Involvement of the Plant Polymer Suberin and the Disaccharide Cellobiose in Triggering Thaxtomin A Biosynthesis, a Phytotoxin Produced by the Pathogenic Agent Streptomyces scabies

Abstract

Streptomyces scabies is a gram-positive soil bacterium recognized as the main causal agent of common scab. Pathogenicity in Streptomyces spp. depends on their capacity to synthesize phytotoxins called thaxtomins. Genes involved in biosynthesis of these secondary metabolites are known to be induced by cellobiose, a plant disaccharide. However, growth of S. scabies in a minimal medium containing cellobiose as a carbon source is very poor and only generates traces of thaxtomins. The effect of suberin, a lipid plant polymer, on thaxtomin A biosynthesis and the expression of genes involved in its biosynthetic pathway was analyzed. S. scabies was grown in a starch-containing minimal medium supplemented with cellobiose (0.5%), suberin (0.1%), or both. The presence of both cellobiose and suberin doubled bacterial growth and triggered thaxtomin A production, which correlated with the upregulation (up to 342-fold) of genes involved in thaxtomins synthesis. The addition of either suberin or cellobiose alone did not affect these parameters. Suberin appeared to stimulate the onset of secondary metabolism, which is a prerequisite to the production of molecules such as thaxtomin A, while cellobiose induced the biosynthesis of this secondary metabolite.

Streptomyces species associated with common scab lesions of potatoes in South Africa

“…Leiminger et al (2012) and Wanner (2009) also isolated pathogenic but txtAB-negative S. acidiscabies, S. stelliscabiei and S. bottropensis from Germany and North America respectively. Lerat et al (2010) pointed out that pathogenicity depends on the ability of the species to synthesize toxins. Little is known about the molecular mechanisms involved in Streptomyces pathogenicity.…”

Potato Suberin Induces Differentiation and Secondary Metabolism in the Genus <i>Streptomyces</i>

“…Morphology of the five Streptomyces species tested in this study was determined as previously described (19). Briefly, 30–50 viable spores from each species were streaked on Petri dishes containing solidified (15 g L −1 agar) CM and SM.…”

“…It was revealed that its presence up-regulated proteins related to the stress response, glycolysis, morphological differentiation and secondary metabolism (17). The effect of suberin on differentiation was corroborated by cultivating S. scabiei in the presence or absence of suberin (19). Suberin strongly stimulates aerial mycelium development in S. scabiei which, in the presence of cellobiose, can lead to the production of the secondary metabolites, thaxtomins (19).…”

“…The effect of suberin on differentiation was corroborated by cultivating S. scabiei in the presence or absence of suberin (19). Suberin strongly stimulates aerial mycelium development in S. scabiei which, in the presence of cellobiose, can lead to the production of the secondary metabolites, thaxtomins (19). …”

Phytotoxin produced by the netted scab pathogen, Streptomyces turgidiscabies strain 65, isolated in Sweden

“…Requirements of plant extracts such as oatmeal for thaxtomin production by S. scabies have been reported (Beauséjour et al 1999), and effective ingredients were shown to be suberin and cellobiose (Beauséjour et al 1999;Johnson et al 2007;Lerat et al 2010). We examined the requirements for phytotoxin production in S. turgidiscabies strain 65 and NBRC16080…”