Bacterial swarming: A biochemical time-resolved FTIR-ATR study of Proteus mirabilis swarm-cell differentiation

Fourier transform infrared spectroscopy was applied to the study of the dif ferentiation process undergone by Proteus mirabilis. This bacterium exhibit s a remarkable dimorphism, allowing the cells to migrate on a solid substra tum in a concerted manner yielding characteristic ring patterns. We perform ed an in situ noninvasive analysis of biochemical events occurring as veget ative cells differentiate into elongated, multinucleate, nonseptate, and hy perflagellated swarm cells. The major Findings arising from this study are (i) the real-time monitoring of flagellar filament assembly, (ii) the evide nce for de novo synthesis of qualitatively different lipopolysaccharides (L PS) and/or exopolysaccharides (EPS) constituting the slime into which bacte ria swarm, and (iii) the alteration in the membrane fatty acid composition with a concomitant 10 degreesC decrease in the gel/liquid crystal phase tra nsition resulting in an elevated membrane fluidity in swarm cells at the gr owth temperature. The time course of events shows that the EPS-LPS synthese s are synchronous with membrane fatty acid alterations and occur about 1 h before massive flagellar filament assembly is detected. This study not only provided a time sketch of biochemical events involved in the differentiati on process but also led to the identification of the major spectral markers of both vegetative and swarm cells. This identification will allow to reso lve the time-space structure of P. mirabilis colonies by using infrared mic roscopy.