Acts as an anti-FlhC(2)FlhD(4) factor by binding to FlhD, decreasing its ability to bind DNA, and thus negatively regulates expression of flagellar class II operons, decreasing motility in nutrient-poor medium. Positively regulates expression of the multicellular rdar morphotype behavior, its major regulator CsgD and suppresses motility. Regulates the rdar morphotype and motility indirectly by affecting the expression of the c-di-GMP-dependent phosphodiesterases YciZ and YhjH. Required for resistance to host phagocyte oxidase. Suppresses killing of macrophages, while promoting resistance to hydrogen peroxide. Data regarding c-di-GMP is controversial; suppresses bacterial c-di-GMP levels (PubMed:15882417) but neither synthesizes nor degrades c-di-GMP (PubMed:19376870). Interacts with FlhD in the FlhC(2)FlhD(4) heterohexamer, inhibiting its ability to activate transcription. Decreased bacterial resistance to hydrogen peroxide and accelerated bacterial killing of macrophages, increased levels of c-di-GMP (PubMed:15882417). Down-regulation of rdar morphology, 50% reduction in CsgD expression, cellulose and curli fimbriae, increased swimming and swarming. Decrease in c-di-GMP levels (PubMed:19376870). The multicellular rdar morphotype is characterized by the expression of the adhesive extracellular matrix components cellulose and curli fimbriae. Belongs to the YdiV family. Has been proposed to be involved in c-di-GMP turnover (PubMed:15882417), but also not be involved in its turnover (PubMed:19376870). Mutagenesis of Glu-29 in the EAL domain suggests if this protein has c-di-GMP phosphdiesterase activity it is not involved in motility regulation (PubMed:21278297). Note that (PubMed:21278297) experiments were done in strain LT2, which is not a 14028 derivative.