Mutagenic effect of microwave radiation on exopolysaccharide production in Xanthomonas campestris

Abstract

The exopolysaccharide produced by the gram-negative bacterium Xanthomonas campestris (known as xanthan gum) is a product of commercial importance. In the present study X. campestris was subjected to two different microwave (MW) powers (90 W and 450 W) for different time durations, and its effect on growth and exopolysaccharide (EPS) production was studied for multiple generations of the xanthan overproducing mutants obtained after MW treatment. As the MW treatment was performed under temperature-controlled condition (by placing the inoculum vial in an ice containing beaker, while exposing to MW), where the temperature did not cross 25°C, whatever alterations were observed in growth and xanthan production seem largely to have resulted from non-thermal effects of MW radiation. As the trait of xanthan overproduction was transferred from one generation of MW treated organism to the next, the MW effect can be said to be mutagenic. However this MW induced mutation was not found to be stable over multiple generations. Both the xanthan overproducing mutants obtained by two different MW treatments reverted back to the parent phenotype, suggesting the reversible nature of the MW induced mutations. Identifying mutagenic frequencies of MW radiation can pave way for large scale screening programmes employing MW mutagenesis as a tool for strain improvement, and yield genetically stable overproducing mutants.