This research was supported by the South Transdanubian Regional Knowledge Centre (RET-08/2005, OMFB-00846/2005) and Iparjog 08 (NKTH IPARJOG-08-1-2009-0026). “
“Vibrio fischeri induces both
anaerobic respiration and bioluminescence during symbiotic infection. In many bacteria, the oxygen-sensitive regulator FNR activates anaerobic respiration, and a preliminary study using the light-generating lux genes from V. fischeri MJ1 cloned in Escherichia coli suggested that FNR stimulates bioluminescence. To test for FNR-mediated regulation of bioluminescence and anaerobic respiration in V. fischeri, we generated fnr mutants of V. fischeri strains MJ1 and ES114. In both strains, FNR was required for normal fumarate- and nitrate-dependent find more respiration. However, contrary to the report in transgenic E. coli, FNR mediated the repression of lux. ArcA represses bioluminescence, and ParcA-lacZ reporters showed reduced expression in fnr mutants, suggesting a possible indirect effect of FNR on bioluminescence via arcA. Finally, the fnr mutant of ES114 was not impaired in colonization of its host squid, Euprymna scolopes. This study extends the characterization
of FNR to the Vibrionaceae and underscores the importance of studying lux regulation in its native background. Vibrio fischeri is a model for investigations of bioluminescence and mutualistic symbioses, two fields connected by the importance of oxygen. O2 is Selleck ABT199 a substrate for the luminescence-producing
enzyme luciferase, and luciferase may benefit V. fischeri by generating Pregnenolone a more reduced environment in or near cells (Visick et al., 2000; Timmins et al., 2001). Reduction of O2 could be especially advantageous for this facultative anaerobe when it is colonizing animal tissue and may minimize the host’s ability to generate reactive oxygen species (Visick et al., 2000). Luminescence emanating from bacteria colonizing the symbiotic light organ of the host indicates that O2 is present; however, evidence suggests that luciferase is O2 limited in this environment (Boettcher et al., 1996) despite its high affinity (Km∼35 nM) for O2 (Bourgois et al., 2001). Moreover, anaerobic respiration is apparently induced in symbiotic V. fischeri (Proctor & Gunsalus, 2000), consistent with the idea that [O2] is low in the light organ. One regulator that might control anaerobic respiration and luminescence in response to [O2] is FNR (so named for its role in fumarate and nitrate reduction). FNR regulates genes during the switch between aerobic and anaerobic growth in Escherichia coli and other bacteria, and it often activates genes responsible for anaerobic respiration (Browning et al., 2002; Reents et al., 2006; Fink et al., 2007).