Bioactivity of bacterial strains isolated from marine biofilms in Hong Kong waters for the induction of larval settlement in the marine polychaete Hydroides elegans

Abstract

In the present study, 38 bacterial isolates were obtained from a marine biofilm, identified by the comparison of 16S rRNA gene sequences, and investigated by laboratory bioassays for their effects on larval settlement of the marine polychaete Hydroides elegans (Haswell). The bacterial isolates belonged to 3 phylogenetic branches: γ-Proteobacteria (26 isolates), Gram-positive (8 isolates) and Cytophaga-Flexibacter-Bacteroides (4 isolates). Most of the isolates were affiliated to the genera Vibrio (7 isolates), Alteromonas (8 isolates) or Pseudoalteromonas (8 isolates), which are in the γ-Proteobacteria branch. According to their efficacy to induce larval settlement of H. elegans in laboratory bioassays, the isolates were categorized as strongly, moderately, and non-inductive for larval settlement. About 42% of the isolates were categorized as non-inductive and the rest of the isolates contained equal numbers of highly and moderately inductive strains. The results indicated that larval settlement of H. elegans could be induced by bacteria in a wide range of taxa. The isolates that induced high and moderate levels of larval settlement belonged to the genus Cytophaga in the Cytophaga-Flexibacter-Bacteroides branch; the genera Bacillus, Brevibacterium, Micrococcus and Staphylococcus in the Gram-positive branch; and the genera Alteromonas, Pseudoalteromonas and Vibrio in the γ-Proteobacteria branch. Results also showed that isolates affiliating to the same genus might have tremendously different activities for the induction of larval settlement. For example, isolates that were affiliated to the genus Alteromonas or Pseudoalteromonas distributed over the 3 categories of activity for induction of larval settlement. KEY WORDS: Hydroides elegans · Larval settlement · Biofilm · Bacteria · 16S rRNA genes Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 226: [301][302][303][304][305][306][307][308][309][310] 2002 ment (i.e. attachment and metamorphosis) are wellknown examples for the secondary driving force.Surface-associated bacteria impose important influences over the settlement of many invertebrate larvae. Bacteria may stimulate (e.g. Szewzyk et al. 1991, Leitz & Wagner 1993, Lau & Qian 1997, Unabia & Hadfield 1999, inhibit (e.g. Holmström et al. 1992, Avelin et al. 1993, Lau & Qian 2000 or not affect (e.g. Brancato & Woollacott 1982, Avelin et al. 1993, Lau & Qian 1997, Unabia & Hadfield 1999) larval settlement, depending on the species of invertebrates and bacteria of concern. Although the presence of surface-associated bacteria is a prerequisite for larval settlement of certain invertebrates, larvae of these invertebrates may respond to individual bacterial isolates to different extents (Kirchman et al. 1982, Lau & Qian 1997, Unabia & Hadfield 1999. Previous studies have suggested the effect of surface-associated bacterial communities on larval settlement to be a function of bacterial species composition (Keough & Raimondi 1996, Lau & Qian 1997, Rodriguez & E...

Effect of ultraviolet radiation on biofilms and subsequent larval settlement of Hydroides elegans

“…It has long been known that biofilms are one of the major sources of settlement cues for the larvae of Hydroides elegans. Although natural multispecies biofilms induce the settlement of this species (Lau et al 2005), monospecies biofilms can have an inductive, neutral or inhibitive effect on settlement (Unabia & Hadfield 1999, Lau & Qian 2001, Lau et al 2002, 2003a, Huang & Hadfield 2003, Lee & Qian 2003. All these results were obtained from laboratory experiments.…”

Effect of amino acids on larval metamorphosis of the polychaete Hydroides elegans

“…However, in the presence of antibiotics, these amino acids showed the same inductive effects as when without antibotics, suggesting that larval metamorphosis was directly triggered by amino acids. Although the bacterial density was relatively high in the treatments without antibiotics, the bacteria did not show inductive Since previous studies demonstrated that many bacterial strains had no inductive effects on the larval metamorphosis of Hydroides elegans (Lau et al 2002), one may speculate that these amino acids may selectively promote the growth of bacteria that have no direct effects on larval settlement and metamorphosis of H. elegans. Further work on the community structure analysis of bacterial biofilms, developed under different treatments of amino acids, will provide insight into the composition of inductive, non-inductive and even inhibitive bacterial strains.…”

“…On smaller spatial scales, active larval behavior such as substrate rejection or substratum exploration determines the success of larval settlement, particularly when larvae descend to the sea floor. Larvae of many marine invertebrates require specific cues to settle and metamorphose and cues can originate from conspecific or congeneric individuals (Crisp 1984, Pawlik 1992, Rodriguez et al 1993, Qian 1999, microbial films (Kirchman et al 1982a, Maki et al 1989, Lau et al 2002, sympatric species, food items, habitat (Bryan et al 1998), and other environmental sources (Pechenik et al 1995). A variety of chemicals have been suggested to be cues that include juvenile hormones (Biggers & Laufer 1992, 1996, free fatty acids (Pawlik 1986, Pawlik & Faulkner 1986, 1988), polysaccharides (Kirchman et al 1982b), protein and small peptides , amino acids , inorganic ions (Yool et al 1986, Bryan et al 1997b, and neurotransmitters other than amino acids (Pawlik 1990).…”

Bacterial community succession and chemical profiles of subtidal biofilms in relation to larval settlement of the polychaete Hydroides elegans

“…Earlier studies (Unabia and Hadfield, 1999;Lau et al, 2002) have isolated bacterial strains that induce H. elegans larval settlement. However, the presence of inductive bacterial strains in a natural biofilm does not necessarily explain this biofilm's inductiveness.…”