RESUMO
Streptomyces are a genus of ubiquitous soil bacteria from which the majority of clinically utilized antibiotics derive1. The production of these antibacterial molecules reflects the relentless competition Streptomyces engage in with other bacteria, including other Streptomyces species1,2. Here we show that in addition to small-molecule antibiotics, Streptomyces produce and secrete antibacterial protein complexes that feature a large, degenerate repeat-containing polymorphic toxin protein. A cryo-electron microscopy structure of these particles reveals an extended stalk topped by a ringed crown comprising the toxin repeats scaffolding five lectin-tipped spokes, which led us to name them umbrella particles. Streptomyces coelicolor encodes three umbrella particles with distinct toxin and lectin composition. Notably, supernatant containing these toxins specifically and potently inhibits the growth of select Streptomyces species from among a diverse collection of bacteria screened. For one target, Streptomyces griseus, inhibition relies on a single toxin and that intoxication manifests as rapid cessation of vegetative hyphal growth. Our data show that Streptomyces umbrella particles mediate competition among vegetative mycelia of related species, a function distinct from small-molecule antibiotics, which are produced at the onset of reproductive growth and act broadly3,4. Sequence analyses suggest that this role of umbrella particles extends beyond Streptomyces, as we identified umbrella loci in nearly 1,000 species across Actinobacteria.
Assuntos
Antibiose , Proteínas de Bactérias , Toxinas Bacterianas , Streptomyces , Antibacterianos/biossíntese , Antibacterianos/química , Antibacterianos/metabolismo , Antibacterianos/farmacologia , Antibiose/efeitos dos fármacos , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Proteínas de Bactérias/farmacologia , Proteínas de Bactérias/ultraestrutura , Toxinas Bacterianas/química , Toxinas Bacterianas/genética , Toxinas Bacterianas/metabolismo , Toxinas Bacterianas/farmacologia , Microscopia Crioeletrônica , Lectinas/química , Lectinas/genética , Lectinas/metabolismo , Lectinas/ultraestrutura , Testes de Sensibilidade Microbiana , Modelos Moleculares , Streptomyces/química , Streptomyces/efeitos dos fármacos , Streptomyces/genética , Streptomyces/crescimento & desenvolvimento , Streptomyces coelicolor/química , Streptomyces coelicolor/genética , Streptomyces coelicolor/metabolismo , Streptomyces griseus/efeitos dos fármacos , Streptomyces griseus/genética , Streptomyces griseus/crescimento & desenvolvimento , Streptomyces griseus/metabolismoRESUMO
Background: The growing problem of environmental pollution caused by synthetic plastics has led to the search for alternative materials such as biodegradable plastics. Of the biopolymers presently under development, starch/natural rubber is one promising alternative. Several species of bacteria and fungi are capable of degrading natural rubber and many can degrade starch. Results: Streptomyces coelicolor CH13 was isolated from soil according to its ability to produce translucent halos on a mineral salts medium, MSM, supplemented with natural rubber and to degrade starch. Scanning electron microscope studies showed that it colonized the surfaces of strips of a new starch/natural rubber biopolymer and rubber gloves and caused degradation by forming holes, and surface degradation. Starch was completely removed and polyisoprene chains were broken down to produce aldehyde and/or carbonyl groups. After 6 weeks of cultivation with strips of the polymers in MSM, S. coelicolor CH13 reduced the weight of the starch/NR biopolymer by 92 percent and that of the rubber gloves by 14.3 percent. Conclusions: This study indicated that this bacterium causes the biodegradation of the new biopolymer and natural rubber and confirms that this new biopolymer can be degraded in the environment and would be suitable as a green plastic derived from natural sources.