Derivation of Extracellular Polysaccharide-Deficient Variants from a Serotype A Strain of Pasteurella multocida

Abstract

The production of serotype A extracellular polysaccharide is thought to be associated with expression of an approximately 40-kDa lipoprotein (P1p-40) present on the outer surface of Pasteurella multocida strains of avian origin. The tendency of certain strains to undergo colonial dissociation concomitantly with serial passaging on laboratory growth media was exploited to derive two variant strains exhibiting the capsule-deficient phenotype from a heavily capsulated parental strain. Assessments of colonial consistency, iridescence, gentian violet binding, and hyaluronidase sensitivity were consistent with cellular observations indicating little or no capsulation of derivative strains. Fluorographic analysis of electrophoretically resolved cellular lipoproteins labeled with [3H]-palmitate revealed capsular loss occurred with a concomitant diminution of P1p-40 production in the variant strains. In contrast, a phenotypically stable strain that did not undergo colonial dissociation under identical conditions exhibited no decrease in P1p-40 content. This work provides a model system for investigating the role of extracellular polysaccharide in the cell surface physiology and pathogenicity of P. multocida. The present results strongly support the notion that P1p-40 is associated with serotype A capsular material and suggest coordinate regulation of their biosynthesis.

Swarming motility in undomesticated Bacillus subtilis

“…Cultivation and manipulation of bacteria in the laboratory can result in the loss of phenotypes characteristic of wild‐type, natural isolates. For instance, domestication promotes the loss of extracellular polysaccharide biosynthesis in Pasteurella multocida (Champlin et al ., 1999), capsule biosynthesis in Haemophilus influenzae (Moxon and Vaughn, 1981), piliation in Neisseria gonorrhoeae (Penn et al ., 1977), virulence in Salmonella typhimurium (Lockman and Curtis, 1990) and social motility in Myxococcus xanthus (Velicer et al ., 1998). A striking example of the effects of domestication is seen in the spore‐forming bacterium Bacillus subtilis .…”

Fis Is Essential for Capsule Production in Pasteurella multocida and Regulates Expression of Other Important Virulence Factors

“…While there is evidence that the level of capsule expression in P. multocida responds to certain environmental conditions (such as growth in the presence of antibiotics, low iron or specific iron sources such as hemoglobin [29]–[32], there is no information on the mechanism of capsule regulation. There have been numerous reports of spontaneous loss of capsule expression in P. multocida strains following in vitro passage [10],[11], but the mechanism by which this occurs has not been determined. Previous work with laboratory-derived, spontaneous acapsular strains has indicated that loss of capsule expression was associated with reduced transcription of genes within the capsule biosynthesis locus [12].…”

“…Interestingly, previous studies on spontaneous acapsular strains have indicated that loss of a 39–40 kDa lipoprotein was correlated with the loss of capsular polysaccharide and it was hypothesized that the lack of expression of this protein on the surface was due to the physical loss of capsule [11], [54]–[56]. We propose that the lipoprotein identified in the above studies is in fact PlpE and its expression is reduced in spontaneous acapsular strains because of the transcriptional down-regulation of the gene due to the absence of Fis.…”

“…Spontaneous capsule loss during in vitro sub-culture has been described in P. multocida [10],[11]. In one study, acapsular variants were derived from capsulated parent strains by repeated laboratory passage (>30 sub-cultures) [12].…”

Regulation of capsule biosynthesis in serotype A strains ofPasteurella multocida

“…Spontaneous loss of capsule production occurs subsequent to subculturing of some capsulated serotype A P. multocida strains on laboratory growth media [9–11]. An increasing percentage of small ‘rough’ colonial variants relative to the percentage of large mucoid colonies is readily observed with each successive passage at frequencies much higher than can be explained by classical point mutations.…”