Cation Reversal of Inhibition of Growth by Valinomycin in Streptococcus pyogenes and Clostridium sporogenes

Abstract

Study of the antimicrobial spectrum of valinomycin revealed that, in addition to the gram-positive bacteria reported in literature, Streptococcus pyogenes and Clostridium sporogenes are also susceptible to this antibiotic. The minimal inhibitory concentrations (MIC) of the antibiotic for S. pyogenes grown aerobically and anaerobically did not differ markedly, negating the hypothesis that oxidative phosphorylation is involved in the mechanism of action of this antibiotic. This conclusion is further strengthened by the inhibition of growth of C. sporogenes, an obligate anaerobe. In a medium with a low K+ concentration, the MIC for S. pyogenes was 0.02 Ag/ml, the lowest ever recorded for this antibiotic.The inhibition of growth of S. pyogenes and C. sporogenes was readily reversed by addition of K+ to the medium, indicating a compensation for net efflux of K+ from the cells when the transmembrane potential reached equilibrium. In contrast to these bacteria, Bacillus subtilis was less susceptible to the antibiotic when the potassium concentration of the medium was low. The addition of potassium in the presence of valinomycin increased the inhibition of growth, which appears to result from dissipation of metabolic energy as in the mitochondrial system.Valinomycin is a cyclic peptide which can selectively increase the permeability of K+ across the natural (9) and artificial membranes (11). Though at one time the antibiotic property of valinomycin was thought to be due to uncoupling of oxidative phosphorylation (13), Pressman and associates have proposed that the primary action of the antibiotic is related to an increase in potassium transport, with consequent dissipation of metabolic energy being secondary (10,12,20,21). This hypothesis is largely based on studies in which the similarities between ion fluxes in isolated mitochondria and aerobic bacteria were noted (19).Detailed work on the mode of action of valinomycin on the growth and metabolism of various bacteria is lacking, with the singular exception of the studies on Streptococcus faecalis by Harold and co-workers (5-8). They observed that valinomycin causes a net loss of K+ from the bacterial cell, the consequence of which is not the dissipation of metabolic energy but an 'Presented in part at the 71st Annual Meeting of the American Society for Microbiology, Minneapolis, Minn., 1971. 63 inhibition of protein synthesis which can be reversed by the addition of k+ to the growth medium. It was the purpose of this investigation to examine the effects of valinomycin and K+ on the growth of bacteria metabolizing aerobically and anaerobically, with Clostridium sporogens, Bacillus subtilis, and S. pyogenes used as representative anaerobic, aerobic, and facultative bacteria, respectively. MATERIALS AND METHODSOrganisms. B. subtilis ATCC 6633 and C. sporogenes ATCC 7955 were the designated organisms used in this investigation. S. faecalis was a gift from J. 0. Mundt, University of Tennessee, Knoxville.

Comparative Analysis of Antimicrobial Activities of Valinomycin and Cereulide, the Bacillus cereus Emetic Toxin

“…Gram-negative strains tested were found to be insensitive under all conditions tested, which confirms and expands upon previous reports (9,64,66). Sensitivity to valinomycin is reduced under anaerobic conditions.…”

“…At this concentration, DMSO neither affected the growth nor the survival of the selected strains in this study. The concentrations of valinomycin and cereulide used in this study are within the range of values reported in the literature, including environmental and (model) food samples (23,29,64,65).…”

“…A wide range of biological activities has been reported for valinomycin, including insecticidal, nematicidal, antiviral, and apoptosis-inducing effects in human cells (11,62). Valinomycin has become a useful tool in the study of ion transport in biological systems, and its inhibitory effect on intact cells and the growth of bacteria and yeast has been studied, although to a limited extent (25,26,61,64). The function of cereulide in B. cereus growth and ecology is unknown.…”

Exploring the diversity and metabolic potential of actinomycetes from temperate marine sediments from Newfoundland, Canada

“…Sungsanpin was tested for antimicrobial activity and was inactive. Valinomycin did not exhibit antibacterial activity against the test organisms utilized in this study, but has been reported to inhibit the growth of C. albicans with a minimum inhibitory concentration of approximately, 12 μg mL −1 [58,69]. The lack of C. albicans activity by the 8LB7 extract is likely due to an insufficient concentration of valinomycins in the extract.…”

“…Culture-dependent analysis indicated that Streptomyces were the most abundant group of cultivable actinomycetes in NL sediments while Nocardiopsis, Actinoalloteichus and Promicromonospora species constituted rare members of the culturable actinomycete community. No sequences of cultured actinomycetes were detected in the culture-independent analysis, underscoring the complimentary nature of culture-dependent and cultureindependent approaches when attempting to describe bacterial diversity [69]. A total of 59 OTUs were identified from 360 actinomycete isolates, indicating a significant level of species-level actinomycete diversity in NL sediments.…”