Combined cellular and proteomics approach suggests differential processing of a native and a foreign vibrio in the...

Phagocytosis is a conserved cellular mechanism for food uptake, defense, and animal-microbe interactions in metazoans. How the discrimination and subsequent processing of different microbes in marine invertebrates is facilitated remains largely unknown. Thereto, we combined a recently developed phagocytic assay with proteomics analysis to compare the phagocytic activity of the sponge Halichondria panicea upon encounter with the native Hal 281 (i.e., H. panicea isolate) and the foreign NJ 1 (i.e., Nematostella vectensis isolate) Vibrio. The sponge cell fraction was recovered after Vibrio exposure of 30 and 60 min and used for cellular (fluorescence-activated cell sorting and microscopy) and proteomics analyses. While the number of phagocytically active cells was similar between the isolates (P = 0.19), the distribution of vibrios over cell types differed (P = 0.02) over time, with the tendency for accumulation of NJ 1 in choanocyte-like cells compared to a shift of Hal 281 being incorporated from choanocyte-like to archaeocyte-like cells. Initially, both vibrios elicited a proteomic response related to bacterial infection and immunity (e.g., ADAM10, RAPTOR), followed by an increase of lysosomal and endocytic proteins (e.g., NPC2) after 60 min. The attenuation of the immune response and concomitant increase of vesicular trafficking in Hal 281 after 60 min corroborates cellular observations suggesting the fast transfer of Hal 281 from choanocyte-like cells to archaeocyte-like cells, compared to an accumulation of NJ 1 in the former. Subtle but distinct differences suggest strain-specific discrimination between the two tested vibrios and may indicate a degree of immune specificity in sponges.

Metazoans recognize and discriminate between different microbes. In marine invertebrates, the underlying mechanisms of microbial discrimination and immune specificity are, however, not well understood. Phagocytosis is a conserved cellular process from amoeba to humans that facilitates the ingestion and digestion of microbial cells and likely plays a role in this discrimination. To elucidate the molecular and cellular basis of this microbial discrimination, we examined the differential phagocytic processing of a native (i.e., sponge-isolated) and foreign (i.e., sea anemone-isolate) Vibrio in a marine sponge. Our findings revealed that both vibrios provoke an initial bacterial infection- and immune-related, followed by a lysosomal- and endocytic-related proteomic response. Nuanced differences in the cellular and molecular processing suggest a strain-specific discrimination between the two vibrios. This study investigates a mechanism for microbial discrimination in an early-divergent metazoan and may provide a valuable model for studying the evolution of immunity and its role in animal-microbe interactions.