Seasonal Dynamics of Various Scab-Causing Streptomyces Genotypes Among Potato Fields on Prince Edward Island.

Potato common scab is an important bacterial plant disease caused by numerous Streptomyces species and strains. A better understanding of the genetic diversity and population dynamics of these microorganisms in the field is crucial to develop effective control methods. Our research group previously studied the genetic diversity of scab-causing Streptomyces spp. in Prince Edward Island, one of Canada's most important potato-growing provinces. Fourteen distinct Streptomyces genotypes were identified and displayed contrasting aggressiveness toward potato tubers. To better understand the distribution and occurrence of these genotypes over time under field conditions, the population dynamics were studied in nine commercial potato fields throughout a growing season. A comparative genomic-driven approach was used to design genotype-specific primers and probes, allowing us to quantify, using quantitative polymerase chain reaction, the abundance of each of the 14 genotypes in field soil. Thirteen of the previously identified genotypes were detected in at least one soil sample, with various frequencies and population sizes across the different fields under study. Interestingly, weakly virulent genotypes dominated, independent of time or location. Among them, three genotypes accounted for more than 80% of the genotypes' combined population. Although the highly virulent genotypes were detected in lower relative abundance than the weakly virulent ones, an increase in the highly virulent genotypes' population size was observed over the growing season in most fields. The results will ultimately be useful for the development of targeted common scab control strategies.

Description of Streptomyces griseiscabiei sp. nov. and reassignment of Streptomyces sp. strain NRRL B-16521 to Streptomyces acidiscabies.

Streptomyces strain NRRL B-2795T (DSM 112329T=NRRL B-2795T) is described as the type strain of Streptomyces griseiscabiei sp. nov. using whole-genome average nucleotide identity and multilocus sequence analyses in addition to phenotypic characterization of carbon source utilization, spore chain morphology, melanin production, salt tolerance, pH tolerance, plant pathogenicity and antibiotic resistance. This strain was previously classified as Streptomyces scabiei but suggested as a potential novel species. A second Streptomyces strain, NRRL B-16521, previously named Streptomyces scabiei, and also previously suggested as a potential novel species, is assigned to Streptomyces acidiscabies based on whole-genome average nucleotide identity. Morphological and biochemical characterizations also support this designation for NRRL B-16521. Both Streptomyces sp. strain NRRL B-2795T and NRRL B-16521 cause common scab on multiple cultivars of potato.

Efecto in vitro del extracto crudo de un estreptomiceto causante de sarna común de papa en Sinaloa, México / In vitro effect of the crude extract of a potato common scab streptomycete in Sinaloa, Mexico

Abstract A strain isolated from potato common scab superficial lesions in El Fuerte Valley in northern Sinaloa, Mexico, was identified by 16S rRNA and morphological methods. Moreover, the effects of the crude extract of strain V2 was evaluated on radish and potato. The isolate was similar to Streptomyces acidiscabies in its morphological properties; however, the 16S rRNA gene sequence of strain V2 was neither 100% identical to this species nor to the streptomycetes previously reported in Sinaloa, Mexico. Strain V2 did not amplify any specific PCR products for genes necl and tomA, which have been found and reported in S. acidiscabies. Strain V2 produced a PCR product for the txtAB operon, which is related to the production of thaxtomin. In vitro assays using crude thaxtomin extract and a spore suspension of the organism caused necrotic symptoms on radish and potato, which were highly virulent in potato. This study reports that Streptomyces sp. V2 has a toxigenic region (TR) that is associated with the thaxtomin gene cluster.

Resumen Se aisló una cepa de una lesión superficial de sarna común de la papa en un ejemplar procedente del Valle del Fuerte, en el norte de Sinaloa, México. La cepa fue identificada por secuenciación del gen 16S ARNr, y por sus características morfológicas. Los efectos del extracto crudo de dicha cepa, llamada V2, fue evaluado en papa y rábano. El aislado fue similar a Streptomyces acidiscabies en sus características morfológicas, pero la secuencia del gen 16S ARNr de la cepa V2 no fue 100% idéntica a la de dicha especie, ni tampoco a las de cepas identificadas dentro de este taxón previamente en Sinaloa, México. La cepa V2 no amplificó los productos específicos de PCR de los genes nec1 y tomA, los cuales sí se han reportado en S. acidiscabies. La cepa V2 amplificó el producto de PCR para del operón txtAB, relacionado con la producción de taxtomina. A través de ensayos in vitro usando un extracto crudo de taxtomina y una suspensión de esporas del organismo aislado se verificó la producción de síntomas necróticos en rábano y papa, con mayor virulencia en esta última especie. Este estudio indica que Streptomyces sp. V2 tiene una región toxigénica (TR) asociada con el cluster de genes de taxtomina.

In vitro effect of the crude extract of a potato common scab streptomycete in Sinaloa, Mexico.

A strain isolated from potato common scab superficial lesions in El Fuerte Valley in northern Sinaloa, Mexico, was identified by 16S rRNA and morphological methods. Moreover, the effects of the crude extract of strain V2 was evaluated on radish and potato. The isolate was similar to Streptomyces acidiscabies in its morphological properties; however, the 16S rRNA gene sequence of strain V2 was neither 100% identical to this species nor to the streptomycetes previously reported in Sinaloa, Mexico. Strain V2 did not amplify any specific PCR products for genes nec1 and tomA, which have been found and reported in S. acidiscabies. Strain V2 produced a PCR product for the txtAB operon, which is related to the production of thaxtomin. In vitro assays using crude thaxtomin extract and a spore suspension of the organism caused necrotic symptoms on radish and potato, which were highly virulent in potato. This study reports that Streptomyces sp. V2 has a toxigenic region (TR) that is associated with the thaxtomin gene cluster.

The dilemma of bacterial expansins evolution. The unusual case of Streptomyces acidiscabies and Kutzneria sp. 744.

Expansins are a superfamily of proteins mainly present in plants that are also found in bacteria, fungi and amoebozoa. Expansin proteins bind the plant cells wall and relax the cellulose microfibrils without any enzymatic action. The evolution of this kind of proteins exposes a complex pattern of horizontal gene transferences that makes difficult to determine the precise origin of non-plant expansins. We performed a genome-wide search of inter-domain horizontal gene transfer events using Streptomyces species and found a plant-like expansin in the Streptomyces acidiscabies proteome. This finding leads us to study in deep the origin and the characteristics of this peculiar protein, also present in the species Kutzneria sp.744. Using phylogenetic analyses, we determine that indeed S. acidiscabies and Kutzneria sp.744 expansins are located inside the plants expansins A clade. Using secondary and tertiary structural information, we observed that the electrostatic potentials and the folding of expansins are similar, independently of the proteins' origin. Using all this information, we conclude that S. acidiscabies and Kutzneria sp.744 expansins have a plant origin but differ from plant and bacterial canonical expansins. This finding suggests that the experimental research around this kind of expansins can be promissory in the future.