plant pathogens. In the present study, alginates derived from commercial kelp and produced byAzotobacter vinelandii isolates ATCC 9104 and 12 837 were compared in their ability to form stable, biodegradable granular formulations of the biocontrol fungiTalaromyces flavus andGliocladium virens. Bacteria were grown in shake flask cultures (180 rpm) at 32°C for 104 h. The cultures were monitored for pH, dissolved oxygen, glucose concentration, dry cell weight, and alginate dry weight. Aqueous solutions of the bacterial alginates, as well as the kelp-derived alginate products, gelled readily in 0.25 M calcium chloride. Mannuronate (M) and guluronate (G) compositions of the alginate samples were determined by circular dichroism. M/G ratios for cultures of isolate 12837 averaged 0.98±0.18; for isolate 9104, 1.59±0.12; and for kelp, 1.54±0.39. The viability ofT. flavus in the kelp and bacterial alginate formulations were similar over 84 days. An exploratory experiment indicated good viability ofG. virens using the same bacterial alginates. This study demonstrated a practical use for bacterial alginate as a potentially less costly substitute for kelp alginate in the preparation of biocontrol agent formulations.