Virulence and genetic variation of Mycoplasma agassizii in the threatened Mojave desert tortoise

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Shalyn N. Bauschlicher and Victoria Martinez, Biology, Colorado State University - Pueblo, Pueblo, CO, Franziska C. Sandmeier, Biology, Colorado State University-Pueblo, Pueblo, CO, Chava L. Weitzman, Biological Sciences, Virginia Tech, Blacksburg, VA, C. Richard Tracy, Biology, University of Nevada, Reno, Reno, NV, David Alvarez-Ponce, Biology, University of Nevada-Reno, Reno, NV

Background/Question/Methods
Mojave desert tortoises are federally listed as threatened in the US. Though there are many threats that contribute to the decline of the species, upper respiratory tract disease (URTD) caused by Mycoplasma agassizii has been the focus of pathogenic research for the past 30 years. The isolated type-strain, PS6T, was thought to be highly virulent for decades, though no infection studies using this strain have ever been published. Recent sequencing of the PS6T genome provided the opportunity to investigate virulence and genetic variation of M. agassizii across the Mojave. Exo-alpha-sialidase is an enzyme commonly linked to virulence in several pathogens, including the hyper-virulent, Mycoplasma alligatoris. We used quantitative polymerase chain reaction (qPCR) to analyze the occurrence of sialidase genes within 140 uncultured M. agassizii-positive Mojave desert tortoise lavage samples collected in surveys during 2010 - 2012. Using each sample's paired disease data, we assessed whether sialidase gene detection may be linked to mycoplasmal load, disease instance, and disease severity.
Results/Conclusions
We found associations with virulence in PS6T sialidase genes and found PS6T to have moderate levels of virulence compared to other strains detected across the landscape. We found evidence of multiple-strain infections in Mojave desert tortoises and describe the importance of possible interactions within multiple-strain communities infecting desert tortoises. Host genomic information further led to our discovery that the PS6T sialidase genes were likely acquired from the tortoise-host by horizontal gene transfer. These results affirm the important benefits of the use of variable qPCR analyses to track pathogenicity and genetic variation of a bacterium which has proved highly difficult to culture and isolate, but for which new pathogen monitoring methods must continue to be developed in the interest of conservation of Gopherus spp. tortoises.