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Maximally Diverse Haemophilus influenzae isolates Undergo Varied Transcriptional Responses during Bi

Evangeline Williams MS, Ari Gordon PhD, Jocelyn Hammond MS, Rachel L. Ehrlich MS, Azad Ahmed PhD, Bhaswati Sen PhD, Garth D. Ehrlich PhD, Joshua Chang Mell PhD

Poster # 93

Haemophilus influenzae is a highly diverse human-restricted bacterium which colonizes the nasopharynx as a commensal but also causes mucosal and invasive diseases. Cells in metabolically dormant biofilms tolerate antibiotic treatments and evade immune responses, which can contribute to persistent or recurrent infections. Because clinical isolates are genetically diverse and vary in many traits including biofilm formation, we sought to identify and characterize a small set of maximally diverse strains to systematically measure natural variation in biofilm development and accompanying changes in global gene expression. From a curated set of 1618 genomes, we used a "greedy algorithm" to find 12 phylogenetically dispersed strains that contained all accessory genes found at >10% frequency (n=966 genes). Phenotypic assays found high variation among strains in planktonic and biofilm growth. To characterize shared and divergent transcriptional differences, RNA sequencing was performed for all 12 strains in 5 conditions in triplicate. Notably, relative RNA abundances from core genes varied widely among strains, even when grown in the same condition. As expected, in static biofilm cultures, all strains showed repression of RNAs encoding translational machinery and induction of those involved in alternative carbon source utilization. However, RNA abundance levels varied depending on strain, condition, and their combination. Results are being analyzed to identify core and accessory gene expression patterns associated with biofilm phenotypes. Identifying conserved transcriptional signatures could provide in vivo biomarkers, whereas diverged patterns correlated with variation among strains could provide new mechanistic insights.

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