Iron regulation of swarmer cell differentiation of Vibrio parahaemolyticus

Vibrio parahaemolyticus has two distinct cell types, the swimmer cell and the swarmer cell, adapted for locomotion in different circumstances. The swimmer cell, produced when the bacterium is grown in liquid media, is a short rod with a single sheathed polar flagellum. The swarmer cell, produced when V. parahaemolyticus is grown on solidified media, is greatly elongated and synthesizes, in addition to the polar flagellum, numerous unsheathed lateral flagella which are responsible for translocation over surfaces. We are interested in understanding how this bacterium differentiates in response to contact with surfaces and have determined in earlier work that the polar flagellum acts as a tactile sensor which controls transcription of genes (laf) encoding the swarmer cell phenotype. Surface recognition involves sensing of forces that obstruct movement of the polar flagellum. In this report we show that a second signal, iron limitation, is also required for swarmer cell differentiation. Production of lateral flagella occurred only when polar flagellar function was perturbed and iron-limiting growth conditions were imposed. The same conditions were required to induce light production in strains of V. parahaemolyticus in which a laf gene was transcriptionally fused to the lux operon encoding the enzymes for bioluminescence. The lafA gene encoding the lateral flagellin subunit was cloned and used in Northern (RNA) blot measurements. Examination of mRNA levels revealed that transcription of lafA is dependent on growth in iron-depleted media. The control of differentiation by multiple environmental stimuli is discussed.