B-204. Genetic Plasticity in Chlamydia pneumoniae pmpG6 Gene

J. A. Carrasco Lopez, C. Tan, P. M. Bavoil;
Univ. of Maryland Dent. Sch., Baltimore, MD.

BACKGROUND: The genome of the obligate intracellular bacteria Chlamydia pneumoniae AR39 contains 21 genes, unique to members of the order Chlamydiales, encoding polymorphic membrane proteins (Pmps). While no function has yet been attributed to the Pmps, they may be involved in an antigenic variation of the chlamydial surface. Comparative analysis within the published genome sequences of different C. pneumoniae strains provided evidence of multiple levels of genetic variation within this gene family. METHODS: Specific primers were designed to amplify a DNA fragment of C pneumoniae pmpG6 by PCR. PCR reaction was done using the Taq DNA Polymerase from New England Biolabs® Inc., according to the manufacturer’s recommendations. The DNA and deduced protein sequences were analysed using programs from the NCBI (http://www.ncbi.nlm.nih.gov). Southern blots were performed with the DIG-High Prime DNA Labeling and Detection Starter Kit II from Roche Applied Science, following the manufacturer's instructions. RESULTS: We found evidence of gene plasticity in C. pneumoniae AR39 pmpG6 by intragenic in-frame deletions and/or insertions of 393 bp repeats. These variations may result in new pmp variants with distinct antigenic properties and function. PCR experiments revealed that amplified fragments of C. pneumoniae AR39 pmpG6 differ from the predicted sizes described in the data banks. We obtained amplified fragments that corresponded to 1 and 2 in-frame additional repeat inserts with regards to the published sequence. These results were confirmed by sequencing analysis and Southern blot experiments. The putative mechanism of this antigenic variation is under study. CONCLUSIONS: Our studies demonstrate the presence of variability in the pmpG6 sequence both among strains and within strains of C. pneumoniae. It is of special interest that the number of the repeats implies variation in the protein size between 1277 and 1539 amino acids (20%). The variability identified within this recently described gene family may modulate the antigenic variation and subsequent physiologic diversity within a C. pneumoniae population.