The quality parameters of biodiesel (i.e., Cetane number, heat of combustion,
cold flow properties, oxidative stability, and viscosity) depend on the characteristics
of individual FA alkyl esters and are determined by the structural features of the
FAs such as chain length, number and the situation of double bonds, and chain
branching) (Ramos et al. 2009; Talebi et al. 2013a, b). The type of the produced
FAs by algal cells is greatly influenced by genetic characteristics and also by the
environmental conditions during cultivation. In general, intrinsic tolerance to higher
temperatures and higher CO 2 concentrations could lead to a high biomass growth
rate with a huge quantity of lipids. Overall, super microalgal strains could be either
isolated or mutated. There are patents which try to introduce methods to mutate and
maintain “old” strains to obtain “prone and powerful” ones, e.g., JP10248553A,
US20130236951A1, US7935515B2, and CN101412965A. Other publications such
as JP8257356A, JP10248553A, and TW291493B highlight the use of thermophilic
microalgae when hot flue gases are employed.
3.1.2 Genetic Engineering Approaches
To obtain superior microalgae strains capable of swift cell growth, efficient photosynthesis, enhanced inorganic carbon fixation, as well as producing improved
type and quality of fuel genetic engineering approaches have been exploited.
Thanks to the developments made in sequencing tools since early 2000s, substantial
advances in genetic manipulation of single-celled photosynthetic microalgal model
organisms such as C. reinhardtii and Chlorella vulgaris have been achieved
(Talebi et al. 2013a, b).
In general, genetically modified microalgae could be efficiently used for biofuel
production, CO 2 sequestration, as well as other bioremediation goals. For instance,
the patent US20170191094A1 claimed that the recombinant algae strains harboring
at least one of the following exogenous genes were able to produce greater amounts
of lipids under nitrogen starvation conditions [acyl-CoA synthetase, acyl-CoA
reductase, acetyl-CoA carboxylase, acyl-ACP thioesterase, phosphatidic acid
phosphatase, or diacylglycerol 0-acyltransferase (DGAT)]. Moreover, the quality of
biodiesel can be also improved by engineering the cells toward the accumulation of
lipids with a more desired FAs profiles. Among the strategies considered to engineer FA biosynthesis toward more compatible lipid profiles are the overexpression
of FAs enzymes and their up-regulation by transcription factors as well as
increasing the availability of precursor molecules (acetyl-CoA) and reducing power
(NADPH). Moreover, down-regulation of FA catabolism by inhibiting b-oxidation,
or lipase hydrolysis is also among the other available strategies (see patents
US8951777B2, WO2011026008A1, WO2013034648A1, and US9593351B2).
Microalgae can also be modified to express different enzymes that influence the
production of long-chain FAs (e.g., patent WO2010019813A2). Also related to
fatty acid synthesis is the polyketide synthase enzyme (PKS), whose impacts on the
production of poly unsaturated FAs are discussed in the US patent
20070244192A1. Altering the saturation degree through the introduction or
14 Recent Patents on Biofuels from Microalgae
297
cold flow properties, oxidative stability, and viscosity) depend on the characteristics
of individual FA alkyl esters and are determined by the structural features of the
FAs such as chain length, number and the situation of double bonds, and chain
branching) (Ramos et al. 2009; Talebi et al. 2013a, b). The type of the produced
FAs by algal cells is greatly influenced by genetic characteristics and also by the
environmental conditions during cultivation. In general, intrinsic tolerance to higher
temperatures and higher CO 2 concentrations could lead to a high biomass growth
rate with a huge quantity of lipids. Overall, super microalgal strains could be either
isolated or mutated. There are patents which try to introduce methods to mutate and
maintain “old” strains to obtain “prone and powerful” ones, e.g., JP10248553A,
US20130236951A1, US7935515B2, and CN101412965A. Other publications such
as JP8257356A, JP10248553A, and TW291493B highlight the use of thermophilic
microalgae when hot flue gases are employed.
3.1.2 Genetic Engineering Approaches
To obtain superior microalgae strains capable of swift cell growth, efficient photosynthesis, enhanced inorganic carbon fixation, as well as producing improved
type and quality of fuel genetic engineering approaches have been exploited.
Thanks to the developments made in sequencing tools since early 2000s, substantial
advances in genetic manipulation of single-celled photosynthetic microalgal model
organisms such as C. reinhardtii and Chlorella vulgaris have been achieved
(Talebi et al. 2013a, b).
In general, genetically modified microalgae could be efficiently used for biofuel
production, CO 2 sequestration, as well as other bioremediation goals. For instance,
the patent US20170191094A1 claimed that the recombinant algae strains harboring
at least one of the following exogenous genes were able to produce greater amounts
of lipids under nitrogen starvation conditions [acyl-CoA synthetase, acyl-CoA
reductase, acetyl-CoA carboxylase, acyl-ACP thioesterase, phosphatidic acid
phosphatase, or diacylglycerol 0-acyltransferase (DGAT)]. Moreover, the quality of
biodiesel can be also improved by engineering the cells toward the accumulation of
lipids with a more desired FAs profiles. Among the strategies considered to engineer FA biosynthesis toward more compatible lipid profiles are the overexpression
of FAs enzymes and their up-regulation by transcription factors as well as
increasing the availability of precursor molecules (acetyl-CoA) and reducing power
(NADPH). Moreover, down-regulation of FA catabolism by inhibiting b-oxidation,
or lipase hydrolysis is also among the other available strategies (see patents
US8951777B2, WO2011026008A1, WO2013034648A1, and US9593351B2).
Microalgae can also be modified to express different enzymes that influence the
production of long-chain FAs (e.g., patent WO2010019813A2). Also related to
fatty acid synthesis is the polyketide synthase enzyme (PKS), whose impacts on the
production of poly unsaturated FAs are discussed in the US patent
20070244192A1. Altering the saturation degree through the introduction or
14 Recent Patents on Biofuels from Microalgae
297