Isolation, screening and characterization of efficient Xanthomonas spp. for enhanced xanthan gum production

Abstract

Xanthan gum, a microbial polysaccharide of significant industrial importance, is widely utilized in food, pharmaceutical, cosmetic, and petroleum sectors owing to its exceptional rheological and stabilizing properties. Members of the genus Xanthomonas are well known for their ability to produce xanthan gum, although their pathogenicity toward agriculturally important crops poses constraints. In the present study, Xanthomonas spp. were isolated from diseased tissues of cabbage (Brassica oleracea), rice (Oryza sativa), French bean (Phaseolus vulgaris), and citrus (Citrus spp.) collected from different agro-ecological regions of India. Forty-five isolates were obtained and subjected to morphological and functional screening. Based on colony characteristics and gum production potential, ten isolates were selected for secondary screening. Growth kinetics were evaluated through serial dilution and colony-forming unit (CFU) counts. Strains derived from cabbage and French bean demonstrated comparatively higher gum yields, highlighting their potential as candidates for large-scale xanthan production. This study explores the morphological, biochemical, cultural, and molecular characteristics of four xanthan-producing isolates. All were rod-shaped, Gram-negative, non-spore-forming, motile (flagellated), capsule-forming bacteria with raised, yellow, mucoid colonies. 16S rDNA sequencing followed by BLAST analysis, multiple sequence alignment, and phylogenetic reconstruction confirmed them as Xanthomonas campestris with minimal genetic divergence. Recent findings on non-pathogenic Xanthomonas spp. from healthy rice seeds underline the importance of accurate molecular characterization.