Chemical Ecology of Seaweeds - Seaweed Biology - page 178

organic molecules may be enough to overcome the pathogen (e.g., Weinberger
et al. 2001 ). In many others, particularly with endophytes, the oxidative burst also
triggers a series of activated and induced chemical and structural defenses to contain
the infection (Potin 2008 ).
Many seaweeds have been shown to produce organic compounds that can inhibit
growth of bacteria or other pathogens (Bhadury and Wright 2004 ; Goecke et al.
2010 ). However, just because an alga makes a compound that can inhibit
a pathogen (or biofouling organism) in vitro does not show that it functions as
such in nature. To establish that, it is necessary to know that the compound is
localized in a way that the pathogen comes into contact with it at a concentration
high enough to be effective. This has been shown with defenses against fungal
pathogens in several seaweeds. The brown alga Lobophora variegata , or more
likely a bacterial symbiont of it, produces lobophoralide, a polycyclic macrolide
which can be extracted from its surface at concentrations which inhibit the growth
of some higher fungi, including seaweed pathogens (Kubanek et al. 2003 ). The red
alga Callophycus serratus produces a suite of diterpene-benzoate macrolides and
diterpene-alcohols which also inhibit fungal growth (Lane et al. 2009 ). In the first
study of its kind, desorption electrospray ionization mass spectrometry was used to
image and quantify these molecules in patches on the seaweed's surface and at
concentrations sufficient to inhibit the pathogenic fungi (Lane et al. 2009 ).
9.3.3 Defenses Against Biofouling
Chemical defenses against biofouling are like those against pathogens in that just
because a seaweed produces a compound that can inhibit fouling in vitro, to show
ecological relevance against biofouling one must establish that the compound is
present at the surface of the alga at a biologically effective concentration (Steinberg
and de Nys 2002 ). Perhaps the most thoroughly studied example of this in seaweeds
is the case of halogenated furanones produced by the red alga Delisea pulchra as
defenses against both predators (see also Chap. 8 by Iken, Chap. 11 by Potin) and
biofoulers. These are present at the cell surface at known concentrations
(Dworjanyn et al. 1999 ). They mimic bacterial AHL quorum sensing molecules
and interfere with numerous bacterial processes, including attachment, at the
concentration range in which they occur on the algal surface (Kjelleberg et al.
1997 ; Maximilien et al. 1998 ). They also inhibit the attachment of propagules from
four species of fouling macroalgae at surface-level concentrations (Dworjanyn
et al. 2006b ). Surface extracts of the brown alga Dictyota menstrualis have been
shown to contain the diterpenoids pachydictyol A and dictyol E, which are also
known to defend against herbivores, and algal surface extracts including these
compounds inhibited the settlement of larvae of a fouling bryozoan when coated
onto artificial surfaces (Schmitt et al. 1995 ). Surface extracts of the red alga
Bonnemaisonia hamifera contain a poly-halogenated 2-heptanone at concentrations