Transcriptomes of Pre-competent, Competent, and Metamorphosed Larvae of Hydroides elegans Reveal the Distinct Role of Innate Immunity Genes in Response to a Bacterial Settlement Cue.

Date
2014-09-26
Authors
Bump, Paul
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Hadfield, Michael
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Biology
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University of Hawaii at Manoa
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The ocean is a microbial world; vast communities of bacteria, archaea, protists, and fungi account for most of the ocean’s biomass (Sogin et al., 2006). Consider a single liter of seawater, it alone can contain over 20,000 species of microbes that are responsible for 98% of primary production in the oceans (Whitman et al., 1998). About 3.8 billion years ago, bacteria were one of the first life forms to appear on Earth and deeply influenced the multicellular life that would follow (McFall-Ngai et al., 2013). Given this undeniable microbial environment, a large number of studies have revealed that bacteria undoubtedly affect life in the ocean, particularly when it comes to metamorphosis. It is now well established that the juvenile or larval forms of coral, snails, and other invertebrates do not randomly settle to become adults, but respond to cues from bacterial biofilms, choosing sites favorable for survival (Hadfield, 2011). In particular, bacterial induction of larval settlement and metamorphosis has been shown in sponges (Whalan et al., 2008), corals (Tran and Hadfield 2011; Webster et al., 2004), bivalve molluscs (Bao et al., 2007), bryozoans (Bertrand and Woollacott, 2003), crabs (Anderson and Epifanio, 2009) as well as variety of other marine fauna. Hydroides elegans, a serpulid polychaete found ubiquitously in tropical and subtropical seas, is an emerging model system in understanding bacteria-induced metamorphosis. Larvae become competent, meaning that they have developed the ability to settle and metamorphose, approximately five days after fertilization (Carpizo-Ituarte and Hafield, 1998). In the presence of a well-developed biofilm, competent larvae are induced to settle and rapidly undergo dramatic metamorphosis (Carpizo-Ituarte and Hafield, 1998). This metamorphosis occurs at an impressive level of bacterial specificity, as research has shown that a particular strain of one species of bacteria, Pseudoalteromonas luteoviolacea (HI1), induces metamorphosis as strongly as a natural, multispecies biofilms and a different strain of the same bacteria, showing 99.95% similarity in the 16s DNA sequence, is not inductive (Huang and Hadfield, 2003). Later studies have even identified specific genes products in P. luteoviolacea (HI1) that are necessary to induce settlement and metamorphosis in H. elegans (Huang et al., 2012).
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ii, 36 pages
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