Ravi V. Durvasula and Durvasula V. Subba Rao

Center for Global Health, Department of Internal Medicine University of New Mexico School of Medicine and The Raymond G. Murphy VA Medical Center Albuquerque, New Mexico, USA

Vadrevu S. Rao

Department of Mathematics

Jawaharlal Nehru Technological University Hyderabad Kukatpally Campus, Hyderabad, India

CONTENTS

13.1 Introduction…………………………………………………………………………………………….. 201

13.2 Cultivation………………………………………………………………………………………………. 203

13.3 Native Strains, Consortia of Species, and Extremophiles……………………….. 206

13.4 Variations in Algal Production: Crucial but Ignored……………………………….. 208

13.5 Lipid Variations: Physiological State………………………………………………………. 210

13.6 Biochemical Manipulation: Higher Yields……………………………………………… 213

13.7 Harvesting………………………………………………………………………………………………. 214

13.8 Genetic Modification of Algae……………………………………………………………….. 216

13.9 Summary………………………………………………………………………………………………… 217

Acknowledgments…………………………………………………………………………………………….. 220

References…………………………………………………………………………………………………………. 220

13.1 INTRODUCTION

As the global use of energy is projected to increase fivefold by 2100, several countries are investing in microalgal biotechnology as a source of renewable energy to enhance their energy security. Although microalgae are a source of high-value chemicals such as nutraceuticals and pharmaceuticals, with a gold-rush mentality many entrepreneurs focus primarily on biofuel as an end-product utilizing a few selected “traditional” algal species not native to the region, and extrapolate results obtained from controlled laboratory culture to large-scale outdoor production systems. For optimization of harvesting algal biomass, it would be crucial to know that wide intra — and interspe­cific variations in the biochemical constituents of microalgae exist, depending on their growth conditions. For example, in eight algal species, the percent lipid per dry weight ranged from 5 to 63, lipid production 10.3 to 90 mg L-1d-1, biomass 0.003 to

2.5 g L-1d-1, and biomass production on an areal basis from 0.91 to 38 g m-2d-1. Also, the commercially important carotene content in Dunaliella strain B32 and strain I3 isolated from the Bay of Bengal varied from 0.68 pg carotene per cell to 17.54 pg carotene per cell. As microalgae are renewable, sustainable, and affordable, their potential to produce biofuels and bioactive compounds is great. However, we argue that (1) improvements in strain selection, particularly the extremophile microalgae that have the required properties for large-scale biotechnology; (2) biochemical mod­ification; (3) utility of engineered “designer algal strains”; (4) optimization of growth, biomass production, and harvesting; and (5) enhancement of extraction of biofuel and conversion to co-products would all be necessary to make microalgal biotechnology an economically viable enterprise. A robust bio-economy built on a platform of inno­vative microalgal technologies is recommended.

Photosynthetic microalgae have been cultivated (Miquel, 1893) and utilized to support the production of animal life in the sea (Allen and Nelson, 1910). The most common “traditional” species used for biotechnology, usually isolated from temper­ate waters, include Botryococcus braunii, Chaetoceros calcitrans, Chlamydomonas reinhardtii, Chlorella vulgaris, Chroomonas sp., Dunaliella bardawil, D. salina, D. tertiolecta, Haematococcus pluvialis, Isochrysis galbana, Nannochloropsis oculata, Neochloris oleoabundans, Phaeodactylum tricornutum, Rhodomonas sp., Scenedesmus obliquus, Skeletonema costatum, Spirulina maxima, and Tetraselmis chuii. Usual practice involves the purchase of a few “traditional” species from a culture center for large-scale propagation, although quite a few researchers are look­ing at isolating species adapted to local environments.

In addition to utilizing algae as biofeed, there is a global surge in microalgal biotechnology activities for commercial applications such as biofuel, bioactive com­pounds, and bioremediation. From virtually none in 1990, the total number of publi­cations on microalgal biotechnology leapt to 153 by June 2011; of these, 103 were on microalgal biofuel. This surge coincides with the 1991 Gulf War, when the mind-set of several countries changed to reduce their dependence on imported crude oil and to enhance their energy security. The annual worldwide consumption of motor fuel is 320 billion gallons, of which United States accounted for 44% (http://eia. doe. gov/ pub/internationjal/iea 2005/table35.xls). At the current rate of usage, the global use of energy will increase fivefold by 2100 (Huesmann, 2000), prompting major invest­ments in renewable energy. Since 2007, the United States alone has injected more than $1 billion into algae-to-energy research and development.

Microalgal biotechnology has received global attention and the attributive advantages include (1) cultivability on nonarable land, (2) bioremediation of wastewater by growing photosynthetic algal biomass, (3) ease of access to metabolic products that are stored intracellularly, (4) production of biofuel and value-added co-products, and (5) carbon sequestration, a result of the accelerated growth of microalgae for biofuel production. Photosynthetic production of algal biomass can be enhanced by an extraneous enrichment with CO2; industrial effluents containing CO2 can be utilized to sustain high algal productivity (Raven, 2009; Benemann, 1993). This could help a nation lower its emissions of greenhouse gases and could be used for carbon tax credit. The International Energy Agency (IEA) estimated that biofuels contribute to approximately 2% of global transport fuel today but could increase to 27% by the year 2050. They project that if biofuel production is sustained, it could displace enough petroleum to avoid the equivalent of 2.1 Gt y-1 CO2 emission— comparable to the net CO2 absorbed by the oceans calculated by Fairley (2011).

The algae-to-biotechnology framework has five stages—that is, algal cultiva­tion, biomass harvesting, algal oil extraction, oil residue conversion, and by-product distribution—and each has several composite processes (Natural Resources Defense Council, 2009). Given the vast potential of microalgal biotechnology, many entre­preneurs focus largely on algal biomass as a source of biofuel rather than high-value chemicals such as nutraceuticals and pharmaceuticals. For example, by the end of this decade, the projected worldwide market value of carotenoids alone will be US$1,000 million (Del Campo et al., 2007). Some of the co-products fetch higher prices; for example, astaxanthin is about 3,000 times more expensive than the $1,000-per-ton crude oil (Cysewski and Lorenz, 2004). Although the payoffs for entre­preneurs are attractive, building biotech businesses based on a new, unproven technol­ogy poses more formidable challenges. Continuous production of vast quantities of algal biomass under optimal conditions is crucial in sustaining economically viable biofuel technology. Although fifty algal biofuel companies exist (http://aquaticbiofuel. com/2008/12/05/2008-the-year-of algae-investments/.), production on a commercial scale at competitive prices has not yet taken place (Pienkos and Darzins, 2009; St. John, 2009). One of the biggest challenges to commercial algal operations is to trans­late laboratory conditions to large scale, and most companies operate in “stealth” mode (Natural Resources Defense Council, 2009). To make it cost effective, Wijffels (2007) suggested that production costs must be reduced up to two orders of magni­tude. When operating an algal biofuel production facility, plans should be in place to tackle unforeseen exigencies such as weather changes, and crashing of algal populations that could disrupt production and cause huge losses. As microalgae are renewable, sustainable, and affordable, their potential to produce biofuels is great if the current practices are cost competitive with petroleum diesel. Improvements in harvesting practices, extraction of biofuels, and conversion to co-products could bring down the production costs. Here we discuss the need to optimize various ele­ments such as algal strains, cultivation, production costs, lipid variations, harvesting biomass, and genetic modification of microalgae to make microalgal biotechnology economically viable.