Environ. I have my scuba diving certification and I love snorkeling; is there a particular spot that I should head to see the urchin and the crab in person? R. Soc. While that is far away for many folks, there are different types of crabs and urchins that are located all around the world, so it's likely you'll be able to spot them in the closest bay or ocean to you! HOST:And what about you, Halle? Evol. Vincenzo Cavalieri. From this stage onwards, significant fractions of the embryos treated with the bacteria suspensions showed overt developmental delay and defects (70%), as well as arrested development (20%). V.C. Gene Expr. Offret, C., Jgou, C., Mounier, J., Fleury, Y. Regulation of microbial populations by coral surface mucus and mucus-associated bacteria. 74, 1738 (2004). 27, 300305 (2012). Rescue! Cite this article. Environ. The analysis involved 48 nucleotide sequences. & Xia, B. Evol. These sequences were used as query for nucleotide BLAST interrogations against 16S ribosomal RNA sequences. Share sensitive information only on official, secure websites.. and V.C. Prog. Overnight suspensions in Marine broth (CONDA) of individual bacterial strains isolated from coelomic fluid were split in two fractions. Appl. Kwazii! Moreover, though Bacillus (A3) and Vibrio (B2), as well as many other bacterial strains, inhabit the coelomic fluid of P. lividus, it should be emphasized that sea urchin larvae and juveniles in aquaculture facilities are apparently more susceptible to bacterial infections than adult echinoderms71. and JavaScript. The microbial communities of the gut tissue revealed a near-exclusive abundance of Campylobacteraceae, whereas the pharynx tissue . Their body area, called a test, can grow to a diameter of 3 . In conclusion, our results not only provide an unexplored and unexploited source of microbial diversity, but also could be helpful for decoding the biological functions of the echinoderm coelomic fluid, for understanding the roles of bacteria in the physiology and ecology of echinoderms, and for the improvement of their aquaculture conditions. Rep. 5, 9743. https://doi.org/10.1038/srep09743 (2015). Appl. J. Syst. Male and female sea urchins are easily induced to shed massive numbers of eggs or sperm. The six reconstructed bacterial 16S rDNA sequences were submitted to GenBank with the following accession numbers: MK492102 (A1); MK492110 (A2); MK492258 (A3); MK491620 (A4); MK492275 (B1); MK492272 (B2). Environ. 104, 8391 (2015). The gut microbiome of the sea urchin, Lytechinus variegatus from their natural habitat demonstrates selective attributes of microbial taxa and predictive metabolic profiles. Cavalieri, V., Melfi, R. & Spinelli, G. Promoter activity of the sea urchin (Paracentrotus lividus) nucleosomal H3 and H2A and linker H1 -histone genes is modulated by enhancer and chromatin insulator. Cavalieri, V., Bernardo, M. D. & Spinelli, G. Regulatory sequences driving expression of the sea urchin Otp homeobox gene in oral ectoderm cells. Putative functional capabilities differentially represented in the coelomic microbiota of specimens from A and B sites. An official website of the United States government. 7, 509. https://doi.org/10.3389/fevo.2019.00509 (2020). Sci. Elbow room is at such a premium and competition is so fierce in the coral reef environment that many reef dwellers have evolved interesting, endearing, wonderful, or, in some cases, downright bizarre symbiotic relationships that help them make the most of their . Article One of my favorite topics is crabs as they are such a diverse group of animals. Even the name, Sea Urchin, comes from the Old English term for spiny hedgehog. 8, 309320 (2014). Google Scholar. In the present work, culture-based and culture-independent investigations were performed to determine the microbiota structure of the coelomic fluid of Mediterranean sea urchin Paracentrotus lividus individuals collected from two distinct geographical sites neighboring a high-density population bay and a nature reserve, respectively. In light of this, the coelomic fluid of these echinoderms has been traditionally supposed to be a microorganism-free compartment35,36. The eggs are mature at release and are fertilized externally simply by mixing egg and sperm. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. Were done with our mission. HALLE BERGER:Not yet, because I have only studied one species of crab that does not participate in symbiosis. Microbiol. The coelomic fluid was centrifuged at 6000g for 10min at 4C in an Eppendorf 5804R centrifuge, and DNA extracted from the resulting cellular component by using the Genomic DNA purification kit (Thermo Scientific), following the manufacturers recommendations. ADS NAST: a multiple sequence alignment server for comparative analysis of 16S rRNA genes. Beneficial effects of four Bacillus strains on the larval cultivation of Litopenaeus vannamei. Biol. The sea sponge is there so the crab can be safe. Cavalieri, V. & Spinelli, G. Ectopic hbox12 expression evoked by histone deacetylase inhibition disrupts axial specification of the sea urchin embryo. Enomoto, M., Nakagawa, S. & Sawabe, T. Microbial communities associated with holothurians: presence of unique bacteria in the coelomic fluid. 9, 1829. https://doi.org/10.3389/fmicb.2018.01829 (2018). conceived and designed the experiments. PubMed Central In light of this, an intriguing hypothesis is that specific bacterial colonization of the coelomic fluid could occur at the critical time of larval settlement. At the phylum level, a predominance of taxa belonging to Proteobacteria, Bacteroidetes and Fusobacteria was observed in the microbiota of all specimens collected from either A or B sites, accounting for about 90% of abundance per each individual (Supplementary Fig. These authors contributed equally: Teresa Faddetta, Francesco Ardizzone and Francesca Faillaci. 74, 24612470 (2008). 708, 260301 (2010). Mol. Spider crabs rely on camouflage by sticking things to their back to hide from predators while looking for soft food often near sea grass. Lawrence, J., Lawrence, A. Smith, L. C. Host responses to bacteria: innate immunity in invertebrates. The urchin is getting a free ride, easier access to food and the crab receives increased protection from predators! PubMed If you happen to be in Naples, Florida I encourage you to visit our Environmental Learning Center to see some of our local crabs and other animals to learn about their role in the estuary. Pivkin, M. V. Filamentous fungi associated with holothurians from the sea of Japan, off the primorye coast of Russia. Faddetta, T., Ardizzone, F., Faillaci, F. et al. Wang, W. et al. Biol. A.) Appl. 33, 18701874 (2016). Length - 2cm Depth - 5-30m In support of this hypothesis, previous reports showed that many bacterial strains normally associate with healthy sea urchin larvae, where they behave as commensal or mutualistic microorganisms (reviewed in69). Ngangbam, A. K., Baten, A., Waters, D. L. E., Whalan, S. & Benkendorff, K. Characterization of bacterial communities associated with the tyrian purple producing gland in a marine gastropod. Proc. Fish Shellfish Immunol. McFall-Ngai, M. J. The first type of symbiosis was seen in the Crab and the Urchin. Urchins are especially important in coral reef ecosystems because they graze on algae that would otherwise overgrow the corals. Microbiol. Article 327, 201209 (2005). and V.C. Following centrifugation at 12,000rpm for 5min, the supernatant containing hydrophilic substances was separated, while the pellet was incubated overnight with 0.5M methanolic hydrochloric acid at room temperature, to extract lipophilic substances. CAS Their relationship developed because when these fish are just born they are extremely vulnerable to predators. Chapter Nat. Next Generation Sequencing analysis of 16S rRNA gene (rDNA) showed that members of the Proteobacteria, Bacteroidetes and Fusobacteria phyla, which have been previously reported to be commonly retrieved from marine invertebrates, dominate the overall population of microorganisms colonizing this liquid tissue, with minority bacterial genera exhibiting remarkable differences among individuals. Nat. The Reserve also welcomes visiting scientists to answer ecological questions in the area. The phylogenetic tree was inferred using micca tree77. To counterbalance possible differences in the composition of the coelomic fluid due to different marine microenvironments, adult P. lividus specimens were collected during Spring 2015 from two distinct localities around the Eastern coast of Palermo (site A: 38.11 N 13.49 E, and site B: 38.21 N 13.24 E, respectively), chosen for their proximity to a high-density population urban area and to a nature reserve, respectively. Nature 457, 480484 (2009). Establishment of symbiotic association in marine organisms has been recognized as a key feature for the correct differentiation of tissues and organs during embryogenesis56,62,63,64,65. Moreover, a pervasive example of microbial signalling in marine invertebrate development is the induction of metamorphosis and settlement of the benthonic larvae63. Thorsen, M. S., Wieland, A., Ploug, P., Kragelund, C. & Nielsen, P. H. Distribution, identity and activity of symbiotic bacteria in anoxic aggregates from the hindgut of the sea urchin Echinocardium cordatum. A. et al. & Ruby, E. G. Symbiont recognition and subsequent morphogenesis as early events in an animalbacterial mutualism. Appl. Creature report, creature report, creature report! Environ. 9, 10201030 (2014). 293320 (Cambridge University Press, Cambridge, 2005). Bacterial isolates that shared similar colony morphology were grouped together and considered to be redundant. Luis-Villaseora, I. E., Macas-Rodrguez, M. E., Gmez-Gil, B., Ascencio-Valle, F. & Campa-Crdova, A. I. Well make sure to pass these questions along to our NOAA scientists and aquarium educators. Forward and reverse primer trimming and quality filtering were performed using micca trim and micca filter, respectively. https://doi.org/10.1093/femsec/fiw146 (2016). Secure .gov websites use HTTPS Another fascinating role in the host speciation and evolution processes could be potentially played by the bacteria of the Bacteroidetes phylum, which have been associated with alterations of the host reproduction64,65. Google Scholar. Red urchins support a thriving fishery, while their purple cousins are often blamed for mowing down kelp forests to create urchin. Mutualism Mutualism is a form of symbiosis in which both species benefit. Sometimes smaller fish also use the urchins for safe shelter from predators while moving throughout the reef. An abundance of Epsilonproteobacteria revealed in the gut microbiome of the laboratory cultured sea urchin. In particular, while all of the control larvae did swim freely exhibiting rapid forward movements throughout the water column, roughly 50% and 80% of the embryos exposed to Bacillus (A3) and Vibrio (B2), respectively, were turning around their axis or circling slowly at the bottom of the culture plate. https://doi.org/10.1186/gb-2011-12-6-r60 (2011). Brothers, C. J. et al. Purple sea urchins, like all sea urchins, are the porcupines of the sea. 7, 124130 (2007). The sea urchin immune system. Bacterial exposure mediates developmental plasticity and resistance to lethal Vibrio lentus infection in purple sea urchin (Strongylocentrotus purpuratus) Larvae. Barnacles! First time, a Sea Urchin Crab, Echinoecus pentagonus (A. Milne-Edwards, 1879) is recorded from the rocky intertidal region of the Andaman Islands. The host urchin's spines do not harm the shrimp, but they usually clear an area on the urchin where they perch. Symbiosis means they depend on one another. Frias-Lopez, J., Klaus, J. S., Bonheyo, G. T. & Fouke, B. W. Bacterial community associated with black band disease in corals. For humans, it may be hard to imagine having any of the first two types, where one or both benefit from the relationship. Biol. The gut microbiome shapes various aspects of a host's physiology. Indeed, this analysis revealed that a core bacterial microbiota formed by members of the Proteobacteria, Bacterioidetes and Fusobacteria phyla is established in all the analyzed specimens, irrespective of the sampling site. Microbiol. And to learn more about the local crabs and urchins found in Florida, check out Rookery Bays website at rookerybay.org. The spines spear food and protect an urchin from predators. Int. Kumar, S., Stecher, G. & Tamura, K. MEGA7: Molecular Evolutionary Genetics Analysis version 7.0 for bigger datasets. Mar. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. For example, bacteria belonging to the Vibrio and Photobacterium genera are among the most recurring taxa in marine metazoan microbiotas, whereas their association may be (i) symbiotic56, (ii) neutral as commensal microorganisms57, or (iii) parasitic as agents of disease58. Microbiol. HALLE BERGER:I worked with Dungeness crab for my masters research. 1). The Arbacia punctulata has a deep purple color all over the spines and body (test). Three replicates were reproduced for each experimental condition, and three independent experiments were performed using distinct embryo batches. PubMed L. debroyeri n . The resulting embryos are optically transparent and develop synchronously in nothing more than sea water. 97, 561571 (2013). ISME J. Sea urchin diseases occur both in the field and in culture. Sea urchins are indeed basal deuterostomes belonging to Echinodermata, the sister phylum to the chordates27, and therefore they are closely related to humans28. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate. But first I want to hear from Halle. Crabs and urchins face many threats including climate change, habitat destruction, disease, and overfishing. It is the symbiotic relationship that is formed when two different species interact with each other. A young urchin sports green spines. The urchin gives the crab protection Microbiol. Lawrence, J. M.) 135154 (Elsevier, Amsterdam, 2013). Biol. In this paper, we describe the microbial composition and their predictive metabolic profile in the sea urchin Lytechinus variegatus gut ecosystem along with samples from its habitat by using NextGen amplicon sequencing and downstream bioinformatics analyses. Rev. Crab & Sea Urchin (commensalism) - Crab holds sea urchin and uses it for protection Sea Lamprey & herring (parasitism) - Sea lamprey attaches to host, . 5, 355362 (2007). I think Ill stick with Dashi as I do assist with capturing images of our animals on exhibit and love reading up on the animals in the reserve. Crab has an urchin on his back https://doi.org/10.1371/journal.pgen.1003847 (2013). Mar. Fact. Med. 3, 453470 (2011). ISSN 2045-2322 (online). National Oceanic and Atmospheric Administration, Bay Watershed Education and Training (B-WET), Ernest F. Hollings Undergraduate Scholarship, Rookery Bay National Estuarine Research Reserve. HOST: Wow, You both come from really different backgrounds and I am curious which Octonauts job you think that you have? Composition and geographic variation of the bacterial microbiota associated with the coelomic fluid of the sea urchin, https://doi.org/10.1038/s41598-020-78534-5. Greengenes, a chimera-checked 16S rRNA gene database and workbench compatible with ARB. Marine microorganism-invertebrate assemblages: perspectives to solve the supply problem in the initial steps of drug discovery. Among these, inquilinism . A snail tells them that a green-blue crab and an orange sea urchin are arguing loudly and keeping all the sea creatures up. In support of this hypothesis, sibling embryos exposed to equivalent amounts of either methanolic extracts (Fig. Sun, Y. et al. This is a great example of symbiosis. Nonetheless, symbiosis is a system that has been in place on Earth among various species for millennia. USA 101, 1103011035 (2004). The urchin relies on the crab, just as the crab relies on the urchin. They have long spines in order to deter predators. Among the echinoderms, the sea urchin Echinometra mathaei (Blainville, 1825), which is widespread in the Indo-Pacific Ocean, is the host for two crustacean symbionts: Tuleariocaris holthuisi. Now crabs are not the only marine creatures to benefit from the urchins' sharp spines. MUSIC: [Octonauts theme music] Octonauts, to your stations! Exp. The richness of the bacterial community associated with sea urchin eggs was inversely proportional to egg size (linear regression, P < 0.0001; R 2 = 0.808; . Development of treated embryos was apparently normal during early cleavage and until the mesenchyme blastula stage. Microbiol. Toxopneustes pileolus, commonly known as the flower urchin, is a widespread and commonly encountered sea urchin Indo-West Pacific. It's fecund in a fairy-tale sort of way, yielding those superlative sea urchins, as well as salmon, scallops, squid, shrimp, sea snailsand those are just the things that start with the letter . Their mission: to explore the worlds ocean, rescue the creatures who live there, and protect their habitats. Microbiol. 3, 2539 (2006). 365, 12851297 (2007). Positive and negative LDA scores indicate the taxa enriched in the coelomic microbiota of P. lividus specimens from A and site B sites, respectively. Get started for FREE Continue. A. et al. A. Ecology and biotechnology of the genus Shewanella. De novo greedy clustering and chimera filtering were performed by using micca otu: operational taxonomic units (OTUs) were assigned by clustering the sequences with a threshold of 97% pairwise identity, and their representative sequences were classified using micca classify with the RDP classifier v2.1174. (Image credit: NOAA OKEANOS Explorer Program, 2013 Northeast U. S. Canyons Expedition). Symbiosis in the Marine Aquarium. 71, 78197830 (2005). The two invertebrates featured have a large amount of diversity in the two groups with over 6,000 different species of crabs and 950 species of sea urchins. Google Scholar. McFall-Ngai, M. J. HOST:Well that sounds like a new graduate thesis if I have ever heard one! Request PDF | Understanding the Symbiotic Relationship between the Sea Urchin Loxechinus albus (Molina, 1782) and the Pea Crab Pinnaxodes chilensis (H. Milne Edwards, 1837): a Potential Parasitism . Cavalieri, V., Melfi, R. & Spinelli, G. The Compass-like locus, exclusive to the ambulacrarians, encodes a chromatin insulator binding protein in the sea urchin embryo. 77, 175186 (2018). Trivia. 4). Kwazii, activate creature report! Symbiosis between Coleman Shrimp and Fire Urchin Matthew Eschenfelder Interesting Coleman Shrimp Facts First discovered in 1975 by A. J. Bruce The scientific name for the Coleman Shrimp is Periclimenes colemani Coleman Shrimp's Role Uses the Fire Urchin as shelter - benefits from. Idiomarina homiensis sp. Octonauts! 10 Animals With Symbiotic Relationships (Pictures and Facts) Categories General. 100, 127130 (2009). Price, M. N., Dehal, P. S. & Arkin, A. P. FastTree 2approximately maximum-likelihood trees for large alignments. Article And many times you can see at least crabs from the beach or in tide pools. Microb. Correspondence to HALLE BERGER:I would say I am a researcher like Shellington because we are both naturally curious and passionate about studying marine life. 81, 58675879 (2015). Bordenstein, S. R. Symbiosis and the origin of species. Have a comment on this page? It is considered highly dangerous, as it is capable of delivering extremely painful and medically significant stings when touched. Microbiol. This podcast is hosted by NOAAs Office of Education and the Coastal Ecosystem Learning Centers network. Article All positions containing gaps and missing data were eliminated. The coelomic fluid is in equilibrium with the surrounding seawater environment and in direct contact with internal tissues, whereas the circulating immunocytes respond to pathogen challenge producing antimicrobial molecules32,33,34. Ecol. & Holmes, S. Phyloseq: an R package for reproducible interactive analysis and graphics of microbiome census data. Lepidepecreella debroyeri n. sp. Similar to the blood of higher metazoans, the main circulatory medium of sea urchins is the coelomic fluid enclosed in the main body cavity. Therefore, the coelomic fluid could be considered a rather complex tissue that mediates responses to wounding and microbial infections by undergoing reactions such as opsonization, coagulation, encapsulation and phagocytosis34. Acad. 73, 52615267 (2007). In this analysis, we focused on Bacillus (A3) and Vibrio (B2) isolates that were randomly selected as representative of the two geographic sites described. Over millions of years, the organisms that inhabit the seas evolved strategies to handle a changing and sometimes invasive environment. 59, 143169 (1995). Article Approximately 7mL of coelomic fluid were drawn, through the peristomial membrane surrounding the Aristoteles lantern, using a sterile syringe with a 21-gauge needle, and 6.5mM EDTA pH 8.0 was immediately added to prevent clot formation. Zhou, Y. et al. wrote the paper. Frank, J. Mar. Hakim, J. Dita, can you maybe kick us off and tell us what you do at the Rookery Bay? 3 (Hesionidae), gastropod, Vitreobalcis sp. Hunter, M. S., Perlman, S. J. 6, 1047. https://doi.org/10.3389/fmicb.2015.01047 (2015). Genome Biol. The first ten hits for each query were selected, exported in FASTA format and then de-replicated. On the other hand, the crab is protected by the sea urchin, because other animals find it scary. 4, 289296 (2009). PLoS ONE 8, e61217. Paul, V. J. Characterization of the bacterial communities associated with the bald sea urchin disease of the echinoid Paracentrotus lividus. In particular, samples were serially diluted in sterile 0.45m-filtered sea water, 100l of each dilution was plated on marine agar medium (CONDA) and incubated for 2448h at 30C to allow bacterial growth. PubMed Controls for this assay included sibling embryos exposed to equal amounts of PBS and methanolic hydrochloric acid solutions, respectively, as well as unperturbed embryos. This point has been addressed in the present study by describing and comparatively analysing the bacterial microbiota residing in the coelomic fluid of sea urchins collected from two distinct geographical sites. ADS Fig. Get the most important science stories of the day, free in your inbox. Lett. ADS People saw the coral dying and lots of sea urchins, so blamed one upon the other. Ainsworth, T. & Hoegh-Guldberg, O. Bacterial communities closely associated with coral tissues vary under experimental and natural reef conditions and thermal stress. Davidson, E. H. A History of Embryology (Cambridge University Press, Cambridge, 1986). Studies of bacterial communities associated with body tissues of marine animals have largely focused on sponges, corals, bryozoans and crustaceans8,9,10,11,12. & Kelly, S. E. A bacterial symbiont in the Bacteroidetes induces cytoplasmic incompatibility in the parasitoid wasp Encarsia pergandiella. Int. Bull. Webster, N. S. et al. Some of my favorites are the spider crab, and stone crab. the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Microbiol. Russ. Reads were pre-processed using the MICCA pipeline v 1.5.072, and the overlapping paired-end reads were merged using micca mergepairs73. I was interested in learning about how the crab will be impacted by climate change in the future. Before we begin our chat, lets set the stage for the deep dive. Octonauts, at ease, until the next adventure! Microbiol. Kwon, S. W. et al. Brown, S. P., Cornforth, D. M. & Mideo, N. Evolution of virulence in opportunistic pathogens: generalism, plasticity, and control. Confidence for tree topologies was estimated by bootstrap values based on 1000 replicates. FEMS Microbiol. Meziti, A., Kormas, K. A., Pancucci-Papadopoulou, M. A. Life on earth began in the oceans. Do you think you are a researcher like Shellington, an oceanographer like Inkling, a systems analyst like Dashi, a leader like Barnacles? This is most likely a commensal relationship, since the tubeworm . Google Scholar. 50, 10351042 (2000). 126, 10231031 (2019). Segata, N. et al. The microbial landscape of sea stars and the anatomical and interspecies variability of their microbiome. The larger one is the female. Immunol. Distances are in the units of the number of base substitutions per site. Rev. PLoS ONE 10, e0143860. The reason of their extensive use as experimental model likely relies in their phylogenetic position. Ecol. PubMed In Sea Urchins: Biology and Ecology (ed. Ocean warming alters predicted microbiome functionality in a common sea urchin. Cavalieri, V., Di Bernardo, M., Anello, L. & Spinelli, G. cis-Regulatory sequences driving the expression of the Hbox12 homeobox-containing gene in the presumptive aboral ectoderm territory of the Paracentrotus lividus sea urchin embryo. Symbiotic Relationships in Marine Ecosystems | National Geographic Society Resource Library | Lesson : 3 hrs 40 mins Symbiotic Relationships in Marine Ecosystems Students analyze videos to make observations about species, populations, and communities of organisms and discuss their symbiotic relationships. Environ. Tamura, K., Nei, M. & Kumar, S. Prospects for inferring very large phylogenies by using the neighbor-joining method. A culture-based investigation of the bacterial populations inhabiting the coelomic fluid of individuals collected from both the mentioned sites revealed an amount of 104105 bacterial isolates/mL. The genome of the sea urchin Strongylocentrotus purpuratus. Sci. Contrarily, recent reports described the identification of microbial communities associated with the coelomic fluid of holothurians, starfish and sea urchins37,38,39,40,41,42,43, suggesting that complex symbiotic associations could exist in such a perivisceral liquid of the echinoderms. https://doi.org/10.1371/journal.pone.0166104 (2016). Just head to NOAAs Office of Education Twitter, Facebook or Instagram to post your questions and we will post their answers! Endean, R. The coelomocytes and coelomic fluids. Fraune, S. & Bosch, T. C. Long-term maintenance of species-specific bacterial microbiota in the basal metazoan Hydra. In the present study, we show that a significant fraction of developing embryos exposed to either Bacillus (A3) or Vibrio (B2) bacterial strains isolated from coelomic fluid samples exhibited similar developmental delay and aberrations. Article Worth to mention, exactly the same phenotypes were obtained following exposure of embryos with amounts of bacterial lysate supernatants corresponding to 1107 cells/mL (Fig. Shellington explains to Captain Barnacles that the crab and urchin are symbiotic, meaning that they have a mutually beneficial relationship, and need each other for food and protection. The role of microorganisms in coral health, disease and evolution. Intraspecific competition impacts vibrio fischeri strain diversity during initial colonization of the squid light organ.