Control of bacterial motility by environmental factors in polarly flagellated and peritrichous bacteria isolated from Lake Baikal

Despite numerous studies on bacterial motility, little is known about the r egulation of this process by environmental factors in natural isolates. In this study we investigated the control of bacterial motility in response to environmental parameters in two strains isolated from the natural habitat of Lake Baikal. Morphological characterization, carbon source utilization, fermentation analysis, and sequence comparison of 16S rRNA genes showed tha t these strains belong to two distinct genera, i.e., Enterobacter and Pseud omonas; they were named strains 22 and Y1000, respectively. Both strains sw armed at 25 degreesC and remained motile at low temperatures (4 degreesC), especially the Pseudomonas strain, which further supports the psychrotrophi c characteristics of this strain. In contrast, a strong inhibition of motil ity was observed at above 30 degreesC and with a high NaCl concentration. T he existence of flagellar regulatory proteins FlhDC and FleQ was demonstrat ed in Enterobacter strain 22 and Pseudomonas strain Y1000, respectively, an d environmental conditions reduced the expression of the structural genes p otentially located at the first level in the flagellar cascade in both orga nisms. Finally, as in Enterobacter strain 22, a strong reduction in the tra nscription of the master regulatory gene fleQ was observed in Pseudomonas s train Y1000 in the presence of novobiocin, a DNA gyrase inhibitor, suggesti ng a link between DNA supercoiling and motility control by environmental fa ctors. Thus, striking similarities observed in the two organisms suggest th at these processes have evolved toward a similar regulatory mechanism in po larly flagellated and laterally flagellated (peritrichous) bacteria.