Regulation of temporal expression of IHF in Legionella pneumophila
The Gram-negative bacillus Legionella pneumophila, possesses a distinct dimorphic life cycle that alternates between the replicative form (RF) and the infectious cyst-like form (CLF). It is proposed that this CLF, when inadvertently inhaled by an individual, manifests as an atypical pneumonia termed Legionnaires' disease. Studies elsewhere have determined that L. pneumophila IHF (LpIHF), a heterodimeric protein encoded by ihfα and ihfβ, plays a key role in the morphological differentiation into CLF. This study was undertaken to elucidate the regulation of LpIHF expression as well as the regulation of targeted genes associated with morphological differentiation by LpIHF. Through green fluorescent protein reporter assays and electrophoretic mobility shift assays, it was shown that both ihfα and ihfβ expression is negatively autoregulated by LpIHF and is positively activated by the L. pneumophila stationary sigma factor RpoS (LpRpoS). In addition, LpIHF positively regulates expression of the non-coding RNAs RsmY and RsmZ.