An ECF41 Family σ Factor Controls Motility and Biogenesis of Lateral Flagella in Azospirillum brasilense Sp245

ECF41 is a large family of bacterial extracytoplasmic function (ECF) o -factors. Their role in bacterial physiology or behavior, however, is not known. One of the 10 ECF o-factors encoded in the genome of Azospirillum brasilense Sp245, RpoE10, exhibits features characteristic of the typical ECF41-type o-factors. Inactiva-tion of rpoE10 in A. brasilense Sp245 led to an increase in motility that could be com-plemented by the expression of rpoE10. By comparing the number of lateral flagella, transcriptome, and proteome of A. brasilense Sp245 with those of its rpoE10::km mutant, we show here that this ECF41-type o-factor is involved in the negative regulation of swimming motility and biogenesis of lateral flagella of A. brasilense Sp245. The genome of A. brasilense Sp245 also encodes two OmpR-type regulators (LafR1 and LafR2) and three flagellins, including Laf1, the major flagellin of lateral flagella. Elevated levels of laf1 transcripts and Laf1 protein in the rpoE10::km mutant indicated that RpoE10 nega-tively regulates the expression of Laf1. The elevated level of LafR1 in the rpoE10::km mu-tant indicated that LafR1 is also negatively regulated by RpoE10. The loss of motility and Laf1 in the lafR1::km mutant, complemented by lafR1 expression, showed that LafR1 is a positive regulator of Laf1 and motility in A. brasilense. In addition, upregulation of laf1:: lacZ and lafR1::lacZ fusions by RpoE10 and downregulation of the laf1::lacZ fusion by LafR1 suggest that RpoE10 negatively regulates swimming motility and the expression of LafR1 and Laf1. However, LafR1 positively regulates the swimming motility and Laf1 expression. p IMPORTANCE Among extracytoplasmic function (ECF) o-factors, ECF41-type o- fac-tors are unique due to the presence of a large C-terminal extension in place of a cognate anti -o-factor, which regulates their activity. Despite their wide distribution and abundance in bacterial genomes, their physiological or behavioral roles are not known. We show here an indirect negative role of an ECF41-type of o-factor in the expression of lateral flagellar genes and motility in A. brasilense. This study suggests that the motility of A. brasilense might be controlled by a regulatory cascade involv-ing RpoE10, an unknown repressor, LafR1, and lateral flagellar genes, including that encoding Laf1.