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.

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.

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.

Evaluation of Morphological Changes in Grapes Coated with a Biosurfactant Extract Obtained from Corn Steep Liquor

In this work, grapes were coated with a multifunctional biosurfactant extract obtained from corn steep liquor after liquid–liquid extraction with ethyl acetate. This biosurfactant extract has been demonstrated to not only possess a surfactant capacity but also antimicrobial activity. Hence, it could be an excellent preservative for fruits, as it is more biodegradable and more biocompatible than chemically synthetized preservatives. However, before applying this biosurfactant as a preservative on fruits, it is necessary to study the changes in the surface properties of fruits produced by the addition of this bioactive compound. Therefore, in this work, grapes coated with an aqueous solution containing 1 g/L of the biosurfactant extract were subjected to surface analysis using non-invasive technologies, including profilometry. 2D digital photographs of the surface and parametric roughness of grapes were obtained. They revealed that the biosurfactant extract decreased the roughness of the grape surface compared with non-coated grapes and reduced the changes in the shape of the grapes over time. Moreover, it was observed that the biosurfactant extract increased the hydrophobicity of the grape surface observing higher contact angle compared with non-coated grapes.

Production, Characterization and Commercial Formulation of a Biosurfactant from Candida tropicalis UCP0996 and Its Application in Decontamination of Petroleum Pollutants

Contamination by oil and its derivatives causes serious damage to the environment, motivating the development of innovative technologies for the removal of these contaminants, such as the use of biosurfactants. In the present study, the biosurfactant from Candida tropicalis UCP0996 produced in the low cost-medium formulated with molasses, residual frying oil, and corn steep liquor, was characterized and its toxicity, formulation, and application in removal and biodegradation of oil were investigated. The surface tension of the medium was reduced to 30.4 mN/m, yielding 4.11 g/L of isolated biosurfactant after 120 h. Tests under extreme environmental conditions indicated the stability of the biosurfactant. Chemical characterization by thin layer chromatography (TLC), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR), and gas chromatography and mass spectroscopy (CG-MS) revealed the glycolipidic nature of the biosurfactant. The isolated biosurfactant showed no toxicity against the microcrustacean Artemia salina, while the properties of the formulated biosurfactant remained stable during 120 days of storage. The biosurfactant removed 66.18% of motor oil adsorbed in marine stones and dispersed 70.95% of oil in seawater. The biosurfactant was also able to increase by 70% the degradation of motor oil by seawater indigenous microorganisms, showing great potential to be applied as a commercial additive in the bioremediation of oil spills.