Bacterial Gene Acquisition May Drive Niche Expansion

The bacterium Streptococcus pneumoniae (pneumococcus) is the prime causal agent of pediatric ear infections. Yet, in some cases, it can also cause eye infections.

To explore how evolution enables bacteria to infect different cell types in the human body, Carnegie Mellon microbiologist Luisa Hiller teamed up with Dannie Durand at the Department of Biological Sciences at Carnegie Mellon University and Robert Shanks and Regis Kowalski at the Department of Ophthalmology at the University of Pittsburgh.

In a study recently reported in mSphere, the team investigated whether pneumococcal strains can gain new genes and in doing so spread to the human eye.  Utilizing a large collection of patient strains assembled by Kowalski, they analyzed pneumococcal genomes sampled from various types of eye infections.

The analysis revealed a set of genes associated with strains that cause conjunctivitis but not other pneumococcal diseases. Irena Antic, a postdoctoral fellow in the Hiller lab, joined forces with the Shanks group and found that presence of a specific gene from this set increases adherence of this bacterium to human eye cells involved in conjunctivitis.

So where did this gene come from? Evolutionary analysis carried out in collaboration with computational biologists in the Durand lab showed that this gene was acquired from Streptococcus suis, a distantly related species commonly found in pigs. The results of this study provide a compelling example of how acquisition of a novel gene can promote bacterial expansion into a new niche in the human body.
 

^{Antic I, Brothers KM, Stolzer M, Lai H, Powell E, Eutsey R, Cuevas RA, Miao X, Kowalski RP, Shanks RMQ, Durand D, Hiller NL. Gene Acquisition by a Distinct Phyletic Group within Streptococcus pneumoniae Promotes Adhesion to the Ocular Epithelium. mSphere. 2017 Oct 25;2(5). pii: e00213-17. doi: 10.1128/mSphere.00213-17. eCollection 2017 Sep-Oct. PubMed PMID: 29085912.}