Chemotaxis mediated by NarX–FrzCD chimeras and nonadapting repellent responses in Myxococcus xanthus

Abstract

SummaryMyxococcus xanthus requires gliding motility for swarming and fruiting body formation. It uses the Frz chemosensory pathway to regulate cell reversals. FrzCD is a cytoplasmic chemoreceptor required for sensing effectors for this pathway. NarX is a transmembrane sensor for nitrate from Escherichia coli. In this study, two NarX-FrzCD chimeras were constructed to investigate M. xanthus chemotaxis: NazDF contains the N-terminal sensory module of NarX fused to the C-terminal signalling domain of FrzCD; NazDR is similar except that it contains a G51R mutation in the NarX domain known to reverse the signalling output of a NarX-Tar chimera to nitrate. We report that while nitrate had no effect on the wild type, it decreased the reversal frequency of M. xanthus expressing NazDF and increased that of M. xanthus expressing NazDR. These results show that directional motility in M. xanthus can be regulated independently of cellular metabolism and physiology. Surprisingly, the NazDR strain failed to adapt to nitrate in temporal assays as did the wild type to known repellents. The lack of temporal adaptation to negative stimuli appears to be a general feature in M. xanthus chemotaxis. Thus, the appearance of biased movements by M. xanthus in repellent gradients is likely due to the inhibition of net translocation by repellents.

Predataxis behavior inMyxococcus xanthus

“…Three, several chemical effectors on M. xanthus movement have been identified. Chemorepellents, such as isoamyl alcohol, cause individual M. xanthus cells to hyperreverse (34,35). Chemoattractants such as phosphatidyl ethanolamine (PE) derivatives with specific fatty acid side chains can elicit a positive chemotaxis response and cause individual cells to inhibit reversals (32,36).…”

DifA, a Methyl-Accepting Chemoreceptor Protein-Like Sensory Protein, Uses a Novel Signaling Mechanism to Regulate Exopolysaccharide Production inMyxococcus xanthus

“…Cellular fractionation and immunoblotting. DifA membrane localization was examined by a fractionation procedure similar to that described previously (33,46). Cultures were grown in CYE to approximately 4 ϫ 10 8 cells/ml.…”

The S Helix Mediates Signal Transmission as a HAMP Domain Coiled-Coil Extension in the NarX Nitrate Sensor fromEscherichia coliK-12

“…The second TM ␣-helix connects to the HAMP domain. Hybrid proteins in which the NarX transmembrane signaling module regulates the kinase control modules of the MCPs Tar, DifA, and FrzCD demonstrate that NarX and MCPs share a mechanism for transmembrane signaling (73,74,81,82).…”