S-Adenosylmethionine (SAM) and antibiotic biosynthesis: effect of external addition of SAM and of overexpression of SAM biosynthesis genes on novobiocin production in Streptomyces

Abstract

The production of antibiotics in different Streptomyces strains has been reported to be stimulated by the external addition of S-adenosylmethionine (SAM) and by overexpression of the SAM synthetase gene metK. We investigated the influence of SAM addition, and of the expression of SAM biosynthetic genes, on the production of the aminocoumarin antibiotic novobiocin in the heterologous producer strain Streptomyces coelicolor M512 (nov-BG1). External addition of SAM did not influence novobiocin accumulation. However, overexpression of a SAM synthase gene stimulated novobiocin formation, concomitant with an increase of the intracellular SAM concentration. Streptomyces genomes contain orthologs of all genes required for the SAM cycle known from mammals. In contrast, most other bacteria use a different cycle for SAM regeneration. Three secondary metabolic gene clusters, coding for the biosynthesis of structurally very different antibiotics in different Streptomyces strains, were found to contain an operon comprising all five putative genes of the SAM cycle. We cloned one of these operons into an expression plasmid, under control of a strong constitutive promoter. However, transformation of the heterologous novobiocin producer strain with this plasmid did not stimulate novobiocin production, but rather showed a detrimental effect on cell viability in the stationary phase and strongly reduced novobiocin accumulation.

Comparative Proteomic Analysis of saccharopolyspora spinosa SP06081 and PR2 strains reveals the differentially expressed proteins correlated with the increase of spinosad yield

“…In spinosad biosynthetic processes, the two N -methyl groups of forosamine and the three O -methyl groups of tri- O -methyl rhamnose are all derived from SAM [1]. Thus, the up-regulation of MHM may contribute to spinosad biosynthesis, in agreement with previous reports in which SAM was documented as a positive regulator for secondary metabolism in Streptomyces [26-28]. The other proteins (PK, PFK, MMSAD, GAPDH and ACAT) related to the biosynthesis of polyketide precursor were all observed to be differentially expressed in the same direction to increase precursor supply in the PR2 strain (Figure 5).…”

Molecular Regulation of Antibiotic Biosynthesis in Streptomyces

“…Nuclear magnetic resonance (NMR) analysis has suggested that AfsK binds S-adenosylmethionine (SAM), though the consequences of this interaction are not known; however, there have been several reports indicating that endogenously increased SAM synthetase or exogenously added SAM increases antibiotic production in different streptomycetes (130)(131)(132)(133)). There appears to be no information about whether endogenous SAM levels increase as growth comes to a stop (for example, if methionine is shunted to SAM biosynthesis when protein synthesis slows down).…”

Structural and functional characterisation of the methionine adenosyltransferase from Thermococcus kodakarensis

“…As MATs are the only known enzymes catalysing the synthesis of SAM, they are believed to be housekeeping enzymes and have been suggested as tools for phylogenetic analyses [4]. Among the most extensively studied MATs are the bacterial representatives from Escherichia coli ( Ec MAT), [5] Bacillus subtilis [6] and several Streptomyces species [7], as well as the enzymes derived from selected eukaryotic organisms, such as Saccharomyces cerevisiae [8], Rattus norvegicus [9], and Homo sapiens ( Hs MAT) [10,11]. MATs catalyse the formation of SAM in a two-step process: in the first step first SAM is formed in a S N 2 reaction from methionine and the adenosine moiety of ATP; in the second step the triphosphate is cleaved to yield pyrophosphate and orthophosphate and the products are released (Figure  1).…”