Rhodotorula glutinis T13 as a potential source of microbial lipids for biodiesel generation.

Single cell oils (SCO) are a promising source of oils that could be exploited in different industrial areas. SCO for biodiesel production circumvents the controversy food vs. fuel, does not require large land areas for culture, and is independent of climate and seasonal variations, among other advantages in comparison to vegetable oils. In this study, a red yeast isolated from a mountain water source, identified as Rhodotorula glutinis T13, showed high potential for lipid production (40% w/w) with suitable growth parameters, yields, and fatty acids profile. Yeast lipids showed a high content of unsaturated fatty acids (56.44%; C18:1, C18:2), and the fuel properties (cetane number, iodine value, density, kinematic viscosity, etc.) of yeast oil analysed were in good agreement with international biodiesel standards. The results show that R. glutinis T13 can be used in the future as a promising microorganism for the commercial production of biodiesel.

Growth and lipid production of Rhodotorula glutinis R4, in comparison to other oleaginous yeasts.

Some Rhodotorula spp. have been characterized as oleaginous yeasts. Under certain culture conditions they can accumulate neutral lipids, which are mainly triglycerides (TAG). Microbial TAG that can be used as raw material for biodiesel synthesis are attractive for the biofuel industry. In this study, the ability to synthesize lipids of Rhodotorula glutinis R4, isolated in Antarctica, was compared with eight strains belonging to the genera Rhodotorula and Yarrowia with the aim of proposing a novel source of oils for biodiesel synthesis. All strains were cultured under nitrogen (N) limiting conditions and an excess of carbon (C) in the culture medium. We found that yeasts accumulated between 9-48.9 % (w/w) of lipids. Among them, R. glutinis R4 showed the highest growth (14 g L-1, µmax 0,092 h-1) and lipid production (7 g L-1; 47 % w/w). Microbial oils produced by R. glutinis R4 are similar to vegetable oils, with 61 % of oleic acid, indicating that it is adequate for biodiesel synthesis. Our results demonstrate that biodiesel derived from R. glutinis R4 complies with international fuel standards ASTM D6751 and EN 14214. Therefore, this work demonstrates that Rhodotorula glutinis R4 is a novel and valuable source of microbial oils for biodiesel synthesis.

Bioremediation strategies for chromium removal: Current research, scale-up approach and future perspectives.

Industrial applications and commercial processes release a lot of chromium into the environment (soil, surface water or atmosphere) and resulting in serious human diseases because of their toxicity. Biological Cr-removal offers an alternative to traditional physic-chemical methods. This is considered as a sustainable technology of lower impact on the environment. Resistant microorganisms (e.g. bacteria, fungi, and algae) have been most extensively studied from this characteristic. Several mechanisms were developed by microorganisms to deal with chromium toxicity. These tools include biotransformation (reduction or oxidation), bioaccumulation and/or biosorption, and are considered as an alternative to remove the heavy metal. The aim of this review is summarizes Cr(VI)-bioremediation technologies oriented on practical applications at larger scale technologies. In the same way, the most relevant results of several investigations focused on process feasibility and the robustness of different systems (reactors and pilot scale) designed for chromium-removal capacity are highlighted.

Oleaginous yeasts from Antarctica: Screening and preliminary approach on lipid accumulation.

The capability of 17 Rhodotorula spp. isolated from Antarctica to accumulate intracellular lipids in nitrogen-limited medium was investigated. As results, 10 isolates were selected by Nile red staining, while 12 isolates were selected as oleaginous by analysis of total lipid content (20.4-73%, w/w of dry biomass). The higher lipid production and accumulation was exhibited for six strains belonging to three species of Rhodotorula (Rhodotorula glutinis, Rhodotorula glacialis, and Rhodotorula laryngis). This is the first report where R. laryngis have been identified within oleaginous specie. Lipid accumulation was evaluated comparatively in two nitrogen-limited glucose-based media (MI and MII). MI (low C/N ratio) was more suitable for biomass and lipid production while in MII (high C/N ratio) total lipid content was improved. R. glutinis R4, R. glacialis R15, and R. glutinis R48 showed high lipid concentrations (4.65-6.93 g L-1 ) and they were able to accumulate large amounts of lipids per gram of biomass (47-77%, w/w). A similar profile in fatty acids composition and content of neutral lipids to vegetable oils was observed, indicating that lipids produced by oleaginous Antarctic yeasts can be considered an alternative feedstock for biodiesel production. Antarctica represents an important source of oleaginous yeasts with adaptive capabilities to accumulate considerable amounts of lipids with biotechnological interest at 15 °C and 25 °C.

Effects of thermal, alkaline and ultrasonic treatments on scleroglucan stability and flow behavior.

Aqueous solutions (0.2%, w/v) of scleroglucans from Sclerotium rolfsii ATCC 201126 from different cultivation time or purification protocol (EPS I, EPS II, EPSi) as well as a commercial scleroglucan (LSCL) exhibited different sensitivity against thermal (65, 95 and 150°C), ultrasonic (1, 5 and 10 min; 20% amplitude) or alkaline (0.01-0.2 N NaOH) treatments. Scleroglucan triple helix usually showed signs of denaturation at 150°C or with 0.2 NaOH with a pronounced decrease in apparent viscosity and loss of pseudoplastic behavior. Differences in sensitivity could be noted depending on the scleroglucan sample, which may be likely related to polysaccharide conformational features, and these latter to production and/or downstream processing conditions. Transmission electron microscopy showed scleroglucan topologies in accordance with thermal and alkaline denaturation. Size exclusion chromatography of control scleroglucans revealed elution profiles compatible with macromolecular aggregates which tended to diminish or disappear as thermal, alkali or sonication treatments progressed. Scleroglucan granule dissolution process took ∼8-14 s, according to DIC-light microscopy, and showed to be facilitated by addition of NaOH.

Scleroglucan compatibility with thickeners, alcohols and polyalcohols and downstream processing implications.

Thickening capacity and compatibility of scleroglucan with commercial thickeners (corn starch, gum arabic, carboxymethylcellulose, gelatin, xanthan and pectin), glycols (ethylene glycol and polyethylene glycol), alcohols (methanol, ethanol, 1-propanol and isopropanol) and polyalcohols (sorbitol, xylitol and mannitol) was explored. Exopolysaccharides (EPSs) from Sclerotium rolfsii ATCC 201126 and a commercial scleroglucan were compared. Compatibility and synergism were evaluated taking into account rheology, pH and sensory properties of different thickener/scleroglucan mixtures in comparison with pure solutions. S. rolfsii ATCC 201126 EPSs induced or increased pseudoplastic behaviour with a better performance than commercial scleroglucan, showing compatibility and synergy particularly with corn starch, xanthan, pectin and carboxymethylcellulose. Compatibility and a slight synergistic behaviour were also observed with 30% (w/v) ethylene glycol whereas mixtures with polyethylene glycol (PEG) precipitated. Scleroglucan was compatible with polyalcohols, whilst lower alcohols led to scleroglucan precipitation at 20% (v/v) and above. PEG-based scleroglucan downstream processing was compared to the usual alcohol precipitation. Downstream processed EPSi (with isopropanol) and EPS-p (with PEG) were evaluated on their yield, purity, rheological properties and visual aspect pointing to alcohol downstream processing as the best methodology, whilst PEG recovery would be unsuitable. The highest purified EPSi attained a recovery yield of ~23%, similar to ethanol purification, with a high degree of purity (88%, w/w vs. EPS-p, 8%, w/w) and exhibited optimal rheological properties, water solubility and appearance. With a narrower molecular weight distribution (M(w), 2.66×10(6) g/mol) and a radius of gyration (R(w), 245 nm) slightly lower than ethanol-purified EPSs, isopropanol downstream processing showed to be a proper methodology for obtaining a refined-grade scleroglucan.

Sclerotium rolfsii scleroglucan: the promising behavior of a natural polysaccharide as a drug delivery vehicle, suspension stabilizer and emulsifier.

Gel matrices of scleroglucans from Sclerotium rolfsii ATCC 201126 (EPS I and EPS II, from 48-h and 72-h fermentations, respectively) were evaluated on their release kinetics of theophylline (Th). Equivalent polymer (2%, w/w) and Th (0.2%, w/w) concentrations showed almost coincident drug release patterns, independently of polymer molecular weight or the microstructural properties of gel matrices. Dynamic rheological studies of scleroglucan hydrogel structures (storage, G', and loss, G'', moduli) indicated a solid-like behavior. Differences on pore size dimensions (EPS I=20 microm and EPS II=7 microm) were in accordance to the differences in G' (EPS I=113 Pa and EPS II=161 Pa), a fact likely related to variations in the cross-linking density of polymer networks. Compared to already known biopolymers, EPS I and EPS II at 0.5 g/L showed a good dispersing ability against particulate suspensions of activated charcoal, bentonite, CaCO(3), celite and quartz powder. Emulsifying ability of both EPSs at 2g/L was high (E=56-60%) when tested with kerosene, moderate ( approximately 30%) with hexadecane, and negligible in the presence of olive oil-in-water emulsions.