Natural reversion promotes LPS elongation in an attenuated Coxiella burnetii strain

Abstract

Lipopolysaccharide (LPS) phase variation is a critical aspect of virulence in many Gram-negative bacteria. It is of particular importance to Coxiella burnetii, the biothreat pathogen that causes Q fever, as in vitro propagation of this organism leads to LPS truncation, which is associated with an attenuated and exempted from select agent status (Nine Mile II, NMII). Here, we demonstrate that NMII was recovered from the spleens of infected guinea pigs. Moreover, these strains exhibit a previously unrecognized form of elongated LPS and display increased virulence in comparison with the initial NMII strain. The reversion of a 3-bp mutation in the gene cbu0533 directly leads to LPS elongation. To address potential safety concerns, we introduce a modified NMII strain unable to produce elongated LPS.

In vitro propagation of the pathogenic bacterium Coxiella burnetii, the causative agent of Q fever, leads to attenuated virulence and lipopolysaccharide (LPS) truncation. Here, Long et al. show that a strain considered to be avirulent (NMII) can be recovered from infected animals, and these isolates display increased virulence and an elongated LPS due to reversion of a 3-bp mutation in a gene.