| In vivo: |
| Appl Microbiol Biotechnol. 2014 Mar;98(5):2231-41. | | Genome-wide analysis of the regulation of pimaricin production in Streptomyces natalensis by reactive oxygen species.[Pubmed: 24413916] | To investigate the molecular mechanisms that interplay between oxygen metabolism and secondary metabolism in Streptomyces natalensis, we compared the transcriptomes of the strains CAM.02 (ΔsodF), pimaricin under-producer phenotype, and CAM.04 (ΔahpCD), pimaricin over-producer phenotype, with that of the wild type at late exponential and stationary growth phases.
METHODS AND RESULTS:
Microarray data interpretation was supported by characterization of the mutant strains regarding enzymatic activities, phosphate uptake, oxygen consumption and pimaricin production.Both mutant strains presented a delay in the transcription activation of the PhoRP system and pimaricin biosynthetic gene cluster that correlated with the delayed inorganic phosphate (Pi) depletion in the medium and late onset of pimaricin production, respectively. The carbon flux of both mutants was also altered: a re-direction from glycolysis to the pentose phosphate pathway (PPP) in early exponential phase followed by a transcriptional activation of both pathways in subsequent growth phases was observed. Mutant behavior diverged at the respiratory chain/tricarboxylic acid cycle (TCA) and the branched chain amino acid (BCAA) metabolism. CAM.02 (ΔsodF) presented an impaired TCA cycle and an inhibition of the BCAA biosynthesis and degradation pathways. Conversely, CAM.04 (ΔahpCD) presented a global activation of BCAA metabolism.
CONCLUSIONS:
The results highlight the cellular NADPH/NADH ratio and the availability of biosynthetic precursors via the BCAA metabolism as the main pimaricin biosynthetic bottlenecks under oxidative stress conditions. Furthermore, new evidences are provided regarding a crosstalk between phosphate metabolism and oxidative stress in Streptomyces. | | Colloids Surf B Biointerfaces. 2014 Oct 1;122:202-8. | | The negligible effects of the antifungal natamycin on cholesterol-dipalmitoyl phosphatidylcholine monolayers may explain its low oral and topical toxicity for mammals.[Pubmed: 25048356] | Natamycin is an effective, broad spectrum antifungal with no reported resistance, in contrast to most antimicrobials. It also exhibits reduced (oral and topical) toxicity to humans, which is probably associated with the lack of effects on mammalian cell membranes.
METHODS AND RESULTS:
In this paper we employ Langmuir monolayers to mimic a cell membrane, whose properties are interrogated with various techniques.
We found that natamycin has negligible effects on Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC), but it strongly affects cholesterol monolayers. Natamycin causes the surface pressure isotherm of a cholesterol monolayer to expand even at high surface pressures since it penetrates into the hydrophobic chains. It also reduces the compressibility modulus, probably because natamycin disturbs the organization of the cholesterol molecules, as inferred with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). In mixed cholesterol/DPPC monolayers, strong effects from natamycin were only observed when the cholesterol concentration was 50mol% or higher, well above its concentration in a mammalian cell membrane.
CONCLUSIONS:
For a sterol concentration that mimics a real cell membrane in mammals, i.e. with 25mol% of cholesterol, the effects were negligible, which may explain why natamycin has low toxicity when ingested and/or employed to treat superficial fungal infections. |
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