Abstract: The method of the invention, to produce a polysaccharide of the xanthane type, makes use of a strain of Xanthemonas, notably of the strain no. ATCC 31 176 deposited on Oct. 14, 1975, which is cultivated on a medium with 5 to 55 g/l or more of carbohydrates and comprising at least one amino-acid selected from glutamic acid, glutamine, arginine, tyrosine, threonine, aspartic acid, asparagine, proline, leucine tryptophane and other amino-acids giving a production of polysaccharide at least equal to 50% of that yielded by corn steep liquor, the total nitrogen of said medium being 0.1 g/l to 5 g/1; the fermentation is carried out at 25.degree.-35.degree. C under aerobiosis.