Complex Intra-Operonic Dynamics Mediated by a Small RNA in Streptomyces coelicolor

Hindra Hindra,Matthew J Moody,Marie A Elliot,Stephanie E Jones,Paul Hoskisson

doi:10.1371/journal.pone.0085856

Abstract

Streptomyces are predominantly soil-dwelling bacteria that are best known for their multicellular life cycle and their prodigious metabolic capabilities. They are also renowned for their regulatory capacity and flexibility, with each species encoding >60 sigma factors, a multitude of transcription factors, and an increasing number of small regulatory RNAs. Here, we describe our characterization of a conserved small RNA (sRNA), scr4677. In the model species Streptomyces coelicolor, this sRNA is located in the intergenic region separating SCO4677 (an anti-sigma factor-encoding gene) and SCO4676 (a putative regulatory protein-encoding gene), close to the SCO4676 translation start site in an antisense orientation. There appears to be considerable genetic interplay between these different gene products, with wild type expression of scr4677 requiring function of the anti-sigma factor SCO4677, and scr4677 in turn influencing the abundance of SCO4676-associated transcripts. The scr4677-mediated effects were independent of RNase III (a double stranded RNA-specific nuclease), with RNase III having an unexpectedly positive influence on the level of SCO4676-associated transcripts. We have shown that both SCO4676 and SCO4677 affect the production of the blue-pigmented antibiotic actinorhodin under specific growth conditions, and that this activity appears to be independent of scr4677.

Highlights

Streptomyces bacteria are best known for their complex developmental life cycle and their vast secondary metabolic capabilities, which include producing the majority of naturally synthesized antibiotics
We found there to be intriguing genetic connections between the different products expressed from this locus, with wild type expression of scr4677 requiring the activity of SCO4677, scr4677 affecting the levels of SCO4676-associated transcripts, and RNase III unexpectedly having a positive effect on SCO4676 and SCO4677 levels while having no effect on scr4677
We found there were no obvious differences in scr4677 transcript levels in Drnc and wild type strains (Figure 4C); the smaller transcripts typically seen during growth on rich medium were present at equivalent levels in wild type and mutant strains, suggesting that these transcripts were not generated as a result of RNase III cleavage

Summary

Introduction

Streptomyces bacteria are best known for their complex developmental life cycle and their vast secondary metabolic capabilities, which include producing the majority of naturally synthesized antibiotics. Germ tube elongation and subsequent hyphal tip extension and branching lead to the formation of a filamentous cellular network known as the vegetative or substrate mycelium. Aerial hyphae formation is coupled, both genetically and temporally, with the onset of secondary metabolism and antibiotic production [3]. In the model organism Streptomyces coelicolor, the different growth and metabolic stages are readily distinguishable. During growth on agar media, aerial hyphae formation results in a fuzzy white colony appearance, while sporulation culminates with the production of a grey polyketide pigment that turns colonies grey [4]. Equivalent visual cues accompany antibiotic production, courtesy of the fact that S. coelicolor produces both blue and red pigmented antibiotics (actinorhodin and undecylprodigiosin, respectively)

Methods

Results

Conclusion