A novel insertion mutation in Streptomyces coelicolor ribosomal S12 protein results in paromomycin resistance and antibiotic overproduction

Genome Shuffling Mutant of Streptomyces diastatochromogenes for Substantial Improvement of Toyocamycin Production

Toyocamycin, a nucleoside antibiotic, is a fungicide with the potential to control plant pathogens. In this study, three rounds of genome shuffling screening were applied to enhance the toyocamycin production in Streptomyces diastatochromogenes 1628. After three rounds of genome-shuffling screening, the toyocamycin production increased by 10.8-fold that of wild-type, and 2.64-fold of its parental strain. By optimization of its nutrition condition in medium, the highest production of toyocamycin reached 1173.6 mg/L in TY-producing medium. In addition, the mechanism for the improvement of shuffled strains was investigated. Recombinants with increased toyocamycin production exhibited higher transcriptional level of the toy cluster and product resistance. Furthermore, the rise of ATP hydrolysis rate indicated that intracellular ATP exhibit a significant role in tuning the toy cluster by an ATP-binding pathway-specific regulator. In all, we obtained S. diastatochromogenes mutants with enhanced toyocamycin production, and provided a valuable clue for the activation of secondary metabolites.

A novel mechanism of streptomycin resistance in Yersinia pestis: Mutation in the rpsL gene

Streptomycin is considered to be one of the effective antibiotics for the treatment of plague. In order to investigate the streptomycin resistance of Y. pestis in China, we evaluated streptomycin susceptibility of 536 Y. pestis strains in China in vitro using the minimal inhibitory concentration (MIC) and screened streptomycin resistance-associated genes (strA and strB) by PCR method. A clinical Y. pestis isolate (S19960127) exhibited high-level resistance to streptomycin (the MIC was 4,096 mg/L). The strain (biovar antiqua) was isolated from a pneumonic plague outbreak in 1996 in Tibet Autonomous Region, China, belonging to the Marmota himalayana Qinghai–Tibet Plateau plague focus. In contrast to previously reported streptomycin resistance mediated by conjugative plasmids, the genome sequencing and allelic replacement experiments demonstrated that an rpsL gene (ribosomal protein S12) mutation with substitution of amino-acid 43 (K43R) was responsible for the high-level resistance to streptomycin in strain S19960127, which is consistent with the mutation reported in some streptomycin-resistant Mycobacterium tuberculosis strains. Streptomycin is used as the first-line treatment against plague in many countries. The emergence of streptomycin resistance in Y. pestis represents a critical public health problem. So streptomycin susceptibility monitoring of Y. pestis isolates should not only include plasmid-mediated resistance but also include the ribosomal protein S12 gene (rpsL) mutation, especially when treatment failure is suspected due to antibiotic resistance.

The plague natural foci are widely distributed in the world, and correspondingly, the plague still poses a significant threat to human health in some countries with endemic plague foci. Streptomycin is used as the first-line treatment against plague in many countries for the antibiotic is considered to be one of the effective antibiotics, particularly for the treatment of pneumonic plague. The resistance to streptomycin had been reported in Y. pestis strains from Madagascar in previous studies. In this study, we reported the high-level resistance to streptomycin in a clinical isolate of Y. pestis from a pneumonic patient in Tibet Autonomous Region, China, and a novel mechanism of streptomycin resistance, i.e. mutation in the rpsL gene were identified. The knowledge acquired about streptomycin resistance in Y. pestis will remain of great practical value. For the emergence of resistance to streptomycin in Y. pestis would render the treatment failure, thus corresponding antibiotic monitoring should be routinely carried out in countries threatened by plague. In addition, based on our further understanding about streptomycin resistance of Y. pestis isolates, such monitoring should not only include plasmid-mediated resistance but also include the ribosomal protein S12 gene (rpsL) mutation in Y. pestis isolates.

The Application of Regulatory Cascades in Streptomyces: Yield Enhancement and Metabolite Mining

Streptomyces is taken as an important resource for producing the most abundant antibiotics and other bio-active natural products, which have been widely used in pharmaceutical and agricultural areas. Usually they are biosynthesized through secondary metabolic pathways encoded by cluster situated genes. And these gene clusters are stringently regulated by interweaved transcriptional regulatory cascades. In the past decades, great advances have been made to elucidate the regulatory mechanisms involved in antibiotic production in Streptomyces. In this review, we summarized the recent advances on the regulatory cascades of antibiotic production in Streptomyces from the following four levels: the signals triggering the biosynthesis, the global regulators, the pathway-specific regulators and the feedback regulation. The production of antibiotic can be largely enhanced by rewiring the regulatory networks, such as overexpression of positive regulators, inactivation of repressors, fine-tuning of the feedback and ribosomal engineering in Streptomyces. The enormous amount of genomic sequencing data implies that the Streptomyces has potential to produce much more antibiotics for the great diversities and wide distributions of biosynthetic gene clusters in Streptomyces genomes. Most of these gene clusters are defined cryptic for unknown or undetectable natural products. In the synthetic biology era, activation of the cryptic gene clusters has been successfully achieved by manipulation of the regulatory genes. Chemical elicitors, rewiring regulatory gene and ribosomal engineering have been employed to crack the potential of cryptic gene clusters. These have been proposed as the most promising strategy to discover new antibiotics. For the complex of regulatory network in Streptomyces, we proposed that the discovery of new antibiotics and the optimization of industrial strains would be greatly promoted by further understanding the regulatory mechanism of antibiotic production.

Substantial improvement of toyocamycin production in Streptomyces diastatochromogenes by cumulative drug-resistance mutations

Toyocamycin is a member of the nucleoside antibiotic family and has been recognized as a promising fungicide for the control of plant diseases. However, low productivity of toyocamycin remains an important bottleneck in its industrial production. Therefore, dramatic improvements of strains for overproduction of toyocamycin are of great interest in applied microbiology research. In this study, we sequentially selected for mutations for multiple drug resistance to promote the overproduction of toyocamycin by Streptomyces diastatochromogenes 1628. The triple mutant strain, SD3145 (str str par), was obtained through sequential screenings. This strain showed an enhanced capacity to produce toyocamycin (1500 mg/L), 24-fold higher than the wild type in GYM liquid medium. This dramatic overproduction was attributed at least partially to the acquisition of an rsmG mutation and increased gene expression of toyA, which encodes a LuxR-family transcriptional regulator for toyocamycin biosynthesis. The expression of toyF and toyG, probably directly involved in toyocamycin biosynthesis, was also enhanced, contributing to toyocamycin overproduction. By addition of a small amount of scandium (ScCl₃·6H₂O), the mutant strain, SD3145, produced more toyocamycin (2664 mg/L) in TPM medium, which was the highest toyocamycin level produced in shake-flask fermentation by a streptomycete so far. We demonstrated that introduction of combined drug resistance mutations into S. diastatochromogenes 1628 resulted in an obvious increase in the toyocamycin production. The triple mutant strain, SD3145, generated in our study could be useful for improvement of industrial production of toyocamycin.

Combined Drug Resistance Mutations Substantially Enhance Enzyme Production in Paenibacillus agaridevorans

This study shows that sequential introduction of drug resistance mutations substantially increased enzyme production in Paenibacillus agaridevorans The triple mutant YT478 (rsmG Gln225→stop codon, rpsL K56R, and rpoB R485H), generated by screening for resistance to streptomycin and rifampin, expressed a 1,100-fold-larger amount of the extracellular enzyme cycloisomaltooligosaccharide glucanotransferase (CITase) than the wild-type strain. These mutants were characterized by higher intracellular S-adenosylmethionine concentrations during exponential phase and enhanced protein synthesis activity during stationary phase. Surprisingly, the maximal expression of CITase mRNA was similar in the wild-type and triple mutant strains, but the mutant showed greater CITase mRNA expression throughout the growth curve, resulting in enzyme overproduction. A metabolome analysis showed that the triple mutant YT478 had higher levels of nucleic acids and glycolysis metabolites than the wild type, indicating that YT478 mutant cells were activated. The production of CITase by the triple mutant was further enhanced by introducing a mutation conferring resistance to the rare earth element, scandium. This combined drug resistance mutation method also effectively enhanced the production of amylases, proteases, and agarases by P. agaridevorans and Streptomyces coelicolor This method also activated the silent or weak expression of the P. agaridevorans CITase gene, as shown by comparisons of the CITase gene loci of P. agaridevorans T-3040 and another cycloisomaltooligosaccharide-producing bacterium, Paenibacillus sp. strain 598K. The simplicity and wide applicability of this method should facilitate not only industrial enzyme production but also the identification of dormant enzymes by activating the expression of silent or weakly expressed genes.IMPORTANCE Enzyme use has become more widespread in industry. This study evaluated the molecular basis and effectiveness of ribosome engineering in markedly enhancing enzyme production (>1,000-fold). This method, due to its simplicity, wide applicability, and scalability for large-scale production, should facilitate not only industrial enzyme production but also the identification of novel enzymes, because microorganisms contain many silent or weakly expressed genes which encode novel antibiotics or enzymes. Furthermore, this study provides a new mechanism for strain improvement, with a consistent rather than transient high expression of the key gene(s) involved in enzyme production.

uS10, a novel Npro-interacting protein, inhibits classical swine fever virus replication

Classical swine fever (CSF) is a severe, febrile and highly contagious disease caused by classical swine fever virus (CSFV) that has resulted in huge economic losses in the pig industry worldwide. CSFV Npro has been actively studied but remains incompletely understood. Few studies have investigated the cellular proteins that interact with Npro and their participation in viral replication. Here, the yeast two-hybrid (Y2H) system was employed to screen Npro-interacting proteins from a porcine alveolar macrophage (PAM) cDNA library, and a blast search of the NCBI database revealed that 15 cellular proteins interact with Npro. The interaction of Npro with ribosomal protein S20, also known as universal S10 (uS10), was further confirmed by co-immunoprecipitation and glutathione S-transferase pull-down assays. Furthermore, uS10 overexpression inhibited CSFV replication, whereas the knockdown of uS10 promoted CSFV replication in PAMs. In addition, Npro or CSFV reduced uS10 expression in PAMs in a proteasome-dependent manner, indicating that Npro-uS10 interaction might contribute to persistent CSFV replication. Our previous research showed that CSFV decreases Toll-like receptor 3 (TLR3) expression. The results showed that uS10 knockdown reduced TLR3 expression, and that uS10 overexpression increased TLR3 expression. Notably, uS10 knockdown did not promote CSFV replication following TLR3 overexpression. Conversely, uS10 overexpression did not inhibit CSFV replication following TLR3 knockdown. These results revealed that uS10 inhibits CSFV replication by modulating TLR3 expression. This work addresses a novel aspect of the regulation of the innate antiviral immune response during CSFV infection.

Development of Microtiter Plate Culture Method for Rapid Screening of ε-Poly-L-Lysine-Producing Strains

ε-Poly-L-lysine (ε-PL) produced by Streptomyces albulus possesses a broad spectrum of antimicrobial activity and is widely used as a food preservative. To extensively screen ε-PL-overproducing strain, we developed an integrated high-throughput screening assay using ribosome engineering technology. The production protocol was scaled down to 24- and 48-deep-well microtiter plates (MTPs). The microplate reader assay was used to monitor ε-PL production. A good correlation was observed between the fermentation results obtained in both 24-(48)-deep-well MTPs and conventional Erlenmeyer flasks. Using this protocol, the production of ε-PL in an entire MTP was determined in <5 min without compromising on accuracy. The high-yielding strain selected through this protocol was also tested in Erlenmeyer flasks. The result showed that the ε-PL production of the high-yielding mutants was nearly 45% higher than that of the parent stain. Thus, development of this protocol is expected to accelerate the selection of ε-PL-overproducing strains.

Identification of a Novel Lincomycin Resistance Mutation Associated with Activation of Antibiotic Production in Streptomyces coelicolor A3(2)

Comparative genome sequencing analysis of a lincomycin-resistant strain of Streptomyces coelicolor A3(2) and the wild-type strain identified a novel mutation conferring a high level of lincomycin resistance. Surprisingly, the new mutation was an in-frame DNA deletion in the genes SCO4597 and SCO4598, resulting in formation of the hybrid gene linR. SCO4597 and SCO4598 encode two histidine kinases, which together with SCO4596, encoding a response regulator, constitute a unique two-component system. Sequence analysis indicated that these three genes and their arrangement patterns are ubiquitous among all Streptomyces genomes sequenced to date, suggesting these genes play important regulatory roles. Gene replacement showed that this mutation was responsible for the high level of lincomycin resistance, the overproduction of the antibiotic actinorhodin, and the enhanced morphological differentiation of this strain. Moreover, heterologous expression of the hybrid gene linR in Escherichia coli conferred resistance to lincomycin in this organism. Introduction of the hybrid gene linR in various Streptomyces strains by gene engineering technology may widely activate and/or enhance antibiotic production.

Insights into microbial cryptic gene activation and strain improvement: principle, application and technical aspects

As bacteria and fungi have been found to contain genes encoding enzymes that synthesize a plethora of potential secondary metabolites, interest has grown in the activation of these cryptic pathways. Homologous and heterologous expression of these cryptic secondary metabolite-biosynthetic genes, often silent under ordinary laboratory fermentation conditions, may lead to the discovery of novel secondary metabolites. This review addresses current progress in the activation of these pathways, describing methods for activating silent genes. It especially focuses on genetic manipulation of transcription and translation (ribosome engineering), the utilization of elicitors, metabolism remodeling and co-cultivation. In particular, the principles and technical points of ribosome engineering and the significance of S-adenosylmethionine in bacterial physiology, especially secondary metabolism, are described in detail.

Streptomycin affinity depends on 13 amino acids forming a loop in homology modelled ribosomal S12 protein (rpsL gene) of Lysinibacillus sphaericus DSLS5 associated with marine sponge (Tedania anhelans)

Streptomycin, an antibiotic used against microbial infections, inhibits the protein synthesis by binding to ribosomal protein S12, encoded by rpsL12 gene, and associated mutations cause streptomycin resistance. A streptomycin resistant, Lysinibacillus sphaericus DSLS5 (MIC >300 µg/mL for streptomycin), was isolated from a marine sponge (Tedania anhelans). The characterisation of rpsL12 gene showed a region having similarity to long terminal repeat sequences of murine lukemia virus which added 13 amino acids for loop formation in RpsL12; in addition, a K56R mutation which corresponds to K43R mutation present in streptomycin-resistant Escherichia coli is also present. The RpsL12 protein was modelled and compared with that of Lysinibacillus boronitolerans, Escherichia coli and Mycobacterium tuberculosis. The modelled proteins docked with streptomycin indicate compound had less affinity. The effect of loop on streptomycin resistance was analysed by constructing three different models of RpsL12 by, (i) removing both loop and mutation, (ii) removing the loop alone while retaining the mutation and (iii) without mutation having loop. The results showed that the presence of loop causes streptomycin resistance (decreases the affinity), and it further enhanced in the presence of mutation at 56th codon. Further study will help in understanding the evolution of streptomycin resistance in organisms.

Screening and analysis on the protein interaction of the protein VP7 in grass carp reovirus

Grass carp reovirus (GCRV) has caused serious economic losses for several decades in China. The protein VP7 is one of the important structural proteins in GCRV. Recent studies indicated that the protein VP7 had the commendable antigenicity and immunogenicity. The protein VP7 cooperated with VP5 could change the conformation of the cell membrane and facilitate entry of GCRV into host cells. We speculated that the protein VP7 should play an important role in the pathogenesis of GCRV. In order to explore the function of the protein VP7, the bait protein expression plasmid pGBKT7-vp7 and the cDNA library of CIK cells were constructed. By yeast two-hybrid system, after multiple screening with the high screening rate medium, rotary verification, sequencing and bioinformatics analysis, the interactions of the protein VP7 with ribosomal protein S20 (RPS20) and eukaryotic translation initiation factor 3 subunit b (eIF3b) in CIK cells were identified. RPS20 played the important roles in the generation of influenza B virus and a variety of diseases. eIF3b was relative to the infection of some viruses. This study suggested that the protein VP7 played the role in viral replication and most likely interacted with host proteins by RPS20 and eIF3b. The interaction mechanisms of the protein VP7 with RPS20 and eIF3b, and the subsequent effector mechanisms needed to be further studied. The corresponding protein interaction of the protein VP7 was not acquired in bioinformatics. The protein VP7 and its untranslated region may have the unknown special function. This study laid the foundation for deeply exploring the function of the protein VP7 in GCRV and had the important scientific significance for exploring the pathogenic mechanism of GCRV.

Streptomycin resistance-aided genome shuffling to improve doramectin productivity of Streptomyces avermitilis NEAU1069

Genome shuffling is an efficient approach for the rapid engineering of microbial strains with desirable industrial phenotypes. In this study, a strategy of incorporating streptomycin resistance screening into genome shuffling (GS-SR) was applied for rapid improvement of doramectin production by Streptomyces avermitilis NEAU1069. The starting mutant population was generated through treatment of the spores with N-methyl-N’-nitro-N-nitrosoguanidine and ultraviolet (UV) irradiation, respectively, and five mutants with higher productivity of doramectin were selected as starting strains for GS-SR. Finally, a genetically stable strain F4-137 was obtained and characterized to be able to yield 992 ± 4.4 mg/l doramectin in a shake flask, which was 7.3-fold and 11.2-fold higher than that of the starting strain UV-45 and initial strain NEAU1069, respectively. The doramectin yield by F4-137 in a 50-l fermentor reached 930.3 ± 3.8 mg/l. Furthermore, the factors associated with the improved doramectin yield were investigated and the results suggested that mutations in ribosomal protein S12 and the enhanced production of cyclohexanecarboxylic coenzyme A may contribute to the improved performance of the shuffled strains. The random amplified polymorphic DNA analysis showed a genetic diversity among the shuffled strains, which confirmed the occurrence of genome shuffling. In conclusion, our results demonstrated that GS-SR is a powerful method for enhancing the production of secondary metabolites in Streptomyces.

Disruption of rimP-SC, encoding a ribosome assembly cofactor, markedly enhances the production of several antibiotics in Streptomyces coelicolor

Background

Ribosome assembly cofactor RimP is one of the auxiliary proteins required for maturation of the 30S subunit in Escherichia coli. Although RimP in protein synthesis is important, its role in secondary metabolites biosynthesis has not been reported so far. Considering the close relationship between protein synthesis and the production of secondary metabolites, the function of ribosome assembly cofactor RimP on antibiotics production was studied in Streptomyces coelicolor and Streptomyces venezuelae.

Results

In this study, the rimP homologue rimP-SC was identified and cloned from Streptomyces coelicolor. Disruption of rimP-SC led to enhanced production of actinorhodin and calcium-dependent antibiotics by promoting the transcription of actII-ORF4 and cdaR. Further experiments demonstrated that MetK was one of the reasons for the increment of antibiotics production. In addition, rimP-SC disruption mutant could be used as a host to produce more peptidyl nucleoside antibiotics (polyoxin or nikkomycin) than the wild-type strain. Likewise, disruption of rimP-SV of Streptomyces venezuelae also significantly stimulated jadomycin production, suggesting that enhanced antibiotics production might be widespread in many other Streptomyces species.

Conclusion

These results established an important relationship between ribosome assembly cofactor and secondary metabolites biosynthesis and provided an approach for yield improvement of secondary metabolites in Streptomyces.

New strategies for drug discovery: activation of silent or weakly expressed microbial gene clusters

Genome sequencing of Streptomyces, myxobacteria, and fungi showed that although each strain contains genes that encode the enzymes to synthesize a plethora of potential secondary metabolites, only a fraction are expressed during fermentation. Interest has therefore grown in the activation of these cryptic pathways. We review current progress on this topic, describing concepts for activating silent genes, utilization of “natural” mutant-type RNA polymerases and rare earth elements, and the applicability of ribosome engineering to myxobacteria and fungi, the microbial groups known as excellent searching sources, as well as actinomycetes, for secondary metabolites.

Production of xylanase by an alkaline-tolerant marine-derived Streptomyces viridochromogenes strain and improvement by ribosome engineering

Xylanase is the enzyme complex that is responsible for the degradation of xylan; however, novel xylanase producers remain to be explored in marine environment. In this study, a Streptomyces strain M11 which exhibited xylanase activity was isolated from marine sediment. The 16S rDNA sequence of M11 showed the highest identity (99 %) to that of Streptomyces viridochromogenes. The xylanase produced from M11 exhibited optimum activity at pH 6.0, and the optimum temperature was 70 °C. M11 xylanase activity was stable in the pH range of 6.0-9.0 and at 60 °C for 60 min. Xylanase activity was observed to be stable in the presence of up to 5 M NaCl. Antibiotic-resistant mutants of M11 were isolated, and among the various antibiotics tested, streptomycin showed the best effect on obtaining xylanase overproducer. Mutant M11-1(10) isolated from 10 μg/ml streptomycin-containing plate showed 14 % higher xylanase activities than that of the wild-type strain. An analysis of gene rpsL (encoding ribosomal protein S12) showed that rpsL from M11-1(10) contains a K88R mutation. This is the first report to show that marine-derived S. viridochromogenes strain can be used as a xylanase producer, and utilization of ribosome engineering for the improvement of xylanase production in Streptomyces was also first successfully demonstrated.

Improvement of A21978C production in Streptomyces roseosporus by reporter-guided rpsL mutation selection

AIMS

Daptomycin, one of the A21978C factors produced by Streptomyces roseosporus, is an acidic cyclic lipopeptide antibiotic with potent activity against a variety of Gram-positive pathogens. To increase the titre of this extensively used and clinically important antibiotic, we applied a reported-guided rpsL mutation selection system to generate strains producing high levels of A21978C.

METHODS AND RESULTS

In the reporter design, dptE was chosen as the overexpressing target, and neo-encoding neomycin phosphotransferase as the reporter. Using this reporter-guided selection system, 20% of the selected, streptomycin-resistant mutants produced greater amounts of A21978C than the starting strain. The selection system increased the screening efficiency about 10-fold with a frequency of 1·7% A21978C overproducing strains among str(r) mutants. A21978C production was increased approximately 2·2-fold in the rpsL K43N mutant.

CONCLUSIONS

The combination of ribosome engineering and reporter-guided mutant selection generated an A21978C overproducing strain that produced about twice as much A21978C as the parental strain.

SIGNIFICANCE AND IMPACT OF THE STUDY

The strategies presented here, which integrated the advantages of both ribosome engineering and reporter-guided mutation selection, could be applied to other bacteria to improve their yield of secondary metabolites.

Novel two-component systems implied in antibiotic production in Streptomyces coelicolor

The abundance of two-component systems (TCSs) in Streptomyces coelicolor A3(2) genome indicates their importance in the physiology of this soil bacteria. Currently, several TCSs have been related to antibiotic regulation, and the purpose in this study was the characterization of five TCSs, selected by sequence homology with the well-known absA1A2 system, that could also be associated with this important process. Null mutants of the five TCSs were obtained and two mutants (ΔSCO1744/1745 and ΔSCO4596/4597/4598) showed significant differences in both antibiotic production and morphological differentiation, and have been renamed as abr (antibiotic regulator). No detectable changes in antibiotic production were found in the mutants in the systems that include the ORFs SCO3638/3639, SCO3640/3641 and SCO2165/2166 in any of the culture conditions assayed. The system SCO1744/1745 (AbrA1/A2) was involved in negative regulation of antibiotic production, and acted also as a negative regulator of the morphological differentiation. By contrast, the system SCO4596/4597/4598 (AbrC1/C2/C3), composed of two histidine kinases and one response regulator, had positive effects on both morphological development and antibiotic production. Microarray analyses of the ΔabrC1/C2/C3 and wild-type transcriptomes revealed downregulation of actII-ORF4 and cdaR genes, the actinorhodin and calcium-dependent antibiotic pathway-specific regulators respectively. These results demonstrated the involvement of these new two-component systems in antibiotic production and morphological differentiation by different approaches. One is a pleiotropic negative regulator: abrA1/A2. The other one is a positive regulator composed of three elements, two histidine kinases and one response regulator: abrC1/C2/C3.

Activation of dormant secondary metabolism neotrehalosadiamine synthesis by an RNA polymerase mutation in Bacillus subtilis

Microorganisms possess the ability to produce a variety of commercially important secondary metabolites such as antibiotics. Although it becomes harder and harder to discover useful new compounds, microorganisms still have the potential to produce unknown compounds. One of the reasons for the difficulty in finding new compounds is that the expression level of many secondary metabolite genes is insufficient in wild-type strains. Therefore, a new method of activating gene expression might be a powerful tool for the screening of novel compounds and for strain improvement to overproduce useful compounds. We found that the rifampicin-resistant RNA polymerase mutations stimulate the expression of antibiotic synthetic gene clusters in several microorganisms. In the case of the Gram-positive model organism Bacillus subtilis, one of the rifampicin-resistance mutations resulted in the activation of a dormant secondary metabolism, neotrehalosadiamine synthesis. To clarify this activation mechanism, we first identified the neotrehalosadiamine biosynthetic operon and investigated its transcriptional regulation. Here we summarize our findings on the transcriptional regulation of the neotrehalosadiamine biosynthetic operon and discuss a crucial effect of the rifampicin-resistance mutation on the expression of dormant genes.

The tmRNA-tagging mechanism and the control of gene expression: a review

The tmRNA-mediated trans-translation system is a unique quality control system in eubacteria that combines translational surveillance with the rescue of stalled ribosomes. During trans-translation, the chimeric tmRNA molecule--which acts as both tRNA and mRNA--is delivered to the ribosomal A site by a ribonucleoprotein complex of SmpB and EF-Tu-GTP, allowing the stalled ribosome to switch template and resume translation on a small coding sequence inside the tmRNA molecule. As a result, the aberrant protein becomes tagged by a sequence that is a target for proteolytic degradation. Thus, the system elegantly combines ribosome recycling with a clean-up function when triggered by truncated transcripts or rare codons. In addition, recent observations point to a specific regulation of the translation of a small number of genes by tmRNA-mediated inhibition or stimulation. In this review, we discuss the most prominent biochemical and structural aspects of trans-translation and then focus on the specific role of tmRNA in stress management and cell-cycle control of morphologically complex bacteria.

Antibiotic overproduction by rpsL and rsmG mutants of various actinomycetes

Certain streptomycin resistance mutations (i.e., rpsL and rsmG) result in the overproduction of antibiotics in various actinomycetes. Moreover, rpsL rsmG double-mutant strains show a further increase in antibiotic production. rpsL but not rsmG mutations result in a marked enhancement of oligomycin production in Streptomyces avermitilis and erythromycin production in Saccharopolyspora erythraea, accompanied by increased transcription of a key developmental regulator gene, bldD, in the latter organism.