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Virginiae butanolide (VB) is a [gamma]-butyrolactone autoregulator that triggers production of the streptogramin antibiotic virginiamycin in Streptomyces virginiae. Our previous studies suggested that the barX gene, an afsA-family gene, is likely to participate in the regulatory pathway for the production of VB, rather than in the biosynthetic pathway of VB itself, in contrast to the function of other afsA-family genes. Mutation analysis now shows that BarX at least plays an enzymic role in the VB biosynthetic pathway. Heterologous expression of the afsA gene from Streptomyces griseus into the barX mutant partially restored the deficiency of virginiamycin production, suggesting that afsA-family genes have a common ability to synthesize the [gamma]-butyrolactone autoregulators. Taken together with previous works relating to the function of an afsA-family gene, these results support the idea that streptomycetes have two biosynthetic pathways for the [gamma]-butyrolactone autoregulators. DOI 10.1099/mic.0.032003-0

Two regulatory genes encoding a Streptomyces antibiotic regulatory protein (vmsS) and a response regulator (vmsT) of a bacterial two-component signal transduction system are present in the left-hand region of the biosynthetic gene cluster of the antibiotic virginiamycin, which is composed of virginiamycin M (VM) and virginiamycin S (VS), in Streptomyces virginiae. Disruption of vmsS abolished both VM and VS biosynthesis, with drastic alteration of the transcriptional profile for virginiamycin biosynthetic genes, whereas disruption of vmsT resulted in only a loss of VM biosynthesis, suggesting that vmsS is a pathway-specific regulator for both VM and VS biosynthesis, and that vmsT is a pathway-specific regulator for VM biosynthesis alone. Gene expression profiles determined by semiquantitative RT-PCR on the virginiamycin biosynthetic gene cluster demonstrated that vmsS controls the biosynthetic genes for VM and VS, and vmsT controls unidentified gene(s) of VM biosynthesis located outside the biosynthetic gene cluster. In addition, transcriptional analysis of a deletion mutant of vmsR located in the clustered regulatory region in the virginiamycin cluster (and which also acts as a SARP-family activator for both VM and VS biosynthesis) indicated that the expression of vmsS and vmsT is under the control of vmsR, and vmsR also contributes to the expression of VM and VS biosynthetic genes, independent of vmsS and vmsT. Therefore, coordinated virginiamycin biosynthesis is controlled by three pathway-specific regulators which hierarchically control the expression of the biosynthetic gene cluster.

Results demonstrate that the gama-butyrolactone autoregulator IM-2 and its receptor FarA are required for the suppression of D-cycloserine biosynthesis in Streptomyces lavendulae FRI-5. Data also show that FarA protein functions as a negative regulator of biosynthesis of nucleoside antibiotics and pigments in the absence of IM-2.

FarA of Streptomyces lavendulae FRI-5 is a specific receptor protein for IM-2, a butyrolactone autoregulator that controls the production of a blue pigment and the nucleoside antibiotics showdomycin and minimycin. Gel shift assays showed that FarA binds to the farA upstream region and that this binding is eliminated in the presence of IM-2. The FarA binding sequence was localized by DNase footprinting to a 28-bp sequence found approximately 70 bp upstream of the farA translational start site.

Serine hydroxymethyltransferase (SHMT) and threonine aldolase are classified as fold type I pyridoxal-5'-phosphate-dependent enzymes and engaged in glycine biosynthesis from serine and threonine, respectively. The acidothermophilic archaeon Thermoplasma acidophilum possesses two distinct SHMT genes, while there is no gene encoding threonine aldolase in its genome. In the present study, the two SHMT genes (Ta0811 and Ta1509) were heterologously expressed in Escherichia coli and Thermococcus kodakarensis, respectively, and biochemical properties of their products were investigated. Ta1509 protein exhibited dual activities to catalyze tetrahydrofolate (THF)-dependent serine cleavage and THF-independent threonine cleavage, similar to other SHMTs reported to date. In contrast, the Ta0811 protein lacks amino acid residues involved in the THF-binding motif and catalyzes only the THF-independent cleavage of threonine. Kinetic analysis revealed that the threonine-cleavage activity of the Ta0811 protein was 3.5 times higher than the serine-cleavage activity of Ta1509 protein. In addition, mRNA expression of Ta0811 gene in T. acidophilum was approximately 20 times more abundant than that of Ta1509. These observations suggest that retroaldol cleavage of threonine, mediated by the Ta0811 protein, has a major role in glycine biosynthesis in T. acidophilum. [ABSTRACT FROM AUTHOR]

The genome of streptomycetes has the ability to produce many novel and potentially useful bioactive compounds, but most of which are not produced under standard laboratory cultivation conditions and are referred to as silent/cryptic secondary metabolites. Streptomyces lavendulae FRI-5 produces several types of bioactive compounds. However, this strain may also have the potential to biosynthesize more useful secondary metabolites. Here, we activated a silent biosynthetic gene cluster of an uncharacterized compound from S. lavendulae FRI-5 using heterologous expression. The engineered strain carrying the silent gene cluster produced compound 5, which was undetectable in the culture broth of S. lavendulae FRI-5. Using various spectroscopic analyses, we elucidated the chemical structure of compound 5 (named lavendiol) as a new diol-containing polyketide. The proposed assembly line of lavendiol shows a unique biosynthetic mechanism for polyketide compounds. The results of this study suggest the possibility of discovering more silent useful compounds from streptomycetes by genome mining and heterologous expression. [ABSTRACT FROM AUTHOR]