Optimization of carbon source efficiency for lipid production with the oleaginous yeast Saitozyma podzolica DSM 27192 applying automated continuous feeding

Abstract

Background Biotechnologically produced microbial lipids are of interest as potential alternatives for crude and plant oils. Their lipid profile is similar to plant oils and can therefore be a substitute for the production of biofuels, additives for food and cosmetics industry as well as building blocks for oleochemicals. Commercial microbial lipids production, however, is still not profitable and research on process optimization and cost reduction is required. This study reports on the process optimization using glucose or xylose with the unconventional oleaginous yeast Saitozyma podzolica DSM 27192 aiming to reduce the applied carbon source amount without sacrificing lipid productivity. Results By optimizing the process parameters temperature and pH, lipid productivity was enhanced by 40%. Thereupon, by establishing a two-phase strategy with an initial batch phase and a subsequent fed-batch phase for lipid production in which a constant sugar concentration of about 10 g/L was maintained, resulted in saving of ~ 41% of total glucose and ~ 26% of total xylose. By performing the automated continuous sugar feed the total sugar uptake was improved to ~ 91% for glucose and ~ 92% for xylose and thus, prevented waste of unused carbon source in the cultivation medium. In addition, reduced glucose cultivation resulted in to 28% higher cell growth and 19% increase of lipid titer. By using xylose, the by-product xylonic acid was identified for the first time as by-product of S. podzolica. Conclusions These findings provide a broad view of different cultivation process strategies with subsequent comparison and evaluation for lipid production with S. podzolica. Additionally, new biotechnological characteristics of this yeast were highlighted regarding the ability to produce valuable organic acids from sustainable and renewable sugars.

Global Transcriptome Profile of the Oleaginous Yeast Saitozyma podzolica DSM 27192 Cultivated in Glucose and Xylose

“…The oleaginous yeast Saitozyma podzolica DSM 27192 was isolated from peat bog soil in the Black Forest of Germany [15]. The yeast is maintained as glycerol stock in −80 • C storage and reactivated on YM agar as previously described [10].…”

“…Cultivation of the yeast was performed in duplicates in 2.5 L benchtop bioreactors (Infors HT, Bottmingen, Switzerland; Minifors fermentor) containing 1.2 L mineral salt medium as previously described [10]. Briefly, the cultivation parameters were pH 4, 22.5 • C, 600 rpm and 1 vvm aeration rate for 144 h of process time.…”

“…The latter induces lipid synthesis and intracellular accumulation for energy storage [2]. Usually, a two-stage process is performed comprising a first nutrient-rich phase for cell mass formation and merging into a nitrogen deficient stage with excess carbon source [10][11][12][13]. To avoid the highly controversial "food-or-fuel" debate, renewable and sustainable carbon sources should be used for microbial lipid production.…”

“…Saitozyma podzolica DSM 27192, isolated from peat bog soil in Karlsruhe, Germany [15], produces microbial lipid under nitrogen limitation and sugar acids, such as gluconic and xylonic acids, from glucose and xylose, respectively [10,15,16]. Characterization of the oleaginous profile of S. podzolica DSM 27192 showed, that the strain accumulates up to 31.8 and 27.53% lipid per dry biomass on glucose and xylose, respectively.…”

“…Characterization of the oleaginous profile of S. podzolica DSM 27192 showed, that the strain accumulates up to 31.8 and 27.53% lipid per dry biomass on glucose and xylose, respectively. A recent process optimisation revealed that both pH and temperature influence oil accumulation in S. podzolica DSM 27192 with~40% increase in lipid productivity achieved under the optimised relative to the standard cultivation condition [10]. Despite these advances, including the improved sugar-uptake efficiency of~91 and 92% for glucose and xylose, respectively, under fed-batch cultivation mode, the genetic basis of carbon flux partitioning between lipid and sugar acids syntheses remains unclear.…”