An aberrant protein synthesis activity is linked with antibiotic overproduction in rpsL mutants of Streptomyces coelicolor A3(2)

Abstract

Certain mutations in the rpsL gene (encoding the ribosomal protein S12) activate or enhance antibiotic production in various bacteria. K88E and P91S rpsL mutants of Streptomyces coelicolor A3(2), with an enhanced actinorhodin production, were found to exhibit an aberrant protein synthesis activity. While a high level of this activity (as determined by the incorporation of labelled leucine) was detected at the late stationary phase in the mutants, it decreased with age of the cells in the wild-type strain. In addition, the aberrant protein synthesis was particularly pronounced when cells were subjected to amino acid shift-down, and was independent of their ability to accumulate ppGpp. Ribosomes of K88E and P91S mutants displayed an increased accuracy in protein synthesis as demonstrated by the poly(U)-directed cell-free translation system, but so did K43N, K43T, K43R and K88R mutants, which were streptomycin resistant but showed no effect on actinorhodin production. This eliminates the possibility that the increased accuracy level is a cause of the antibiotic overproduction in the K88E and P91S mutants. The K88E and P91S mutant ribosomes exhibited an increased stability of the 70S complex under low concentrations of magnesium. The authors propose that the aberrant activation of protein synthesis caused by the increased stability of the ribosome is responsible for the remarkable enhancement of antibiotic production in the K88E and P91S mutants.

The mthA Mutation Conferring Low-Level Resistance to Streptomycin Enhances Antibiotic Production in Bacillus subtilis by Increasing the S -Adenosylmethionine Pool Size

“…The rpsL mutant ribosomes carrying an amino acid substitution in S12, which confers a high level of resistance to Sm, are more stable than those of wild-type controls, indicating that this increase in stability could enhance protein synthesis during the late growth phase (20). We later found that increased expression of the translation factor ribosome-recycling factor also contributes to the enhanced protein synthesis observed during the late growth phase in the rpsL K88E mutant (21).…”

Identification and Characterization of a Novel Multidrug Resistance Operon,mdtRP(yusOP), ofBacillus subtilis

“…These findings indicated that bacterial gene expression can be altered dramatically by modulating ribosomal proteins and/or RNA polymerase (12,16). The rpsL mutant ribosomes carrying an amino acid substitution in S12, which confers a high level of resistance to streptomycin, are more stable than those of wild-type controls at low magnesium concentrations, indicating that this increase in stability could enhance protein synthesis at the late growth phase (11,20,31,33). We later found that increased expression of the translation factor ribosome recycling factor also contributes to the enhanced protein synthesis observed during the late growth phase in the rpsL K88E mutant of S. coelicolor.…”

Mutations in rpsL that confer streptomycin resistance show pleiotropic effects on virulence and the production of a carbapenem antibiotic in Erwinia carotovora

“…Shima et al, 1996;Okamoto-Hosoya et al, 2003a, b;Hu & Ochi, 2001). In Streptomyces coelicolor A3(2), a K88E rpsL mutant exhibited increased actinorhodin production (in addition to streptomycin resistance) due to an increase in protein synthesis caused by upregulation of expression of the ribosome recycling factor (Okamoto-Hosoya et al, 2003a;Hosaka et al, 2006). K43N, K43T and K43R mutations resulted in streptomycin resistance, but had no impact on antibiotic production in S. coelicolor (Okamoto-Hosoya et al, 2003a).…”

“…In Streptomyces coelicolor A3(2), a K88E rpsL mutant exhibited increased actinorhodin production (in addition to streptomycin resistance) due to an increase in protein synthesis caused by upregulation of expression of the ribosome recycling factor (Okamoto-Hosoya et al, 2003a;Hosaka et al, 2006). K43N, K43T and K43R mutations resulted in streptomycin resistance, but had no impact on antibiotic production in S. coelicolor (Okamoto-Hosoya et al, 2003a). A recent study by Kurosawa et al (2006) showed that amylase and protease production in Bacillus subtilis strain 168 was enhanced in rpsL K56R mutants (equivalent to K43R of E. coli or Ecc), but production was unaffected in K56T and K56N mutants.…”