Chemoattraction of Vibrio fischeri to Serine, Nucleosides, and N -Acetylneuraminic Acid, a Component of Squid Light-Organ Mucus

Abstract

Newly hatched juveniles of the Hawaiian squid Euprymna scolopes rapidly become colonized by the bioluminescent marine bacterium Vibrio fischeri. Motility is required to establish the symbiotic colonization, but the role of chemotaxis is unknown. In this study we analyzed chemotaxis of V. fischeri to a number of potential attractants. The bacterium migrated toward serine and most sugars tested. V. fischeri also exhibited the unusual ability to migrate to nucleosides and nucleotides as well as to N-acetylneuraminic acid, a component of squid mucus.Upon hatching, the light organ of the juvenile Hawaiian squid, Euprymna scolopes, is specifically colonized by the luminous marine bacterium Vibrio fischeri (reviewed in references 7 and 13). V. fischeri cells present in the seawater aggregate in mucus secreted from the light organ and then appear to stream into the openings of the light organ (10), suggesting directed movement by the bacterium. The light-organ mucus, secreted upon bacterial exposure (10) and subsequently within the light organ in response to symbiotic colonization (9), contains two sugars, N-acetylgalactosamine (NAGal) and N-acetylneuraminic acid (NANA) (10). These sugars, as well as amino acids and peptides within the light organ (6), may serve as nutrient sources and/or chemoattractants to enhance entry by V. fischeri, which must be motile to colonize successfully (5). To begin investigating the potential role of chemotaxis in symbiotic initiation, we characterized the response of the bacterium to various nutrients.Motile cells inoculated onto a soft agar medium containing two attractants form an outermost ring in response to a spatial gradient that results from the consumption and subsequent diffusion of the preferred attractant (14). Similarly, an inner ring forms to the second attractant (11 and B. M. Pruss and A. J. Wolfe, unpublished data). When inoculated onto TB-SW soft agar plates (1% tryptone, 0.88% NaCl, 0.62% MgSO 4 , 0.072% CaCl 2 , 0.038% KCl, 0.25% agar), cells of V. fischeri strain ES114 (2) formed two concentric rings (Fig. 1A). Cells of Escherichia coli also form two rings on tryptone-based soft agar, with the outer and inner rings sensing serine and aspartate, respectively (1). We therefore tested whether V. fischeri also migrated to serine and aspartate. While the bacterium did not respond to aspartate (data not shown), the addition of increasing concentrations of serine to the soft agar slowed the migration of the inner ring of V. fischeri, indicating that the cells present in that ring consume, sense, and migrate to serine ( Fig. 1B and C). We used an excess of serine to disrupt the gradient and found that serine perturbed migration of the inner ring (arrows in Fig. 1 depict the location of the spot of serine). Closer inspection of the rings revealed that a doublet we occasionally observed (e.g., Fig. 1B) consisted of fastermigrating cells on the surface of the plate and slower-migrating cells deeper in the agar, both of which responded to serine. Because the doublet responded as ...

Chemotaxis by natural populations of coral reef bacteria

“…Marine bacteria have been shown to exhibit chemotaxis towards carbohydrates present in the exudates of phytoplankton (Hellebust, 1965;Bell and Mitchell, 1972) and in the mucus of the Hawaiian squid Euprymna scolopes light organ (DeLoney-Marino et al, 2003). Despite the prominence of carbohydrates in coral mucus (Ducklow and Mitchell, 1979b;Meikle et al, 1988;Wild et al, 2005), the chemotactic response of coral-associated bacteria towards the tested carbohydrates in both the syringe assays and the ISCAs were never significantly different from the FSW control.…”

A genomic comparison of 13 symbiotic Vibrio fischeri isolates from the perspective of their host source and colonization behavior

“…Among squid symbionts, nine of these MCP genes are specific to strain ES114 and, therefore, are unlikely to be critical for colonization; however, it is possible that their functions are compensated by non-homologous members of the other strains' MCP repertoires, thereby complicating any inference of their importance in light-organ colonization. Although some chemoattractants of V. fischeri have been identified, the specific ligands of the MCPs present in V. fischeri are known for only three (DeLoney-Marino et al, 2003;Brennan et al, 2013;Nikolakakis et al, 2015), none of which is required for light-organ colonization.…”

Deep-sea hydrothermal vent bacteria related to human pathogenic Vibrio species

“…Several culturedependent and -independent studies have confirmed the ubiquity of vibrios, and suggested Vibrio populations generally comprise approximately 1% (by molecular techniques) of the total bacterioplankton in estuaries (19), in contrast to culture-based studies demonstrating that vibrios can comprise up to 10% of culturable marine bacteria (20). Clearly, vibrios are ubiquitous and abundant in the aquatic environment on a global scale, including both seawater and sediment (19,(21)(22)(23)(24)(25), and repeatedly shown to be present in high densities in and on marine organisms, such as corals (26), fish (27-29), mollusks (30), seagrass, sponges, shrimp (28, 31), and zooplankton (16,17,28,32,33).…”

“…Several culturedependent and -independent studies have confirmed the ubiquity of vibrios, and suggested Vibrio populations generally comprise approximately 1% (by molecular techniques) of the total bacterioplankton in estuaries (19), in contrast to culture-based studies demonstrating that vibrios can comprise up to 10% of culturable marine bacteria (20). Clearly, vibrios are ubiquitous and abundant in the aquatic environment on a global scale, including both seawater and sediment (19,(21)(22)(23)(24)(25), and repeatedly shown to be present in high densities in and on marine organisms, such as corals (26), fish (27-29), mollusks (30), seagrass, sponges, shrimp (28, 31), and zooplankton (16,17,28,32,33).During dives of the deep-sea submersibles Alvin and Nautile in 1999 along the East Pacific Rise, southwest of the Mexico coast, samples of water surrounding sulfide chimneys of a hydrothermal vent community were collected and four mesophilic bacterial isolates were cultured, which were subsequently tested for phenotypic traits, including growth on V. cholerae selective thiosulfate-citrate-bile-salts-sucrose (TCBS) agar (Oxoid). The sampling locations from where these four mesophilic bacteria were isolated are described in Table 1.…”