Isolation and Evaluation of Oil-Producing Microalgae from Subtropical Coastal and Brackish Waters

David K Y Lim,Yan Li,Peer M Schenk,Holger Schuhmann,Matthew Timmins,Sourabh Garg,Eugene S B Zhang,Skye R Thomas-Hall,Jonathan H Badger

doi:10.1371/journal.pone.0040751

Abstract

Microalgae have been widely reported as a promising source of biofuels, mainly based on their high areal productivity of biomass and lipids as triacylglycerides and the possibility for cultivation on non-arable land. The isolation and selection of suitable strains that are robust and display high growth and lipid accumulation rates is an important prerequisite for their successful cultivation as a bioenergy source, a process that can be compared to the initial selection and domestication of agricultural crops. We developed standard protocols for the isolation and cultivation for a range of marine and brackish microalgae. By comparing growth rates and lipid productivity, we assessed the potential of subtropical coastal and brackish microalgae for the production of biodiesel and other oil-based bioproducts. This study identified Nannochloropsis sp., Dunaniella salina and new isolates of Chlorella sp. and Tetraselmis sp. as suitable candidates for a multiple-product algae crop. We conclude that subtropical coastal microalgae display a variety of fatty acid profiles that offer a wide scope for several oil-based bioproducts, including biodiesel and omega-3 fatty acids. A biorefinery approach for microalgae would make economical production more feasible but challenges remain for efficient harvesting and extraction processes for some species.

Highlights

Interest in a renewable source of biofuels has recently intensified due to the increasing cost of petroleum-based fuel and the dangers of rising atmospheric CO2 levels
fatty acid methyl ester (FAME) productivity and fatty acids (FAs) composition as criteria, this study identified several algae strains to be suitable for biodiesel, including Tetraselmis sp. and Nannochloropsis sp. as highly versatile candidate strains for a multiple-product algal biorefinery
Additional microalgae strains were obtained from culture collections at Australian National Algae Culture Collection (ANACC), CSIRO, and two local isolates from Queensland Sea Scallops Trading Pty Ltd (QSST), Bundaberg

Summary

Introduction

Interest in a renewable source of biofuels has recently intensified due to the increasing cost of petroleum-based fuel and the dangers of rising atmospheric CO2 levels. Theoretical calculations of microalgal oil production (liter/ha) are 10 to 100-fold greater than traditional biodiesel crops such as palm oil [7], corn and soybeans [6,8,9], large-scale commercial algal oil production has yet to be established. Another major advantage of microalgae over higher plants as a fuel source is their environmental benefits. Despite having to grow in an aquatic medium, microalgae production may require less water than terrestrial oleaginous crops and can make use of saline, brackish, and/or coastal seawater [10,11]. Sequestering carbon into hard C-chips (Agri-char) via pyrolysis can be used to improve soil fertility, mitigating climate change by reintroducing durable carbon back into the soil [14], it is debatable how long this carbon will stay in the soil

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Results

Conclusion