Algae Based Bio-Plastics: Future of Green Economy

Plastic has become one of the most crucial requirements of the modern-day living. The continuous reliance on the petroleum-based, non-biodegradable plastics has resulted in increased global environmental damage and rapid depletion of fossil fuels. Bioplastic, with remarkably similar properties to petroleum-based plastics is a promising alternative to overcome these emerging challenges. Despite the fact that algae and cyanobacteria are feasible alternative source for bio-plastic, there have been limited studies on strain selection and optimization of culture conditions for the bio plastic production. Naturally, algae and cynobacteria can accumulate higher amount of metabolites under stress conditions however one of the recent study on genetic engineering of Synechocystis sp. coupled with abiotic stresses showed up to 81% of increase in PHB level in the transformed lines. This chapter provides summary of various studies done in the field of algal bio-plastics, including bioplastic properties, genetic engineering, current regulatory framework and future prospects of bioplastic. Further the applications of bioplastics in industrial sector as well as opportunities and role of bio plastic in green economy are also discussed

PSR1 is a global transcriptional regulator of phosphorus deficiency responses and carbon storage metabolism in Chlamydomonas reinhardtii.

Many eukaryotic microalgae modify their metabolism in response to nutrient stresses such as phosphorus (P) starvation, which substantially induces storage metabolite biosynthesis, but the genetic mechanisms regulating this response are poorly understood. Here, we show that P starvation-induced lipid and starch accumulation is inhibited in a Chlamydomonas reinhardtii mutant lacking the transcription factor Pi Starvation Response1 (PSR1). Transcriptomic analysis identified specific metabolism transcripts that are induced by P starvation but misregulated in the psr1 mutant. These include transcripts for starch and triacylglycerol synthesis but also transcripts for photosynthesis-, redox-, and stress signaling-related proteins. To further examine the role of PSR1 in regulating lipid and starch metabolism, PSR1 complementation lines in the psr1 strain and PSR1 overexpression lines in a cell wall-deficient strain were generated. PSR1 expression in the psr1 lines was shown to be functional due to rescue of the psr1 phenotype. PSR1 overexpression lines exhibited increased starch content and number of starch granules per cell, which correlated with a higher expression of specific starch metabolism genes but reduced neutral lipid content. Furthermore, this phenotype was consistent in the presence and absence of acetate. Together, these results identify a key transcriptional regulator in global metabolism and demonstrate transcriptional engineering in microalgae to modulate starch biosynthesis

Metabolic responses of eukaryotic microalgae to environmental stress limit the ability of FT-IR spectroscopy for species identification

AbstractFourier Transform Infrared (FT-IR) spectroscopy is a robust method for macromolecular analysis and differentiation of microorganisms. However, most studies are performed in controlled conditions and it is unclear whether this tool is appropriate for the identification of eukaryotic microalgae species from variable environments. In order to address this, nine closely-related species of marine and freshwater microalgae were grown under controlled (non-stressed) and variable (non-stressed and stressed) conditions, including nutrient-stressed and wastewater-stressed conditions. Following optimization of data processing methods, FT-IR spectra from all species and conditions were compared. The substantial metabolic changes that were caused by nutrient starvation restricted the ability of FT-IR spectroscopy to differentiate the microalgal species grown under variable conditions efficiently. Comparison of unsupervised and supervised multivariate data analysis methods found that principal component-discriminant function analysis was able best to differentiate between some species under controlled conditions but still gave poor differentiation under variable environmental conditions

Production of lipid-based fuels and chemicals from microalgae: An integrated experimental and model-based optimization study

Abstract Cultivation of microalgae is a promising long-term, sustainable candidate for biomass and oil for the production of fuel, food, nutraceuticals and other added-value products. Attention has been drawn to the use of computational and experimental validation studies aiming at the optimisation and the control of microalgal oil productivity either through the improvement of the growth mechanism or through the application of metabolic engineering methods to microalgae. Optimisation of such a system can be achieved through the evaluation of organic carbon sources, nutrients and water supply, leading to high oil yield. The main objective of this work is to develop a novel integrated experimental and computational approach, utilising a microalgal strain grown at bench-scale, with the aim to systematically identify the conditions that optimise growth and lipid production, in order to ultimately develop a cost-effective process to improve the system economic viability and overall sustainability. To achieve this, a detailed model has been constructed through a multi-parameter quantification methodology taking into account photo-heterotrophic biomass growth. The corresponding growth rate is based on carbon substrate concentration, nitrogen and light availability. The developed model also considers the pH of the medium. Parameter estimation was undertaken using the proposed model in conjunction with an extensive number of experimental data taken at a range of operating conditions. The model was validated and utilised to determine the optimal operating conditions for bench-scale batch lipid oil production

Metal bioremediation by CrMTP4 over-expressing Chlamydomonas reinhardtii in comparison to natural wastewater-tolerant microalgae strains

Metal pollution in freshwater bodies is a long-standing challenge with large expense required to clean-up pollutants such as Cd. There is widespread interest in the potentially low-cost and sustainable use of biological material to perform bioremediation, such as the use of microalgae. Efficient metal bioremediation capacity requires both the ability to tolerate metal stress and metal accumulation. Here, the role of a Chlamydomonas reinhardtii metal tolerance protein (MTP) was examined for enhanced Cd tolerance and uptake. The CrMTP4 gene is a member of the Mn-CDF clade of the cation diffusion facilitator family of metal transporters but is able to provide tolerance and sequestration for Mn and Cd, but not other metals, when expressed in yeast. Over-expression of CrMTP4 in C. reinhardtii yielded a significant increase in tolerance to Cd toxicity and increased Cd accumulation although tolerance to Mn was not increased. In comparison, the metal tolerance of three chlorophyte microalgae strains (Chlorella luteoviridis, Parachlorella hussii, and Parachlorella kessleri) that had previously been adapted to wastewater growth was examined. In comparison to wild type C. reinhardtii, all three natural strains showed significantly increased tolerance to Cd, Cu, Al and Zn, and furthermore their Cd tolerance and uptake was greater than that of the CrMTP4 over-expression strains. Despite CrMTP4 gene over-expression being a successful strategy to enhance the Cd bioremediation potential of a metal-sensitive microalga, a single gene manipulation cannot compete with naturally adapted strain mechanisms that are likely to be multigenic and due in part to oxidative stress tolerance

Changes in lipid and carotenoid metabolism in Chlamydomonas reinhardtii during induction of CO2-concentrating mechanism: Cellular response to low CO2 stress

Photosynthetic organisms strictly depend on CO2 availability and the CO2:O-2 ratio, as both CO2/O-2 compete for catalytic site of Rubisco. Green alga Chlamydomonas reinhardtii, can overcome CO2 shortage by inducing CO2-concentrating mechanism (CCM). Cells transferred to low-CO2 are subjected to light-driven oxidative stress due to decrease in the electron sink. Response to environmental perturbations is mediated to some extent by changes in the lipid and carotenoid metabolism. We thus hypothesize that when cells are challenged with changes in CO2 availability, changes in the lipidome and carotenoids profile occur. These changes expected to be transient, when CCM is activated, CO2 limitation will be substantially ameliorated. In our experiments, cells were transferred from high (5%) to low (air equilibrium) CO2. qPCR analysis of genes related to CCM and lipid metabolism was carried out. Lipidome was analyzed both in whole cells and in isolated lipid droplets. We characterized the changes in polar lipids, fatty acids and ketocarotenoids. In general, polar lipids significantly and transiently increased in lipid droplets during CCM. Similar pattern was observed for xanthophylls, ketocarotenoids and their esters. The data supports our hypothesis about the roles of lipids and carotenoids in tackling the oxidative stress associated with acclimation to sub-saturating CO2