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Isolation of a Xanthomonas campestris strain with elevated β‐galactosidase activity for direct use of lactose in xanthan gum production

Aims: To isolate a Xanthomonas campestris strain that can use lactose directly for xanthan gum production.   Methods and Results: The presence of indigenous β‐galactosidase gene in the wild‐type Xc17 was detected by PCR and Southern hybridization. Treatment of Xc17 with nitrous acid resulted in the isolation of Xc17L with a 3·5‐fold elevation of β‐galactosidase activity capable of growing in lactose‐based medium. Xc17L is stable for at least 100 generations in terms of β‐galactosidase expression. The amounts of xanthan produced by Xc17L in lactose‐based medium are comparable to those in glucose‐based medium.   Conclusions: Xc17L is potentially useful for xanthan production from whey, a waste containing lactose.   Significance and Impact of the Study: A lactose‐utilizing strain of X . campestris strain can be constructed without incorporation of any exotic DNA or antibiotic resistance gene and therefore concern of a gene‐modified organism and fear of a spread of an antibiotic‐resistant gene are avoided.