Studying the role of PLLs, the family of lectins produced by Photorhabdus sp., the bacterial symbiont of entomopathogenic nematodes
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| Year of publication | 2022 |
| Type | Conference abstract |
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| Description | Entomopathogenic nematodes are known for efficiently killing insect hosts and their symbiotic relationship with bacteria of the genus Photorhabdus and Xenorhabdus. Both nematodes and symbiotic bacteria produce a variety of bioactive molecules that inhibit the host immune system, digest its tissues, and transform them into the source of nutrients for developing nematodes and bacteria. Our research focused on lectins produced by P. laumondii, formerly classified as P. luminescens subsp. laumondii, and their role in the complex life cycle of this bacterium. The family of PLLs comprises five identified and closely related proteins with fucose-binding activity and an unknown role in the life of Photorhabdus bacteria. These lectins were structurally characterised and prepared in recombinant forms, enabling us to study their biological activity. In general, lectins can participate in three main stages of nematobacterial infection: i) they can help to overwhelm host defences and kill it; i) they can promote the growth of nematode symbionts; or iii) they can be used to harbour Photorhabdus in its nematode vector. Our current results suggest that lectins from the PLL family are not produced to primarily support nematode growth and development in later stages of nematobacterial infections since they do not mediate a biofilm formation by bacterial cells. The lectins were also not observed to bind to the surface of nematodes, except of the slight affinity to the surface of nematode eggs. However, it remains to be clarified whether they bind to the internal tissues of nematodes and support their growth and development during symbiosis. On the other hand, the lectins from the PLL family were found to interfere with the host immune system suggesting that they participate in overcoming host defences. Some members of this family were shown to activate the insect phenoloxidase system, possibly leading to an exhaustion of this immune response within the initial stage of infection. Interestingly, they were shown to impair the production of reactive oxygen species (ROS) in human blood cells, although P. laumondii is not a human pathogen, suggesting its possible role in the inhibition of phagocytosis. It is of note that PLL is a homologue of PHL, the lectin produced by the human pathogen P. asymbiotica, which also has an inhibitory effect on ROS production by human blood cells. Whether the PLLs modulate the oxidative response in insect hosts and by which mechanisms are some of our current research questions. The reason why bacteria of the genera Photorhabdus invest in producing a number of closely related lectins can help us understand the regulation of its complex life cycle and discover novel mechanisms underlying their virulence. |
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