Synthesis and secretion of hemolysin by Escherichia coli

Abstract

Hemolytic Escherichia coli cells were found to synthesize and secrete significant amounts of hemolysin into a mineral salt-glucose medium containing hemoglobin. The release of de novo-synthesized hemolysin was stopped in the presence of energy metabolism inhibitors such as 2,4-dinitrophenol, sodium azide, or potassium cyanide, resulting in an accumulation of intracellular hemolysin. A similar effect was observed in the presence of procaine, a neuroactive drug which inhibits the processing of exoproteins. Small amounts of hemolysin were secreted into the medium within approximately 10 min of inhibition of protein synthesis by chloramphenicol. This represented the final release of preformed periplasmic hemolysin en route to secretion through the outer membrane and was not caused by adsorption of extemal hemolysin to the cell surface. This secretion was not energy dependent but was inhibited above pH 8 and at low temperatures (10 to 200C). We concluded that two transport processes are involved in hemolysin secretion. De novo-synthesized hemolysin is extruded by an energy-dependent process through the cytoplasmic membrane and probably requires processing. In the periplasmic space a small internal pool ofpreforned hemolysin is accumulated temporarily before being transported through the outer membrane. Release of hemolysin through the outer membrane does not require energy or de novo protein synthesis.Bacteria are able to produce a large variety of extracellular toxic proteins (1, 3). Among these, the cytolytic toxins or cytolysins (1) have attracted much attention as pathogenic factors, particularly in gram-positive bacteria (1). These proteins cause damage to membranes by mechanisms which are only partially understood (1). A related exotoxin, hemolysin, is also produced by some Escherichia coli strains (21,22). Recent studies in our laboratory have shown that its production by E. coli strain PM152 (8) is controlled by a cluster of three plasmid-borne cistrons determining not only the synthesis of biologically active hemolysin but also a function(s) required for its secretion through the outer membrane (15). There is now evidence that this gene cluster is common to many if not all he-

Haemolysin genes of Vibrio cholerae: presence of homologous DNA in non-haemolytic O1 and haemolytic non-O1 strains

“…The haemolysin is not excreted in E. coli K-12 but remains localised in the periplasm [5]. This differs from the E. coli haemolysin described by Goebel and co-workers [6][7][8], and by Mackman and Holland [9,10] in which the genes for haemolysin production and excretion are contiguous. The E. coli haemolysin differs also in that it is usually plasmid-encoded [6].…”

Export and secretion of proteins by bacteria

“…The 62-kDa, mainly outer-membrane, product of the independently transcribed hlyBb gene is required for the release of the haemolysin into the medium [277,278,[351][352][353]. Haemolysin release is energydependent [354].…”

Spontaneous deletions and flanking regions of the chromosomally inherited hemolysin determinant of an Escherichia coli O6 strain

“…Hemolysin produced by Escherichia coli is an extracellular protein that is considered to be a virulence factor in E. coli causing extraintestinal infections (7,17,27,28; J. Hacker, C. Hughes, H. Hof, and W. Goebel, submitted for publication). The genetic determinant for hemolysin synthesis and secretion (22) is located either on transmissible plasmids (10, 11,21) or on the chromosome (2, 17; D. Muller, C. Hughes, and W. Goebel, in press).…”