Our data suggests the Pl TT01 ΔexbD mutant strain is unable to grow in the insect implying that Pt K122 is better at scavenging iron in the insect. Although we have not investigated the BVD-523 reasons for this difference we have confirmed that, similar to what has been reported in other pathogens, TonB complex-mediated iron-uptake is critical for the virulence of Photorhabdus. Nutritional interactions are one

of the major driving forces in symbiotic associations https://www.selleckchem.com/products/Staurosporine.html [28–31] and our data suggests that iron is an important nutrient in Photorhabdus-Heterorhabditis interactions. During growth and development the nematodes feed on the bacterial biomass implying that this biomass must be able to satisfy all of the nematodes nutritional requirements, including the requirement for iron. We have previously shown that iron uptake in Pt K122

is required for the normal growth and development of Hd nematodes SIS3 ic50 [11]. Therefore the Pt K122 exbD::Km mutant was not able to support Hd growth and development but this defect could be rescued by the addition of Fe3+ to the media [11]. However, in contrast to this previous work, we have now shown that the exbD gene in Pl TT01 is not required for the normal growth and development of the Hb nematode. Cross-feeding experiments, where the Hb nematode was grown on Pt K122 and the Hd nematode was grown on Pl TT01, suggested that the nematode was responsible for this difference in iron dependency as the Hb nematode grew equally well on the Pt K122 exbD::Km mutant and the Pl TT01 exbD cAMP mutant. In addition, although the Hd nematode was observed to grow and develop on both Pl TT01 and the Pl TT01 exbD mutant, we did observe that the development of Hd IJ nematodes growing on the Pl TT01 exbD mutant was significantly delayed compared to Hb growing on the same bacteria (data not shown). This suggests

that the Hd nematode might be more sensitive to the presence of the exbD mutation (and therefore iron levels) in their symbiotic bacteria. Such differences in sensitivity to iron levels may be one of the driving forces in the evolution and diversification of the Photorhabdus-Heterorhabditis system. The FeoB protein is an inner membrane Fe2+ permease that requires the FeoA-dependent hydrolysis of GTP [21]. The Feo transporter is present in many bacteria and has been reported to have a role in the anaerobic-microaerophilic environment of the gastrointestinal tract of mammals. In this study we show that the FeoABC transporter has no apparent role in either the pathogenic or mutualistic life-styles of Photorhabdus. The yfeABCD operon (also found in Yersinia and annotated as sitABCD in Salmonella, Shigella and avian pathogenic Escherichia coli (APEC) and afeABCD in Actinobacillus) encodes an ATP-dependent divalent cation transporter with affinity for Fe2+ and Mn2+ [32–36].