FIG 4.

Roles of unique domains of A. brasilense strain Sp7 CheA1 in chemotaxis. (A) Chemotaxis of the ΔcheA1 mutant strain expressing CheA1 or truncated versions of this protein from a broad-host-range plasmid was analyzed in the soft agar plate assay supplemented with appropriate antibiotics. The chemotaxis of the wild-type strain Sp7 carrying an empty vector control [Sp7(pBBR)]; not shown) was similar to that of the ΔcheA1(pBBRCheA1) strain, and the average chemotaxis ring diameter was 30.2 ± 2.9 mm. The picture was taken at 48 h postinoculation. The average chemotaxis ring diameters obtained from three replicates are shown. (B) The temporal gradient assay for aerotaxis was used to measure transient increases in cell swimming speed upon switching free-swimming cells from an anaerobic atmosphere (nitrogen gas) to air. Each strain is identified, with the parental or variant protein it expresses from the broad-host-range vector in parentheses. *, statistically significant difference in the swimming speed between before and after switching to air (P < 0.05 by Student's t test).