Legionella pneumophila, an intracellular parasite of protozoa, possesses a distinct dimorphic life cycle that alternates between the vegetative replicative form and the resilient but highly infectious cyst form. Previously, temporally expressed heterodimeric integration host factor (IHF) was shown to be required for differentiation into the cyst form. However, the precise regulatory mechanisms controlling the expression of IHF have not been identified. Microplate kinetic assays with GFP reporter promoter fusion constructs in wild-type, ?ihf, ?rpoS and ?letA mutant strain backgrounds were employed to assess differences in expression levels of ihfA, ihfB, rsmY and rsmZ. Loss of IHF, RsmY and RsmZ expression in various mutant strain backgrounds was confirmed by quantitative PCR. Here we report that the stationary phase sigma factor RpoS is a positive regulator of IHF, whereas IHF appears to act as a positive autoregulator assisting RpoS. Bioinformatic analyses identified a set of IHF binding sites upstream of one RpoS binding site in the promoter region for both ihfA and ihfB. Recombinant IHF protein bound ihfA and ihfB promoter regions in vitro, confirming the functionality of these IHF binding sites that may assist in the bending of the promoter DNA to facilitate transcription activation of ihfA and ihfB by RpoS. Interestingly, the consensus binding site for IHF is very similar to that of the two-component response regulator LetA. LetA negatively regulates transcription of ihfA and ihfB, implying titrational regulatory control by LetA and IHF. Along with LetA, IHF was found to positively regulate expression of the non-coding regulatory RNAs RsmY and RsmZ responsible for the de-repression of CsrA-repressed transcripts associated with cyst formation, and coordinated post-exponential virulent phenotypes. Taken together, these observations indicate that IHF may have more of an integral role in the global regulatory system governing the transition from replicative to cyst forms than previously thought.
Diver-based Underwater Visual Censuses (UVCs), particularly transect-based surveys, are key tools in the study of coral reef fish ecology. These techniques, however, have inherent problems that make it difficult to collect accurate numerical data. One of these problems is the diver effect (defined as the reaction of fish to a diver). Although widely recognised, its effects have yet to be quantified and the extent of taxonomic variation remains to be determined. We therefore examined relative diver effects on a reef fish assemblage on the Great Barrier Reef. Using common UVC methods, the recorded abundance of seven reef fish groups were significantly affected by the ongoing presence of SCUBA divers. Overall, the diver effect resulted in a 52% decrease in the mean number of individuals recorded, with declines of up to 70% in individual families. Although the diver effect appears to be a significant problem, UVCs remain a useful approach for quantifying spatial and temporal variation in relative fish abundances, especially if using methods that minimise the exposure of fishes to divers. Fixed distance transects using tapes or lines deployed by a second diver (or GPS-calibrated timed swims) would appear to maximise fish counts and minimise diver effects.
The dynamic nature of coral reefs offers a rare opportunity to examine the response of ecosystems to disruption due to climate change. In 1998, the Great Barrier Reef experienced widespread coral bleaching and mortality. As a result, cryptobenthic fish assemblages underwent a dramatic phase-shift. Thirteen years, and up to 96 fish generations later, the cryptobenthic fish assemblage has not returned to its pre-bleach configuration. This is despite coral abundances returning to, or exceeding, pre-bleach values. The post-bleach fish assemblage exhibits no evidence of recovery. If these short-lived fish species are a model for their longer-lived counterparts, they suggest that (1) the full effects of the 1998 bleaching event on long-lived fish populations have yet to be seen, (2) it may take decades, or more, before recovery or regeneration of these long-lived species will begin, and (3) fish assemblages may not recover to their previous composition despite the return of corals.
Relationship violence is a common problem faced by adolescents in the United States. In general, adolescents are at higher risk for relationship victimization than adults (Silverman, Raj, Mucci, & Hathaway, 2001), and females between the ages of 16 and 24 years are at the highest risk of relationship victimization (Rennison, 2001). This study uses data from the 2007 Youth Risk Behavior Surveillance (YRBSS) System (or referred to as Youth Risk Behavior Survey [YRBS]; N = 11,781) of adolescents between the ages of 14 and 17 years to estimate two logistic regression models on the association between relationship violence and suicidal behaviors controlling for variables such as sexual assault and drug use. The findings indicated that victimized adolescents are at higher risk for planning and/or attempting suicide compared to nonvictimized adolescents. Implications for research and practice are explored.
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