MSH temperature adaptation

The MS-H vaccine strain (Vaxsafe MS; Bioproperties Pty. Ltd., Australia) is a live attenuated temperature sensitive derivative of a virulent strain of M. synoviae, 86079/7NS, and is used to prevent diseases from M. synoviae challenges in poultry farms. The genome sequence of MS-H includes 32 single nucleotide polymorphisms (SNPs) compared to that of 86079/7NS. To investigate the nature of mutations responsible for temperature sensitivity, MS-H strain was subjected to thermal adaptation in vitro and in vivo. The only observed variation detected in the MS-H culture following sequential passages with incremental incubation temperature was an Ala210Val variation in ObgE protein, associated with loss of temperature sensitivity phenotype. An identical variation was detected in the MS-H culture reisolated from one out of five bird 28 days after inoculation with MS-H. These findings suggest that M. synoviae is capable of thermoadaptive evolution and ObgE plays a significant role in this trait.