Enzymatic in-situ transesterification of neutral lipids from simulated wastewater cultured Chlorella emersonii and Pseudokirchneriella subcapitata to sustainably produce fatty acid methyl esters

Priyanka Priyanka,Gemma K Kinsella,Gary T Henehan,Barry J Ryan

doi:10.1016/j.biteb.2020.100489

Priyanka Priyanka, Gemma K Kinsella + Show 2 more

Open Access

https://doi.org/10.1016/j.biteb.2020.100489

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Abstract

Alternative, more sustainable and environmentally positive, sources of energy are one of the current global challenges. One approach to achieving more sustainable sources of energy is to use waste from one system as a raw material for energy production, following the circular biosystem philosophy. This study successfully adopted this approach whereby microalgae strains Chlorella emersonii and Pseudokirchneriella subcapitata were bioprospected and metabolically engineered in simulated wastewater supplemented with glucose to produce neutral lipids. Using a two-step cultivation approach neutral lipid content was enhanced in Chlorella emersonii and Pseudokirchneriella subcapitata biomass. Via in-situ transesterification, these neutral lipids were subsequently bioconverted to biodiesel feedstock fatty acid methyl esters using novel solvent stable lipase(s) from Pseudomonas reinekei and Pseudomonas brenneri. The culturing of appropriate microalgae on wastewater, and bioconversion via organo-stable lipases may provide a commercially viable and sustainable biodiesel feedstock to help address the current global energy challenge.

Highlights

Fossil fuels, such as petrol, coal, and natural gas, contribute 88% of global energy consumption; with the transport sector subsequently being a major contributor of CO2 global emissions, which, by 2050 is estimated to increase to 2 billion vehicles (Balat and Balat, 2010)
The lipid content in microalgae varies from 20-40% biomass dry weight, lipid content as high as 85% biomass dry weight has been reported in certain microalgal strains (Mairet et al, 2011)
Nile Red dye was used for quantification of neutral lipids in the current study as a high correlation between neutral lipid content and Nile Red fluorescence has been established and the assay is used as the quantitative analysis method for neutral lipid quantification in a variety of microalgae, such as Chlorella sp. (Chen et al, 2009; Huang, Chen and Chen, 2009)

Summary

Introduction

Fossil fuels, such as petrol, coal, and natural gas, contribute 88% of global energy consumption; with the transport sector subsequently being a major contributor of CO2 global emissions, which, by 2050 is estimated to increase to 2 billion vehicles (Balat and Balat, 2010). FAMEs, as a precursor for biodiesel, were synthesized via in-situ transesterification using novel lipases and the neutral lipids from the biomass of Chlorella emersonii and Pseudokirchneriella subcapitata. Lipases can catalyse both hydrolysis and synthesis of long-chain acylglycerols and most importantly can catalyse biodiesel production since they are the only enzymes that catalyse the synthesis of esters (i.e. transesterification (Jaeger and Reetzb, 1998). This study employed novel, solvent stable lipases from P. reinekei (H1) and P. brenneri (H3) for the in-situ transesterification of neutral lipids from Chlorella emersonii and Pseudokirchneriella subcapitata to produce sustainable, economical and environmentally positive FAMEs that were chemically comparable to commercially available biodiesel FAMEs mix

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