Halide peroxidase in tissues that interact with bacteria in the host squidEuprymna scolopes

Abstract

An enzyme with similarities to myeloperoxidase, the antimicrobial halide peroxidase in mammalian neutrophils, occurs abundantly in the light organ tissue of Euprymna scolopes, a squid that maintains a beneficial association with the luminous bacterium Vibrio fischeri. Using three independent assays typically applied to the analysis of halide peroxidase enzymes, we directly compared the activity of the squid enzyme with that of human myeloperoxidase. One of these methods, the diethanolamine assay, confirmed that the squid peroxidase requires halide ions for its activity. The identification of a halide peroxidase in a cooperative bacterial association suggested that this type of enzyme can function not only to control pathogens, but also to modulate the interactions of host animals with their beneficial partners. To determine whether the squid peroxidase functions under both circumstances, we examined its distribution in a variety of host tissues, including those that typically interact with bacteria and those that do not. Tissues interacting with bacteria included those that have specific cooperative associations with bacteria (i.e., the light organ and accessory nidamental gland) and those that have transient nonspecific interactions with bacteria (i.e., the gills, which clear the cephalopod circulatory system of invading microorganisms). These bacteria-associated tissues were compared with the eye, digestive gland, white body, and ink-producing tissues, which do not typically interact directly with bacteria. Peroxidase enzyme assays, immunocytochemical localization, and DNA-RNA hybridizations showed that the halide-dependent peroxidase is consistently expressed in high concentration in tissues that interact bacteria. Elevated levels of the peroxidase were also found in the ink-producing tissues, which are known to have enzymatic pathways associated with antimicrobial activity. Taken together, these data suggest that the host uses a common biochemical response to the variety of types of associations that it forms with microorganisms.

The occurrence of chitin in the hemocytes of invertebrates

“…The position and size of CBP-positive compartments in E. scolopes hemocytes were consistent with their co-localization within acidic and halide-peroxidase-positive lysosomes of these cells (Nyholm and McFall-Ngai, 1998; Small and McFall-Ngai, 1999). Although their function is unknown, other polysaccharides have been reported to be present in lysosomes in other systems.…”

“…4A). The CBP staining also co-localized with an antibody specific to E. scolopes halide peroxidase (Weis et al, 1996; Small and McFall-Ngai, 1999), a protein that typically localizes to lysosomes (Baggiolini et al, 1969; Nauseef, 1998). Taken together, these data suggest that the intracellular chitin occurs in or is associated with the lysosomes of E. scolopes hemocytes.…”

Host-selected mutations converging on a global regulator drive an adaptive leap towards symbiosis in bacteria

“…Furthermore, to our knowledge, no study has yet evaluated whether biofilm imparts symbiotic fitness beyond aggregation. Because of the potential that biofilm could confer survival in the face of environmental insults, we evaluated whether binK1 impacted survival upon peroxide exposure, as oxidation is among the host’s defensive arsenal (Small and McFall-Ngai, 1999; Visick and Ruby, 1998) (Figure 1A). The binK1 and ∆binK variants survived oxidation better than MJ11, and overexpression of the Syp repressor sypE or the cellulose repressor binA decreased survival (Figure 5C).…”

“…Once newly hatched squid entrap bacteria in mucus near the light organ, symbionts aggregate in this mucus and, in response to host attractants , subsequently swim through pores at the entrance of the nascent light organs (Nyholm et al, 2000). As V. fischeri bacteria swim down the ducts and into the crypts, they face a 'gauntlet' of defenses that includes host-derived oxidative species (Davidson et al, 2004; Weis et al, 1996; Small and McFall-Ngai, 1999), as well as patrolling macrophage-like hemocytes that attach to other species of marine bacteria with higher affinity, subsequently killing these invading cells (Nyholm et al, 2009; Nyholm and McFall-Ngai, 1998; Koropatnick et al, 2007). These barriers ensure that only the correct symbiotic partner gains access to the crypts where host-provided nutrients support bacterial growth (Graf and Ruby, 1998; Heath-Heckman and McFall-Ngai, 2011).…”

Infectious (Non)tolerance--Frustrated Commensalism Gone Awry?

“…The squid peroxidase is also found in gill tissue, where it non-specifically eliminates pathogenic bacteria filtered through the circulatory system. That the same enzyme is found in symbiotic light organs argues that it may produce ROS as a signal to select or limit bacterial symbionts (Small and McFall-Ngai 1999). …”