Helicobacter pylori ATCC43504 responds chemotactically to aspartic acid and serine, but not to arginine, nor to sodium bicarbonate. In contrast, H. pylori ATCC700392 (strain 26695) shows chemotaxis to all four attractants. Open reading frame HP0099 from H. pylori 26695 is predicted to encode one of three methyl-accepting chemotaxis receptor proteins (MCPs). When Escherichia coli is transformed with a plasmid carrying HP0099 from strain 26695, the recombinants acquire chemotaxis to arginine, bicarbonate, and urea. In H. pylori 43504, the HP0099 gene is interrupted with a mini-IS605 insertion, which accounts for its inability to recognize arginine and bicarbonate as attractants. Together, these results argue that the H. pylori HP0099 gene encodes an MCP for arginine and bicarbonate.

To determine the existence of an acid stress response in Helicobacter pylori the global changes in the proteins synthesized by the bacterium when subjected to an acid stress were studied. H. pylori ATCC43504 previously adapted to pH 7 did not show an acid stress response as detected by the two-dimensional electrophoretic pattern of 35S-labeled proteins when incubated at pH 3. This was probably due to the neutralization of the external medium by the action of urease. However, H. pylori DW504UreI-negative, a mutant strain unable to transport urea into the cell, showed a large number of proteins changed, as is typical in an acid stress response. Some of these proteins were identified by N-terminal sequencing.

Based on amino acid sequence similarities between the methylated elongation factor EF-Tu from Escherichia coli and the EF-Tu from Euglena gracilis chloroplast, we predicted that the latter could also be methylated in the presence of an appropriate methyltransferase. We found that, as reported for the eubacterial homologous protein, the organellar factor could be methylated in vivo and in vitro to yield monomethyllysine.

Based on amino acid sequence similarities between the methylated elongation factor EF‐Tu from Escherichia coli and the EF‐Tu from Euglena gracilis chloroplast, we predicted that the latter could also be methylated in the presence of an appropriate methyltransferase. We found that, as reported for the eubacterial homologous protein, the organellar factor could be methylated in vivo and in vitro to yield monothyllysine.