Characterization of the activity and expression of arginine decarboxylase in human and animal C hlamydia pathogens

C hlamydia pneumoniae encodes a functional arginine decarboxylase (Arg DC ), AaxB , that activates upon self‐cleavage and converts l ‐arginine to agmatine. In contrast, most C hlamydia trachomatis serovars carry a missense or nonsense mutation in aaxB abrogating activity. The G 115 R missense mutation was not predicted to impact AaxB functionality, making it unclear whether AaxB variations in other C hlamydia species also result in enzyme inactivation. To address the impact of gene polymorphism on functionality, we investigated the activity and production of the C hlamydia AaxB variants. Because A rg DC plays a critical role in the E scherichia coli acid stress response, we studied the ability of these C hlamydia variants to complement an E . coli A rg DC mutant in an acid shock assay. Active AaxB was detected in four additional species: C hlamydia caviae, C hlamydia pecorum, C hlamydia psittaci , and C hlamydia muridarum . Of the C . trachomatis serovars, only E appears to encode active enzyme. To determine when functional enzyme is present during the chlamydial developmental cycle, we utilized an anti‐ AaxB antibody to detect both uncleaved and cleaved enzyme throughout infection. Uncleaved enzyme production peaked around 20 h postinfection, with optimal cleavage around 44 h. While the role A rg DC plays in C hlamydia survival or virulence is unclear, our data suggest a niche‐specific function.