Abstract
The poultry-associated bacterium Mycoplasma iowae colonizes multiple sites in embryos, with disease or death resulting. Although M. iowae accumulates in the intestinal tract, it does not cause disease at that site, but rather only in tissues that are exposed to atmospheric O2. The activity of M. iowae catalase, encoded by katE, is capable of rapid removal of damaging H2O2 from solution, and katE confers a substantial reduction in the amount of H2O2 produced by Mycoplasma gallisepticum katE transformants in the presence of glycerol. As catalase-producing bacteria are often beneficial to hosts with inflammatory bowel disease, we explored whether M. iowae was exclusively protective against H2O2-producing bacteria in a Caenorhabditis elegans model, whether its protectiveness changed in response to O2 levels, and whether expression of genes involved in H2O2 metabolism and virulence changed in response to O2 levels. We observed that M. iowae was in fact protective against H2O2-producing Streptococcus pneumoniae, but not HCN-producing Pseudomonas aeruginosa, and that M. iowae cells grown in 1% O2 promoted survival of C. elegans to a greater extent than M. iowae cells grown in atmospheric O2. Transcript levels of an M. iowae gene encoding a homolog of Mycoplasma pneumoniae CARDS toxin were 5-fold lower in cells grown in low O2. These data suggest that reduced O2, representing the intestinal environment, triggers M. iowae to reduce its virulence capabilities, effecting a change from a pathogenic mode to a potentially beneficial one.
Highlights
H2O2 is a dangerous reactive oxygen species (ROS) involved in both pathogenesis and defense against infectious agents
M. iowae or wild-type M. gallisepticum resuspended to OD550 = 1.0 and incubated under the same conditions produced less than 1 mg L−1 H2O2, respectively, and the same outcome occurred when mycoplasma cells were coincubated with S. pneumoniae in the absence of sucrose
Host-associated bacteria live in the presence of a consortium of other microorganisms, some of which may be H2O2 producers
Summary
H2O2 is a dangerous reactive oxygen species (ROS) involved in both pathogenesis and defense against infectious agents. Pritchard and Balish Veterinary Research (2015) 46:36 gallisepticum, a robust H2O2 producer that elaborates no other known toxins [13,17,18] It is unclear how M. iowae causes disease, but in addition to its attachment organelle-mediated adherence and motility functions [19], its genome encodes potential virulence factors, including two closely linked genes encoding proteins similar to Mycoplasma pneumoniae CARDS toxin [13], an ADPribosylating toxin that is associated with many of the symptoms of M. pneumoniae infection [20,21,22]. Our results indicate that catalase contributes to M. iowae being protective toward the host against H2O2-producing organisms, even though catalase activity is reduced under conditions of low O2 They indicate that M. iowae grown in low O2 results in increased survival of C. elegans upon co-incubation as compared with M. iowae grown in atmospheric conditions, accompanied by a 5-fold decrease in expression of at least one of the CARDS toxin-like protein genes
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