Isoprene hotspots at the Western Coast of Antarctic Peninsula during MASEC′16

Isoprene (C⁠5H⁠8) plays an important role in the formation of surface ozone (O3) and the secondary organic aerosol (SOA) which contributed to the climate change. This study aims to determine hourly distribution of tropospheric isoprene over the Western Coast of Antarctic Peninsula (WCAP) during the Malaysian Antarctic Scientific Expedition Cruise 2016 (MASEC′16). In-situ measurements of isoprene were taken using a custom-built gas chromatography with photoionization detector, known as iDirac. Biological parameters such as chlorophyll a (chl-a) and particulate organic carbon (POC) were compared to the in-situ isoprene measurements. Significant positive correlation was observed between isoprene and POC concentrations (r2=0.67, p<0.001), but not between isoprene and chl-a. The hotspots of isoprene over maritime Antarctic were then were investigated using NAME dispersion model reanalysis. Measurements showed that isoprene mixing ratio were the highest over region of King George Island, Deception Island and Booth Island with values of ∼5.0, ∼0.9 and ∼5.2ppb, respectively. Backward trajectory analysis showed that air masses may have lifted the isoprene emitted by marine algae. We believe our findings provide valuable data set of isoprene estimation over the under sampled WCAP

Combined effects of glufosinate ammonium and temperature on the growth, photosynthetic pigment content and oxidative stress response of Chlorella sp. and Pseudokirchneriella subcapitata

There has been concern over the potential adverse effects of glufosinate ammonium, a widely used herbicide, on microalgae. This study aimed to assess the combined effects of glufosinate and temperature on Chlorella sp. CHSS262, which was isolated from a farmland in Malaysia, in comparison with the model microalga Pseudokirchneriella subcapitata. The following parameters were assessed: growth, pigment content and oxidative stress response. Results showed that Chlorella sp. (EC25 = 120 μg mL−1) was more tolerant to glufosinate than P. subcapitata (EC25 = 43 μg mL−1) when grown at 28 °C. Both microalgae were then exposed to glufosinate at EC25 at different temperatures (10, 18, 28, 33 and 38 °C) for 8 days. While P. subcapitata could grow from 10 to 38 °C, with optimal temperature between 18 and 28 °C, the lower temperature limit of Chlorella sp. was 18 °C. There was only minimal growth inhibitory effect of glufosinate on Chlorella sp. over the range of temperatures tested. In comparison, the inhibitory effect of glufosinate on P. subcapitata was less pronounced at extreme temperatures (10 and 38 °C) compared to that at 18 to 33 °C. High ROS levels and increased lipid peroxidation were detected in P. subcapitata at 10 and 38 °C in both the control and glufosinate-treated cultures. Principal component analysis (PCA) showed that there was significant correlation between ROS and lipid peroxidation in P. subcapitata but not in Chlorella sp. Overall, the results showed that Chlorella sp. and P. subcapitata responded differently to temperature and glufosinate, especially in regard to oxidative stress response although both species were highly resistant to the herbicide

Metabolic and physiological regulation of Chlorella sp. (Trebouxiophyceae, Chlorophyta) under nitrogen deprivation

A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel production. In this study, photosynthetic efficiency, biochemical profiles and non-targeted metabolic profiling were studied to compare between the nitrogen-replete and deplete conditions. Slowed growth, change in photosynthetic pigments and lowered photosynthetic efficiency were observed in response to nitrogen deprivation. Biochemical profiles of the cultures showed an increased level of carbohydrate, lipids and total fatty acids, while the total soluble protein content was lowered. A trend of fatty acid saturation was observed in the nitrogen-deplete culture with an increase in the level of saturated fatty acids especially C16:0 and C18:0, accompanied by a decrease in proportions of monounsaturated and polyunsaturated fatty acids. Fifty-nine metabolites, including amino acids, lipids, phytochemical compounds, vitamins and cofactors were significantly dysregulated and annotated in this study. Pathway mapping analysis revealed a rewiring of metabolic pathways in the cells, particularly purine, carotenoid, nicotinate and nicotinamide, and amino acid metabolisms. Within the treatment period of nitrogen deprivation, the key processes involved were reshuffling of nitrogen from proteins and photosynthetic machinery, together with carbon repartitioning in carbohydrates and lipids