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Characteristic bacteria associated with surfaces of coralline algae: a hypothesis for bacterial induction of marine invertebrate larvae


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Johnson, CR, Muir, DG and Reysenbach, AL 1991 , 'Characteristic bacteria associated with surfaces of coralline algae: a hypothesis for bacterial induction of marine invertebrate larvae' , Marine Ecology Progress Series, vol. 74, no. 2-3 , pp. 281-294 .

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Crustose coralline algae (CCA) induce high rates of settlement and metamorphosis in a
diversity of marine invertebrate larvae. It is often assumed that inducers associated with CCA are algal
in origin, but an alternative hypothesis is that they originate from bacteria on the algal surface. Because
many species manifest specificity in settling on CCA, a necessary condition of the hypothesis of
bacterial origin is that bacterial assemblages on CCA are distinctive. Bacteria isolated from surfaces of 2
South African species of CCA (Sporolithon sp. and Clathromorphum sp.), 2 seawater samples collected
adjacent to the CCA, and ground-glass slides incubated next to the corallines were examined for 34
morphological and physiological characters. Bacteria from the 2 CCA were distinct from those from
other microhabitats and from each other, whereas isolates from the 2 seawater samples were similar,
and those from glass slides were more similar to seawater populations than to coralline-associated
bacteria. Bacteria from corallines were distinguished by narrower temperature ranges for growth, and in
general, inability to (1) utilize glucose, (2) hydrolyse complex carbohydrates and urea, (3) utilize simple
amino acids, and (4) reduce nitrate. These characteristics and the distributions of bacteria on crust
surfaces suggest that epiphytic bacteria may utilise compounds from the algae for growth. Bacteria on
Sporolithon sp. grew mostly from within recently damaged cells, whereas on Clathromorphum sp. they
proliferated on a mucus-like matrix on its surface For some strains the association of bacteria with host
alga may be specialised. These results are consistent with the hypothesis of bacterial origin of inducers
associated with CCA, but they do not provide a critical test and thus do not resolve the question of algal
or bacterial origin of inducers. In examining both hypotheses, we suggest methods to critically discern
among these 2 alternatives. There was no trace of free GABA (y-aminobutyric acid) or L-DOPA (L-beta-3,4-
dihydroxyphenylalanine) in cell-free extracts of either species of South African coralline algae or in
bacteria isolated from the corallines and the other microhabitats. This finding supports other work
suggesting that these compounds have no ecological relevance as inducers.

Item Type: Article
Authors/Creators:Johnson, CR and Muir, DG and Reysenbach, AL
Journal or Publication Title: Marine Ecology Progress Series
ISSN: 0171-8630
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