AIMSTo examine flagella role and cell motility in adhesion of Achromobacter piechaudii to chalk.METHODS AND RESULTSTransmission electron microscopy revealed that stationary cells have thicker and longer flagella than logarithmic cells. SDS-PAGE analysis showed that flagellin was more abundant in stationary cells than logarithmic ones. Sonication or inhibition of flagellin synthesis caused a 30% reduction in adhesion to chalk. Preincubation of chalk with flagella extracts reduced adhesion, by 50%. Three motility mutants were isolated. Mutants 94 and 153 were nonmotile, expressed normal levels of flagellin, have regular flagella and exhibited reduced adhesion. Mutant 208 expressed low levels of flagellin, no flagella and a spherical cell shape but with normal adhesion capacity.CONCLUSIONSMultiple cell surface factors affect the adhesion efficiency to chalk. Flagella per se through physical interaction and through cell motility contribute to the adhesion process. The adhesion behaviour of mutant 208 suggests that cell shape can compensate for flagellar removal and motility.SIGNIFICANCE AND IMPACT OF THE STUDYPhysiological status affects bacterial cell surface properties and hence adhesion efficiency to chalk. This interaction is essential to sustain biodegradation activities and thus, remediation of contaminated chalk aquifers.