# Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review
## 7 SCO Production from Hydrolyzed Lignocellulosic Biomass
However, the additional treatment needed for detoxification increases the production cost and results in a loss of assimilable sugars [271]. Detoxification of pretreated lignocellulosic biomass does not seem to be a very attractive approach, as the techniques used result in sugar loss, and also imply an increase in costs due to the addition of more stages in the process [19]. On the contrary, the use of ULH can be a good alternative with lower processing costs, provided that tolerant oleaginous microorganisms, such as strains of _Trichosporon_, _Cryptococcus_, _Lipomyces_, _Rhodotorula_, _Umbelopsis_ (_Mortierella_), _Rhodosporidiobolus_, _Rhodosporidium_, _Rhodococcus_, _Meyerozyma_, _Pichia_ and _Candidida_ will be used (Table 4). ULH obtained from agricultural residues pretreated with weak acids seems to be suitable as a substrate for SCO production by the aforementioned oleaginous microorganisms, supporting lipid accumulation at high rates, even above 60% _w/v_b (Table 4). Likewise, some oleaginous yeasts also  
Figure 4: A conceptual scheme of lignocellulosic hydrolysates conversion into SCO (Single Cell Oil). accumulate high lipid amounts growing on ULH derived from combined (e.g., acid and other) pretreatments. For example, [PERSON] et al. [113] showed that the yeast _Rhodosporidiobulus fluvialis_ was able to produce up to 75% _uv/w_ of lipids growing on hydrolyzed sugarcane biomass obtained after acid/oxidative pretreatment. The alkaline pretreatment is also an important possibility dealing to high lipids productivities. [PERSON] et al. [47] have shown an efficient bioconversion of ULH derived from alkaline pretreatment of corncob into _Rhodosporidium paludigenum_ oily biomass containing approximately 70% _uv/w_ lipid. On the other hand, agricultural residues pretreated using steam explosion are also an interesting option. For instance, significant lipid accumulation (ranging from 22% to 38% _uv/w_) was observed by [PERSON] et al. [48] in different conventional oleaginous microorganisms growing on ULH agricultural biomass pretreated with steam explosion. The physiological response of oleaginous microorganisms to inhibitors generated during pretreatment of lignocellulosic biomass has been studied in various microorganisms including _Candida_, _Rhodosporidium_, _Cryptococcus_, _Trichosporon_, _Rhodococcus_, _Wickerhamomyces_ and _Vanrija_, and interesting results have been obtained regarding tolerance and even degradation of inhibitors [36; 41; 104; 113; 146; 240; 262]. For example, _T. cutaneum_ can convert 3 g/L of furfural and 3 g/L of HMF into the corresponding alcohols (furfuryl alcohol and HMF alcohol) and completely degrade 15 g/L of formic acid and 10 g/L of acetic acid [146]. In addition, enzymes involved in the degradation of furfural and HMF, including alcohol dehydrogenase, aldehyde reductase and aldehyde dehydrogenase, have been identified in yeasts strains such as _T. cutaneum_ ACCC 20271, _R. toruloides_ NP11, _Y. lipolytica_ CLIB122 and _T. oleaginous_ IBC0246. The number of putative functional genes in the genomes involved in the synthesis of the aforementioned enzymes is higher in _T. cutaneum_ ACCC 20271, providing a strong support for high degradation capacity and tolerance to inhibitors [147]. However, more metabolic studies are required to understand the physiology of oleaginous microorganisms against lignocellulosic biomass derived inhibitors. Tolerance to inhibitors is a required, but not a sufficient, property for selecting an oleaginous microorganism to be used in lignocellulosic hydrolyses conversion to SCO; effective growth and lipogenicity are also needed for a sustainable process. As shown in Table 3, naturally tolerant microorganisms usually have a restricted capacity to effectively convert sugars into lipid-rich biomass. To overcome these difficulties, recombinant microorganisms could be constructed, simultaneously presenting tolerance, efficient growth and lipogenicity.