Affiliation:
1. Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA
2. University of Toledo, Toledo, Ohio, USA
Abstract
ABSTRACT
The processing of lipoproteins (Lpps) in Gram-negative bacteria is generally considered an essential pathway. Mature lipoproteins in these bacteria are triacylated, with the final fatty acid addition performed by Lnt, an apolipoprotein N-acyltransferase. The mature lipoproteins are then sorted by the Lol system, with most Lpps inserted into the outer membrane (OM). We demonstrate here that the
lnt
gene is not essential to the Gram-negative pathogen
Francisella tularensis
subsp.
tularensis
strain Schu or to the live vaccine strain LVS. An LVS Δ
lnt
mutant has a small-colony phenotype on sucrose medium and increased susceptibility to globomycin and rifampin. We provide data indicating that the OM lipoprotein Tul4A (LpnA) is diacylated but that it, and its paralog Tul4B (LpnB), still sort to the OM in the Δ
lnt
mutant. We present a model in which the Lol sorting pathway of
Francisella
has a modified ABC transporter system that is capable of recognizing and sorting both triacylated and diacylated lipoproteins, and we show that this modified system is present in many other Gram-negative bacteria. We examined this model using
Neisseria gonorrhoeae
, which has the same Lol architecture as that of
Francisella
, and found that the
lnt
gene is not essential in this organism. This work suggests that Gram-negative bacteria fall into two groups, one in which full lipoprotein processing is essential and one in which the final acylation step is not essential, potentially due to the ability of the Lol sorting pathway in these bacteria to sort immature apolipoproteins to the OM.
IMPORTANCE
This paper describes the novel finding that the final stage in lipoprotein processing (normally considered an essential process) is not required by
Francisella tularensis
or
Neisseria gonorrhoeae
. The paper provides a potential reason for this and shows that it may be widespread in other Gram-negative bacteria.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
57 articles.
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