pumped and in which particles are
filtered. C. Detail of a channel, a
flagellated chamber and the mesohyl.
p=pinacocyte (skin cell),
c=choanocyte, a=archaeocyte (free
floating cell), s=spongine, sp=spicula.
channel while digesting the particle. Undigestible parts of the food particle are released
into the outflowing channel.
Smaller particles are trapped by the choanocytes in the choanocyte chambers. The
flagellae of the choanocytes are surrounded by a collar of so-called microvilli. This collar
acts as a sieve with a very small mesh size. Sponges are capable of trapping even the
smallest picoplanktonic particles such as ultramicrobacteria and prochlorophytes.
Particles trapped in the collar are transported into the choanocyte cells, where some
particles are digested and others are stored in food vacuoles. The content of these food
vacuoles is regularly transferred to archaeocytes that make cell-to-cell contact with the
choanocytes to take up the food. Similar to the processing of larger particles, the
undigestible parts are released by the archaeocytes into the outflowing channels.
Metabolites of interest produced by the sponges or their endosymbionts are often
present only in trace amounts. Several authors have stressed the fact that much greater
sponge biomass is needed for commercial production of these sponge metabolites than
can be harvested from the seas (Munro et al., 1999, Pomponi et al., 1994, Osinga et al.,
1998, 1999, Ilan et al., 1996). Currently, this “supply problem” still hampers the
development of many promising metabolites from sponges and other marine
macroorganisms (Munro et al., 1999; Pomponi et al., 1999). A good example is the case
of halichondrin B, one of several compounds that have been isolated from Halichondria
okadai and Lissodendorix sp. This potential anti-cancer agent has successfully proceeded
through the first preclinical test phase, but can not be studied further until the supply of
sufficient material has been solved (Munro et al., 1999).
In order to give an idea of the amount of sponge biomass that is necessary to produce
one kg of final product, two examples are given: i. Latrunculins are cytotoxic compounds
isolated from the sponge Latrunculia magnified (Ilan et al., 1996). The latrunculin
concentrations in the sponge tissue are relatively low (up to 0.35% of the dry weight). For
the production of 1 kg lactrunculin 286 kg dry sponge or 9.5 m^3 of sponge biomass needs
to be produced; ii. The anti-bacterial polybrominated biphenyl ethers in the Indo-Pacific,
encrusting sponge Dysidea herbacea can make up to 12% of the sponge dry weight
(Unson et al., 1994). Production of a kilogram of target compound would in this case
require 8.3 kg dry sponge or 0.3 m^3 of sponge volume.
Commercialisation of bio-active compounds from sponges has been limited so far.
The molecules are often very complex which makes then difficult to synthesize
chemically. The metabolic pathways are unknown, which make it difficult to transfer the
genetic information for the metabolite production into other organisms.
Sponges as production organisms are therefore very interesting. Direct harvesting
from the ocean, however, would be environmentally unacceptable. Production of
metabolites with sponge cells could therefore be the best production method.
Marine sponges as biocatalysts 511