Differences in photoprotective pigment production between Japanese and Australian strains of Chattonella marina (Raphidophyceae)

Previous studies have shown that isolates of Chattonella marina from Australia and Japan exhibit differences in tolerance to high intensities of visible light. Here we show that the Australian strain of C. marina produces around five times more UV-absorbing mycosporine amino acids (MAAs) than the Japanese strain. This corresponds with 66% increased growth by the Australian strain under UVB exposure compared to no UV exposure. The MAA mycosporine-glycine, which reportedly acts as an antioxidant, was found in high quantity (110 fg cell^-1) in the Australian but was absent in the Japanese strain. In contrast, changes in the concentration of violaxanthin and zeaxanthin per cell were 4.7-4.8 times greater in the Japanese relative to the Australian strain suggesting that the Japanese strain uses a xanthophyll cycle to moderate inhibition by high photosynthetically active radiation (PAR) irradiance. Increased MAA production under high irradiance was also observed in other Australian strains of Chattonella, but not noted in other Japanese strains suggesting ecophenotypic adaptation due to differing environmental conditions.     

Transesterification of Nannochloropsis oculata microalga’s lipid to biodiesel on Al2O3 supported CaO and MgO catalysts

In this study, we present the activities of Al₂O₃ supported CaO and MgO catalysts in the transesterification of lipid of yellow green microalgae, Nannochloropsis oculata, as a function of methanol amount and the CaO and MgO loadings at 50 °C. We found that pure CaO and MgO were not active and CaO/Al₂O₃ catalyst among all the mixed oxide catalysts showed the highest activity. Not only the basic site density but also the basic strength is important to achieve the high biodiesel yield. Biodiesel yield over 80 wt.% CaO/Al₂O₃ catalyst increased to 97.5% from 23% when methanol/lipid molar ratio was 30.     

Development of microsatellite markers in red-tide causative species Prorocentrum micans (Dinophyceae)

We isolated eight polymorphic microsatellites from the red-tide causing microalgae Prorocentrum micans. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from two to six with an average of 3.9, and the estimate of gene diversity was from 0.15 to 0.55 with an average of 0.41 across the eight microsatellites. We consider that these loci have a potential to reveal the genetic structure and gene flow among P. micans populations.     

The strain concept in phytoplankton ecology

Laboratory cultures are important tools for investigating the biology of microalgae, allowing experimentation under controlled conditions. This control is critical for comparative studies, such as those often used to investigate intra-specific variation in properties of interest. By holding the environment constant, the experimentalist can gain insight into the genetic basis of phytoplankton phenotypes and by extension, into the adaptive history of those genotypes. In most cases the adaptations of interest are those that the algae have evolved in response to their natural environment. However, here it is argued that such experiments may instead reveal evolutionary adaptations to, and/or non-adaptive changes induced by, the culture conditions under which the alga is maintained. We present a review of the processes of evolution as they pertain to microalgal culture, and illustrate this discussion with examples of in-culture evolution from both within and outside the field of phycology. With these considerations in mind, recommendations are made for experimental practice focusing on comparative physiology, for which the effects of in-culture evolution are particularly confounding. Finally we argue that, although problematic in some contexts, the evolutionary propensities of phytoplankton cultures actually present an important opportunity for experimental evolutionary research with direct environmental significance.     

Extractive disruption process integration using ultrasonication and an aqueous two‐phase system for protein recovery from Chlorella sorokiniana

Microalgae emerge as the most promising protein sources for aquaculture industry. However, the commercial proteins production at low cost remains a challenge. The process of harnessing microalgal proteins involves several steps such as cell disruption, isolation and extraction. The discrete processes are generally complicated, time‐consuming and costly. To date, the notion of integrating microalgal cell disruption and proteins recovery process into one step is yet to explore. Hence, this study aimed to investigate the feasibility of applying methanol/potassium ATPS in the integrated process for proteins recovery from Chlorella sorokiniana. Parameters such as salt types, salt concentrations, methanol concentrations, NaCl addition were optimized. The possibility of upscaling and the effectiveness of recycling the phase components were also studied. The results showed that ATPS formed by 30% (w/w) K₃PO₄ and 20% (w/w) methanol with 3% (w/w) NaCl addition was optimum for proteins recovery. In this system, the partition coefficient and yield were 7.28 and 84.23%, respectively. There were no significant differences in the partition coefficient and yield when the integrated process was upscaled to 100‐fold. The recovered phase components can still be recycled effectively at fifth cycle. In conclusions, this method is simple, rapid, environmental friendly and could be implemented at large scale.     

Palm oil mill effluent (POME) cultured marine microalgae as supplementary diet for rotifer culture

Malaysia is the world’s leading producer of palm oil products that contribute US$ 7.5 billion in export revenues. Like any other agro-based industries, it generates waste that could be utilized as a source of organic nutrients for microalgae culture. Present investigation delves upon Isochrysis sp. culture in POME modified medium and its utilization as a supplement to Nanochloropsis sp. in rotifer cultures. The culture conditions were optimized using a 1 L photobioreactor (Temp: 23°C, illumination: 180 ∼ 200 μmol photons m⁻²s⁻¹, n = 6) and scaled up to 10 L outdoor system (Temp: 26–29°C, illumination: 50 ∼ 180 μmol photons m⁻²s⁻¹, n = 3). Algal growth rate in photobioreactor (μ = 0.0363 h⁻¹) was 55% higher compared to outdoor culture (μ = 0.0163 h⁻¹), but biomass production was 1.3 times higher in outdoor culture (Outdoor = 91.7 mg m⁻²d⁻¹; Photobioreactor = 69 mg m⁻²d⁻¹). Outdoor culture produced 18% higher lipid; while total fatty acids (FA) was not significantly affected by the change in culture systems as both cultures yield almost similar concentrations of fatty acids per gram of sample (photobioreactor = 119.17 mg g⁻¹; outdoor culture = 104.50 mg g⁻¹); however, outdoor cultured Isochrysis sp. had 26% more polyunsaturated fatty acids (PUFAs). Rotifers cultured in Isochrysis sp./ Nanochloropsis sp. (1:1, v/v) mixture gave similar growth rate as 100% Nanochoropsis sp. culture (μ = 0.40 d⁻¹), but had 45% higher counts of rotifers with eggs (t = 7, maximum). The Isochrysis sp. culture successfully lowered the nitrate (46%) and orthophosphate (83%) during outdoor culture.     

Effects of nitrogen sources on cell growth and lipid accumulation of green alga <Emphasis Type="Italic">Neochloris oleoabundans</Emphasis>

Microalgal lipids are the oils of future for sustainable biodiesel production. However, relatively high production costs due to low lipid productivity have been one of the major obstacles impeding their commercial production. We studied the effects of nitrogen sources and their concentrations on cell growth and lipid accumulation of Neochloris oleoabundans, one of the most promising oil-rich microalgal species. While the highest lipid cell content of 0.40 g/g was obtained at the lowest sodium nitrate concentration (3 mM), a remarkable lipid productivity of 0.133 g l⁻¹ day⁻¹ was achieved at 5 mM with a lipid cell content of 0.34 g/g and a biomass productivity of 0.40 g l⁻¹ day⁻¹. The highest biomass productivity was obtained at 10 mM sodium nitrate, with a biomass concentration of 3.2 g/l and a biomass productivity of 0.63 g l⁻¹ day⁻¹. It was observed that cell growth continued after the exhaustion of external nitrogen pool, hypothetically supported by the consumption of intracellular nitrogen pools such as chlorophyll molecules. The relationship among nitrate depletion, cell growth, lipid cell content, and cell chlorophyll content are discussed.     

Studies on the transmission of WSSV (white spot syndrome virus) in juvenile Marsupenaeus japonicus via marine microalgae

We studied the possible role that marine microalgae may play during the outbreaks of WSS (white spot syndrome). In order to elucidate the possibility of marine microalgae carrying WSSV (white spot syndrome virus), six marine microalgae (Isochrysis galbana, Skeletonema costatum, Chlorella sp., Heterosigma akashiwo, Scrippsiella trochoidea, Dunaliella salina) were co-cultured with adult Marsupenaeus japonicus infected with WSSV and were assayed daily by nested-PCR to study whether they could carry WSSV. Further experiments were conducted to investigate whether the virus carried by microalgae could re-infect juvenile M. japonicus. Results showed that all of the experimental microalgae, except H. akashiwo could carry WSSV, and among them, Chlorella sp. and S. trochoidea had the strongest WSSV-carrying ability. Unlike other invertebrate carriers of WSSV, the WSSV detections in microalgae, which were positive after 1 and 3 days, were negative after 10days of incubation. WSSV detection results in juvenile M. japonicus showed that the juvenile shrimp were re-infected by co-cultured Chlorella sp., although the juvenile M. japonicus carried so small an amount of WSSV that it could only be detected by nested-PCR. The results of this experiment suggest that microalgae might be one possible horizontal transmission pathway for WSSV. Further research, however, is required to better understand the factors behind the different carrying abilities and virus-carrying mechanisms of different microalgae.     

微藻油脂合成代谢途径及调控机制的研究进展

随着经济的快速发展,各国对石油的需求仍有增无减,但是石油作为不可再生能源不利于可持续发展。相比之下,生物柴油应运而生且已发展到了第三代,而微藻作为第三代生物柴油的主角因为具有生长速度快,不占用耕地等优势,已逐渐成为具有极大发展潜力的能源原料,所以利用微藻生产生物柴油的技术近年来也成为研究的重点。本综述针对微藻容易进行基因改造的优势,综述了国内外对微藻油脂代谢通路的研究现状及进展,讨论了目前的基因改造方法对通路中关键酶产生的影响,以求找到能有效并稳定增强微藻油脂代谢途径的方法,为以后的研究提供理论指导。     

产油微藻Auxenochlorella protothecoides UTEX 2341对镉胁迫的生理响应及抗性机理

【背景】重金属镉(Cd)污染问题日益严峻。微藻是一种良好的生物吸附剂。目前研究多关注于微藻对Cd的去除率及吸附性能方面,对其抗Cd机理的研究比较少。【目的】以产油微藻Auxenochlorella protothecoides UTEX 2341为材料,研究Cd胁迫对UTEX 2341生理性状、抗性机理及产油的影响。【方法】测定微藻在0-5mmol/LCd胁迫下的生长产油情况,并进一步分析2mmol/LCd胁迫下藻体中色素、可溶性蛋白和油脂含量的变化,以及藻体亚显微结构、抗氧化酶和抗氧化剂、脂肪酸组分的改变情况。【结果】Auxenochlorella protothecoides UTEX 2341能够耐受2 mmol/L Cd胁迫,虽然其生物量和叶绿素含量在Cd胁迫下略有降低,但油脂产量显著增加,胁迫168 h时为1.60 g/L,是对照的1.77倍。此外,高浓度Cd引起了胞内活性氧的积累。抗性机理分析表明高Cd胁迫显著抑制了微藻体内的抗氧化酶活性,但非酶抗氧化剂类胡萝卜素和还原性谷胱甘肽的含量显著增加,分别是对照的1.42倍和4.5倍,从而缓解高浓度Cd对微藻细胞造成的氧化损伤,减轻Cd的毒性。脂肪酸组分分析结果表明,Cd胁迫下油酸(C18:1)含量增加,且脂肪酸成分中C16-C18的含量达96%-98%,符合生物柴油的生产标准。【结论】该研究为揭示微藻抗Cd的机理以及Cd胁迫下微藻柴油合成的调控机理提供了一定的研究基础。