Izabela Krzemińska

Alterations of the lipid content and fatty acid profile of Chlorella protothecoides under different light intensities.

Chlorella protothecoides is a valuable source of lipids that may be used for biodiesel production. The present work shows analysis of the potential of photoheterotrophic cultivation of C. protothecoides under various light intensities aiming to identify the conditions with maximal biomass and lipid content. An increase in light intensity was associated with an increased specific growth rate and a shortened doubling time. Also, the relative total lipid content increased from 24.8% to 37.5% with increase of light intensity. The composition of fatty acid methyl esters was affected by light intensity with the C16-18 fatty acids increased from 76.97% to 90.24% of total fatty acids. However, the content of linolenic acids decreased with the increase of the culture irradiance. These studies indicate that cultures irradiated with high light intensities achieve the minimal specifications for biodiesel quality on linolenic acids and thus are suitable for biodiesel production.

Physical methods of microalgal biomass pretreatment

Abstract The prospect of depletion of natural energy resources on the Earth forces researchers to seek and explore new and alternative energy sources. Biomass is a composite resource that can be used in many ways leading to diversity of products. Therefore, microalgal biomass offers great potential. The main aim of this study is to find the best physical method of microalgal biomass pretreatment that guarantees efficient lipid extraction. These studies identifies biochemical composition of microalgal biomass as source for biodisel production. The influence of drying at different temperatures and lyophilization was investigated. In addition, wet and untreated biomass was examined. Cell disruption (sonication and microwave) techniques were used to improve lipid extraction from wet biomass. Additionally, two different extraction methods were carried out to select the best method of crude oil extraction. The results of this study show that wet biomass after sonication is the most suitable for extraction. The fatty acid composition of microalgal biomass includes linoleic acid (C18:2), palmitic acid (C16:0), oleic acid (C18:1), linolenic acid (C18:3), and stearic acid (C18:0), which play a key role in biodiesel production.

Glucose supplementation-induced changes in the Auxenochlorella protothecoides fatty acid composition suitable for biodiesel production.

This study evaluates the effect of different concentrations of glucose supplementation on growth, lipid accumulation, and the fatty acid profile in the Auxenochlorella protothecoides. Addition of glucose promoted the growth rate and decreased the chlorophyll content. Compared with photoautotrophic cells, an increase in the lipid content was observed in mixotrophic cells. The glucose addition induced changes in the fatty acid profile. Higher content of saturated fatty acids was found in the case of cells growing in the glucose-free medium. Oleic acid was the predominant component in mixotrophic cells supplemented with 5gL(-1) glucose, while linoleic acids dominated in cultures supplemented with both 1 and 3gL(-1) glucose. The use of glucose was associated with decreased levels of linolenic acid and PUFA. The changes in the fatty acid profile in mixotrophic cells are favourable for biodiesel production.

Cultivation of Chlorella protothecoides in photobioreactors: The combined impact of photoperiod and CO2 concentration

Algal biomass is regarded as an alternative source for producing renewable fuels, given the chemical nature of storage products: lipids, starch, and proteins. Many factors affecting the production of microalgal biomass and lipid accumulation include the light and CO2 concentration, i.e. critical factors for determination of the biochemical composition of microalgal biomass. Our objective was to evaluate the effect of three different light/dark photoperiods (12/12 h, 16/8 h, 24/0 h) and the CO2 concentration (from air and 5% v/v CO2‐enriched air) on the growth rate, productivity, and changes in the biochemical composition of Chlorella protothecoides biomass. Continuous illumination stimulated growth under supplementation of air CO2. At 5% CO2, the maximum C. protothecoides growth rate was found under 16/8 light/dark cycles and longer duration of light yielded a decrease in the specific growth rate. The photoperiods and CO2 concentrations influenced the biomass productivity. Chlorella protothecoides produced biomass more efficiently at the 24/0 and 16/8 light/dark cycles under supplementation of air CO2 than at addition of 5% CO2. However, under the 12/12 light/dark cycle, biomass productivity was higher at 5% CO2. The light photoperiod greater than 16 h did not increase biomass productivity. These factors also influenced the content of lipids and carbohydrates. A maximal lipid content was observed for the 24‐h photoperiod for air CO2, whereas the addition of 5% CO2 affected lipid and carbohydrate production.

Stimulatory effect of indole-3-acetic acid and continuous illumination on the growth of Parachlorella kessleri

Abstract The effects of the phytohormone indole-3-acetic acid and various conditions of illumination on the growth of Parachlorella kessleri were investigated. Two variants of illumination: continuous and photoperiod 16/8 h (light/dark) and two concentrations of the phytohormone – 10−4 M and 10−5 M of indole-3-acetic acid were used in the experiment. The results of this study show that the addition of the higher concentration of indole-3-acetic acid stimulated the growth of P. kessleri more efficiently than the addition of the lower concentration of indole-3-acetic acid. This dependence can be observed in both variants of illumination. Increased biomass productivity was observed in the photo-period conditions. Both the addition of the phytohormone and the conditions of the illumination had an impact on the number of P. kessleri cells. An increased number of cells was observed under the conditions of continuous illumination. This result has shown that the continuous illumination and the higher concentration of the phytohormone stimulated the growth of P. kessleri more effectively than the shorter duration of light (16/8 h (light/dark)).

Effect of stress conditions on improvement of lipid and carbohydrate accumulation under photoautotrophic cultivation of Chlorophyta

Abstract Microalgae are a valuable source of biologically active compounds, e.g. lipids, carbohydrates, and pigments. In recent years, considerable interest has focused on unicellular photoautotrophic Chlorophyta. Green microalgae are characterized by their rapid growth and carbon dioxide binding in photosynthesis. Depending on the type of accumulated molecules (lipids or starch), photosynthetic cells can be used in the production of biodiesel, bioethanol, or biogas. However, low starch and lipid content may be an obstacle for using microalgal biomass as feedstocks for biofuels and bioproducts. Commercial cultivation of microalgae depends on a high content of valuable metabolites accumulated in cells. In this review, we evaluated factors controlling the synthesis and accumulation of lipids and starch, i.e. nitrogen and phosphorus availability and the impact of inorganic carbon, light, and temperature, under photoautotrophic growth conditions. The composition of microalgal biomass can be improved by variou...

Effectiveness of Parachlorella kessleri cell disruption evaluated with the use of laser light scattering methods

The main objective of this study is to demonstrate the possibilities of using laser light scattering methods, dynamic light scattering and laser Doppler electrophoresis, as suitable methods in investigations of algal production biosystems and biotechnology. This paper highlights the innovative use of the dynamic light scattering (DLS) methods for monitoring the destruction of Parachlorella kessleri cells. Additionally, these results indicate electrophoretic mobility as a new parameter to investigate the effectiveness of cell disruption prior to extraction conducted to optimise the biotechnological processes of recovery of microalgal intracellular metabolites. The efficacy of P. kessleri cell disintegration by ultrasound was determined by measurements of the number of cells with the algal cell reduction (CRns), relative mean hydrodynamic diameter (Rdt) and electrophoretic mobility after applying different lengths of ultrasound exposure to a cell suspension. It was found that stationary-phase cells were the most resistant to the ultrasound treatment, especially at low values of the optical density. Both the relative hydrodynamic diameter and the electrophoretic mobility of cells were correlated statistically significantly with the time of sonication (t) and the algal cell reduction. The relationships allowed estimation of the sonication time needed for total cell disruption.