Investigating quorum-quenching marine bacilli as potential biocontrol agents for protection of shrimps against Early Mortality Syndrome (EMS)

Early Mortality Syndrome (EMS) has been a major problem for shrimp aquaculture in Southeast Asia due to its epizootic prevalence within the region since the first reported case in 2009. This study explores the application of halophilic marine bacilli isolated from coral mucus and their quorum-quenching abilities as potential biocontrol agents in aquaculture systems to combat the causative agent of EMS, Vibrio parahaemolyticus. N-acylhomoserine lactone (AHL)-degrading (AiiA) activity was first screened by PCR then confirmed by bio-reporter assay, and a combination of 16S rDNA sequence analysis and quantitative phenotype assays including biofilm-formation and temperature-growth responses were used to demonstrate diversity amongst these quorum-quenching isolates. Three phenotypically distinct strains showing notable potential were chosen to undergo co-cultivation as a method for strain improvement via long term exposure to the pathogenic V. parahaemolyticus. The novel approach taken led to significant improvements in antagonism and quorum quenching activities as compared to the ancestral wild-type strains and offers a potential solution as well as pathway to improve existing beneficial microbes for one of the most pressing issues in shrimp aquacultures worldwide

Investigating quorum-quenching marine bacilli as potential biocontrol agents for protection of shrimps against Early Mortality Syndrome (EMS)

Early Mortality Syndrome (EMS) has been a major problem for shrimp aquaculture in Southeast Asia due to its epizootic prevalence within the region since the first reported case in 2009. This study explores the application of halophilic marine bacilli isolated from coral mucus and their quorum-quenching abilities as potential biocontrol agents in aquaculture systems to combat the causative agent of EMS, Vibrio parahaemolyticus. N-acylhomoserine lactone (AHL)-degrading (AiiA) activity was first screened by PCR then confirmed by bio-reporter assay, and a combination of 16S rDNA sequence analysis and quantitative phenotype assays including biofilm-formation and temperature-growth responses were used to demonstrate diversity amongst these quorum-quenching isolates. Three phenotypically distinct strains showing notable potential were chosen to undergo co-cultivation as a method for strain improvement via long term exposure to the pathogenic V. parahaemolyticus. The novel approach taken led to significant improvements in antagonism and quorum quenching activities as compared to the ancestral wild-type strains and offers a potential solution as well as pathway to improve existing beneficial microbes for one of the most pressing issues in shrimp aquacultures worldwide

Initial screening of mangrove endophytic fungi for antimicrobial compounds and heavy metal biosorption potential

Endophytic fungi provide protection to their host plant and the fungi often produce antimicrobial compounds to aid the host fighting off pathogens. These bioactive compounds were secondary metabolites which were often produced as waste- or by-products. In the present study, endophytic fungi isolated from mangrove plants and soils were characterized and their antimicrobial production and bioremediation potential of heavy metals copper (Cu) and zinc (Zn) were assessed. Twelve (12) isolated and identified endophytic fungi belonged to seven species; Penicillium, Curvularia, Diaporthe, Aspergillus, Guignardia, Neusartorya and Eupenicillium. Antimicrobial activities of these 12 fungal endophytes were tested against Gram negative bacteria; Bacillus subtilis, Staphylococcus aureus, Gram positive bacteria; Escherichia coli and fungi; Candida albicans and Aspergillus Niger among others. Two isolates (related to Guignardia sp. and Neusartoya sp.) showed strong antimicrobial (and antifungal) activity whereas the rest showed no activity. Compounds were isolated from both isolates and screened using HPLC. Both isolates displayed chemically very interesting chromatograms as they possessed a high diversity of basic chemical structures and peaks over a wide range of polarities, with structures similar to Trimeric catechin and Helenalin among others. For bioremediation assessment, the results showed maximum biosorption capacity for two isolates related to Curvularia sp. and Neusartorya sp., with the former removing 25 mg Cu/g biomass and the latter removing 24 mg Zn/g biomass. Our results indicated the potential of mangrove endophytic fungi in producing bioactive compounds and also highlighted their potential for the treatment of heavy metal-contaminated wastewate

Isolation, Identification and Screening of Antimicrobial Properties of the Marine-Derived Endophytic Fungi from Marine Brown Seaweed

Marine seaweeds are known to produce valuable medicinal compounds such as antioxidants and anticoagulants, and have been reported to display antimicrobial activity against gram positive and gram negative bacteria. Several studies have identified so-called endophytic fungi living inside their hosts as the source of active compounds. In this study marine brown seaweed, Padina sp., was studied with regards to their endophytic fungi to assess if they are the source of the reported antimicrobial activity. Twenty fungal isolates were isolated from Padina sp. collected off Talang-Talang Island, Sarawak, Malaysia. All isolates were screened for their antimicrobial properties and 11 out of 20 isolates displayed positive results. DNA was successfully extracted for five isolates and sequence analysis grouped all of them with other endophytic fungi. “Fungus 2” seems to be related to a so far uncultured endophytic fungus. “Fungus 19” showed the most promising antimicrobial properties and was chosen for further agar well assay and cytotoxicity testing. Its ethyl-acetate extract showed positive results in the agar well assay and also a cytotoxic effect on Artemia nauplii. The extract was screened using HPLC and showed a compound similar to a known anti-cancer compound, dihydromyricetin, which is also an anti-intoxicant, anti-inflammatory and anti-oxidative agent which may be responsible for the observed antimicrobial activity

Temperature and Salinity Profiling Analysis off Sarawak Waters, Malaysia

Prime Scientific Sailing Expedition (EPSP 2009), was carried out in the South China Sea (SCS) along Sarawak waters for nine days from 20 to 29 June 2009. The main objective was to enhance physical oceanography data to support the management of marine ecosystem and other marine resources off Sarawak waters. The main purpose of this present study is to construct vertical temperature and salinity structures off Sarawak waters and to define the water properties based on differ water depths. The temperature and salinity data were obtained using Conductivity-Temperature-Depth (CTD) from sea surface down to 523 m water depth. The measurement was done along the transect line that consists of 60 sampling stations involved with furthest distance offshore at ~471 km. Vertical profiles of temperature, salinity and temperature-salinity (T-S) diagrams of each station were plotted and analyzed based on location and water depth. Offshore sampling stations at water depth greater than 50 m are known as deep waters while near shore sampling station at water depth less than 50m is known as shallow waters. The constructed vertical profiles showed that as water depth increases, salinity increases whereas temperature decreases. Comparison of minimum and maximum temperature range of shallow and deep waters is 15°C and 1°C respectively. However, there is only 0.71°C difference of salinity between minimum salinity of shallow waters and deep waters. The seawater variable of Sarawak waters are impacted by the distance from mainland and its geographical location as well as the rivers influx into the SCS. Constant climate change due to seasonal monsoon and high rainfall as it is located in the tropical region contribute to the spatial temperature and salinity in this area. High rivers runoff into the SCS can reduce the salinity of the water at coastal area. Salinity increases as sampling location further offshore. High rainfall may decreases water temperature and salinity at water surface

Physicochemical parameters of Bakun Reservoir in Belaga, Sarawak, Malaysia 13 months after reaching full supply level

Determining the water quality of Bakun Reservoir 13 months after it operates at full supply level is crucial for better understanding of changes in the physicochemical parameters, which may enable the prediction of its effects on the survival of aquatic life in the reservoir. This study determined 13 physicochemical parameters at six stations within the reservoir at fixed depths. The results showed that the minimum 5 mg/L of dissolved oxygen (DO) required for sensitive aquatic organisms was recorded at 6 m depth. However, DO was not detectable at depths exceeding 7 m. The water was acidic at depths of more than 10 m. Turbidity and total suspended solids increased corresponding with depth. Inorganic nitrogen were predominantly in the form of ammonia-nitrogen, creating an unhealthy environment for aquatic life. Concentration of Chl-a was significantly higher at the subsurface water than 30 m depth in four out of six stations. The present study shows changes in water quality as compared to the pre-impounded period and 15 months after the filling phase, in particular, stratification of dissolved oxygen, thermocline conditions and alkalinity. The changes varied according to the distance from the dam and may have been influenced by existing land developments within the area such as the construction of the Murum Hydroelectric Dam, oil palm plantations and timber concessionares. Though the water quality might have deteriorated, further study is needed to determine if this condition will prolong