Oleaginous yeasts- substrate preference and lipid productivity: a view on the performance of microbial lipid producers

Background Oleaginous yeasts are promising microbial platforms for sustainable, bio-based production of biofuels and oleochemical building blocks. Bio-based residues provide sustainable and cost-effective carbon sources for fermentative yeast oil production without land-use change. Considering the regional abundancy of different waste streams, we chose complex biomass residue streams of marine origin; macroalgae hydrolysate, and terrestrial origin; wheat straw hydrolysate in the presence, and absence of corn steep liquor as a complex nitrogen source. We investigated the biomass and lipid yields of an array of well-described oleaginous yeasts; R. glutinis, T. asahii, R. mucilaginosa, R. toruloides, C. oleaginosus growing on these hydrolysates. Furthermore, their sugar utilization, fatty acid profile, and inhibitory effect of the hydrolysates on yeast growth were compared. For correlative reference, we initially performed comparative growth experiments for the strains on individual monomeric sugars separately. Each of these monomeric sugars was a dominant carbon source in the complex biomass hydrolysates evaluated in this study. In addition, we evaluated N-acetylglucosamine, the monomeric building block of chitin, as a low-cost nitrogen and carbon source in yeast fermentation. Results C. oleaginosus provided the highest biomass and lipid yields. In the wheat straw and brown algae hydrolysates, this yeast strain gained 7.5 g/L and 3.8 g/L lipids, respectively. Cultivation in algae hydrolysate resulted in a higher level of unsaturated fatty acids in the lipids accumulated by all yeast strains. R. toruloides and C. oleaginosus were able to effectively co-utilize mannitol, glucose, and xylose. Growth rates on wheat straw hydrolysate were enhanced in presence of corn steep liquor. Conclusions Among the yeast strains investigated in this study, C. oleaginosus proved to be the most versatile strain in terms of substrate utilization, productivity, and tolerance in the complex media. Various fatty acid profiles obtained on each substrate encourage the manipulation of culture conditions to achieve the desired fatty acid composition for each application. This could be accomplished by combining the element of carbon source with other formerly studied factors such as temperature and oxygen. Moreover, corn steep liquor showed promise for enhancement of growth in the oleaginous strains provided that carbon substrate is available.

The advanced performance of microbial consortium for simultaneous utilization of glucose and xylose to produce lactic acid directly from dilute sulfuric acid pretreated corn stover

Background Lignocellulosic feedstocks have attracted much attention as a potential carbon source for lactic acid (LA) production because of their ready availability, sustainability, and renewability. However, there are at least two major technical challenges to producing LA from lignocellulose. Inhibitors derived from lignocellulose pretreatment have a negative impact on the growth of cells producing LA. Furthermore, pentose sugars produced from the pretreatment are difficultly utilized by most LA producers, which is known as the carbon catabolite repression (CCR) effect. This complex feedstock can be utilized by a robust microbial consortium with high bioconversion efficiency. Results In this study, a thermophilic consortium DUT50 producing LA was enriched and employed to improve corn stover (CS) utilization. Enterococcus was the dominant family in the consortium DUT50, accounting for 93.66% of the total abundance, with Lactobacillus, Bacillus, Lactococcus, and Trichococcus accounted for the remaining 2.68%. This consortium could be resistant to inhibitors concentration up to 9.74 g/L (2.88 g/L acetic acid, 2.46 g/L furfural, 2.20 g/L 5-HMF, and 2.20 g/L vanillin derived from pretreatment of CS), and simultaneously metabolizes hexose and pentose without CCR effect. Based on the promising consortium features, an efficient process of simultaneous saccharification and co-fermentation (SSCF) was developed to produce LA from acid pretreated corn stover, in which solid–liquid separation and detoxification were avoided. The key influencing factors were investigated and optimized, including dry biomass and cellulase loading, corn steep liquor powder concentration, and the pre-hydrolysis time. The highest LA titer of 71.04 g/L with a yield of 0.49 g/g-CS was achieved at a dry biomass loading of 20% (w/v), which is the highest LA production from non-detoxified acid pretreated corn stover via the SSCF process without wastewater generation reported to date. The simultaneous metabolism of hexose and pentose revealed collaboration between Enterococcus in the consortium, whereas xylose may be efficiently metabolized by Lactobacillus and Bacillus with low abundance via the pentose phosphate pathway. Conclusions The experimental results demonstrated the potential advantage of symbiosis in microbial consortia used for LA production from lignocellulosic biomass.

Raw Glycerol Based Medium for DHA and Lipids Production, Using the Marine Heterotrophic Microalga Crypthecodinium cohnii

Crude glycerol, a biodiesel industry byproduct, and corn steep liquor (CSL) derived from a starch industry, were used as carbon and nitrogen sources, respectively, for lipid production, using the heterotrophic microalga C. cohnii grown in a bench bioreactor, in a batch culture. The maximum biomass concentration, lipid content and lipid productivity attained were 5.34 g/L, 24.6% (w/w Dry Cell Weight-DCW) and 0.016 g L−1 h−1, respectively. Flow cytometry analysis was used to evaluate the impact of these substrates on the microalgae cells. A high proportion of intact cells with enzymatic (esterases) activity (>50%) was present throughout the cultivation time course. These results indicate that crude glycerol and CSL can be used in the medium formulation for DHA and lipid production using this microalga, which reduce the process costs in an expected maximum of 84%.

The Advanced Performance of Microbial Consortium for Simultaneous Utilization of Glucose and Xylose to Produce Lactic Acid Directly from Dilute Sulfuric Acid Pretreated Corn Stover

Background: Lignocellulosic feedstocks have attracted much attention as an alternative carbon source for lactic acid (LA) production with the advantages of ready availability, sustainability, and renewability. However, the production of LA from lignocellulose faces at least two major technical obstacles. The inhibitors derived from pretreatment of lignocellulose inhibit the growth of microorganism used in downstream hydrolysis and fermentation processes. In addition, most LA producers cannot to ferment pentose sugars and have carbon catabolite repression (CCR) effect. Microbial consortium with great robustness can use complex feedstocks displaying high bioconversion efficiency and has received great attention nowadays.Results: in this study, a thermophilic LA producing consortium DUT50 was enriched and employed to enhance the utilization of corn stover (CS). Enterococcus was the dominant family, accounting for 93.66% abundance in DUT50, and the abundance of Lactobacillus, Bacillus, Lactococcus and Trichococcus, accounted for 2.68% in total. This consortium was highly resistant to inhibitors up to 10.90 g/L derived from pretreatment of CS, metabolized hexose and pentose simultaneously without CCR effect. Based on consortium promising features, an efficient process of simultaneous saccharification and co-fermentation (SSCF) was developed to produce LA from acid-pretreated corn stover. The economical route avoided the operations of solid–liquid separation and detoxification. The key influential factors, including dry biomass and cellulase loading, corn steep liquor powder concentration, and the pre-hydrolysis time were investigated and optimized. The highest LA titer of 71.04 g/L with a yield of 0.49 g/g-CS was achieved at a dry biomass loading of 20% (w/v). This is the reported highest LA production from non-detoxified acid-pretreated corn stover via the SSCF process without wastewater generation. The interaction mode of Enterococcus was collaboration while the low abundance of Lactobacillus and Bacillus might metabolize xylose efficiently via the pentose phosphate pathway.Conclusions: Our results demonstrated the potential advantage of symbiosis and provided a feasible and economical route to produce LA from lignocellulosic biomass in industrial scale.

Biohydrogen Production From Agro-industrial Wastes Using Clostridium Beijerinckii and Isolated Bacteria as Inoculum

The search for renewable and sustainable sources of energy has been one of the main goals of society in recent years, especially to reduce the environmental impacts of fossil fuels. One promising alternative is the production of hydrogen, which does not emit greenhouse gases and can be produced from agro-industrial wastes. The Clostridium genus is recorded as having high hydrogen yields compared to other genus, with several producing species. The objective of this work was to evaluate biohydrogen production potential of four agro-industrial residues, which were soft drink wastewater, corn steep liquor, cheese whey, and expired Guaraná soft drink, using one model strain Clostridium beijerinckii ATCC 8260 and newly isolated Clostridium butyricum DEBB-B348. The agro-industrial wastes were characterised in terms of monosaccharide, organic acid, amino acid, cation, and anion concentrations and compared to the literature. After performing subsequent experimental designs, the significant factors were cheese whey concentration, corn steep liquor concentration, and fermentation time for C. beijerinckii, and corn steep liquor concentration and fermentation time for C. butyricum (p ≤ 0.05), with an R2 of 0.950 and 0.895, respectively. The maximum hydrogen volume production was 18.5 ± 1.68 mL and 27.4 ± 1.84 mL for each strain, respectively. The C. butyricum 16s rRNA gene phylogenetic tree and the carbohydrate, organic acid, and amino acid kinetics of the optimum medium are also presented. These results indicate a potential hydrogen production process utilising less expensive substrates, proposing more proper disposal for agro-industrial wastes and using an isolated strain with high yield.

Batch and Fed-Batch Production of β-carotene by Rhodotorula Toruloides KP324973 Using Corn Steep Liquor As Sole Carbon Source

Application of agro-industrial waste in microbial fermentation is interesting in economic and environmental aspects. Carotenoids production by Rhodotorula toruloides KP324973 was investigated using corn steep liquor (CSL) as sole carbon source. Haldane model with constants µmax = 0.056 h-1, KS = 1.54 vv-1%, and KI = 58.58 vv-1% showed best describe of cell growth kinetics on CLS. A same maximum carotenoid production rate (Rp) about 2.23 μg gcell-1 h-1 was obtained at initial CSL concentration of 5 v/v% after 72 h and 21 h in batch cultivation in shaken flasks and bubble column reactor (BCR), respectively. Further improvement of carotenogenesis was followed by fed-batch cultivation in BCR where the optimal setting of factors at feed flow rate of 5 mL h-1, pH of 5.66, and temperature 14 ˚C gained a highest Rp = 8.686 μg gcell-1 h-1. Chromatographic analysis showed more than 94% of produced carotenes was β-carotene.

Integration of Ultrasound into the Development of Plant-Based Protein Hydrolysate and its Bio-Stimulatory Effect for Growth of Wheat Grain Seedlings In Vivo

This study was dedicated to increasing the efficiency of producing plant-based protein hydrolysate using traditional and non-traditional treatments. Low- and high frequency ultrasound (US) at different intensities were applied to corn steep liquor (CSL) at 50 °C for 30 min, and enzymatic hydrolysis was performed using industrially produced alkaline protease. The efficiency of US and enzymatic treatments was characterized by protein solubility (soluble protein (SP) content, hydrolyzed protein (HP) concentration, and free amino acid (FAA) profile) and kinetic parameters: Michaelis–Menten constant (KM) and apparent breakdown rate constant (kA). A significant effect of 37 kHz US pre-treatment for CSL enzymatic hydrolysis was found and resulted in the highest HP concentration (17.5 g/L) using the lowest enzyme concentration (2.1 g/L) and the shortest hydrolysis time (60 min). By using US pre-treatment, on average, a 2.2 times higher FAA content could be achieved compared to traditional hydrolysis. Additionally, results for the kinetic parameters KM and kA confirmed the potential of applying US treatment before hydrolysis. The effect of CSL protein hydrolysate on plant growth was tested in vivo on wheat grain seed germination and resulted in the significant increase in germination parameters compared to the control treatment. These findings indicate that by-products of starch industry could be a promising source for the production of low-cost sustainable biostimulants.

Optimization of medium components to improve the antimicrobial activity of a new Saharan actinobacterial strain Saccharothrix tamanrassetensis DSM 45947

Saccharothrix tamanrassetensis DSM 45947 previously isolated from a Saharan soil sample and characterized as a new species, was found to be a potential candidate in the search for novel antibiotics. The strain was found to exhibit a strong antimicrobial activity against a wide range of bacteria and fungi. In this study, statistical methods were applied to optimize the fermentation medium for enhanced antimicrobial activity production. A basal medium supplemented with sucrose and corn steep liquor was used as the original medium for optimization experiments. Plackett-Burman design showed that sucrose, corn steep liquor and KH2PO4, were recognised to have significant effect on antimicrobial activity production. Response surface methodology with Box-Behnken design determined the optimal concentrations. Optimal values for maximum antibiotic production were as follows: 7 g L-1 of sucrose, 52 g L-1 of corn steep liquor and 0.9 g L-1 of KH2PO4. Under these conditions, antimicrobial activities of DSM 45947 showed a global increase by 32% against the bacterium methicillinresistant Staphylococcus aureus and 36% against the fungus Umbelopsis ramanniana. This study provided an economical and efficient method to cultivate Saccharothrix tamanrassetensis DSM 45947 for enhanced antimicrobial activity production.