Effect of methionine on xanthan formation by Xanthomonas campestris

In Xanthomonas campestris cultures the xanthan formation is reduced by about 40% by the addition of methionine in quantities as small as 1.3 mM. Structural analogues of this amino acid exhibit a similar inhibitory effect on polysaccharide formation. Xanthan formation is also influenced in non-growing cells: cells precultured with methionine synthesize less xanthan than cells precultured without methionine. It therefore follows that apparently the composition of the cell is altered resulting in an altered flow of glucose. In accordance with this, cells grown with methionine excrete a greater portion of carbohydrates with M_rs smaller than xanthan.