Targeted gene modification in animal pathogenic chlamydia

The human pathogenic bacterium

Chlamydia


trachomatis

is the most common sexually transmitted bacterial pathogen worldwide. It is estimated to infect more than 100 million people each year and is a frequent cause of infertility. Moreover,

Chlamydia


trachomatis

also causes eye infections and represents the most frequent infectious cause of blindness in developing areas of the world.

Less widely known is that

Chlamydia

affects not only humans, but also animals. By causing disease in farm animals, such as in cows, sheep, pigs and chicken,

Chlamydia

can cause significant economic damage. Moreover,

Chlamydia

also infects pet animals, such as cats, guinea pigs, and parrots. While the

Chlamydia

species that infect animals are biologically different from the human pathogen

Chlamydia


trachomatis

, some animal pathogenic

Chlamydia

can occasionally also infect humans. These zoonotic infections in which the bacteria are transmitted from an infected animal to a human can be severe and life-threatening.

In a collaborative study published in the journal

PLOS ONE

, researchers from the University of Maryland Baltimore (USA), Duke University (USA), and Umeå University (Sweden), joined forces to adapt a novel genetic tool for zoonotic

Chlamydia

.

“In order to understand why some

Chlamydia

can cause infections in humans and others not, we need to investigate how these different bacterial species differ in their ability to interact with their hosts”, says infection biologist Barbara Sixt from the Laboratory for Molecular Infection Medicine Sweden (MIMS) at Umeå University, one of the project leaders.

All known

Chlamydia

are intracellular bacteria, which means that the bacteria can enter into human or animal cells and multiply in the inside of the host cell. To remodel the host cell into a perfect home for the bacteria,

Chlamydia

produce virulence factors that can modify the normal functions of the cell. Interestingly, different

Chlamydia

species appear to produce distinct sets of these factors. “It is possible that the presence or absence of different virulence factors during infection with different

Chlamydia

species can determine their ability to infect different hosts and their ability to cause different diseases in these hosts”, says Barbara Sixt.

Our ability to test the function and importance of specific virulence factors depends on experimental strategies that enable researchers to generate mutant variants of the bacteria that can further be investigated in the laboratory. While such strategies were recently developed for the human pathogen

Chlamydia


trachomatis

, similar experiments had so far not been conducted in zoonotic

Chlamydia

. “Using an approach that allows us to destroy specific bacterial genes by inserting a DNA fragment at a specific position in the bacterial genome, we managed to generate two mutants of

Chlamydia


caviae

that lack distinct virulence factors”, says Kimberly Filcek, first author of the study. “This shows that the recently developed method for insertional gene disruption in

Chlamydia


trachomatis

can be applied more widely for different

Chlamydia

species”.

The authors of the study focused on

Chlamydia


caviae

, a

Chlamydia

species that primarily infects guinea pigs, but was more recently also identified as an agent of severe lung infections in humans. The species is also related to

Chlamydia

psittaci, a bird pathogen that causes “parrot fever” in humans. This disease, also called psittacosis, is the most frequent zoonotic

Chlamydia

infection.

In

C.


caviae

, the authors disrupted two virulence factors, known as IncA and Sin

C.

An IncA-deficient mutant displayed an altered morphology of the inclusion, which is the membranous vacuole in the host cell inside which the bacteria grow. Moreover, the authors observed that a SinC mutant displayed reduced virulence towards chicken embryos, suggesting that SinC contributes to

C.


caviae

‘s ability to cause disease in animals. Interestingly, SinC is a factor that is only produced by zoonotic

Chlamydia

, but not by the main human pathogen

C.


trachomatis

. “Future work will exploit the availability of the mutant to explore the molecular mode of action of SinC”, explains Patrik Bavoil from the University of Maryland.

“While there is much left to be learned about the function of IncA and SinC in

C.


caviae

, our recent break-through in genetic modification of

C.


caviae

will open up exciting new opportunities to investigate the biology of these pathogens. This may in the future potentially also enable alternative ways to treat infections”, Barbara Sixt concludes.

###

In this study the following researchers and research institutes were involved:

Kimberly Filcek and Patrik M Bavoil, Department of Microbial Pathogenesis, University of Maryland, School of Dentistry, Baltimore, MD, USA

Raphael H. Valdivia, Department of Molecular Genetics and Microbiology, Duke University, Durham, NC, USA

Katarina Vielfort, Samada Muraleedharan, Johan Henriksson and Barbara Sixt, The Laboratory for Molecular Infection Medicine Sweden (MIMS), Department of Molecular Biology, Umeå University, Umeå, Sweden

Original publication:

Kimberly Filcek, Katarina Vielfort, Samada Muraleedharan, Johan Henriksson, Raphael H. Valdivia, Patrik M. Bavoil, Barbara S. Sixt: Insertional mutagenesis in the zoonotic pathogen

Chlamydia


caviae

.

PLOS ONE

, The Public Library of Science ONE, 07 November 2019,

Read the publication in

PLOS ONE:

https:/

/

journals.

plos.

org/

plosone/

article?id=

10.

1371/

journal.

pone.

0224324

Contact information:

Barbara S Sixt, Assistant Professor

The Laboratory for Molecular Infection Medicine Sweden (MIMS)

Department of Molecular Biology

Umeå University

Umeå, Sweden


[email protected]

, phone: +46 90-785 67 42


http://www.

mims.

umu.

se/

groups/

barbara-sixt.

html

Patrik M Bavoil, Professor

Department of Microbial Pathogenesis

University of Maryland, School of Dentistry

Baltimore, MD, USA


[email protected]

, phone: +1 410 706 6789


https:/

/

www.

dental.

umaryland.

edu/

micropath/

research/

dr-patrik-bavoil-lab/