Surfactin, a highly powerful biosurfactant produced by various strains of the genus Bacillus, exhibits antibacterial, antiviral, antitumor and hemolytic action. This anionic cyclic lipopeptide is constituted by a heptapeptide interlinked with a β-hydroxy fatty acid. Due to its amhipathic nature surfactin incorporates into the phospholipid bilayer and induces permeabilization and perturbation of target cells. The rising antibiotic resistance as well as a number of remarkable surfactin activities shows that it deserves special interest and is considered as a candidate compound for combating several health related issues. In this review, the current state of knowledge of surfactin properties, biomedical potential and limitations for its application is presented.

The antibacterial activity of diamond nanoparticles depends both on the size and surface termination of the nanoparticles and also on the structure of the bacte

To find out membrane tolerance strategy to ethanol in Bacillus subtilis that possesses a powerful system of protection against environmental stresses. Cytoplasmic membranes of B. subtilis were severely affected by even short-term exposure to 3% (v/v) ethanol: the growth rate and membrane protein synthesis were markedly reduced, and no adaptive alterations in phospholipids were detected. Simultaneously, steady-state DPH fluorescence anisotropy (r(ss)) showed that the membrane rigidity increased substantially. Analysis of the membrane phosphoproteome using in vitro labelling with [γ-(32) P]ATP revealed the association of DnaK and GroEL chaperones with membrane, indicating a stress induction process. Upon a long-term 3% (v/v) ethanol stress, the cell growth accelerated slightly and the composition of polar head groups and fatty acids of membrane phospholipids underwent an extensive reconstruction. Correspondingly, membrane fluidity turned back to the original r(ss) values of the control cells. In B. subtilis, the adaptive response to short-term ethanol stress comprises the recruitment of molecular chaperones on the impaired membrane structure; consequently, the phospholipid synthesis is restored and membrane fluidity adapts properly to the continuing ethanol stress. These findings underline the role of membrane lipids in establishing tolerance towards ethanol and also suggest the contribution of molecular chaperones to the membrane and cell recovery.

Daptomycin is a calcium-dependent lipodepsipeptide antibiotic clinically used to treat serious infections caused by Gram-positive pathogens. Its precise mode of action is somewhat controversial; the biggest issue is daptomycin pore formation, which we directly investigated here. We first performed a screening experiment using propidium iodide (PI) entry to Bacillus subtilis cells and chose the optimum and therapeutically relevant conditions (10 µg/mL daptomycin and 1.25 mM CaCl₂) for the subsequent analyses. Using conductance measurements on planar lipid bilayers, we show that daptomycin forms non-uniform oligomeric pores with conductance ranging from 120 pS up to 14 nS. The smallest conductance unit is probably a dimer, however tetramers and pentamers occur in the membrane most frequently. Moreover, daptomycin pore-forming activity is exponentially dependent on the applied membrane voltage. We further analyzed the membrane permeabilizing activity in B. subtilis cells using fluorescence methods (PI, DiSC₃(5)). Daptomycin most rapidly permeabilizes cells with high initial membrane potential and dissipates it within a few minutes. Low initial membrane potential hinders daptomycin pore formation.