The roseoflavin producer Streptomyces davaonensis has a high catalytic capacity and specific genetic adaptations with regard to the biosynthesis of riboflavin

Isolation, characterisation and description of the roseoflavin producer Streptomyces berlinensis sp. nov

The Gram-positive bacteria Streptomyces davaonensis and Streptomyces cinnabarinus have been the only organisms known to produce roseoflavin, a riboflavin (vitamin B2) derived red antibiotic. Using a selective growth medium and a phenotypic screening, we were able to isolate a novel roseoflavin producer from a German soil sample. The isolation procedure was repeated twice, that is, the same strain could be isolated from the same location in Berlin 6 months and 12 months after its first isolation. Whole genome sequencing of the novel roseoflavin producer revealed an unusual chromosomal arrangement and the deposited genome sequence of the new isolate (G + C content of 71.47%) contains 897 genes per inverted terminal repeat, 6190 genes in the core and 107 genes located on an illegitimate terminal end. We identified the roseoflavin biosynthetic genes rosA, rosB and rosC and an unusually high number of riboflavin biosynthetic genes. Overexpression of rosA, rosB and rosC in Escherichia coli and enzyme assays confirmed their predicted functions in roseoflavin biosynthesis. A full taxonomic analysis revealed that the isolate represents a previously unknown Streptomyces species and we propose the name Streptomyces berlinensis sp. nov. for this roseoflavin producer.

The Probiotic Potential and Metabolite Characterization of Bioprotective Bacillus and Streptomyces for Applications in Animal Production

Probiotics are increasingly recognized for their potential in managing bacterial challenges in animal production. This study aimed to evaluate the probiotic potential of Bacillus and Streptomyces strains, specifically their bioprotective ability against Salmonella. In agar inhibition assays, these bacteria supported Salmonella-inhibition zones, ranging from 2.5 ± 0.5 to 6.3 ± 2.0 mm. Analyses of antimicrobial metabolites revealed their capacity to produce compounds with anti-Salmonella properties, except for Bacillus subtilis MLB2. When Salmonella was exposed to lyophilized metabolites, inhibition occurred in both liquid (at concentrations between 250 and 500 g/L) and solid cultures (at 500 g/L). To confirm their probiotic potential, the S. griseus and Bacillus strains underwent evaluations for antimicrobial resistance, bile salt tolerance, auto- and co-aggregation, pH resistance, and their ability to adhere to and inhibit Salmonella in Caco-2 cells. These assessments confirmed their probiotic potential. The probiotic strains were further encapsulated and subjected to simulated swine and poultry digestion. They demonstrated survival potential through the gastrointestinal tract and significantly reduced the Salmonella population. Thus, these strains exhibit considerable promise for producing biotechnological products aimed at controlling Salmonella in animal production. This approach ensures the health and hygiene of farming facilities, mitigates the spread of zoonotic bacteria, and contributes positively to public health.

A second riboflavin import system is present in flavinogenic Streptomyces davaonensis and supports roseoflavin biosynthesis

The antibiotic roseoflavin is produced by Streptomyces davaonensis in the stationary phase of growth. To support biosynthesis of the secondary metabolite roseoflavin, S. davaonensis underwent several genetic adaptations with regard to metabolism of the roseoflavin precursor and primary metabolite riboflavin. In addition to 17 riboflavin biosynthesis genes at different chromosomal locations, S. davaonensis contains the riboflavin transporter gene ribM being part of the riboflavin biosynthetic operon ribE1MAB5H. Deletion of this operon generated riboflavin auxotrophic S. davaonensis strains. The finding that S. davaonensis ΔribE1MAB5H was able to grow in a culture medium containing low levels of riboflavin indicated that in addition to RibM, a second riboflavin transporter is present in this bacterium. The S. davaonensis genes ribXY (former rosXY) represented candidate genes for such a second riboflavin transport system and the results of our experiments now show that RibXY from S. davaonensis is a highly efficient riboflavin importer but not a roseoflavin importer.