Strain Improvement Program of Streptomyces roseosporus for Daptomycin Production

Daptomycin production enhancement by ARTP mutagenesis and fermentation optimization in Streptomyces roseosporus

AIMS

We evaluated whether the randomness of mutation breeding can be regulated through a double-reporter system. We hope that by establishing a new precursor feeding strategy, the production capacity of industrial microorganisms after pilot scale-up can be further improved.

METHODS AND RESULTS

In this study, the industrial strain Streptomyces roseosporus L2796 was used as the starter strain for daptomycin production, and a double-reporter system with the kanamycin resistance gene Neo and the chromogenic gene gusA was constructed to screen for high-yield strain L2201 through atmospheric and room temperature plasma (ARTP). Furthermore, the composition of the culture medium and the parameters of precursor replenishment were optimized, resulting in a significant enhancement of the daptomycin yield of the mutant strain L2201(752.67 mg/l).

CONCLUSIONS

This study successfully screened a high-yield strain of daptomycin through a double-reporter system combined with ARTP mutation. The expression level of two reporter genes can evaluate the strength of dptEp promoter, which can stimulate the expression level of dptE in the biosynthesis of daptomycin, thus producing more daptomycin. The developed multi-stage feeding rate strategy provides a novel way to increase daptomycin in industrial fermentation.

Development of a native-locus dual reporter system for the efficient screening of the hyper-production of natural products in Streptomyces

Streptomyces is renowned for its abundant production of bioactive secondary metabolites, but most of these natural products are produced in low yields. Traditional rational network refactoring is highly dependent on the comprehensive understanding of regulatory mechanisms and multiple manipulations of genome editing. Though random mutagenesis is fairly straightforward, it lacks a general and effective strategy for high throughput screening of the desired strains. Here in an antibiotic daptomycin producer S. roseosporus, we developed a dual-reporter system at the native locus of the daptomycin gene cluster. After elimination of three enzymes that potentially produce pigments by genome editing, a gene idgS encoding the indigoidine synthetase and a kanamycin resistant gene neo were integrated before and after the non-ribosomal peptidyl synthetase genes for daptomycin biosynthesis, respectively. After condition optimization of UV-induced mutagenesis, strains with hyper-resistance to kanamycin along with over-production of indigoidine were efficiently obtained after one round of mutagenesis and target screening based on the dual selection of the reporter system. Four mutant strains showed increased production of daptomycin from 1.4 to 6.4 folds, and significantly improved expression of the gene cluster. Our native-locus dual reporter system is efficient for targeting screening after random mutagenesis and would be widely applicable for the effective engineering of Streptomyces species and hyper-production of these invaluable natural products for pharmaceutical development.

Can intracellular Staphylococcus aureus in osteomyelitis be treated using current antibiotics? A systematic review and narrative synthesis

Approximately 40% of treatments of chronic and recurrent osteomyelitis fail in part due to bacterial persistence. Staphylococcus aureus, the predominant pathogen in human osteomyelitis, is known to persist by phenotypic adaptation as small-colony variants (SCVs) and by formation of intracellular reservoirs, including those in major bone cell types, reducing susceptibility to antibiotics. Intracellular infections with S. aureus are difficult to treat; however, there are no evidence-based clinical guidelines addressing these infections in osteomyelitis. We conducted a systematic review of the literature to determine the demonstrated efficacy of all antibiotics against intracellular S. aureus relevant to osteomyelitis, including protein biosynthesis inhibitors (lincosamides, streptogramins, macrolides, oxazolidines, tetracyclines, fusidic acid, and aminoglycosides), enzyme inhibitors (fluoroquinolones and ansamycines), and cell wall inhibitors (beta-lactam inhibitors, glycopeptides, fosfomycin, and lipopeptides). The PubMed and Embase databases were screened for articles related to intracellular S. aureus infections that compared the effectiveness of multiple antibiotics or a single antibiotic together with another treatment, which resulted in 34 full-text articles fitting the inclusion criteria. The combined findings of these studies were largely inconclusive, most likely due to the plethora of methodologies utilized. Therefore, the reported findings in the context of the models employed and possible solutions for improved understanding are explored here. While rifampicin, oritavancin, linezolid, moxifloxacin and oxacillin were identified as the most effective potential intracellular treatments, the scientific evidence for these is still relatively weak. We advocate for more standardized research on determining the intracellular effectiveness of antibiotics in S. aureus osteomyelitis to improve treatments and patient outcomes.