Effect of elevated temperature on the physiological responses of marine <Emphasis Type="Italic">Chlorella</Emphasis> strains from different latitudes

The increased frequency of heat waves due to climate change poses a threat to all organisms. Microalgae are the basis of aquatic food webs, and high temperatures have significant impacts on their adaptation and survival rates. Algae respond to environmental changes by modulating their photosynthetic rates and biochemical composition. This study aims to examine the effect of elevated temperature on similar taxa of marine Chlorella originating from different latitudes. Strains from the Antarctic, temperate zone, and the tropics were grown at various temperatures, ranging from 4 to 38, 18 to 38, and 28 to 40 °C, respectively. A pulse-amplitude modulated (PAM) fluorometer was used to assess their photosynthetic responses. Parameters including maximum quantum efficiency (F _v/F _m), relative electron transport rate (rETR), and light harvesting efficiency (α) were determined from the rapid light curves (RLCs). In addition, the composition of fatty acids was compared to evaluate changes induced by the temperature treatments. Increasing the temperature from 35 to 38 °C for both Antarctic and temperate strains and from 38 to 40 °C for the tropical strain resulted in severe inhibition of photosynthesis and suppressed growth. Although all the strains demonstrated the ability to recover from different stress levels, the tropical strain was able to recover most rapidly while the Antarctic strain had the slowest recovery. The results underline that the thermal threshold for the analysed Chlorella strains temperature ranges between 38 and 40 °C. Furthermore, the analysed strains exhibited different trends in their response to elevated temperatures and recovery capabilities.     

Biosynthesis and mobilization of poly(3-hydroxybutyrate) [P(3HB)] by Spirulina platensis

Three strains of Spirulina platensis isolated from different locations showed capability of synthesizing poly(3-hydroxybutyrate) [P(3HB)] under nitrogen-starved conditions with a maximum accumulation of up to 10 wt.% of the cell dry weight (CDW) under mixotrophic culture conditions. Intracellular degradation (mobilization) of P(3HB) granules by S. platensis was initiated by the restoration of nitrogen source. This mobilization process was affected by both illumination and culture pH. The mobilization of P(3HB) was better under illumination (80% degradation) than in dark conditions (40% degradation) over a period of 4 days. Alkaline conditions (pH 10-11) were optimal for both biosynthesis and mobilization of P(3HB) at which 90% of the accumulated P(3HB) was mobilized. Transmission electron microscopy (TEM) revealed that the mobilization of P(3HB) involved changes in granule quantity and morphology. The P(3HB) granules became irregular in shape and the boundary region was less defined. In contrast to bacteria, in S. platensis the intracellular mobilization of P(3HB) seems to be faster than the biosynthesis process. This is because in cyanobacteria chlorosis delays the P(3HB) accumulation process.     

Environmental effects on growth and biochemical composition ofNitzschia inconspicua Grunow

The effects of nitrate and silicate levels, and carbon source on growth, biochemical composition and fatty acid composition ofNitzschia inconspicua were investigated using batch cultures. Within the range of silicate levels supplied (8.8–176 M), no marked variations in growth trend, biochemical composition or fatty acid composition were shown. Biomass at stationary phase, ranging from 64–66 mg ash-free dry weight (AFDW) L^–1, and specific growth rate () based on chlorophylla (0.41–0.50 d^–1) of the cultures grown within 0.3–3.0 mM NaNO₃ were not significantly different. Cultures supplemented with glucose (0.1 % w/v), acetate (0.1 % w/v) or 5% CO₂ attained higher biomass (85, 85, 97 mg AFDW L^–1) than the control which was grown in synthetic seawater and agitated by magnetic stirring. Cells grown at <3.0 mM NaNO₃ contained higher carbohydrate contents (14.8–21.5% AFDW) than those grown at 3.0 mM (4.0% AFDW). Lipid content increased at the expense of proteins in cells aerated with 5% CO₂. The dominant fatty acids, 16:0 and 16:1, ranged from 35.7–45.0% and 36.4–45.4% total fatty acids (TFA), respectively, while the relative proportions of 20:4 (n-6) and 20:5 (n-3) ranged from 1.7–5.4% and 3.4–5.9% TFA respectively. Cultures aerated with 5% CO₂ attained the highest biomass (97 mg AFDW L^–1) and yield of 20:5 (n-3) (0.34 mg L^–1).     

Transient expression of lacZ in particle bombarded Gracilaria changii (Gracilariales, Rhodophyta)

Using a Biolistic PDS 1000/He system, healthy thalli of Gracilaria changii were bombarded with gold particles coated with plasmid DNA containing the lacZ reporter gene. Transient expression of lacZ was observed in bombarded thalli under the rupture-disc pressures of 4482, 6206, 7584 and 8963 KPa, two days after bombardment. Although G. changii exhibits a slight blue background, positive expression and the background colour can be clearly differentiated. The results indicate that lacZ could be a useful reporter gene and that SV40 promoter could be an effective promoter for Gracilaria transformation.     

Influence of culture temperature on the growth,biochemical composition and fatty acid profiles of six Antarctic microalgae

The growth, biochemical composition and fatty acid profiles of six Antarctic microalgae cultured at different temperatures, ranging from 4, 6, 9, 14, 20 to 30 ^∘C, were compared. The algae were isolated from seawater, freshwater, soil and snow samples collected during our recent expeditions to Casey, Antarctica, and are currently deposited in the University of Malaya Algae Culture Collection (UMACC). The algae chosen for the study were Chlamydomonas UMACC 229, Chlorella UMACC 234, Chlorella UMACC 237, Klebsormidium UMACC 227, Navicula UMACC 231 and Stichococcus UMACC 238. All the isolates could grow at temperatures up to 20 ^∘C; three isolates, namely Navicula UMACC 231 and the two Chlorella isolates (UMACC 234 and UMACC 237) grew even at 30 ^∘C. Both Chlorella UMACC 234 and Stichococcus UMACC 238 had broad optimal temperatures for growth, ranging from 6 to 20 ^∘C (μ = 0.19 – 0.22 day^–1) and 4 to 14 ^∘C (μ = 0.13 – 0.16 day^–1), respectively. In contrast, optimal growth temperatures for NaviculaUMACC 231 and Chlamydomonas UMACC 229 were 4 ^∘C (μ = 0.34 day^–1) and 6–9 ^∘C (μ = 0.39 – 0.40 day^–1), respectively. The protein content of the Antarctic algae was markedly affected by culture temperature. All except Navicula UMACC 231 and Stichococcus UMACC 238 contained higher amount of proteins when grown at low temperatures (6–9 ^∘C). The percentage of PUFA, especially 20:5 in Navicula UMACC 231 decreased with increasing culture temperature. However, the percentages of unsaturated fatty acids did not show consistent trend with culture temperature for the other algae studied.     

Volatile halocarbon emissions by three tropical brown seaweeds under different irradiances

The emission rates of eight volatile halogenated compounds by three tropical brown seaweed species collected from Cape Rachado, west coast Peninsular Malaysia, under different irradiances have been determined. A purge-and-trap sample preparation system with a gas chromatograph and mass-selective detector was used to measure a suite of halocarbons released by Sargassum binderi Sonder ex J. Agardh, Padina australis Hauck, and Turbinaria conoides (J. Agardh) Kützing. All species are widely distributed in Peninsular Malaysia, with S. binderi a dominant seaweed species at our survey site. Release of few halocarbons was found to be influenced by irradiance. Correlations were also observed between emission of certain halocarbons with photosynthetic activity, especially bromo-and iodinated compounds (0.6?<?r?<0.9; p?<?0.01) suggesting that environmental factors such as light can affect the release of these volatile halogenated compounds by the seaweeds into the atmosphere. Compared with temperate and polar brown seaweeds, tropical species, such as T. conoides, may emit higher levels of bromoform, CHBr₃, and other halocarbons. It is therefore important to investigate the contribution of tropical seaweeds towards the local atmospheric composition of halocarbons.     

Assessment of Four Molecular Markers as Potential DNA Barcodes for Red Algae Kappaphycus Doty and Eucheuma J. Agardh (Solieriaceae,Rhodophyta)

DNA barcoding has been a major advancement in the field of taxonomy, seeing much effort put into the barcoding of wide taxa of organisms, macro and microalgae included. The mitochondrial-encoded cox1 and plastid-encoded rbcL has been proposed as potential DNA barcodes for rhodophytes, but are yet to be tested on the commercially important carrageenophytes Kappaphycus and Eucheuma. This study gauges the effectiveness of four markers, namely the mitochondrial cox1, cox2, cox2-3 spacer and the plastid rbcL in DNA barcoding on selected Kappaphycus and Eucheuma from Southeast Asia. Marker assessments were performed using established distance and tree-based identification criteria from earlier studies. Barcoding patterns on a larger scale were simulated by empirically testing on the commonly used cox2-3 spacer. The phylogeny of these rhodophytes was also briefly described. In this study, the cox2 marker which satisfies the prerequisites of DNA barcodes was found to exhibit moderately high interspecific divergences with no intraspecific variations, thus a promising marker for the DNA barcoding of Kappaphycus and Eucheuma. However, the already extensively used cox2-3 spacer was deemed to be in overall more appropriate as a DNA barcode for these two genera. On a wider scale, cox1 and rbcL were still better DNA barcodes across the rhodophyte taxa when practicality and cost-efficiency were taken into account. The phylogeny of Kappaphycus and Eucheuma were generally similar to those earlier reported. Still, the application of DNA barcoding has demonstrated our relatively poor taxonomic comprehension of these seaweeds, thus suggesting more in-depth efforts in taxonomic restructuring as well as establishment.