Veterinary Microbiology 251 (2020) 108891 Available online 10 October 2020 0378-1135/© 2020 Elsevier B.V. All rights reserved. Short communication The infuence of host tissue on M. gallisepticum vlhA gene expression K. Pfaum a , E.R. Tulman a , J. Canter a , K.V. Dhondt b , M.T. Reinoso-Perez b, c , A.A. Dhondt c , S. J. Geary a, * a Center of Excellence for Vaccine Research, Department of Pathobiology and Veterinary Science, University of Connecticut, Storrs, CT, United States b Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14850, United States c Laboratory of Ornithology, Cornell University, Ithaca, NY, 14850, United States A R T I C L E INFO Keywords: Mycoplasma gallisepticum Phase variable RNAseq Gene expression ABSTRACT Mycoplasma gallisepticum, a signifcant poultry pathogen, has evolved rapidly in its new passerine host since its frst reported isolation from house fnches in the US in 1994. In poultry, M. gallisepticum infects the upper res- piratory tract, causing tracheal mucosal thickening and infammation, in addition to infammation of the reproductive tract. However, in house fnches M. gallisepticum primarily causes infammation of the conjunctiva. Given that different tissues are primarily affected by the same pathogen in different hosts, we have compared the early changes in gene expression of the phase-variable lipoproteins (vlhA) gene family of M. gallisepticum collected directly from target tissues in both hosts. Previous data have demonstrated that vlhA genes may be related to virulence, exhibiting changes in expression in a non-stochastic, temporal progression and we hy- pothesize that this may be infuenced by differences in the target host tissue. If this is true, we would expect M. gallisepticum to display a different vlhA gene expression pattern in the chicken trachea compared to its expression pattern in house fnch conjunctiva. Here we report signifcant differences in vlhA gene expression patterns between M. gallisepticum collected from chicken tracheas compared to those collected from house fnch conjunctiva. While many of the predominant vlhA genes expressed in the input population showed an increase in expression in the chicken trachea at day one postinfection, those same vlhA genes decreased in expression in the house fnch. These data suggest that discrete suites of vlhA genes may be involved in M. gallisepticum pathogenesis and tropism for unique tissues in two disparate avian hosts. 1. Introduction Mycoplasma gallisepticum is the bacterial pathogen commonly asso- ciated with chronic respiratory disease in domestic poultry. Infection with M. gallisepticum in poultry is classically associated with infam- mation of the air sacs, lungs, and trachea (Razin et al., 1998). In 1994 M. gallisepticum emerged and spread among wild songbird populations, notably the house fnch (Haemorhous mexicanus), in the USA (Fischer et al., 1997; Dhondt et al., 1998, 2006). In stark contrast to poultry, affected house fnches present with an ocular form of disease (Hawley et al., 2011) characterized by severe and chronic lymphoplasmacytic conjunctivitis, sinusitis, and rhinitis (Ley et al., 1996, 1997; Fischer et al., 1997). It is unclear how the mechanisms of pathogenesis, persis- tence, and virulence employed by M. gallisepticum differ between the respiratory manifestation in the poultry and the ocular manifestation in the house fnch. Interestingly, as the house-fnch M. gallisepticum (HFMG) adapted and its virulence increased in house fnch, it decreased in chickens (Pfaum et al., 2017). Previous data have shown a strong correlation between HFMG virulence phenotypes and the pre- sence/absence and/or the genomic locations of vlhA genes encoding surface exposed, phase-variable lipoprotein hemagglutinins (vlhAs) (Tulman et al., 2012; Pfaum et al., 2017). To investigate this phenomenon, we conducted a series of in vivo challenge studies wherein HFMG strain VA94, the initial index isolate from house fnch, was inoculated into both chickens and house fnch at their respective target sites (respiratory tract or conjunctiva, respec- tively). HFMG RNA was collected directly from the target tissue of each host and the vlhA expression patterns were compared over the course of early infection. Herein, we report signifcant differences in the vlhA gene expression patterns between HFMG collected from chicken tracheas compared to those collected from the house fnch conjunctiva. * Corresponding author. E-mail address: Steven.geary@uconn.edu (S.J. Geary). Contents lists available at ScienceDirect Veterinary Microbiology journal homepage: www.elsevier.com/locate/vetmic https://doi.org/10.1016/j.vetmic.2020.108891 Received 23 July 2020; Accepted 7 October 2020