Gracilaria species are an important source of agar. The South African Gracilaria industry has experienced a number of setbacks over the last decade in the form of complete or partial die-offs of the agarophyte growing in Saldanha Bay, which may be attributed to @entity2348 . Since a positive correlation was observed between the presence of agarolytic epiphytes and bacterial pathogenicity, we investigated the role of an agarase in the virulence mechanism employed by a bacterium that elicits disease in Gracilaria gracilis. The recombinant plasmid pDA1, isolated from a @entity16854 gracilis B9 genomic library, was responsible for the agarolytic activity exhibited by @entity526 transformants when grown on solid medium. A BLAST search of the GenBank database showed that an 873 bp ORF (aagA) located on pDA1 had 85 % identity to the beta-agarase (dagA) from @entity16854 @entity16854 (T) (or @entity16854 (T)) at the @entity535 level. AagA was purified from the extracellular medium of an @entity526 transformant harbouring pDA1 by using a combination of gel filtration and ion-exchange chromatography. AagA has an M(r) of 30 000 on @entity214 -PAGE. TLC of the digestion products of AagA showed that the enzyme cleaves the beta-(1,4) linkages of agarose to yield predominately neoagarotetraose. Western hybridization confirmed that the cloned agarase was in fact the extracellular beta-agarase of @entity68958 B9. The observed relationship between disease symptoms of G. gracilis and the agarolytic phenotype of @entity68958 B9 was confirmed. Transmission electron microscope examination of cross sections of both healthy G. gracilis and G. gracilis infected with @entity68958 , revealed a weakening of the cell structure in the latter plants. Immunogold-labelled antibodies localized the agarase in situ to the cell walls of bleached G. gracilis. Thus, the weakening observed in the cell structure of G. gracilis infected with @entity68958 can be attributed to degradation of the mucilaginous component of the cell wall of the bleached thalli.

Investigation of the role of a beta(1-4) agarase produced by XXXX gracilis B9 in eliciting disease symptoms in the red alga Gracilaria gracilis.

@entity68958 :: ('329963', 'Species') :: ['P. gracilis'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity2348 :: ('MESH:D001424', 'Disease') :: ['bacterial infection'] @entity16854 :: ('288', 'Species') :: ['IAM 12927', 'Pseudoalteromonas', 'ATCC 19262', 'Pseudoalteromonas atlantica'] @entity214 :: ('CHEBI:8984', 'Chemical') :: ['SDS'] @entity526 :: ('562', 'Species') :: ['Escherichia coli', 'E. coli']
@entity16854 :: (288,Species) :: ['Pseudoalteromonas']
