Ankyrin‐repeat proteins from sponge symbionts modulate amoebal phagocytosis

Abstract

Bacteria-eukaryote symbiosis occurs in all stages of evolution, from simple amoebae to mammals, and from facultative to obligate associations. Sponges are ancient metazoans that form intimate symbiotic interactions with complex communities of bacteria. The basic nutritional requirements of the sponge are in part satisfied by the phagocytosis of bacterial food particles from the surrounding water. How bacterial symbionts, which are permanently associated with the sponge, survive in the presence of phagocytic cells is largely unknown. Here, we present the discovery of a genomic fragment from an uncultured gamma-proteobacterial sponge symbiont that encodes for four proteins, whose closest known relatives are found in a sponge genome. Through recombinant approaches, we show that these four eukaryotic-like, ankyrin-repeat proteins (ARP) when expressed in Eschericha coli can modulate phagocytosis of amoebal cells and lead to accumulation of bacteria in the phagosome. Mechanistically, two ARPs appear to interfere with phagosome development in a similar way to reduced vacuole acidification, by blocking the fusion of the early phagosome with the lysosome and its digestive enzymes. Our results show that ARP from sponge symbionts can function to interfere with phagocytosis, and we postulate that this might be one mechanism by which symbionts can escape digestion in a sponge host.

The Holo-Transcriptome of a Calcified Early Branching Metazoan

“…These classes of proteins have been found in various facultative and obligate symbionts, as well as in intracellular pathogens and are thought to play a role in host microbe interactions by interfering with eukaryotic protein-protein interactions. For example, recent work provides evidence that ANK proteins of an uncultured gamma-proteobacterial sponge symbiont can interfere with phagocytosis which could provide a mechanism for bacteria to avoid digestion by their host (Nguyen et al, 2013). Vaceletia sp.…”

Ontogenetic Changes in the Bacterial Symbiont Community of the Tropical Demosponge Amphimedon queenslandica: Metamorphosis Is a New Beginning

“…ANK-repeat proteins (ARPs) have been identified in abundance in the genomes of multiple sponge-associated bacteria (Liu et al, 2010;Thomas et al, 2010;Siegl et al, 2011;Fan et al, 2012;Hentschel et al, 2012;Tian et al, 2014;Alex and Antunes, 2015;Burgsdorf et al, 2015b;Britstein et al, 2016), including in the most dominant core symbiont of A. queenslandica, OTU 1, although not in OTU 4 (Gauthier et al, 2016). ARPs from bacterial symbionts have been experimentally shown to influence sponge-bacterial interactions, specifically via interfering with phagocytosis as a possible mechanism to escape digestion in a sponge host (Nguyen et al, 2014). Together, these findings lead us to suggest that the ANK-and TPR-containing proteins upregulated in Cluster 1 might well be important in mediating sponge-bacterial crosstalk through larval settlement and metamorphosis because they could directly interact with symbiont proteins containing the same domains.…”

Deciphering the genomic toolkit underlying animal-bacteria interactions – insights through the demosponge Amphimedon queenslandica

“…In both these studies, it was observed that a significantly greater number of nonsymbiont bacteria were removed from the water column by the sponges than the symbiont bacteria (Wilkinson, et al 1984;Wehrl, et al 2007). Two mechanisms were thus hypothesised to explain this discriminatory treatment of symbiont and non-symbiont bacteria (Wilkinson, et al 1984;Wehrl, et al 2007;Nguyen, et al 2013). First, the sponge host does not recognise its symbiont bacteria as food and deliberately avoids taking them up for digestion.…”

“…Alternatively, symbiont bacteria deploy extracellular masking factors to avoid being trapped and phagocytosed. In an innovative experiment, Nguyen, et al (2013) examined the second hypothesis using E. coli expressing eukaryotic-like proteins -which could function as masking factors -found in the genome of sponge symbiont bacteria. As sponge cells remain uncultivable, the authors fed the E. coli to amoebae, and observed that bacteria expressing the eukaryotic-like proteins were able to modulate phagocytosis, ultimately leading to the accumulation of bacterial cells in the phagosomes of the amoebae (Nguyen, et al 2013).…”

“…In an innovative experiment, Nguyen, et al (2013) examined the second hypothesis using E. coli expressing eukaryotic-like proteins -which could function as masking factors -found in the genome of sponge symbiont bacteria. As sponge cells remain uncultivable, the authors fed the E. coli to amoebae, and observed that bacteria expressing the eukaryotic-like proteins were able to modulate phagocytosis, ultimately leading to the accumulation of bacterial cells in the phagosomes of the amoebae (Nguyen, et al 2013). Although, these findings may not be directly translatable to sponges, eukaryotic like-proteins are abundant in sponge symbiont bacterial genomes, which suggests they could play an important role in sponge-bacterial interactions (Fan, et al 2012;Gauthier, et al 2016).…”