Bioconversion of Shrimp Waste into Functional Lipid by a New Oleaginous Sakaguchia sp

Chitin, the second most abundant biomolecule after cellulose in nature, is a significant aquaculture by-product, and is estimated at 6-8 million tons annually. Chitin is composed of monomeric N-acetylglucosamine (NAG) which can be seen as an alternative feedstock for biotechnology. Microbial functional lipids have gained attention due to their bioactivity and sustainable production. In this study, a new oleaginous yeast strain named Sakaguchia sp. HKC2 was found to be able to use NAG as the carbon source for growth and accumulate functional lipids such as PUFAs and carotenoids. When cultured on the NAG-containing medium, strain HKC2 exhibited slower growth and slower intracellular lipid accumulation compared to those on a glucose-containing medium. However, the lipids obtained from HKC2 grown on NAG medium were richer in PUFAs. Notably, torularhodin-a powerful bioactive carotenoid-was found in all HKC2 cultures on NAG, while torulene was abundant in glucose medium. These findings highlight a novel avenue for utilizing aquatic by-products and unlocking their potential.

Dual-stage biorefinery to convert spentwash hydrolysate into oleochemicals using Trichosporon cutaneum and Yarrowia lipolytica

Yeast lipids from low-cost renewable feedstock are valuable resources for oleochemicals thus enabling circular chemistry. Current study focuses on lipid and volatile fatty acid (VFA) production through dual-stage fermentation of spentwash in a biorefinery framework with Trichosporon cutaneum (Tc) and Yarrowia lipolytica (Yl). During cell proliferation phase, Tc and Yl accumulated 2.9 and 2.5 g/L of dry biomass respectively in acid-hydrolysed spentwash (AHSW) and produced 16 and 5.5 g/L of total VFA respectively. Lipid yields (29.8%) and lipid titres (0.89 g/L) were higher in Tc/AHSW, when compared to Yl indicating the efficacy of Tc in spentwash bioremediation. Lipid accumulation was enhanced to 35% in Tc/AHSW, in presence of 0.05% NH₄Cl due to oxidative stress of ammonium ions. Analysis of fatty acid composition revealed the presence of higher oleic acid, which is ideal for biodiesel production. The results demonstrate a sustainable biorefinery model for bioremediation of spentwash and its value addition.

Enhancing microbial lipids yield for biodiesel production by oleaginous yeast Lipomyces starkeyi fermentation: A review

The enhanced production of microbial lipids suitable for manufacturing biodiesel from oleaginous yeast Lipomyces starkeyi is critically reviewed. Recent advances in several aspects involving the biosynthetic pathways of lipids, current conversion efficiencies using various carbon sources, intensification strategies for improving lipid yield and productivity in L. starkeyi fermentation, and lipid extraction approaches are analyzed from about 100 papers for the past decade. Key findings on strategies are summarized, including (1) optimization of parameters, (2) cascading two-stage systems, (3) metabolic engineering strategies, (4) mutagenesis followed by selection, and (5) co-cultivation of yeast and algae. The current technical limitations are analyzed. Research suggestions like examination of more gene targets via metabolic engineering are proposed. This is the first comprehensive review on the latest technical advances in strategies from the perspective of process and metabolic engineering to further increase the lipid yield and productivity from L. starkeyi fermentation.

Engineering xylose metabolism in yeasts to produce biofuels and chemicals

Xylose is the second most abundant sugar in lignocellulosic biomass. Efficient and rapid xylose utilization is essential for the economic bioconversion of lignocellulosic biomass into value-added products. Building on previous pathway engineering efforts to enable xylose fermentation in Saccharomyces cerevisiae, recent work has focused on reprogramming regulatory networks to enhance xylose utilization by engineered S. cerevisiae. Also, potential benefits of using xylose for the production of various value-added products have been demonstrated. With increasing needs of lipid-derived bioproducts, activation and enhancement of xylose metabolism in oleaginous yeasts have been attempted. This review highlights recent progress of metabolic engineering to achieve efficient and rapid xylose utilization by S. cerevisiae and oleaginous yeasts, such as Yarrowia lipolytica, Rhodosporidium toruloides, and Lipomyces starkeyi.

Isolation of a new Papiliotrema laurentii strain that displays capacity to achieve high lipid content from xylose

In this work, we isolated and selected oleaginous yeasts from rock field soils from two National Parks in Brazil (Caparaó and Serra dos Órgãos) with the potential to accumulate oil from xylose, the main pentose sugar found in lignocellulosic biomass. From the 126 isolates, two were selected based on their lipid contents. They were taxonomically identified as Papiliotrema laurentii (UFV-1 and UFV-2). Of the two, P. laurentii UFV-1 was selected as the best lipid producer. Under unoptimized conditions, lipid production by P. laurentii UFV-1 was higher in glucose than in xylose. To improve its lipid production from xylose, we applied response surface methodology (RSM) with a face-centered central composite design (CCF). We evaluated the effects of agitation rate, initial cell biomass (OD₆₀₀), carbon/nitrogen ratio (C/N ratio) and pH on lipid production. P. laurentii UFV-1 recorded the highest lipid content, 63.5% (w/w) of the cell dry mass, under the following conditions: C/N ratio = 100:1, pH value = 7.0, initial OD₆₀₀ = 0.8 and agitation = 300 rpm. Under these optimized conditions, biomass, lipid titer and volumetric lipid productivity were 9.31 g/L, 5.90 g/L and 0.082 g/L.h, respectively. Additionally, we determined the fatty acid composition of P. laurentii UFV-1 as follows: C14:0 (0.5%), C16:0 (28.4-29.4%), C16:1 (0.2%), C18:0 (9.5-11%), C18:1 (58.6-60.5%), and C20:0 (0.7-0.8%). Based on this composition, the predicted properties of biodiesel showed that P. laurentii UFV-1 oil is suitable for use as feedstock in biodiesel production.

A Deuteromycete Isolate Geotrichum candidum as Oleaginous Cell Factory for Medium-Chain Fatty Acid-Rich Oils

Single cell oils (SCO) are oils derived from microorganisms which have potential to hyperaccumulate intracellular lipids (called oleaginous) under some essential nutrient (nitrogen, phosphorous or sometimes sulphur) starvation and an excess of carbon. The present work investigates the influence of these key parameters (for triggering oleaginicity), i.e. carbon (C) and nitrogen (N) on oleaginous behaviour of an oleaginous isolate, with the objective of improving the lipid content and obtaining oils of applicative interest. Eleven yeasts were isolated from rotten fruits and a unique yeast from rotten apple was screened on the basis of its ~ 20% (of dry mass) lipid content (LC), trademark of oleaginicity under nitrogen-stressed culture conditions. Subsequent investigation on influence of C, N and w/w ratio of carbon source concentration (Cs) to nitrogen source concentration (Ns) was conducted on this isolate. The isolate was identified as a Deuteromycete-Geotrichum candidum. 4.8 g/l was found to be minimum N concentration and glucose as suitable C source for optimum balance between biomass and lipid content. The highest LC of 73.6% (172.5% higher compared to 27% LC at Cs/Ns 80/4.8) was obtained at Cs/Ns 150/4.8 with a lipid coefficient of 8.7 (g lipid/100 g substrate). While remarkably higher production economy (lipid coefficient of 28.45) was noted at Cs/Ns 100/4.8 with significant LC of 54.4% (~ 100% higher than at Cs/Ns 80/4.8). The derived oils were predominantly rich in medium-chain fatty acids (MCFA)-caprylic acid, rare in plant oils. G. candidum is a previously referred oleaginous species; however, for the first time this study illustrates its detailed oleaginous behaviour and lipid compositional characteristics with varying nutritional parameters. The work is a progressive contribution towards current and upcoming researches in field of SCOs. Compositional characteristics of derived oils, make it an important candidate for potential medical and nutritional applications in future.

Lipid Production by Yeasts Growing on Commercial Xylose in Submerged Cultures with Process Water Being Partially Replaced by Olive Mill Wastewaters

Six yeast strains belonging to Rhodosporidium toruloides, Lipomyces starkeyi, Rhodotorula glutinis and Cryptococcus curvatus were shake-flask cultured on xylose (initial sugar—S0 = 70 ± 10 g/L) under nitrogen-limited conditions. C. curvatus ATCC 20509 and L. starkeyi DSM 70296 were further cultured in media where process waters were partially replaced by the phenol-containing olive mill wastewaters (OMWs). In flasks with S0 ≈ 100 g/L and OMWs added yielding to initial phenolic compounds concentration (PCC0) between 0.0 g/L (blank experiment) and 2.0 g/L, C. curvatus presented maximum total dry cell weight—TDCWmax ≈ 27 g/L, in all cases. The more the PCC0 increased, the fewer lipids were produced. In OMW-enriched media with PCC0 ≈ 1.2 g/L, TDCW = 20.9 g/L containing ≈ 40% w/w of lipids was recorded. In L. starkeyi cultures, when PCC0 ≈ 2.0 g/L, TDCW ≈ 25 g/L was synthesized, whereas lipids in TDCW = 24–28% w/w, similar to the experiments without OMWs, were recorded. Non-negligible dephenolization and species-dependent decolorization of the wastewater occurred. A batch-bioreactor trial by C. curvatus only with xylose (S0 ≈ 110 g/L) was performed and TDCW = 35.1 g/L (lipids in TDCW = 44.3% w/w) was produced. Yeast total lipids were composed of oleic and palmitic and to lesser extent linoleic and stearic acids. C. curvatus lipids were mainly composed of nonpolar fractions (i.e., triacylglycerols).

Feeding Strategies of Two-Stage Fed-Batch Cultivation Processes for Microbial Lipid Production from Sugarcane Top Hydrolysate and Crude Glycerol by the Oleaginous Red Yeast Rhodosporidiobolus fluvialis

Microbial lipids are able to produce from various raw materials including lignocellulosic biomass by the effective oleaginous microorganisms using different cultivation processes. This study aimed to enhance microbial lipid production from the low-cost substrates namely sugarcane top hydrolysate and crude glycerol by Rhodosporidiobolus fluvialis DMKU-SP314, using two-stage fed-batch cultivation with different feeding strategies in a 3 L stirred-tank fermenter. The effect of two feeding strategies of 147.5 g/L crude glycerol solution was evaluated including pulse feeding at different starting time points (48, 24, and 72 h after initiation of batch operation) and constant feeding at different dilution rates (0.012, 0.020, and 0.033 h-1). The maximum lipid concentration of 23.6 g/L and cell mass of 38.5 g/L were achieved when constant feeding was performed at the dilution rate of 0.012 h-1 after 48 h of batch operation, which represented 1.24-fold and 1.27-fold improvements in the lipid and cell mass concentration, respectively. Whereas, batch cultivation provided 19.1 g/L of lipids and 30.3 g/L of cell mass. The overall lipid productivity increased to 98.4 mg/L/d in the two-stage fed-batch cultivation. This demonstrated that the two-stage fed-batch cultivation with constant feeding strategy has the possibility to apply for large-scale production of lipids by yeast.

Microbial conversion of xylose into useful bioproducts

Microorganisms can produce a number of different bioproducts from the sugars in plant biomass. One challenge is devising processes that utilize all of the sugars in lignocellulosic hydrolysates. D-xylose is the second most abundant sugar in these hydrolysates. The microbial conversion of D-xylose to ethanol has been studied extensively; only recently, however, has conversion to bioproducts other than ethanol been explored. Moreover, in the case of yeast, D-xylose may provide a better feedstock for the production of bioproducts other than ethanol, because the relevant pathways are not subject to glucose-dependent repression. In this review, we discuss how different microorganisms are being used to produce novel bioproducts from D-xylose. We also discuss how D-xylose could be potentially used instead of glucose for the production of value-added bioproducts.

A two-stage process facilitating microbial lipid production from N-acetylglucosamine by Cryptococcus curvatus cultured under non-sterile conditions

N-acetylglucosamine (GlcNAc), the monomeric constituent of chitin, is rarely studied for lipid production by oleaginous species. This study demonstrated that Cryptococcus curvatus had a great capacity to convert GlcNAc into lipid with high yield using a two-stage production process. Optimal inoculum age and inoculation size strongly improved the two-stage lipid production efficiency. More interestingly, this process rendered superior lipid production under non-sterile condition. The acetate liberated from GlcNAc was consumed timely, while the NH₄⁺ released was rarely assimilated. Lipid titre, lipid content and lipid yield reached 9.9 g/L, 56.9% and 0.23 g/g, respectively, which were significantly higher than those from the conventional process where cell growth and lipid accumulation were coupled. The resulting lipid samples had similar fatty acid compositional profiles to those of vegetable oil, suggesting their potential for biodiesel production. These findings strongly supported the two-stage process as an attractive strategy for better techno-economics of the chitin-to-biodiesel routes.

Non-sterile fermentations for the economical biochemical conversion of renewable feedstocks

Heavy reliance on petroleum-based products drives continuous exploitation of fossil fuels, and results in serious environmental and climate problems. To address such an issue, there is a shift from petroleum sources to renewable ones. Biochemical conversion via fermentation is a primary platform for converting renewable sources to biofuels and bulk chemicals. In order to provide cost-competitive alternatives, it is imperative to develop efficient, cost-saving, and robust fermentation processes. Non-sterile fermentation offers several benefits compared to sterile fermentation, including elimination of sterility, reduced maintenance requirements, relatively simple bioreactor design, and simplified operation. Thus, cost effectiveness of non-sterile fermentation makes it a practical platform for low cost, large volume production of biofuels and bulk chemicals. Many approaches have been developed to conduct non-sterile fermentation without sacrificing the yields and productivities of fermentation products. This review focuses on the strategies for conducting non-sterile fermentation. The challenges facing non-sterile fermentation are also discussed.

Efficient bioconversion of high-content volatile fatty acids into microbial lipids by Cryptococcus curvatus ATCC 20509

The lower utilization ratios of high-content VFAs resulted in less lipid yield by the oleaginous yeast Cryptococcus curvatus ATCC 20509. In this work, increasing the inoculation concentration to OD600=5.1 improved the acetic acid utilization ratio (99.8%) and lipids production (4.63g/L) in mediums with 30g/L of acetic acid. For the higher acetic acid concentration (40g/L), increasing the nitrogen to carbon ratio (0.033) and raising the initial pH (pH=8) was superior over improvement in the inoculate, with the lipid production increased from 1.08g/L to 6.49g/L. Subsequently, mixed VFAs at concentrations of 30g/L and 40g/L were used as the carbon source to simulate waste-derived VFAs. High lipid production (4.82 and 7.45g/L, respectively) was correspondingly achieved with similar high lipid yield (0.187g/g). This study provides an effective strategy to enhance the bioconversion of high-content VFAs into microbial lipids.

Effects of Salts Contained in Lignocellulose-Derived Sugar Streams on Microbial Lipid Production

This study aimed at developing low-cost, robust non-sterile fermentation processes for microbial lipid production from lignocellulose-derived sugars. Three representative oleaginous yeasts, Lipomyces tetrasporus (NRRL Y-11562), Rhodotorula toruloides (NRRL Y-1091), and Yarrowia lipolytica (NRRL YB-437), were tested for lipid production via non-sterile fermentation. Under optimal non-sterile conditions, all the tested strains had good performance on salt tolerance and lipid production. L. tetrasporus (NRRL Y-11562) gave the highest lipid titer of 12.79 g/L along with the depletion of both glucose and xylose, while Y. lipolytica (NRRL YB-437) showed the lowest lipid production and limited capability of xylose utilization. The key factors, including inoculation size, initial pH, and salt, all contributed to successful non-sterile fermentation. This study demonstrated that it is feasible to perform both sterile and non-sterile fermentation for lipid production using salt-containing lignocellulose-derived sugar streams.

Culture strategies for lipid production using acetic acid as sole carbon source by Rhodosporidium toruloides

Rhodosporidium toruloides AS 2.1389 was tested using different concentrations of acetic acid as a low-cost carbon source for the production of microbial lipids, which are good raw materials for biodiesel production. It grew and had higher lipid contents in media containing 4-20 g/L acetic acid as the sole carbon source, compared with that in glucose-containing media under the same culture conditions. At acetic acid concentrations as high as 20 g/L and the optimal carbon-to-nitrogen ratio (C/N) of 200 in a batch culture, the highest biomass production was 4.35 g/L, with a lipid content of 48.2%. At acetic acid concentrations as low as 4 g/L, a sequencing batch culture (SBC) with a C/N of 100 increased biomass production to 4.21 g/L, with a lipid content of 38.6%. These results provide usable culture strategies for lipid production by R. toruloides AS 2.1389 when using diverse waste-derived volatile fatty acids.