Effects of sulfur and phosphorus concentration on the lipid accumulation and fatty acid profile in Chlorella vulgaris (Chlorophyta).

Nutrient deficiency induces a variety of cellular responses, including an increase in lipid accumulation in microalgae. Nitrogen starvation is the most studied deprivation. Here, we determine the effects of phosphorus and sulfur limitation on lipid accumulation in Chlorella vulgaris. A set of 9 experiments were performed, varying the initial concentration of these nutrients (set to 0, 50, and 100% of their original composition in Bold's basal medium). According to our results, the variation of P and S modified the specific growth rate, lag phase, and cell generation time. The ratio of 50%P and 0%S significantly increased the total lipid concentration. The fatty acid profile was dominated by C16:0, C18:0, and C18:1; a considerable increase in C20:5 was observed with 0%P and 50%S and 0%P and 100%S. Regarding neutral lipids, the response surface methodology (RSM) indicates that the maximum was observed when S was between 40 and 60% and P was between 95 and 100%. Therefore, the enhanced production of lipids caused by P and S limitation may contribute to the efficient oil production useful for algal biofuels.

Effect of green and red light in lipid accumulation and transcriptional profile of genes implicated in lipid biosynthesis in Chlamydomonas reinhardtii.

Microalgae have the potential to accumulate triacylglycerols under different light spectra. In this work, Chlamydomonas reinhardtii was grown under white (400-700 nm), red (650 nm), and green (550 nm) lights. According to our results, red light (650 nm) has a positive effect in the microalgae growth and chlorophyll concentration. About the lipid content, the control culture (white light-illuminated) reached a 4.4% of dry cell weight (dcw), whereas the culture grown at 550 nm showed an increase of 1.35-fold in the lipids accumulation (5.96% dcw). Interestingly, the most significant accumulation was found in the culture grown at 650 nm (14.78% dcw) which means 3.36-fold higher with respect to the white light-illuminated culture. The most abundant fatty acids found in lipid extracts obtained from the cultures under different light wavelength were palmitic (C16: 0), oleic (C18: 1n9), stearidonic (C18: 4), and linoleic (C18: 2), which are useful in the biodiesel production. Changes in gene expression in response to different wavelength illuminations were assessed; however, an in-depth analysis of a larger number of genes involved in lipid biosynthesis is necessary to fully explain the highest accumulation of lipids in the culture grown under red light. This approach will be useful to find a sustainable source of lipids for biodiesel production. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1404-1411, 2016.

Identification of gene transcripts involved in lipid biosynthesis in Chlamydomonas reinhardtii under nitrogen, iron and sulfur deprivation.

Chlamydomonas reinhardtii is able to accumulate large amounts of triacylglycerides, the major feedstock for biodiesel production, when grown under stress conditions. In order to characterize gene transcripts induced under nitrogen, iron, and sulfur deprivation in C. reinhardtii; 583 expressed sequence tags (ESTs) were generated through a cDNA library. These sequences were subjected to contig assembly resulting in 30 contigs and 76 singletons. The comparison of the ESTs obtained with public databases allowed to assign putative functions to 66.7 % of the sequences. An important group of the identified genes are related to the lipid metabolic process. A phylogenetic analysis of these sequences identified five isoforms of diacylglycerol O-acyltransferase type 2 (DGAT-2). These genes were selected to measure their relative expression under these stress conditions by means of qRT-PCR. According to the results, the accumulation of DGTT1 mRNA increases considerably under nitrogen and iron inanition when compared to the other isoforms, which indicated that each isoform participates at different levels under each stress condition. These results can help to identify potential genes to be overexpressed by genetic engineering in C. reinhardtii.

Características físico-químicas de la leche de ovejas Rambouillet bajo manejo intensivo / Physicochemical characteriztics of Rambouillet ewes's milk under intensive management

El propósito de este trabajo fue determinar la composición fisicoquímica de la leche de ovejas Rambouillet manejadas en estabulación. Para tal efecto se utilizaron durante un periodo de lactancia de 12 semanas, 36 ovejas Rambouillet entre 2 y 5 años de edad con un peso promedio de 60 ± 5 kg, que habían parido solamente una cría. Se tomaron muestras de la leche en las semanas 1, 3, 6, 8 y 12, y el análisis físicoquímico se realizó utilizando métodos tradicionales de laboratorio. El análisis estadístico se efectuó utilizando el paquete “R” y teniendo como variables dependientes sólidos totales, grasa, proteína, lactosa, cenizas, acidez real, densidad y pH, mientras que laúnica variable independiente fue etapa de lactancia. Los promedios generales de la composición de la leche fueron: sólidos totales 16,89 ± 2,14; grasa 5,78 ± 2,09; proteína 5,26 ± 0,49; lactosa 4,54 ± 0,35; cenizas 0,92 ± 0,07; acidez real 2,05 ± 0,30; densidad 1,036 ± 2,9 x 10 –3; y pH 6,68 ± 0,17. Se presentaron diferencias significativas (P<0,05) de los componentes de la leche durante el transcurso de la lactancia, excepto en el pH (P>0,05). En sólidos totales, grasa, proteína y densidad hubo un incremento a partir de la semana 6; la lactosa y cenizas tuvieron un decremento en las semanas 12 y 8, respectivamente, mientras que la acidez real aumentó a partir delinicio de la lactancia. Las características fisicoquímicas de la leche de ovejas Rambouillet son semejantes a las que se encuentran en otras razas, por lo que es posible utilizar su leche durante periodos cortos y procesarla con fines industriales, principalmente en quesos.

The aim of this work was to determine the physicochemical composition of Rambouillet ewe’s milk in intensive management for this, 36 Rambouillet ewes, 2-5 years old, with an average body weight of 60 kg, that had given birth to a single lamb, were utilized during 12-week lactation period. Milk simples were taken in weeks 1, 3, 6, 8 and 12 and the physicochemical analysis was performed utilizing traditional laboratory methods. The statistical analysis was carried out utilizing the “R” statistical package with total solids, fat, protein, lactose, ashes, real acidity, density, and pH as dependent variables, and lactation stage as the only independent variable. Overall means for the milk composition were: total solids 16.89 ± 2.14%, fat 5.78 ± 2.09 percent, protein 5.26 ± 0.49 percent, lactose 4.54 ± 0.35 percent, ashes 0.92 ± 0.07 percent, real acidity 2.05 ± 0.30 percent, density 1.036 ± 2.9 x 10 –3 and pH 6.68 ± 0.17. There were significant differences (P<0.05) of the milk components during lactation. except in pH (P>0.05). From week 6 on there was an increase in total solids, fat, protein, and density; lactose and ashes had a decrease in weeks 12 and 8, respectively, whereas real acidity had an increase from week 1 on. Physicochemical characteristics of Rambouilet ewes’s milk are not very different from those found in other breeds, for which it is possible to utilize the milk of these ewes for short periods and process it with industrial purposes, mainly in cheese.