Morphological characterization and molecular detection of potential harmful diatom, pseudo-nitzschia from Malaysian water
The diatom, Pseudo-nitzschia is a genus that associated with harmful algal blooms (HABs) worldwide. One third of the species produce the neurotoxin, domoic acid (DA) which is a causative agent of amnesic shellfish poisoning (ASP). Research interest in toxic Pseudo-nitzschia thrived after the outb...
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|Summary:||The diatom, Pseudo-nitzschia is a genus that associated with harmful algal blooms
(HABs) worldwide. One third of the species produce the neurotoxin, domoic acid (DA)
which is a causative agent of amnesic shellfish poisoning (ASP). Research interest in
toxic Pseudo-nitzschia thrived after the outbreak of the first ASP case stroked Canada in
1987. Following the incidence, numerous studies have been undertaken throughout the
open oceans. However, occurrences of Pseudo-nitzschia spp. were reported as species
complex/complexes due to the taxonomic uncertainty in the genus. This has lead to
enormous confusion in species identification) In this study, a thorough field survey
focused on Pseudo-nitzschia species were undertaken to investigate the spatial
distribution pattern and species composition in Malaysian waters. Samplings covered
locations in the Andaman Sea, the Straits of Malacca, the South China Sea, Sulu Sea
and Celebes Sea. Plankton samples were collected from 17 locations using a 20 gmmesh
plankton net haul. Samples were subjected to acid wash treatment before detailed
morphological observations under transmission electron microscope (TEM).
Identification of Pseudo-nitzschia species was based on the frustules morphology with
morphometric measurements. In total, 22 species were identified; in which 16 were new
records in Malaysia, and a new morphotype discovered. Among the toxic species found,
including P. brasiliana, P. caciantha, P. calliantha, P. cuspidata, P. delicatissima, P.
multistriata, P. pseudodelicatissima, P. pungens, and P. turgidula were previously
reported to associate with ASP events worldwide.
In order to aid the species identification of this complex species, molecular
approaches have been introduced in Pseudo-nitzschia taxonomy. Molecular
phylogenetic analyses are applied based on a genetic marker to resolve the Pseudonitzschia
species complex/complexes. In this study, whole cell fluorescence in situ
hybridization (FISH), a rapid molecular detection tool was applied on both field and
cultured samples. Two toxic species, P. pungens were used as model species in FISH
optimization and on-field application. Species-specific probes were designed in silico.
The accessibilities of probes were tested in silico based on complete 28S rRNA
secondary structure information. The probes were successfully optimized on clonal
cultures and natural spiked samples. Whole-cell FISH was proven as a potential rapid
detection tool for monitoring of toxic Pseudo-nitzschia species in Malaysia. This study
has provided further insight and better understanding on Pseudo-nitzschia taxonomy
using both the morphological and molecular approaches. The finding of a new
morphotype warrants further investigation to obtain genetic evidence. FISH method
with species specific probes on targeted Pseudo-nitzschia species are proposed as
monitoring tools for the related agency in Malaysia.|