Comparison of Nitrogen Depletion and Repletion on Lipid Production in Yeast and Fungal Species

Abstract

Abstract:Although it is well known that low nitrogen stimulates lipid accumulation, especially for algae and some oleaginous yeast, few studies have been conducted in fungal species, especially on the impact of different nitrogen deficiency strategies. In this study, we use two promising consolidated bioprocessing (CBP) candidates to examine the impact of two nitrogen deficiency strategies on lipid production, which are the extensively investigated oleaginous yeast Yarrowia lipolytica, and the commercial cellulase producer Trichoderma reesei. We first utilized bioinformatics approaches to reconstruct the fatty acid metabolic pathway and demonstrated the presence of a triacylglycerol (TAG) biosynthesis pathway in Trichoderma reesei. We then examined the lipid production of Trichoderma reesei and Y. lipomyces in different media using two nitrogen deficiency strategies of nitrogen natural repletion and nitrogen depletion through centrifugation. Our results demonstrated that nitrogen depletion was better than nitrogen repletion with about 30% lipid increase for Trichoderma reesei and Y. lipomyces, and could be an option to improve lipid production in both oleaginous yeast and filamentous fungal species. The resulting distinctive lipid composition profiles indicated that the impacts of nitrogen depletion on yeast were different from those for fungal species. Under three types of C/N ratio conditions, C16 and C18 fatty acids were the predominant forms of lipids for both Trichoderma reesei and Y. lipolytica. While the overall fatty acid methyl ester (FAME) profiles of Trichoderma reesei were similar, the overall FAME profiles of Y. lipolytica observed a shift. The fatty acid metabolic pathway reconstructed in this work supports previous reports of lipid production in T. reesei, and provides a pathway for future omics studies and metabolic engineering efforts. Further investigation to identify the genetic targets responsible for the effect of nitrogen depletion on lipid production improvement will facilitate strain engineering to boost lipid production under more optimal conditions for productivity than those required for nitrogen depletion.

Ameliorating the Metabolic Burden of the Co-expression of Secreted Fungal Cellulases in a High Lipid-Accumulating Yarrowia lipolytica Strain by Medium C/N Ratio and a Chemical Chaperone

“…For glucose consumption, after 6 days of culturing, the control strain HA1 (EV) and transformant YL165-1 cells consumed 12.6 and 48.0 g L -1 glucose in the medium, respectively (Table 4, rows 3–4). The control strain HA1 (EV) had a relative low OD600 of 5.1 but a high % FAME of 28% (DCW basis) (Table 4), which is consistent with previous reports showing that while a high C/N ratio medium benefited lipid accumulation, it limited the cell growth of Y. lipolytica (Back et al, 2016; Yang et al, 2016).…”

“…It is noteworthy that since high C/N ratio medium has been broadly used as a lipid production medium to maximize fatty acids synthesis and lipid accumulation by severely restricting protein synthesis in oleaginous organisms (Back et al, 2016; Yang et al, 2016), the cellulase production of YL165-1 grown in high C/N plus TMAO medium was not assessed in this study. Future studies are needed to investigate any potential effects of TMAO on the cellulase production in engineered Y. lipolytica strains.…”

“…The high C/N ratio, limited-nitrogen media have been used to cultivate a range of yeast and algae to achieve high levels of lipid accumulation (Li et al, 2008; Chaisawang et al, 2012; Lamers et al, 2012; Sharma et al, 2012; Braunwald et al, 2013; Sitepu et al, 2013; Blazeck et al, 2014; Hirooka et al, 2014; Zhang et al, 2014; Yu et al, 2015; Yang et al, 2016). As observed in this study, the cellulase co-expression route had an unexpected benefit in enhancing lipid accumulation when grown in medium with high C/N ratio; we propose the likely underlying mechanism would be that the high C/N ratio medium effectively lowers the levels of protein synthesis (because of nitrogen limitation) and ER stress, which leads to boosting nitrogen-limitation-induced lipid production, as shown in Figure 6E (scenario 2).…”

Determination of Various Parameters during Thermal and Biological Pretreatment of Waste Materials

“…An optimal C/N ratio in the feedstocks is important for the optimal growth of microorganisms [40], for the reduction of VFA accumulation [41], to prevent inhibition [39], to mitigate C and N emissions [42], to analyze organic matter in aquatic ecosystems [43], and for the production of lipids in yeasts [44], among other effects. For example, the optimal C/N ratio for anaerobic digestion [45] and composting [46] is between 20 and 30.…”

Physiological, Biochemical and Energetic Characteristics of Torulaspora globosa, a Potential Producer of Biofuel

“…Lipid synthesis in yeasts occurs under nitrogen limitation and depends on the strain, carbon source, and composition of the growth medium [8][9][10][11]. It should be noted that zinc ions play a very important regulatory role in the yeast metabolism.…”