Submitted to: Archives Of Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/14/2007
Publication Date: 3/6/2007
Citation: Wach, M.J., Loria, R., Krasnoff, S.B., Gibson, D.M. 2007. Effect of carbohydrates on the production of thaxtomin a by streptomyces acidiscabies. Archives Of Microbiology. 188:81-88 Interpretive Summary: Several Streptomyces species cause "scab" diseases on potato tubers, sweet potato storage roots and expanded tap roots of radish, beet and similar crops. All of these species produce a family of toxins known as thaxtomins that are critical for pathogenicity, and the compounds are known to affect cell wall biosynthesis by some unknown mechanism. This work describes a series of experiments that define the nutritional requirements essential to elicit the production of thaxtomin. The data show that complex cell wall carbohydrates are the essential factor necessary to signal biosynthesis of thaxtomins by plant pathogenic Streptomyces. These compounds then aid the bacteria in colonizing its plant host. These studies point out the difficulties in breeding for plant resistance to scab since the key to pathogenicity is linked to an essential plant component.
Technical Abstract: Three plant pathogenic species of Streptomyces, S. scabies, S. acidiscabies, and S. turgidiscabies, cause common scab of potato and other root crops. The disease symptoms are induced by a family of dipeptide phytotoxins called thaxtomins, which are produced by all three species. Thaxtomins are produced in vivo on diseased potato tissue and in vitro in oat-based culture media, but the regulation of thaxtomin biosynthesis is not understood. S. acidiscabies strain 84.104 was grown in a variety of media to assess the impact of medium components on thaxtomin A (ThxA) production. We found that ThxA biosynthesis is not correlated with bacterial biomass production, nor is it stimulated by a-solanine or a-chaconine, the two most prevalent glycoalkaloids in potato tissue. ThxA production was stimulated by oat bran broth, even after the bran had been extracted with hexane, ethyl acetate, methanol, and water, suggesting that oat bran contains one or more polymeric elicitors of ThxA biosynthesis. Oat bran contains high levels of xylans and glucans, and both of these carbohydrates, as well as xylans from wheat and tamarind, stimulated ThxA production, but not to the same extent as oat bran broth. Starches and simple sugars did not stimulate ThxA production. The data indicate that complex carbohydrates act as environmental signals to plant pathogenic Streptomyces, eliciting the production of thaxtomin and enabling the bacteria to colonize its host.