Expression of the quorum-sensing regulatory protein LasR is strongly affected by iron and oxygen concentrations in cultures of Pseudomonas aeruginosa irrespective of cell density

Abstract

Expression of the quorum-sensing regulatory protein LasR is strongly affected by iron and oxygen concentrations in cultures of Pseudomonas aeruginosa irrespective of cell density The expression of the transcriptional regulatory protein LasR, a main component of the quorum-sensing (QS) system in Pseudomonas aeruginosa, was recently found to be sensitive to several environmental factors in addition to its dependency on cell density. However, the inherent effects of the different factors have seldom been separately demonstrated due to concurrent changes of culture conditions in typical experimental settings. Furthermore, the interplays of the different factors are unknown. In this work, the effects and interplay of iron concentration and dissolved oxygen tension (pO 2 ) on the expression of lasR in P. aeruginosa were studied in defined growth media with varied iron concentration and pO 2 values in computer-controlled batch and continuous cultures. b-Galactosidase activity in a recombinant P. aeruginosa PAO1 (NCCB 2452) strain with a lasRp-lacZ fusion was used as a reporter for lasR expression. In batch culture with a constant pO 2 <10 % air saturation, a strong correlation between the exhaustion of iron and the increase of lasR expression was observed. In continuous culture with nearly constant cell density but varied pO 2 values, lasR expression generally increased with increasing oxidative stress with the exception of growth under O 2 -limited conditions (pO 2 <0 %). Under O 2 limitation, the expression of lasR strongly depended on the concentration of iron. It showed a nearly twofold increase in cells grown under iron deprivation in comparison with cells grown in iron-replete conditions and reached the expression level seen at high oxidative stress. A preliminary proteomic analysis was carried out for extracellular proteins in samples from batch cultures grown under different iron concentrations. Several of the extracellular proteins (e.g. AprA, LasB, PrpL) which were up-regulated under iron-limited conditions were found to be QS regulated proteins. Thus, this study clearly shows the links between QS and genes involved in iron and oxygen regulation in P. aeruginosa. INTRODUCTIONPseudomonas aeruginosa, a Gram-negative opportunistic human pathogen, is often found in nosocomial infections. In particular, it can cause chronic pulmonary infection of cystic fibrosis patients, leading to a high mortality rate due to the formation of virulence factors and the inappropriate host response (Hybiske et al., 2004;Wolfgang et al., 2004;Lyczak et al., 2002). In P. aeruginosa, the formation of numerous virulence factors is controlled to a large extent by a mechanism called quorum sensing (QS) (Fuqua & Greenberg, 1998;Wagner et al., 2003;Schuster et al., 2003;Hentzer et al., 2003;Juhas et al., 2004). Two major genetic components of QS, the las and rhl systems, have been identified in P. aeruginosa. The las system consists of LasR, a transcriptional regulatory protein, and LasI, the autoinducer synthase that controls the producti...

The Pseudomonas aeruginosa oxidative stress regulator OxyR influences production of pyocyanin and rhamnolipids: protective role of pyocyanin

“…Quorum sensing is mainly dependent on cell density. However, it has been demonstrated that quorum sensing is not only cell-densitydependent, but is also influenced by the presence of iron and/or oxygen (Bollinger et al, 2001;Kim et al, 2005). This could explain the observations in our study related to pyoverdine utilization and growth in the presence of oxidizing compounds, which was possible only at high inoculum sizes (Vinckx et al, 2008).…”

RhlR Expression inPseudomonas aeruginosaIs Modulated by thePseudomonasQuinolone Signal via PhoB-Dependent and -Independent Pathways

“…However, the production of these secondary metabolites also seems to be dependent on environmental cues (3,62). A link between QS and iron homeostasis was suggested previously (5,11,21,24,25,52,60). Moreover, PQS was shown to exhibit an iron-chelating activity, and PQS-dependent rhlR induction seems to be at least in part a consequence of iron depletion (6).…”

Characterization of protease IV expression in Pseudomonas aeruginosa clinical isolates

“…Controlled expression of several key P. aeruginosa virulence factors, including elastase (lasB) (Pearson et al, 1997), exotoxin A , type II secretory pathway proteins (xcp) (Chapon-Hervé et al, 1997) and pyoverdine (Kim et al, 2005;Stintzi et al, 1998) are mediated by population density bio-sensor mechanisms, a process known as quorum sensing. P. aeruginosa has two quorum-sensing systems, the Las and Rhl systems, each influencing the expression of a range of virulence factors (Passador et al, 1993;Pearson et al, 1994).…”