Colour of heterorhabditis zealandica-infected-Galleria mellonella dependent on the Photorhabdus symbiont, with two new nematode-symbiotic associations reported

Bacterial symbionts associated with entomopathogenic nematodes (EPNs) play an important role in terms of the insecticidal properties of nematodes in pest control. Galleria mellonella larvae, shortly after being infected with three different strains of Heterorhabditis zealandica, which were isolated from South African soil, changed from pale white to steel grey-blue (blue), bright red, and yellow with a green tint (green), respectively. The genetic relatedness of the bacterial symbionts that were isolated from the three strains of H. zealandica was determined by means of comparing the 16S rRNA, recA, gyrB, dnaN, gltX and infB gene sequences. Subsequently, comparing the concatenated sequences revealed the presence of three distinct Photorhabdus species. The H. zealandica strain SF41, associated with Photorhabdus heterorhabditis, produced 'blue' G. mellonella larvae. The H. zealandica strain MJ2C, associated with Photorhabdus thracensis, yielded 'green' G. mellonella larvae, while the H. zealandica strain LLM associated with Photorhabdus laumondii subsp. laumondii yielded red larvae. The colour changes in G. mellonella larvae were found to have been instigated by a particular Photorhabdus species associated with H. zealandica. The red and 'green' phenotypes of G. mellonella larvae were found to represent new combinations of Heterorhabditis and Photorhabdus. In future studies, the colour of infected G. mellonella larvae needs to be reported as a phenotypic character, as it indicates the different bacterial species associated with the same nematode host, as shown in the case of H. zealandica.

Automated summary

Bacterial symbionts associated with entomopathogenic nematodes (EPNs) have a significant impact on the insecticidal properties of nematodes in pest control. In this study, different strains of Heterorhabditis zealandica infected Galleria mellonella larvae and induced color changes. The genetic relatedness of bacterial symbionts isolated from the three strains of H. zealandica was determined by comparing gene sequences. Three distinct Photorhabdus species were identified. The color changes in G. mellonella larvae were instigated by specific Photorhabdus species associated with H. zealandica. The red and "green" phenotypes represented new combinations of Heterorhabditis and Photorhabdus.