Potato scab, a serious soilborne disease caused by Streptomyces spp., occurs in potato-growing areas worldwide and results in severe economic losses. In this paper, the pathogenicity of Streptomyces strain AMCC400023, isolated from potato scabs in Hebei Province, China, was verified systematically by the radish seedling test, the potato tuber slice assay, the potted back experiment, and the detection of phytotoxin thaxtomin A. Morphological, physiological, and biochemical characteristics were determined, and the 16S ribosomal RNA analyses of Streptomyces sp. AMCC400023 were carried out. To obtain the accurate taxonomic status of the pathogen strain, the whole genome was sequenced, and the phylogenetic tree among 31 Streptomyces genomes was formed. The average nucleotide identity (ANI) and in silico DNA-DNA hybridization (isDDH) were analyzed, and at the same time, the toxicity-related genes between Streptomyces sp. AMCC400023 and Streptomyces scabiei were compared, all based on the whole-genome level. All of the data supported that, instead of a member of S. scabiei, test strain Streptomyces sp. AMCC400023 was a distinct phytopathogen of potato common scab, which had a relatively close relationship with S. scabiei while separating clearly from S. scabiei at least in the species level of taxonomic status. The complete pathogenicity island (PAI) composition of Streptomyces sp. AMCC400023 was identified, which contained a toxin region and a colonization region. It was conjectured that the PAI of Streptomyces sp. AMCC400023 might be directly or indirectly acquired from S. scabiei 87-22 by horizontal gene transfer, or at the very least, there was a very close homologous relationship between the two pathogens as indicated by a series of analyses, such as phylogenetic relationships among 31 Streptomyces species, ANI and isDDH analyses, PAI structure mapping, thaxtomin A synthetic gene cluster tree construction, and most important, the collinearity analysis at the genome level.

Disease-suppressive soil refers to soil in which the incidence or severity of plant diseases is lower than the general environment or the surrounding soil, and this inhibitory effect is attributed to diverse microbes. In this study, bacteria from suppressive soil were cultured, and preliminarily identification was made based on the 16S rRNA gene sequence, and the nematocidal activity was evaluated in both in vitro and greenhouse conditions. A total of 110 isolates were obtained from 13 sampling sites in Shandong Province, China. Using phylogenetic analysis, 110 sequenced isolates were clustered into 16 genera, belonging to 4 phyla, Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria, indicating that the diversity of cultivable bacteria in suppressive soil is high. Among the genera, Bacillus was dominant; 85 isolates were classified into 30 Bacillus species based on BLAST data. Twenty three of these isolates caused >75% mortality of second-stage juveniles of the root-knot nematode Meloidogyne incognita in in vitro assays. Lastly, pot experiments revealed that the 10 selected strains inhibited the development of M. incognita to different degrees. This is the first investigation of the diversity and nematocidal activity of cultivable bacteria from suppressive soil in Shandong province, China. The results confirmed that suppressive soil is a rich source of bacterial activity against root-knot nematodes.

As important silkworm varieties reared on artificial diet, Youshi No. 1 (YS) and Guangshi No. 1 (GS) showed remarkable differences in physiological characteristics. GS had significantly better performance than YS in body weight, cocooning ability, food intake, feed utilization efficiency, and digestive enzyme activities. We further performed metabolomics and 16S rRNA high-throughput sequencing to analyze their metabolic profiles and midgut microbiota. More than 40 differential metabolites were screened out, and four metabolic pathways related to feeding divergence were determined via KEGG enrichment, among which L-valine was enriched in multiple pathways. Significant structural differences were also observed in midgut microbiota, and Bacillus was positively correlated with pantothenic acid and valine metabolism. These correlational results disclosed that differential metabolites and gut microbiota might underlie the phenotypic variations between the two varieties. Integrated analysis combined with functional verification experiments demonstrated that supplementation of 1% L-valine or specific Bacillus strains in an artificial diet was associated with the improvement of the growth performance, cocoon quality, and feed utilization efficiency of the YS silkworm variety.

Florfenicol (FF) is widely used in animal husbandry due to its broad-spectrum bactericidal activity, while there is little research focused on its toxic ef