Pretreatment Strategies to Improve Crude Glycerol Utilisation and Metabolite Production by Aspergillus terreus

Abstract

Crude glycerol (CG) can be used as a substrate for microbial bioconversion. However, due to presence of many impurities, many microorganisms are unable to utilise this substrate efficiently. The present study is trying to improve CG using as the feedstock of Aspergillus terreus for the production of lovastatin, (+)-geodin, and sulochrin. The CG was pretreated chemically (solvents) and physically (activated carbon (AC) and water softener (WS)) to separate most of the impurities from the CG. For solvent pretreatments, petroleum ether (PE) produced the largest increase of lovastatin (92.8%) when compared to positive control and pure glycerol (PG) and up to 820% when compared to negative control (CG). In contrast, diethyl ether (DE) produced the largest increase in (+)-geodin at 80.81% (versus CG) and 176.23% (versus PG). The largest increase in toluene (Tol) was observed in sulochrin production, at 67.22% (versus CG) and 183.85% (versus PG). For physical pretreatments, the pattern of metabolite production in AC (lovastatin: 20.65 mg/L, (+)-geodin: 7.42 mg/L, sulochrin: 11.74 mg/L) resembled PG (lovastatin: 21.8 mg/L, (+)-geodin: 8.60 mg/L, sulochrin: 8.18 mg/L), while WS (lovastatin: 11.25 mg/L, (+)-geodin: 15.38 mg/L, sulochrin: 16.85 mg/L) resembled CG (lovastatin: 7.1 mg/L, (+)-geodin: 17.10 mg/L, sulochrin: 14.78 mg/L) at day 6 of fermentation. These results indicate that solvent pretreatments on CG are excellent for metabolites production in A. terreus, depending on the solvents used. In contrast, physical pretreatments are only feasible for (+)-geodin and sulochrin production. Therefore, different strategies can be employed to manipulate the A. terreus bioconversion using improved CG by using a few simple pretreatment strategies.

Exogenous l-proline improved Rhodosporidium toruloides lipid production on crude glycerol

“…Previously, crude glycerol has been utilized as a carbon source for valued microbial products like citric acid [14], biopolymers [15], 1,3-propanediol [16], succinic acid [17], and microbial lipid, however, the lipid yield remained lower [18]. Many microbes are unable to utilize it efficiently [19], due to the presence of methanol, salts, organic acids, and heavy metals etc., which induce toxicity at high level [20]. On the contrary, different organisms accumulate l-proline during hostile conditions.…”

Optimisation of xanthan production on glycerol-based medium using response surface methodology

“…Possible solutions to overcome these problems are the use of microorganisms that are tolerant to the impurities in crude glycerol (Konstantinović et al 2016), the application of appropriate treatments (Pan et al 2019) and the implementation of fed-batch cultivation systems in which crude glycerol is added gradually (Samul et al 2014). However, all of these activities can decrease the economic potential of processes that utilise crude glycerol as the raw material (Rahim et al 2019).…”