Antibacterial 6.5 kDa protein

The role of Pseudomonas aeruginosa exotoxin A in the modulation of humoral immune response parameters in the hemolymph of Galleria mellonella larvae was investigated. Our results indicate that exoA can play a role of a virulence factor by inhibiting insect PO, lysozyme, and antibacterial activity and decreasing the apoLp-III protein level significantly. No peptide bands with molecular mass below 6.5 kDa were detected in the hemolymph of exoA-treated larvae. We provided evidence for involvement of exoA in the pathogenicity of P. aeruginosa against G. mellonella and the usefulness of the insect as a model for analysis of P. aeruginosa toxins.

This study was designed to evaluate the potential of using newly purified Salmonella phage-encoded endolysin LysPB32 as novel antibiotic alternative. The endolysin LysPB32 was characterized by analyzing pH and thermal stability, lytic spectrum, antimicrobial activity, and mutant frequency against Salmonella Typhimurium KCCM 40253 (STKCCM), S. Typhimurium ATCC 19585 (STATCC), S. Typhimurium CCARM 8009 (STCCARM), Klebsiella pneumoniae ATCC 23357 (KPATCC), K. pneumoniae CCARM 10237 (KPCCARM), Pseudomonas aeruginosa ATCC 27853 (PAATCC), Listeria monocytogenes ATCC 1911 (LMATCC), Staphylococcus aureus ATCC 25923 (SAATCC), and S. aureus CCARM 3080 (SACCARM). The molecular weight of LysPB32 is 17 kDa that was classified as N-acetyl-β-d-muramidase. The optimum activity of LysPB32 against the outer membrane (OM) permeabilized STKCCM, STATCC, and STCCARM was observed at 37 °C and pH 6.5. LysPB32 had a broad spectrum of muralytic activity against antibiotic-sensitive STKCCM (41 mOD/min), STATCC (32 mOD/min), and SBKACC (25 mOD/min) and antibiotic-resistant STCCARM (35 mOD/min) and KPCCARM (31 mOD/min). The minimum inhibitory concentrations (MICs) of polymyxin B against STKCCM, STCCARM, and STATCC were decreased by 4-, 4-, and 8-folds, respectively, when treated with LysPB32. The combination of LysPB32 and polymyxin B effectively inhibited the growth of STKCCM, STCCARM, and STATCC after 24 h of incubation at 37 °C, showing 4.9-, 4.4-, and 3.3-log reductions, respectively. The mutant frequency was low in STKCCM, STCCARM, and STATCC treated with combination of LysPB32-polymyxin B system. The results suggest the LysPB32-polymyxin system can be a potential candidate for alternative therapeutic agent to control antibiotic-resistant pathogens.

Ralstonia solanaceraum is the quarantine plant pathogenic bacterium that causes bacterial wilt in over 200 host plants, which include economically important crops such as potato, tomato, tobacco, banana, and ginger. Alternative biological methods of disease control that can be used in integrated pest management are extensively studied. In search of new proteins with antibacterial activity against R. solanacearum, we identified L-amino acid oxidases (LAOs) from fruiting bodies of Amanita phalloides (ApLAO) and Infundibulicybe geotropa (CgLAO). We describe an optimized isolation procedure for their biochemical characterization, and show that they are dimeric proteins with estimated monomer molecular masses of 72 and 66 kDa, respectively, with isoelectric point of pH 6.5. They have broad substrate specificities for hydrophobic and charged amino acids, with highest Km for L-Leu, and broad pH optima at pH 5 and pH 6, respectively. An enzyme with similar properties is also characterized from the mycelia of I. geotropa (CgmycLAO). Fractionated aqueous extracts of 15 species of mushrooms show that LAO activity against L-Leu correlates with antibacterial activity. We confirm that the LAO activities mediate the antibacterial actions of ApLAO, CgLAO, and CgmycLAO. Their antibacterial activities are greater against Gram-negative versus Gram-positive bacteria, with inhibition of growth rate, prolongation of lag-phase, and decreased endpoint biomass. In Gram-positive bacteria, they mainly prolong the lag phase. These in vitro antibacterial activities of CgLAO and CgmycLAO are confirmed in vivo in tomato plants, while ApLAO has no effect on disease progression in planta. Transmission electron microscopy shows morphological changes of R. solanacearum upon LAO treatments. Finally, broad specificity of the antibacterial activities of these purified LAOs were seen for in vitro screening against 14 phytopathogenic bacteria. Therefore, these fungal LAOs show great potential as new biological phytoprotective agents and show the fruiting bodies of higher fungi to be a valuable source of antimicrobials with unique features.