Bacteriocin from Bacillus megaterium ATCC 19213: comparative studies with megacin A-216

A bacteriocin produced by Bacillus megaterium ATCC 19213 was identified, purified, and compared with megacin A from B. megaterium 216. The ATCC 19213 bacteriocin was inducible with mitomycin C and showed phospholipase A activity. Both megacin A-216 and megacin A-19213 contained two dissimilar polypeptide subunits. Megacin A-216 contains a 30,000-dalton alpha subunit and a 15,000-dalton beta subunit. Megacin A-19213 is composed of an alpha subunit 18,000 daltons in mass and a beta subunit about 7,500 daltons in mass. No sequence similarities between alpha and beta subunits of either megacin were detected. The two megacins were further distinguished by quantitative differences in activity spectra and by immunodiffusion analyses.     

Improved purification and some properties of megacin Cx, a bacteriocin produced by Bacillus megaterium

Megacin Cx is a bacteriocidal protein, previously described by Durner and Mach (Durner, K. (1970) Z. Allg. Mikrobiol. 10, 93-102; Durner, K. (1970) Z. Allg. Mikrobiol. 10, 373-382; Durner, K., and Mach, F. (1966) Zentralbl. Bakteriol. Parasitenkd. Infektionskr. Hyg. Abt. I Orig. 2, 120, 565-575), which is released into the medium during growth by Bacillus megaterium strain 337. We have optimized the culturing conditions to achieve reproducibly high yields of this protein; under these conditions, megacin Cx represents about one-half of the protein secreted into the medium. We have developed improved methods of purifying the protein to homogeneity. The active form of megacin Cx is a monomeric protein, a single polypeptide of Mr = 210,000, as determined by analytical ultracentrifugation and gel electrophoresis in sodium dodecyl sulfate. Like many other proteins secreted by Gram-positive organisms, megacin Cx contains remarkably little methionine and cysteine. The purified protein blocks protein synthesis in sensitive cells, but has little immediate effect upon nucleic acid synthesis. Our purification procedure separates megacin Cx from another activity in the culture medium which blocks the synthesis of RNA and DNA, as well as synthesis of protein, in sensitive cells.     

A monoclonal antibody to ochratoxin A

The production of patulin by P. expansum Link ex Gray growing in apple juice was determined over a range of pH. Patulin was found to be produced in large quantities over a narrow range of pH from 3-2 to 3–8. The biomass produced increased with increasing pH. The changes in pH due to growth of the organism were found to be small.     

A molecular genetic approach to the functioning of the immunity protein to colicin A

Summary A plasmid (pColAF1), derived from pColA, and lacking the region encoding Cai (colicin A immunity protein) and Cal (colicin A lysis protein) has been constructed. The strains carrying pColAF1 produce normal amounts of colicin A which remains in the cell cytoplasm and does not result in loss of viability. Similar results have also been obtained for transposon insertion mutants lacking Cai. Structure prediction analysis indicates that four peptide regions of Cai might span the cytoplasmic membrane. Since the NH₂-and COOH-terminal regions are charged, this analysis suggests a topology of the 178 residues polypeptide chain in which regions 38 to 70 and 124 to 143 might be exposed at the outer side of the cytoplasmic membrane. With mutants constructed using recombinant DNA techniques, we could demonstrate that the removal of a 30 residue COOH-terminal region, and mutations altering the surface exposed loop comprised of aminoacid residues 124–143 abolish the protecting function of Cai.     

A Tribute to Thomas A. Sebeok

According to the approach developed by Thomas A. Sebeok (1921–2001) and his ‘global semiotics,’ semiosis and life converge. This leads to his cardinal axiom: ‘semiosis is the criterial attribute of life.’ His global approach to sign life presupposes his critique of anthropocentrism and glottocentrism. Global semiotics is open to zoosemiotics, indeed, even more broadly, biosemiotics which extends its gaze to semiosis in the whole living universe to include the realms of macro- and microorganisms. In Sebeok’s conception, the sign science is not only the study of communication in culture, but of communicative behaviour from a biosemiotic perspective.     

A detour to mature

In this issue of Molecular Cell, Ye et?al. (2012) show an unexpected cytoplasmic assembly of Arabidopsis ARGONAUTE4/siRNA complexes and that siRNA binding could facilitate the nuclear import of mature AGO4/siRNA complexes, revealing a key regulatory process during RNA-directed DNA methylation (RdDM).