Violacein
is a tryptophan-derived purple pigment produced by environmental bacteria,
which displays multiple biological activities, including strong inhibition
of Gram-positive pathogens. Here, we applied a combination of experimental
approaches to identify the mechanism by which violacein kills Gram-positive
bacteria. Fluorescence microscopy showed that violacein quickly and
dramatically permeabilizes B. subtilis and S. aureus cells. Cell permeabilization was accompanied
by the appearance of visible discontinuities or rips in the cytoplasmic
membrane, but it did not affect the cell wall. Using in vitro experiments,
we showed that violacein binds directly to liposomes made with commercial
and bacterial phospholipids and perturbs their structure and permeability.
Furthermore, molecular dynamics simulations were employed to reveal
how violacein inserts itself into lipid bilayers. Thus, our combined
results demonstrate that the cytoplasmic membrane is the primary target
of violacein in bacteria. The implications of this finding for the
development of violacein as a therapeutic agent are discussed.
Antimicrobial peptides (AMPs) work as a primary defense against pathogenic microorganisms. BP100, (KKLFKKILKYL-NH), a rationally designed short, highly cationic AMP, acts against many bacteria, displaying low toxicity to eukaryotic cells. Previously we found that its mechanism of action depends on membrane surface charge and on peptide-to-lipid ratio. Here we present the synthesis of two BP100 analogs: BP100‑alanyl‑hexadecyl‑1‑amine (BP100-Ala-NH-CH) and cyclo(1‑4)‑d‑Cys, Ile, Leu, Cys-BP100 (Cyclo(1‑4)‑cILC-BP100). We examined their binding to large unilamellar vesicles (LUV), conformational and functional properties, and compared with those of BP100. The analogs bound to membranes with higher affinity and a lesser dependence on electrostatic forces than BP100. In the presence of LUV, BP100 and BP100-Ala-NH-CH acquired α-helical conformation, while Cyclo(1‑4)‑cILC-BP100) was partly α-helical and partly β-turn. Taking in conjunction: 1. particle sizes and zeta potential, 2. effects on lipid flip-flop, 3. leakage of LUVs internal contents, and 4. optical microscopy of giant unilamellar vesicles, we concluded that at high concentrations, all three peptides acted by a carpet mechanism, while at low concentrations the peptides acted by disorganizing the lipid bilayer, probably causing membrane thinning. The higher activity and lesser membrane surface charge dependence of the analogs was probably due to their greater hydrophobicity. The MIC values of both analogs towards Gram-positive and Gram-negative bacteria were similar to those of BP100 but both analogues were more hemolytic. Confocal microscopy showed Gram-positive B. subtilis killing with concomitant extensive membrane damage suggestive of lipid clustering, or peptide-lipid aggregation. These results were in agreement with those found in model membranes.
A new method of screening was developed to generate 770 organic and water-soluble fractions from extracts of nine species of marine sponges, from the growth media of 18 species of marine-derived fungi, and from the growth media of 13 species of endophytic fungi. The screening results indicated that water-soluble fractions displayed significant bioactivity in cytotoxic, antibiotic, anti-Leishmania, anti-Trypanosoma cruzi, and inhibition of proteasome assays. Purification of water-soluble fractions from the growth medium of Penicillium solitum IS1-A provided the new glutamic acid derivatives solitumine A (1), solitumine B (2), and solitumidines A−D (3−6). The structures of compounds 1−6 have been established by analysis of spectroscopic data, chemical derivatizations, and vibrational circular dichroism calculations. Although no biological activity could be observed for compounds 1−6, the new structures reported for 1−6 indicate that the investigation of water-soluble natural products represents a relevant strategy in finding new secondary metabolites.
The emergence and re-emergence of bacterial strains resistant
to
multiple drugs represent a global health threat, and the search for
novel biological targets is a worldwide concern. AhpC are enzymes
involved in bacterial redox homeostasis by metabolizing diverse kinds
of hydroperoxides. In pathogenic bacteria, AhpC are related to several
functions, as some isoforms are characterized as virulence factors.
However, no inhibitor has been systematically evaluated to date. Here
we show that the natural ent-kaurane Adenanthin (Adn)
efficiently inhibits AhpC and molecular interactions were explored
by computer assisted simulations. Additionally, Adn interferes with
growth and potentializes the effect of antibiotics (kanamycin and
PMBN), positioning Adn as a promising compound to treat infections
caused by multiresistant bacterial strains.
Here, we describe the genomic features of the Actinobacteria Kocuria sp. SM24M-10 isolated from mucus of the Brazilian endemic coral Mussismilia hispida. The sequences are available under accession number LDNX01000000 (http://www.ncbi.nlm.nih.gov/nuccore/LDNX00000000). The genomic analysis revealed interesting information about the adaptation of bacteria to the marine environment (such as genes involved in osmotic and oxidative stress) and to the nutrient-rich environment provided by the coral mucus.
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