Mohamed Shariff

Screening of Malaysian indigenous microalgae for antioxidant properties and nutritional value

Fourteen indigenous microalgal samples from Malaysia were isolated, purified and cultured from fresh, brackish and marine waters. The ability of the microalgae to be natural sources of antioxidants was studied by a screening test using three antioxidant chemical assays [ferric thiocyanate (FTC), thiobarbituric acid (TBA) and 1, 1’-diphenyl-2-picrylhydrazyl (DPPH)]. The results showed that six microalgal methanolic crude extracts (Isochrysis galbana, Chaetoceros calcitrans, Scenedesmus quadricauda, Chlorella vulgaris, Nannochloropsis oculata and Tetraselmis tetrathele) were active in inhibiting the lipid peroxidation of linoleic acid. Among all the microalgae, I. galbana and C. calcitrans showed the highest antioxidant activity (>90%) in FTC and TBA assays, indicating that these microalgae might contain active compounds for protection from lipid peroxidation. Nutritional analyses were performed on microalgae with high antioxidant activities (I. galbana and C. calcitrans) in order to investigate their nutritive value. Both microalgae were found to be rich in nutrients. For examples, I. galbana had average percentage composition of protein, carbohydrate, and lipid, as 47.9 ± 2.5; 26.8 ± 0.2; 14.5 ± 1.4%, respectively, while the corresponding values for C. calcitrans were 36.4 ± 1.7; 27.4 ± 3.0; 15.5 ± 0.9%. In addition, they contained high levels of omega-3 polyunsatrated fatty acids (PUFA) (28.0% ± 0.7 in I. galbana and 28.5% ± 1.4 in C. calcitrans), omega-6 PUFA (6.5% ± 1.8 in I. galbana and 23.0% ± 2.5 in C. calcitrans) and a high composition of essential amino acids. This study illustrates that some microalgae such as I. galbana and C. calcitrans have the potential to be used as natural sources of antioxidants with high nutritional value.

Effect of different flocculants on the flocculation performance of microalgae, Chaetoceros calcitrans, cells

The possibility of using flocculation technique for the separation of microalgae, Chaetoceros calcitrans, biomass from the culture broth was investigated. The flocculation experiments were conducted in 500 mL beaker using culture broth obtained from 10 L photobioreactor. The harvesting efficiency of 90 and 60% was obtained in flocculation without flocculants conducted for 10 days at 27oC (in light and dark) and 4oC (dark), respectively. Harvesting efficiency higher than 90% with short settling time was achieved by adjusting the culture pH to 10.2 using either sodium hydroxide (NaOH) or potassium hydroxide (KOH). Improved cell viability (> 80%) and settling time with a slight improvement of flocculation efficiency was achieved by the addition of polyelectrolytes flocculant (Magnafloc® LT 27 and LT 25). However, the flocculants were only functioned when the pH of the microalgae culture was pre-adjusted to a certain value that promotes cells entrapment and surface charge neutralization prior to flocculation process. The flocculation efficiency and cell viability obtained in flocculation with Magnafloc® (LT 25 and LT 27) was comparable to that obtained in flocculation with chitosan. When chitosan and Magnafloc® (LT 25 and LT 27) were used as flocculants, the highest flocculation efficiency of C. calcitrans cells was observed at pH 8 and 10.2, respectively. Substantial increased in sedimentation rate was observed with increasing flocculants dosage though the flocculation efficiency and cell viability were not significantly varied.

Microalgae as Sustainable Renewable Energy Feedstock for Biofuel Production

The world energy crisis and increased greenhouse gas emissions have driven the search for alternative and environmentally friendly renewable energy sources. According to life cycle analysis, microalgae biofuel is identified as one of the major renewable energy sources for sustainable development, with potential to replace the fossil-based fuels. Microalgae biofuel was devoid of the major drawbacks associated with oil crops and lignocelluloses-based biofuels. Algae-based biofuels are technically and economically viable and cost competitive, require no additional lands, require minimal water use, and mitigate atmospheric CO2. However, commercial production of microalgae biodiesel is still not feasible due to the low biomass concentration and costly downstream processes. The viability of microalgae biodiesel production can be achieved by designing advanced photobioreactors, developing low cost technologies for biomass harvesting, drying, and oil extraction. Commercial production can also be accomplished by improving the genetic engineering strategies to control environmental stress conditions and by engineering metabolic pathways for high lipid production. In addition, new emerging technologies such as algal-bacterial interactions for enhancement of microalgae growth and lipid production are also explored. This review focuses mainly on the problems encountered in the commercial production of microalgae biofuels and the possible techniques to overcome these difficulties.

Changes in bacterial populations and shrimp production in ponds treated with commercial microbial products

Commercial ponds receiving two microbial products were monitored for changes in bacterial populations and shrimp production. Nine ponds of 0.5 ha each were treated; three with microbial Product 1, three with Product 2 and three left untreated to serve as control ponds. The products were screened for species composition and administered following manufacturers instructions throughout the culture period of 110 days. Product 1 contained Bacillus sp. and Saccharomyces sp. and Product 2 contained Bacillus sp., Nitrosomonas sp. and Nitrobacter sp. Water and sediment samples were collected once every 14 days for bacteriological analyses. Various heterotrophic (total plate count, presumptive vibrios, protein mineralising, ammonifying and sulphur reducing) and autotrophic (ammonia oxidising, nitrite oxidising, presumptive sulphur oxidising) bacterial groups were estimated for their population densities in water and sediment. Results showed that the Bacillus spp. were dominant in all ponds. Sediment of ponds treated with Product 1 had significantly higher (P<0.05) number of total plate count (1.24×106±0.27×106 cfu g−1) and presumptive sulphur oxidising bacteria (1.01×102±0.19×102 cfu g−1). The average density of sulphur reducing bacteria (2.74±0.27 cfu ml−1) in water of the control ponds was significantly lower (P<0.05) than that from treated ponds. The average production at the end of the culture period was relatively, but not statistically higher in ponds treated with Product 1 (5837.14±715.22 kg ha−1) when compared with those for Product 2 (4877.42±438.46 kg ha−1) and control (5102.28±262.28 kg ha−1) ponds. Some bacterial populations and feed conversion ratio (FCR) were significantly different in Product 1 ponds compared to others, but the economical returns were not statistically different between treatments. Further studies to show the benefits of using microbial products in commercial aquaculture farms should be conducted utilizing larger sample size.

Bacteriosis associated with epizootic in the giant sea perch, Lates calcarifer, and the estuarine grouper, Epinephelus tauvina, cage cultured in Malaysia

Abstract A mass mortality in marine cage-reared adult sea perch, Lates calcarifer , and grouper, Epinephelus tauvina , offshore Kukup Laut, State of Johore, southern Peninsular Malaysia was investigated. The quantity and quality of trash fish fed to the fish was determined to be inadequate and the water quality was reduced during the northeast monsoon occurring at this time. Histologically, affected fish presenting extensive multiple skin lesions demonstrated severe haemorrhagic ulcerative dermatitis with additional changes in the internal organs consistent with a subacute septicaemia and an underlying malnutrition. Pseudomonas sp., probably Pseudomonas anguilliseptica , was identified as the agent responsible for the haemorrhagic septicaemia in the fish. With the end of the northeast monsoon, improved nutrition and water quality eliminated the problem in the adult fish, emphasizing the secondary opportunistic role of Pseudomonas and the importance of primary stresses such as that caused by suboptimal nutrition and environment in the initiation of disease in fish.

Availability and Utilization of Pigments from Microalgae

Microalgae are the major photosynthesizers on earth and produce important pigments that include chlorophyll a, b and c, β-carotene, astaxanthin, xanthophylls, and phycobiliproteins. Presently, synthetic colorants are used in food, cosmetic, nutraceutical, and pharmaceutical industries. However, due to problems associated with the harmful effects of synthetic colorants, exploitation of microalgal pigments as a source of natural colors becomes an attractive option. There are various factors such as nutrient availability, salinity, pH, temperature, light wavelength, and light intensity that affect pigment production in microalgae. This paper reviews the availability and characteristics of microalgal pigments, factors affecting pigment production, and the application of pigments produced from microalgae. The potential of microalgal pigments as a source of natural colors is enormous as an alternative to synthetic coloring agents, which has limited applications due to regulatory practice for health reasons.

Diversity of Malaysian aquatic ecosystems and resources

Malaysia has rich aquatic ecosystems that supply vital resources such as water, food, medicine, commercial aquatic resources, energy and transport for economic and social development of its people. In addition, they also provide other services such as flood control, erosion prevention and shoreline protection, recreational fisheries and resources for tourism industry. However, the ubiquitous and abundant supplies of these resources in the past have resulted in minimal concern about their conservation and sustainable exploitation. In fact, these resources are continuously threatened by human activities such as overexploitation of living resources, massive land reclamation and development, discharge of harmful industrial and domestic wastes, and large energy development projects. Threats to the sustainability of these resources in the form of land-based and sea-based pollution are becoming serious, and have affected the health and wealth of the people. The manifestations of the disregard to the aquatic environment are already obvious, as evidenced by the frequent reports on water shortage, polluted rivers and seas, decrease in fisheries commodities, decline of aesthetic values in water-based recreational areas and decrease in biodiversity. Various laws and regulations have not been able to deter some of these ecosystems from being continually exploited on unsustainable basis. Concerted efforts from all stakeholders are critical to protect these valuable ecosystems such that their resources would continue to provide life necessities for generations to come. Preventive measures, such as the implementation of holistic environmental management, increased public education and the early use of efficient and cost-effective pollution control measures through research efforts and the acquisition of clean technology, should be implemented to achieve desired level of pollution abatement. These efforts by the Government should be complemented and supplemented by investments from the private sector to achieve a clean, healthy and productive aquatic environment for both present and future generations.

Antibiotic Resistant Salmonella and Vibrio Associated with Farmed Litopenaeus vannamei

Salmonella and Vibrio species were isolated and identified from Litopenaeus vannamei cultured in shrimp farms. Shrimp samples showed occurrence of 3.3% of Salmonella and 48.3% of Vibrio. The isolates were also screened for antibiotic resistance to oxolinic acid, sulphonamides, tetracycline, sulfamethoxazole/trimethoprim, norfloxacin, ampicillin, doxycycline hydrochloride, erythromycin, chloramphenicol, and nitrofurantoin. Salmonella enterica serovar Corvallis isolated from shrimp showed individual and multiple antibiotic resistance patterns. Five Vibrio species having individual and multiple antibiotic resistance were also identified. They were Vibrio cholerae (18.3%), V. mimicus (16.7%), V. parahaemolyticus (10%), V. vulnificus (6.7%), and V. alginolyticus (1.7%). Farm owners should be concerned about the presence of these pathogenic bacteria which also contributes to human health risk and should adopt best management practices for responsible aquaculture to ensure the quality of shrimp.

TaqMan real-time PCR assay for relative quantification of white spot syndrome virus infection in Penaeus monodon Fabricius exposed to ammonia

White spot disease is caused by a highly virulent pathogen, the white spot syndrome virus (WSSV). The disease is usually triggered by changes in environmental parameters causing severe losses to the shrimp industry. This study was undertaken to quantify the relative WSSV load in shrimp exposed to ammonia, using a TaqMan-based real-time PCR, and their subsequent susceptibility to WSSV. Shrimp were exposed to different levels of total ammonia nitrogen (TAN) (8.1, 3.8 and 1.1 mg L⁻¹) for 10 days and challenged with WSSV by feeding WSSV-positive shrimp. WSSV was detected simultaneously in haemolymph, gills and pereopods at four hours post-infection. The TaqMan real-time PCR assay showed a highly dynamic detection limit that spanned over 6 log₁₀ concentrations of DNA and high reproducibility (standard deviation 0.33-1.42) and small correlation of variability (CV) (1.89-3.85%). Shrimp exposed to ammonia had significantly higher (P < 0.01) WSSV load compared to the positive control, which was not exposed to ammonia. Shrimp exposed to 8.1 mg L⁻¹ of TAN had the highest (P < 0.01) WSSV load in all three organs in comparison with those exposed to 3.8 and 1.1 mg L⁻¹ of TAN. However, haemolymph had significantly higher (P < 0.01) viral load compared to the gills and pereopods. Results showed that shrimp exposed to ammonia levels as low as 1.1 mg L⁻¹ (TAN) had increased susceptibility to WSSV.

Phytoplankton population patterns in marine shrimp culture ponds with different sources of water supply

Six shrimp culture ponds of 1 ha each, located between 101° 22′ E 2° 49′N −101° 22′ E 3° 17′N, were used to elucidate the effects of using eutrophic waters on phytoplankton communities. Three ponds were filled with unpolluted water, while the other three received eutrophic water. Water quality and phytoplankton populations were analyzed fortnightly over a period of 110 days to coincide with the shrimp culture cycle. In ponds with eutrophic water, the cyanobacteria (nine species) were the dominant phytoplankton group (>90% of the total phytoplankton density), followed by the green algae (seven species) and diatoms (six species). Ponds with originally unpolluted water were dominated by the diatoms with 18 species, followed by the cyanobacteria (six species) and one species of green algae. Shrimp production in ponds with unpolluted water was significantly higher (4,877.4 ± 438.5 kg ha-1 when compared to 1,385.0 ± 243.8 kg ha-1 in ponds using eutrophic water. This study illustrated that initial water quality supply influenced the phytoplankton dominance, which in turn determined the aquaculture production in shrimp culture ponds.