Ulva zoospores preferentially settle on N-acylhomoserine
lactone (AHL) producing marine bacterial
biofilms. To investigate whether AHL signal molecules
also affect the success and rate of zoospore germination
in addition to zoospore attraction, the epiphytic
bacteria associated with mature Ulva linza were characterized
and bacterial isolates representative of this
community tested for the ability to produce AHLs. Two
of these AHL-producing isolates, Sulfitobacter spp.
376 and Shewanella spp. 79, were transformed with
plasmids expressing the Bacillus spp. AHL lactonase
gene aiiA to generate AHL-deficient variants. The germination
and growth of U. linza zoospores was studied
in the presence of these AHL-deficient strains and
their AHL-producing counterparts. This revealed that
the AHLs produced by Sulfitobacter spp. and
Shewanella spp. or the bacterial products they regulate
have a negative impact on both zoospore germination
and the early growth of the Ulva germling.
Further experiments with Escherichia coli biofilms
expressing recombinant AHL synthases and synthetic
AHLs provide data to demonstrate that zoospores
germinated and grown in the absence of AHLs were
significantly longer than those germinated in the presence
of AHLs. These results reveal an additional role
for AHLs per se in the interactive relationships
between marine bacteria and Ulva zoospores
