No abstract

Members of the genus Bacillus produce a wide variety of antimicrobial compounds. Cyclic lipopeptides (CLP) produced by Bacillus subtilis strains have been shown to protect host plants from a numbers of pathogens. The representative families of these CLP (surfactins, fengycins, and iturins) share a polypeptide ring linked to a lipid tail of varying length. CLP provide plant protection through a variety of unique mechanisms. Members of the surfactin and fengycin families elicit induced systemic resistance in certain host plants, and they also function by directly affecting the biological membranes of bacterial and fungal pathogens, mainly resulting in membrane pore formation. Specific pore forming mechanisms differ between CLP families, causing differential activities. CLP also may aid in enhanced B. subtilis colonization of the plant environment in addition to potentially preventing the adhesion of competitive microorganisms. Several recent studies have highlighted the control of plant pathogens by CLP-producing B. subtilis strains. Strong ecological advantages through multifaceted activities of CLP provide these strains with immense promise in controlling pathogens in a variety of plant ecosystems.

Lipids are the major form of carbon storage in arbuscular-mycorrhizal fungi. We studied fatty acid synthesis by Glomus intraradices and Gigaspora rosea. Our data strongly suggest that the fatty acid synthase activity of arbuscular-mycorrhizal fungi is expressed exclusively in the intraradical mycelium and indicate that fatty acid metabolism may play a major role in the obligate biotrophism of arbuscular-mycorrhizal fungi.

cis-9-Heptadecenoic acid (CHDA), an antifungal fatty acid produced by the biocontrol agent Pseudozyma flocculosa, was studied for its effects on growth and/or spore germination in fungi. Inhibition of growth and/or germination varied considerably and revealed CHDA sensitivity groups within tested fungi. Analysis of lipid composition in these fungi demonstrated that sensitivity was related primarily to a low intrinsic sterol content and that a high level of unsaturation of phospholipid fatty acids was not as involved as hypothesized previously. Our data indicate that CHDA does not act directly with membrane sterols, nor is it utilized or otherwise modified in fungi. A structural mechanism of CHDA, consistent with the other related antifungal fatty acids produced by P. flocculosa, is proposed in light of its activity and specificity. The probable molecular events implicated in the sensitivity of fungi to CHDA are (i) partitioning of CHDA into fungal membranes; (ii) a variable elevation in fluidity dependent on the buffering capability (sterol content) in fungi; and (iii) higher membrane disorder causing conformational changes in membrane proteins, increased membrane permeability and, eventually, cytoplasmic disintegration.Pseudozyma flocculosa (Traquair, Shaw, et Jarvis) Boekhout et Traquair (ϭ Sporothrix flocculosa Traquair, Shaw, et Jarvis) (8) is a yeast-like fungus with biocontrol properties against powdery mildew fungi (3, 14, 15, 20). Cytochemical observations revealed that it induces a rapid collapse of powdery mildew conidial chains and a cytoplasmic disintegration of the cells (16) through the production of unusual extracellular fatty acids with antifungal properties (1, 4, 11). These antifungal fatty acids cause the release of intracellular ions and proteins when in contact with sensitive fungi (16), suggesting that they disrupt properties and functions of the cytoplasmic membrane. Benyagoub et al. (5) hypothesized that this fungal sensitivity was related to a low sterol content and to a high degree of unsaturation of phospholipid fatty acids in fungal membranes, factors which increase membrane fluidity. Indeed, they showed that the antifungal fatty acids caused a dose-dependent elevation in fluidity in artificial membranes constructed from the total lipids of the sensitive fungus Cladosporium cucumerinum Ellis et Arth, whereas artificial membranes made with lipids of P. flocculosa demonstrated no changes in fluidity (5).In general, elevated fluidity is known to cause disorder, i.e., a higher degree of mobility of phospholipid acyl chains in the membrane bilayer. This alteration in acyl chain packing can result in changes in membrane dynamics which would affect the activity of membrane-bound proteins (12). Since toxic fatty acids, in general, seem to interfere with multiple, apparently unrelated membrane enzymes (13), it has been proposed that the interaction between the fatty acids and cellular enzymes in sensitive fungi is indirect and nonspecific (19). However, to our knowledge, there are no document...

Discovery of new antimicrobials is highly desired due to the emergence of microorganisms that have multi-drug resistant capability. The purpose of this study was to investigate the antimicrobial effect of dopamine (DA) on Escherichia coli. DA's inhibitory activity was tested at different initial E. coli cell concentrations. Significant 3.5 and 4.2 log inhibitions were observed for 1 Â 10 8 and 1 Â 10 7 cells per mL, when compared to controls, corresponding to 99.97 and 99.99% inhibitions. Microscopic techniques (optical, fluorescence, and scanning electron) and Fourier transform infrared spectroscopy confirmed a polydopamine coating on the bacterial cells. Capillary electrophoresis with ultra-violet detection indicated a significant change in the cell structure caused by a low dose (100 mg L À1 ) of DA within 200 min of incubation.