Antibacterial Activity of Different Blossom Honeys: New Findings.

Antibacterial activity is the most investigated biological property of honey. The goal of this study was to evaluate the antibacterial activity of 57 Slovak blossom honeys against Staphylococcus aureus and Pseudomonas aeruginosa and investigate the role of several bioactive substances in antibacterial action of honeys. Inhibitory and bactericidal activities of honeys were studied to determine the minimum inhibitory and bactericidal concentrations. The contents of glucose oxidase (GOX) enzyme, hydrogen peroxide (H2O2), and total polyphenols (TP) were determined in honeys. We found that honey samples showed different antibacterial efficacy against the tested bacteria as follows: wildflower honeys > acacia honeys > rapeseed honeys. Overall antibacterial activity of the honeys was statistically-significantly correlated with the contents of H2O2 and TP in honeys. A strong correlation was found between the H2O2 and TP content. On the other hand, no correlation was found between the content of GOX and level of H2O2. Antibacterial activity of 12 selected honeys was markedly reduced by treatment with catalase, but it remained relatively stable after inactivation of GOX with proteinase-K digestion. Obtained results suggest that the antibacterial activity of blossom honeys is mainly mediated by H2O2 levels present in honeys which are affected mainly by polyphenolic substances and not directly by GOX content.

Characterization of the N-Terminal Catalytic Domain of Lytµ1/6, an Endolysin from Streptomyces aureofaciens Phage µ1/6.

Previous characterization of Lytµ1/6, an endolysin from Streptomyces aureofaciens phage µ1/6, suggested that the N-terminal domain is responsible for the catalytic activity of Lytµ1/6. Mutational analyses (deletions and site-directed mutagenesis) demonstrated that lytic activity of Lytµ1/6 relies on the N-terminal part of about 200 amino acid residues. Various C-terminally truncated versions of Lytµ1/6 failed to cause lysis, indicating the necessity of the CBD for full enzyme activity. Functional analysis of the point mutants suggested that the residues K27, H31, E109, H176, and D184 were essential for lytic activity of the µ1/6 endolysin. Further characterization of the purified Lytµ1/6 revealed that this endolysin is an N-acetylmuramoyl-L-alanine amidase which seems to be unrelated to any of the known conserved catalytic domains of phage endolysins or bacterial autolysins.

Bacteriophage endolysin Lyt µ1/6: characterization of the C-terminal binding domain.

The gene product of orf50 from actinophage µ1/6 of Streptomyces aureofaciens is a putative endolysin, Lyt µ1/6. It has a two-domain modular structure, consisting of an N-terminal catalytic and a C-terminal cell wall binding domain (CBD). Comparative analysis of Streptomyces phage endolysins revealed that they all have a modular structure and contain functional C-terminal domains with conserved amino acids, probably associated with their binding function. A blast analysis of Lyt µ1/6 in conjunction with secondary and tertiary structure prediction disclosed the presence of a PG_binding_1 domain within the CBD. The sequence of the C-terminal domain of lyt µ1/6 and truncated forms of it were cloned and expressed in Escherichia coli. The ability of these CBD variants fused to GFP to bind to the surface of S. aureofaciens NMU was shown by specific binding assays.

Analysis of the site-specific integration system of the Streptomyces aureofaciens phage µ1/6.

The bacteriophage µ1/6 integrates its DNA into the chromosome of tetracycline producing strains of Streptomyces aureofaciens by a site-specific recombination process. A bioinformatic analysis of the µ1/6 genome revealed that orf5 encodes a putative integrase, a basic protein of 416 amino acids. The µ1/6 integrase was found to belong to the integrase family of site-specific tyrosine recombinases. The phage attachment site (attP) was localized downstream of the int gene. The attachment junctions (attL and attR) were determined, allowing identification of the bacterial attachment site (attB). All attachment sites shared a 46-bp common core sequence within which a site-specific recombination occurs. This core sequence comprises the 3' end of a putative tRNA(Thr) gene (anticodon TGT) which is completely restored in attL after integration of the phage into the host genome. An integration vector containing µ1/6 int-attP region was inserted stably into the S. aureofaciens B96, S. lividans TK24, and S. coelicolor A3. The µ1/6 integrase was shown to be functional in vivo in heterologous Escherichia coli without any other factors encoded by Streptomyces. In vitro recombination assay using purified µ1/6 integrase demonstrated its ability to catalyze integrative recombination in the presence of a crude extract of E. coli cells.

The lysis system of the Streptomyces aureofaciens phage mu1/6.

Previously, two genes, designated as lyt and hol, were identified in the lysis module of phage mu1/6. They were cloned and expressed in Escherichia coli. An additional candidate holin gene, hol2, was found downstream from the hol gene based on one predicted transmembrane domain and a highly charged C-terminal sequence of the encoded protein. Expression of hol or hol2 in E. coli was shown to cause cell death. The concomitant expression of lambda endolysin (R) and mu1/6 holin resulted in cell lysis. Similarly, the coexpression of the endolysin and holin of phage mu1/6 led to lysis, apparently due to the ability of mu1/6 endolysin to hydrolyze the peptidoglycan layer of this bacterium. In contrast, the simultaneous expression of mu1/6 hol2 and the endolysin gene (lambdaR or mu1/6 lyt) did not cause detectable lysis of the host cells. Demonstration of the holin function in streptomycetes was achieved by providing for the release of mu1/6 endolysin to the periplasm and subsequent cleavage of the peptidoglycan, which strongly suggested that the holin produces lesions in the streptomycete membrane.