Mycoplasma iowae: relationships among oxygen, virulence, and protection from oxidative stress

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 O(2). The activity of M. iowae catalase, encoded by katE, is capable of rapid removal of damaging H(2)O(2) from solution, and katE confers a substantial reduction in the amount of H(2)O(2) 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 H(2)O(2)-producing bacteria in a Caenorhabditis elegans model, whether its protectiveness changed in response to O(2) levels, and whether expression of genes involved in H(2)O(2) metabolism and virulence changed in response to O(2) levels. We observed that M. iowae was in fact protective against H(2)O(2)-producing Streptococcus pneumoniae, but not HCN-producing Pseudomonas aeruginosa, and that M. iowae cells grown in 1% O(2) promoted survival of C. elegans to a greater extent than M. iowae cells grown in atmospheric O(2). Transcript levels of an M. iowae gene encoding a homolog of Mycoplasma pneumoniae CARDS toxin were 5-fold lower in cells grown in low O(2). These data suggest that reduced O(2), representing the intestinal environment, triggers M. iowae to reduce its virulence capabilities, effecting a change from a pathogenic mode to a potentially beneficial one.