Helicobacter pylori Biofilm Involves a Multigene Stress-Biased Response, Including a Structural Role for Flagella

Helicobacter pylori has an impressive ability to persist chronically in the human stomach. Similar characteristics are associated with biofilm formation in other bacteria. The H. pylori biofilm process, however, is poorly understood. To gain insight into this mode of growth, we carried out comparative transcriptomic analysis between H. pylori biofilm and planktonic cells, using the mouse-colonizing strain SS1. Optimal biofilm formation was obtained with a low concentration of serum and 3 days of growth, conditions that caused both biofilm and planktonic cells to be ∼80% coccoid. Transcriptome sequencing (RNA-seq) analysis found that 8.18% of genes were differentially expressed between biofilm and planktonic cell transcriptomes. Biofilm-downregulated genes included those involved in metabolism and translation, suggesting these cells have low metabolic activity. Biofilm-upregulated genes included those whose products were predicted to be at the cell envelope, involved in regulating a stress response, and surprisingly, genes related to formation of the flagellar apparatus. Scanning electron microscopy visualized flagella that appeared to be a component of the biofilm matrix, supported by the observation that an aflagellated mutant displayed a less robust biofilm with no apparent filaments. We observed flagella in the biofilm matrix of additional H. pylori strains, supporting that flagellar use is widespread. Our data thus support a model in which H. pylori biofilm involves a multigene stress-biased response and that flagella play an important role in H. pylori biofilm formation.