Biologie und Vorklinische Medizin

Prof. Dr. Rüdiger Schmitt

Sinorhizobium meliloti
Volvox carteri

Chemotaxis of Rhizobia – Variations on a Theme


Molecular mechanisms governing chemotaxis and motility in the soil bacterium Sinorhizobium meliloti and related species differ from the well-studied taxis systems of enterobacteria by new features.

(i) In addition to seven transmembrane  receptors, S.meliloti has two cyto-plasmic receptor proteins, McpY  and IcpA, that probably monitor the metabolic state of the bacterial cell.

(ii) The tactic response is mediated by two response regulators, CheY1 and CheY2, but no phosphatase, CheZ.  The phosphorylated CheY2 (Che2-P)) is the dominant regulator of flagellar motor rotation by binding to the C-ring (FliM, whereas CheY1 assumes the role of a ‘sink’ for phosphate that is retro-transferred from CheY-P to the cognate kinase, CheA.  This phosphate shuttle from surplus CheY2-P to CheA to CheY1 is a new reaction that replaces the CheZ phosphatase.

(iii) S.meliloti flagella have a complex structure with helical ribbons that render the filaments rigid and unable to undergo polymorphic transitions from right- to lefthandedness. The flagella rotate only clockwise and their motor can increase and decrease rotary speed. Hence, swimming cells change their direction during slow-down, when one or more flagella rotate at different speeds and the flagellar bundle disintegrates. We have shown that certain charged amino acid residues at the stator (MotA) – rotor (FliG) interface are directly involved in the modulation of rotary motor speed.

A working model of the rotary flagellar motor has been proposed.


H. Riepl, T. Maurer, H.R. Kalbitzer, V.M. Meier, M. Haslbeck, R. Schmitt & B. Scharf (2008) Mol. Microbiol. 69, 1373-1384.

V.M. Meier, P. Muschler & B.E Scharf (2007) J.Bacteriol. 189, 1816-1826.

C. Rotter, S. Mühlbacher, D. Salamon, R. Schmitt & B. Scharf (2006) J. Bacteriol. 188, 6932-6942.

U. Attmannspacher, B. Scharf & R. Schmitt (2005) Mol.Microbiol. 56, 708-718.

H. Riepl, B. Scharf, R. Schmitt, H.R. Kalbitzer & T. Maurer (2004) J.Mol.Biol. 338, 287-297.

E. Eggenhofer, M. Haslbeck & B. Scharf (2004) Mol.Microbiol. 52, 701-712.

R. Schmitt (2003) Biophys. J. 85, 843-852.

R. Schmitt (2002) Microbiology 148, 627-631 (Review).

B. Scharf, (2002) J.Bacteriol. 184, 5979-5986.

B. Scharf, H. Schuster-Wolf-Bühring, R. Rachel & R. Schmitt (2001) J.  Bacteriol. 183, 5334-5342.

V.Sourjik, P.Muschler, B.Scharf & R. Schmitt (2000) J.Bacteriol. 182, 782-788.

J. Platzer, W. Sterr, M. Hausmann & R. Schmitt (1997) J.Bacteriol. 179, 6391-6399.

V. Sourjik, W. Sterr, J. Platzer, I. Bos, M. Haslbeck & R. Schmitt (1998) Gene 223, 283-290.

V. Sourjik & R. Schmitt (1998) Biochemistry 37, 2327-2335.

V. Sourjik & R. Schmitt (1996) Mol.Microbiol. 22, 427-436.

M. Greck, J. Platzer, V. Sourjik & R. Schmitt (1995) Mol. Microbiol. 15, 889-1000.

E. Pleier & R. Schmitt (1991) J.Bacteriol. 173, 337-346.

R.Götz & R. Schmitt (1987) J. Bacteriol. 169, 3146-3150.

Juli 2010