pelD is required downstream of c-di-GMP for host specialization of Pseudomonas lurida

The bacterial second messenger c-di-GMP is known to influence the formation of biofilms and thereby persistence of pathogenic and beneficial bacteria in hosts. A previous evolution experiment with Pseudomonas lurida MYb11, occasional symbiont of the nematode Caenorhabditis elegans, led to the emergence of host-specialized variants with elevated intracellular c-di-GMP. Thus far, the molecular underpinnings of c-di-GMP-mediated host specialization were unknown in this symbiosis. Therefore, the current study aimed at identifying candidate molecular processes by combining transcriptomic and functional genetic analyses. We found that MYb11 host specialists differentially expressed genes related to attachment, motility and biofilm production, including pelD from the pel gene cluster. pelD deletion resulted in reduced intra-host competitive fitness, lower bacterial numbers in C. elegans and loss of biofilm biomass. Our results identify pelD as a previously unknown key modulator of beneficial symbiont-host associations that acts downstream of c-di-GMP. RNA-seq data of the wild type of P. lurida MYb11 and evolved P. lurida MYb11 with mutations in either wspE, wspF or rph from tryptic soy broth (liquid) and tryptic soy agar (colony). Five replicates each.