Publication Date:
2021-05-19
Description:
Harmful algal blooms are global and expanding phenomena that cause adverse effects on human health, structure
and function of ecosystems, fishery industries and aesthetics of the coastal regions. One of the major methods
that was considered in integrated management strategy to control HABs is biological control using indigenous
bacteria. The main aim of the present study was to achieve indigenous bacteria that could control HABs in
Persian Gulf in lab scale. The water and sediment samples were collected seasonally from 10 stations throughout
the Hormozgan province. In addition, four sponge species and three coral species were collected as isolation
source of bacteria. The seasonal frequency pattern of bacteria in water and sediment samples showed that the
minimum frequency was recorded in winter and the maximum was observed in the spring and summer. The
diversity pattern of isolated bacteria revealed the higher bacterial diversity in sediment samples rather to water
samples. The Vibrionacea, Bacillaceae, Enterobacteriaceae and Pseudomonadaceae families were dominated in
sediments and water samples. While in sponge and coral samples the Streptomycetaceae and Alteromonadaceae
families were prevalent. The algicidal pattern of isolated bacteria against Cochlodinium polykrikoides as a
screening index revealed that sponges and corals included the highest proportion of potent algicidal bacteria
(〉90%) with 40% and 28% respectively. Among 30 selected isolates, extracted secondary metabolites from 26
isolates exhibited LC50 less than 1 mg/ml against C. polykrikoides. Stepwise screening strategy was used to
obtain bacteria with selective spectrum activity. Hence, biological activity of potent isolates were determined
against related organisms. In this regard, the result of algicidal assay showed that 9 isolates could not inhibit the
growth of galbana Isochrysis and Chlorella vulgaris as useful algal strains. The extracted metabolites from 90%,
55%, and 35 % of potent isolates exhibited antifungal activity against Candida albicans, Aspergillus niger and
Penicillium chrysogenum at range of 64 to 1024 µg/ml. Moreover 65, 40, 80 and 25% of isolates showed
antibacterial activity against Staphylococcus aureus ،Escherichia coli, Micrococcus luteus and Pseudomonas
aeroginosa varied from 32 to 1024 µg/ml. Toxicity assay against Artemia salina revealed 30 % of isolates were
not toxic up to 1000 µg/ml. in addition, 6 isolates showed any toxicity against shrimp larva in vitro.
Determination of toxicity against human umbilical vein endothelial cells revealed that five isolates were not
toxic and one isolate exhibited low toxicity. Finally, these six isolates selected for further studies. The growth
kinetics of these six isolates revealed the relationship between the number of bacteria and their algicidal activity
in co-culture condition. Moreover, the production of secondary metabolites determined as the main algicidal
mechanism. The results of polyphasic identification showed that S 202, SP 149, SC 77, SP 158 and SC 41
isolates were new strains of Streptomyces rochei،Streptomyces olivaceus ،Streptomyces cavourensis،
Pseudomonas azotoformans، Vibrio alginolyticus and W12 was belonged to Vibrio rotiferianus. The
evolutionary route, genetic distance and divergency rate of the strains were determined. Chemical screening
revealed the chemical profile and identity of extracted secondary metabolites from the six strains. Their chemical
profile showed the presence of some functional groups, including terpenoids, flavonoids, peptides, indole
alkaloids and phenols in crude extracts. The chemical identity of algicidal fractions of S 202, SP 149, SC 77, SC
41 strains were determined as terpenoid or flavonoid. While, the active fraction of SP 158 and W 12 belonged to
phenols and peptide groups respectively. After the purification using chromatographic methods, high
performance liquid chromatography recorded the retention time 10.58 and 11 for the active fractions of SC 41
and SP 149 respectively. This project led to the discovery of six strains of indigenous bacteria with selective
algicidal activity against C. polykrikoides as the main cause of HABs in Persian Gulf and Oman Sea. These
indigenous strains have essential prerequisites for biological control agent in situ condition and can consider as
potential candidates in marine environments and aquaculture farms and cages in field studies. In addition, this
study provided new understanding of seasonal distribution pattern and biodiversity of culturable bacteria in
marine sediments and waters as well as bacterial diversity of collected indigenous sponge and coral samples
from the Persian Gulf.
Description:
Iranian Fisheries Science Research Institute
Description:
Published
Keywords:
Biological control
;
Harmful algal blooms
;
Marine bacteria
;
Algicidal compounds
;
Cochlodinium polykrikoides
Repository Name:
AquaDocs
Type:
Report
,
Refereed
Format:
150pp.
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