In an effort to formally describe the
epiphytic
cyanobacteria responsible for AVM, investigators are working to
describe the
target species, based on morphological and molecular characteristics.
Morphological and genetic data revealed this target species is a
previously
unidentified species in the Stigonematales order. Morphologic
images are shown in Figure 1. 16S rRNA
sequence identity was determined
from environmental isolates of this unknown stigonematalan species
using DGGE
(density gradient gel electrophoresis). The
entire 16S gene sequence has been submitted to
the international
database GenBank and received a unique accession number # AY785313. 16S rRNA sequence data has been aligned with
additional cyanobacteria sequences to determine designations for
Real-time PCR
assays in order to rapidly genetically detect the Stigonematales
species from
environmental samples. The morphological
and genetic information will also be used to determine phylogeny and
formally
describe this species.
We detected the presence of this suspect species in two new
locations
during April-Sept. 2004. The first was
in a reservoir from Alabama, Alyceville Reservoir. The
Alabama Department of Conservation and Natural Resources will be
monitoring the
waterfowl at Alyceville this fall and sending additional hydrilla
samples. We also found the suspect Stigonematales
species in a new South
Carolina site, Lake Moultrie. This
new location is very concerning due to the history of hydrilla and
eagles at
this site.
Figure 1. Hydrilla frond with
epiphytic
cyanobacterial colonies and microscopic images of the unknown Stigonematales
species suspected of producing the AVM agent. a,
Colonies visible to the unaided eye are
growing on stems and
the undersides of hydrilla leaves (scale bar, 1 mm); b, Differential interference contrast image of
colonies (scale bar, 100 µm); c,
Epifluorescent image of colonies using Rhodamine Red filter set,
showing
phycobiliprotein fluorescence (scale bar, 100 µm).
