Identification of different promoters in the absA1–absA2 two-component system, a negative regulator of antibiotic production in Streptomyces coelicolor

An overview on the two-component systems of Streptomyces coelicolor

The two-component system (TCS) found in various organisms is a regulatory system, which is involved in the response by the organism to stimuli, thereby regulating the internal behavior of the cell. It is commonly found in prokaryotes and is an important signaling system in bacteria. TCSs are involved in the regulation of physiological and morphological differentiation of the industrially important microbes from the genus Streptomyces, which produce a vast array of bioactive secondary metabolites (SMs). Genetic engineering of TCSs can substantially increase the yield of target SMs, which is valuable for industrial-scale production. Research on TCS has mainly been completed in the model strain Streptomyces coelicolor. In this review, we summarize the recent advances in the functional identification and elucidation of the regulatory mechanisms of various TCSs in S. coelicolor, with a focus on their roles in the biosynthesis of important SMs.

Two-Component Systems of Streptomyces coelicolor: An Intricate Network to Be Unraveled

Bacteria of the Streptomyces genus constitute an authentic biotech gold mine thanks to their ability to produce a myriad of compounds and enzymes of great interest at various clinical, agricultural, and industrial levels. Understanding the physiology of these organisms and revealing their regulatory mechanisms is essential for their manipulation and application. Two-component systems (TCSs) constitute the predominant signal transduction mechanism in prokaryotes, and can detect a multitude of external and internal stimuli and trigger the appropriate cellular responses for adapting to diverse environmental conditions. These global regulatory systems usually coordinate various biological processes for the maintenance of homeostasis and proper cell function. Here, we review the multiple TCSs described and characterized in Streptomyces coelicolor, one of the most studied and important model species within this bacterial group. TCSs are involved in all cellular processes; hence, unravelling the complex regulatory network they form is essential for their potential biotechnological application.

Genome-wide analysis of the role of the antibiotic biosynthesis regulator AbsA2 in Streptomyces coelicolor A3(2)

The AbsA1-AbsA2 two component signalling system of Streptomyces coelicolor has long been known to exert a powerful negative influence on the production of the antibiotics actinorhodin, undecylprodiginine and the Calcium-Dependent Antibiotic (CDA). Here we report the analysis of a ΔabsA2 deletion strain, which exhibits the classic precocious antibiotic hyper-production phenotype, and its complementation by an N-terminal triple-FLAG-tagged version of AbsA2. The complemented and non-complemented ΔabsA2 mutant strains were used in large-scale microarray-based time-course experiments to investigate the effect of deleting absA2 on gene expression and to identify the in vivo AbsA2 DNA-binding target sites using ChIP-on chip. We show that in addition to binding to the promoter regions of redZ and actII-orfIV AbsA2 binds to several previously unidentified sites within the cda biosynthetic gene cluster within and/or upstream of SCO3215—SCO3216, SCO3217, SCO3229—SCO3230, and SCO3226, and we relate the pattern of AbsA2 binding to the results of the transcriptomic study and antibiotic phenotypic assays. Interestingly, dual ‘biphasic’ ChIP peaks were observed with AbsA2 binding across the regulatory genes actII-orfIV and redZ and the absA2 gene itself, while more conventional single promoter-proximal peaks were seen at the CDA biosynthetic genes suggesting a different mechanism of regulation of the former loci. Taken together the results shed light on the complex mechanism of regulation of antibiotic biosynthesis in Streptomyces coelicolor and the important role of AbsA2 in controlling the expression of three antibiotic biosynthetic gene clusters.

[Causes, consequences and treatment of hypophosphatemia: A systematic review]

CONTEXT

Although hypophosphatemia is usually very seldom, it can reach two to 3% of hospitalized patients and until 28% of intensive care unit patients. Due to the lack of knowledge, clinical practice regarding seeking or treatment of hypophosphatemia is very heterogenous. However its clinical consequences might be heavy. A better knowledge of its causes, physiopathological effects and treatment should lead to a documented and homogenous care of these patients in clinics.

OBJECTIVE

The aim of our study was a systematic review of littérature, seeking for publications about causes, consequences and treatment of hypophosphatemia.

DOCUMENTARY SOURCES (KEYWORDS AND LANGUAGE)

A research has been conducted on the Medline database by using the following keywords "phosphorus supplementation", "hypophosphatemia" and ("physiopathology" or "complications").

RESULTS

Three mains mechanisms might be responsible for hypophosphatemia: a decrease in digestive absorption, a rise in kidney excretion and a transfer of phosphorus to the intracellular compartment. Denutrition, acid base balance troubles, parenteral nutrition or several drugs are capable of provoking or favouring hypophosphatemia. All these situations are frequently encountered in intensive care unit. Consequences of hypophosphatemia might be serious. Best studied and documented are cardiac and respiratory muscle contractility decrease, sometimes leading to acute cardiac and respiratory failure, cardiac rhythm troubles and cardiac arrest. Hypophosphatemia is frequent during sepsis. It could be responsible for leucocyte dysfunction that might favour or increase sepsis. The treatment of hypophosphatemia is usually simple through a supplementation that quickly restores a regular concentration, with few adverse effects when regularly used.

CONCLUSION

During at-risk situations, the systematic search for hypophosphatemia and its treatment may limit the occurrence of serious consequences.

Identification of a novel unpaired histidine sensor kinase affecting secondary metabolism and morphological differentiation in Streptomyces acidiscabies ATCC 49003

Two-component systems (TCSs) are an important signaling transduction pathway that adapt to changing environments. Commonly, a TCS comprises a sensor kinase that is usually an integral membrane histidine sensor kinase and a response regulator that mediates the cellular responses. Presently, however, we cloned a novel sensor kinase gene (tcsK) that is not adjacent to its cognate response regulator from Streptomyces acidiscabies that produces two secondary metabolites, thaxtomin A and WS5995B, and identified its functional involvement in the production of secondary metabolites and morphological differentiation. The elevated expression and disruption of the tcsK gene enhanced 7.1-fold and almost abolished WS5995B production in S. acidiscabies, respectively, but did not affect the production of thaxtomin A. In addition, spore formation of S. acidiscabies was decreased 120-fold by the disruption of tcsK, and the actinorhodin production of Streptomyces lividans TK24 was increased 5.7-fold by the high expression of tcsK. These results indicate that the novel unpaired tcsK gene may be related to the control of secondary metabolite production and spore formation in actinomycetes.

Transcriptional response to vancomycin in a highly vancomycin-resistant Streptomyces coelicolor mutant

ABSTRACT: 

Aim: The main objective of this study is to understand the mechanism of vancomycin resistance in a Streptomyces coelicolor disrupted mutant highly resistant to vancomycin. Materials & methods: Different techniques have been performed in the study including gene disruption, primer extension, antibiotic susceptibility tests, electron microscopy, confocal microscopy, cell wall analysis and microarrays. Results: During the phenotypical characterization of mutant strains affected in phosphate-regulated genes of unknown function, we found that the S. coelicolor SCO2594 disrupted mutant was highly resistant to vancomycin and had other phenotypic alterations such as antibiotic overproduction, impaired growth and reduction of phosphate cell wall content. Transcriptomic studies with this mutant indicated a relationship between vancomycin resistance and cell wall stress. Conclusion: We identified a S. coelicolor mutant highly resistant to vancomycin in both high and low phosphate media. In addition to Van proteins, others such as WhiB or SigE appear to be involved in this regulatory mechanism.