Wolbachia endosymbionts subvert the endoplasmic reticulum to acquire host membranes without triggering ER stress

Abstract

The reproductive parasite Wolbachia are the most common endosymbionts on earth, present in a plethora of arthropod species. They have been introduced into mosquitos to successfully prevent the spread of vector-borne diseases, yet the strategies of host cell subversion underlying their obligate intracellular lifestyle remain to be explored in depth in order to gain insights into the mechanisms of pathogen-blocking. Like some other intracellular bacteria, Wolbachia reside in a host-derived vacuole in order to replicate and escape the immune surveillance. Using here the pathogen-blocking Wolbachia strain from Drosophila melanogaster, introduced into two different Drosophila cell lines, we show that Wolbachia subvert the endoplasmic reticulum to acquire their vacuolar membrane and colonize the host cell at high density. Wolbachia redistribute the endoplasmic reticulum to increase contact sites, and time lapse experiments reveal tight coupled dynamics suggesting important signalling events or nutrient uptake. They however do not affect the tubular or cisternal morphologies. A fraction of endoplasmic reticulum becomes clustered, allowing the endosymbionts to reside in between the endoplasmic reticulum and the Golgi apparatus, possibly modulating the traffic between these two organelles. Gene expression analyses and immunostaining studies suggest that Wolbachia achieve persistent infections at very high titers without triggering endoplasmic reticulum stress or enhanced ERAD-driven proteolysis, suggesting that amino acid salvage is achieved through modulation of other signalling pathways.Author summaryWolbachia are a genus of intracellular bacteria living in symbiosis with millions of arthropod species. They have the ability to block the transmission of arboviruses when introduced into mosquito vectors, by interfering with the cellular resources exploited by these viruses. Despite the biomedical interest of this symbiosis, little is known about the mechanisms by which Wolbachia survive and replicate in the host cell. We show here that the membrane composing the Wolbachia vacuole is acquired from the endoplasmic reticulum, a central organelle required for protein and lipid synthesis, and from which originates a vesicular trafficking toward the Golgi apparatus and the secretory pathway. Wolbachia modify the distribution of this organelle to increase their interactions with this source of membrane and likely of nutrients as well. In contrast to some intracellular pathogenic bacteria, the effect of Wolbachia on the cell homeostasis does not induce a stress on the endoplasmic reticulum. One of the consequences of such a stress would be an increased proteolysis used to relieve the cell from an excess of misfolded proteins. Incidentally, this shows that Wolbachia do not acquire amino acids from the host cell through this strategy.

Deep data mining reveals variable abundance and distribution of microbial reproductive manipulators within and among diverse host species

“…One of the most strongly associated SNPs is found in a gene associated with the endoplasmic reticulum (ER) membrane (XBP1) [69]. Consistent with this functional prediction, a recent study on a wMel-infected D. melanogaster cell line found that Wolbachia resides within ER-derived membrane near and within the ER itself [70]. Modifying this membrane might therefore enable the host to impact Wolbachia titer on the cellular level.…”

The Association of Wolbachia on the Gene Expression in Drosophila Adult Testis

“…Wolbachia and its host have a long history of co-evolution, and the interaction between both parters is very complex, which has not been clearly clari ed so far [30]. Wolbachia is mainly located in the insect host reproductive system [26], including female ovary and male testis which makes them good materials for studying Wolbachia-host interaction. Previous results based on the transcriptomic data of the testis tissue of the third instar larvae of Drosophila have shown that Wolbachia infection can affect the expression of genes related to spermatogenesis and thus may induce CI [27].…”

“…Wolbachia is mainly localized in the reproductive tissues of host [26], which is a good material for studying the interaction between Wolbachia and host. Previous studies have showed that Wolbachia affects the early spermatogenesis process [27].…”

Trends in symbiont-induced host cellular differentiation

“…Thus, Wolbachia may alter host protein synthesis as well as ubiquitination-mediated proteolysis to obtain amino acids as their primary source of nutrition. Consistent with using host protein synthesis and degradation pathways for its own nutrition, Wolbachia induces the reorganization of host cell endoplasmic reticulum (ER) and surrounds itself with ER-derived membrane (Fattouh et al 2019), creating a niche near translation and proteolysis machinery. Given that ubiquitination and protein turnover is involved in host cellular differentiation (Kimata 2019), Wolbachia may have co-opted its nutrition-provisioning genes for host manipulation.…”

“…Reciprocal control over host/symbiont processes works through endogenous and mimicked mechanisms (dashed lines). B) An example of how host-symbiont interactions (straight arrows) function with endogenous mechanisms (curved arrows) to cause phenotypic changes in cell state, such as symbiont-induced formation of an intracellular replicative niche derived from the endoplasmic reticulum membrane, as has been reported for Wolbachia (Fattouh et al 2019) and a variety of other symbionts (see text). The theory of bacterial endosymbiont genome evolution posits that upon host restriction, bacterial chromosomes begin degrading due to the accumulation of deleterious mutations and the subsequent deletion of pseudogenized regions.…”