Abstract
Microbial lipids, also known as single-cell oils (SCOs), are highly attractive feedstocks for biodiesel production due to their fast production rates, minimal labor requirements, independence from seasonal and climatic changes, and ease of scale-up for industrial processing. Among the SCO producers, the less explored filamentous fungi (molds) exhibit desirable features such as a repertoire of hydrolyzing enzymes and a unique pellet morphology that facilitates downstream harvesting. Although several oleaginous filamentous fungi have been identified and explored for SCO production, high production costs and technical difficulties still make the process less attractive compared to conventional lipid sources for biodiesel production. This review aims to highlight the ability of filamentous fungi to hydrolyze various organic wastes for SCO production and explore current strategies to enhance the efficiency and cost-effectiveness of the SCO production and recovery process. The review also highlights the mechanisms and components governing lipogenic pathways, which can inform the rational designs of processing conditions and metabolic engineering efforts for increasing the quality and accumulation of lipids in filamentous fungi. Furthermore, we describe other process integration strategies such as the co-production with hydrogen using advanced fermentation processes as a step toward a biorefinery process. These innovative approaches allow for integrating upstream and downstream processing units, thus resulting in an efficient and cost-effective method of simultaneous SCO production and utilization for biodiesel production.
Highlights
Biofuels derived from low-cost substrates such as agro-industrial waste are promising alternative sources of liquid energy (Carvalho et al, 2015; Dong et al, 2016)
The production of single-cell oils (SCOs) is not impacted by factors such as seasonal changes, geographic location, harvest time and transport, which are of concern when using plant and animal materials (Abghari and Chen, 2014; Dong et al, 2016)
Single-cell oils produced by oleaginous microorganisms such as filamentous fungi are desirable as starting material for biodiesel production due to their high degree of unsaturation
Summary
Biofuels derived from low-cost substrates such as agro-industrial waste are promising alternative sources of liquid energy (Carvalho et al, 2015; Dong et al, 2016). Single-cell oils produced by oleaginous microorganisms such as filamentous fungi are desirable as starting material for biodiesel production due to their high degree of unsaturation. Other factors which affect the accumulation and fatty acid composition of cellular lipids include temperature, pH, cultivation period, fortification of culture media with specific nutrients such as nitrogen, the inclusion of growth enhancers, agitation, aeration and incorporation of substrates at different concentrations and time points (Hansson and Dostálek, 1988; Kendrick and Ratledge, 1992b; Carvalho et al, 1999; Somashekar et al, 2003; Papanikolaou et al, 2004; Jang et al, 2005; Fakas et al, 2009; Liu et al, 2010; Dey et al, 2011). PH 5.0 at exponential growth phase/pH 7 at stationary growth phase pH 3.0 pH 6.5 for 48 h and pH 4.5 for 214 h pH 4.0 Adjusted pH of 6.0 after 18 h of growth
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