Host genotype-specific microbiota do not influence the susceptibility of D. magna to a bacterial pathogen

Abstract

Host-associated microbiota have been claimed to play a role in hosts’ responses to parasitic infections, often protecting the hosts from infection. We tested for such a role in the crustacean Daphnia and the parasitic bacterium Pasteuria ramosa, a widely used model system for host-parasite interactions. We first determined the infection phenotype (i.e., resistotype) of eight clonal D. magna genotypes against four strains of P. ramosa by attachment test, followed by 16 S rDNA amplicon sequencing to determine if their genotype or their parasite resistotype influences the composition of their microbiome. We then reciprocally transplanted the microbiota of two host genotypes with opposite resistotypes to four P. ramosa isolates, followed by a reassessment of their resistotype after transplantation. We found significant differences in microbiome composition and structure between Daphnia genotypes and between Daphnia resistotypes to specific P. ramosa strains. Reciprocal microbiota exchange or making the Daphnia hosts bacteria-free, however, did not influence the resistotypes of the hosts. Thus, in contrary to what has been observed in some taxa, our results suggest that D. magna susceptibility to P. ramosa is strongly dictated by the genetic differences of the hosts and is still dependent on Daphnia’s first line of immune defense against the esophageal attachment of P. ramosa, which appears to be uninfluenced by the host’s microbiota.

Variation in the Microbiota Associated with Daphnia magna Across Genotypes, Populations, and Temperature

“…They also serve as a bioindicator species for ecosystem health and, thus, are an important focus for research on the ecological impacts of global climate change. Research has shown that, as with other study systems, changes to microbial communities affect Daphnia fitness [5,6,26,40,41]. There is evidence from other systems that host genotype and environmental conditions may have an interactive effect on host microbiomes [1,7], and a recent study in D. magna provided the first report of such dynamics in this species [44].…”

Disparate effects of antibiotic-induced microbiome change and enhanced fitness in Daphnia magna

“…This also speaks for functional redundancy although additional studies would be required to show this. At the genus level, only Bosea and Galbitalea had significantly positive association with Daphnia growth and fecundity, whereas the association for Leadbetterella and Hydrogenophaga, which are commonly found in Daphnia [63], was negative. The Bradyrhizobiaceae (Bosea) and Microbacteriaceae (Galbitalea) are bio-degraders capable of producing hydrolytic enzymes such as chitinase, cellulase, glucanase, protease, etc.…”

An interaction between host and microbe genotypes determines colonization success of a key bumble bee gut microbiota member

“…; Sison‐Mangus et al. ). Such symbionts are facultative and experience a free‐living stage between hosts, making survival in both their host and external environment paramount.…”

“…The influence of these factors on the success of colonization also depends upon the route of microbe transmission between hosts (Bright and Bulgheresi 2010). Where symbionts are environmentally acquired, abiotic factors can serve as the primary driving force behind microbial colonization (Thursz et al 1999;Sison-Mangus et al 2018). Such symbionts are facultative and experience a free-living stage between hosts, making survival in both their host and external environment paramount.…”