ABSTRACT
The two-component system DesK-DesR regulates the synthesis of unsaturated fatty acids in the soil bacteria Bacillus subtilis. This system is activated at low temperature and maintains membrane lipid fluidity upon temperature variations. Here, we found that DesK-the transmembrane histidine kinase-also responds to pH and studied the mechanism of pH sensing. We propose that a helix linking the transmembrane region with the cytoplasmic catalytic domain is involved in pH sensing. This helix contains several glutamate, lysine, and arginine residues At neutral pH, the linker forms an alpha helix that is stabilized by hydrogen bonds in the i, i + 4 register and thus favors the kinase state. At low pH, protonation of glutamate residues breaks salt bridges, which results in helix destabilization and interruption of signaling. This mechanism inhibits unsaturated fatty acid synthesis and rigidifies the membrane when Bacillus grows in acidic conditions.
Subject(s)
Bacillus subtilis/enzymology , Histidine Kinase/chemistry , Histidine Kinase/metabolism , Bacterial Proteins/chemistry , Bacterial Proteins/metabolism , Histidine Kinase/genetics , Hydrogen Bonding , Hydrogen-Ion Concentration , Models, Molecular , Mutation , Protein Domains , Protein Stability , Protein Structure, Secondary , Signal TransductionABSTRACT
Determining an accurate count of intestinal bacteria from Caenorhabditis elegans is one critical way to assess colonization proficiency by a given bacteria. This can be accomplished by culturing appropriate dilutions of worm gut bacteria on selective or differential agarized media. Because of the high concentration of bacteria in gut worm, dilution is necessary before plating onto growth media. Serial dilutions can reduce the concentration of the original intestinal sample to levels low enough for single colonies to be grown on media plates, allowing for the calculation of the initial counts of bacteria in the intestinal sample.
ABSTRACT
The cell-to-cell communication and division of labour that occurs inside a beneficial biofilm produce significant differences in gene expression compared with the gene expression pattern of cells grew under planktonic conditions. In this sense, the levels of NO (nitric oxide) and CSF (Competence Sporulation Stimulating Factor) produced in Bacillus subtilis cultures have been measured only under planktonic growth conditions. We sought to determine whether NO and/or CSF production is affected in B. subtilis cells that develop as a biofilm. To measure the production levels of the two prolongevity molecules, we grew B. subtilis cells under planktonic and biofilm supporting condition.