Abstract
The molecular mechanisms that allow pathogenic bacteria to infect animals have been intensively studied. On the other hand, the molecular mechanisms by which bacteria acquire virulence functions are not fully understood. In the present study, we experimentally evaluated the evolution of a non-pathogenic strain of Escherichia coli in a silkworm infection model and obtained pathogenic mutant strains. As one cause of the high virulence properties of E. coli mutants, we identified amino acid substitutions in LptD (G580S) and LptE (T95I) constituting the lipopolysaccharide (LPS) transporter, which translocates LPS from the inner to the outer membrane and is essential for E. coli growth. The growth of the LptD and LptE mutants obtained in this study was indistinguishable from that of the parent strain. The LptD and LptE mutants exhibited increased secretion of outer membrane vesicles containing LPS and resistance against various antibiotics, antimicrobial peptides, and host complement. In vivo cross-linking studies revealed that the conformation of the LptD-LptE complex was altered in the LptD and LptE mutants. Furthermore, several clinical isolates of E. coli carried amino acid substitutions of LptD and LptE that conferred resistance against antimicrobial substances. This study demonstrated an experimental evolution of bacterial virulence properties in an animal infection model and identified functional alterations of the growth-essential LPS transporter that led to high bacterial virulence by conferring resistance against antimicrobial substances. These findings suggest that non-pathogenic bacteria can gain virulence traits by changing the functions of essential genes, and provide new insight to bacterial evolution in a host environment.
Highlights
Uncovering the difference between pathogenic bacteria and non-pathogenic bacteria is important toward understanding the mechanisms of bacterial virulence and developing novel medicines against bacterial infectious diseases
We utilized a silkworm infection model to perform an experimental evolution of bacterial virulence activity
The mutations changed the structure of the LPS transporter, increased the secretion of outer membrane vesicles, and enabled bacterial survival in the presence of host antimicrobial substances
Summary
Uncovering the difference between pathogenic bacteria and non-pathogenic bacteria is important toward understanding the mechanisms of bacterial virulence and developing novel medicines against bacterial infectious diseases. Experimental evolution is a novel, recently developed system to uncover the molecular mechanisms by which cells acquire various functions, such as temperature resistance [1] and antibiotic resistance [2]. Experimental evolution of virulence properties was evaluated in vitro with viruses against eukaryotic cells [3], bacteriophages against bacteria [4, 5], and bacteria against macrophages [2, 6]. We performed an experimental evolution of a non-pathogenic laboratory strain of Escherichia coli into a pathogenic strain in the silkworm infection model, which is highly useful for infection experiments [7, 8]. We successfully obtained bacterial mutants with 500-fold higher virulence than the original strain and found that amino acid substitutions of the lipopolysaccharide (LPS) transporter increase E. coli virulence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
