DETERMINATION OF MEDIAN LETHAL DOSES (LD50) FOR MUTAGENESIS OF BIOFERTILISER BACTERIA THROUGH GAMMA IRRADIATION

Abstract

Gamma irradiation for mutation induction in microbes has been utilised to improve antagonistic effects on plant pathogens in agriculture, and to enhance enzyme production during fermentation.  Radiation mutagenesis to induce multifunctional activities in biofertiliser microorganisms, is a recent endeavour in Malaysia.  Bacteria mutagenesis is complex and is affected by many factors. There is no prior standard or information in this area of research.  Therefore, it is crucial to have a standard optimum dose and median lethal dose (LD₅₀) data as a guideline. In this study, eight Gram-negative and four Gram-positive isolates of biofertiliser bacteria, which were isolated from compost, soil, and plants, were subjected to gamma irradiation at Malaysian Nuclear Agency to improve their plant growth-promoting activities, such as N₂ fixation, phosphate, and potassium solubilisation. Gram staining was carried out on the isolates.   The isolates were identified as Acinetobacter sp., Klebsiella sp., Enterobacter sp., Pseudomonas sp., Pantoea sp., Bacillus sp. and Priestia sp. by using the 16S rRNA method.  These isolates were gamma-irradiated at doses of 50 to 400 Gy. Survival curves revealed that the bacterial levels (log number of cfu/mL) decreased with increasing gamma irradiation doses.  The LD₅₀ of the Gram-negative isolates ranged from 380 to 500 Gy, while for Gram-positive isolates it ranged from 800 to 1600 Gy.  These LD₅₀ ranges will be refined further and used for improvement of multifunctional activities of these isolates.