Exploring the use of hexadecane by Yarrowia lipolytica: Effect of dissolved oxygen and medium supplementation

This work aimed to evaluate the effect of medium composition and volumetric oxygen transfer coefficient (kLa) on Y. lipolytica growth and production of microbial lipids and enzymes from hexadecane. In the stirred tank bioreactor, increasing kLa from 11 h-1 to 132 h-1 improved the hexadecane assimilation rate, biomass concentration, and lipids synthesis (0.90 g·L-1). A cost-effective hexadecane-based medium supplemented with corn steep liquor and a low amount of ammonium sulfate boosted lipids production up to 2.1 g·L-1, composed of palmitic, palmitoleic, oleic, and linoleic acids. The unsaturated/saturated fraction was dependent on the C/N ratio. Lipids of Y. lipolytica CBS 2075 are promising feedstock for animal feed, food additives, or the biodiesel industry. Simultaneous synthesis of extracellular lipase and protease from hexadecane was observed, which is a new feature that was not previously reported. The highest enzyme activity was obtained at the highest C/N ratio conditions. These results open new perspectives on the application of Y. lipolytica-based cultures for the biotransformation of hexadecane-polluted streams into valuable compounds, fulfilling an interesting strategy towards the circular economy concept.

Computational assessment of hexadecane freezing by equilibrium atomistic molecular dynamics simulations

HYPOTHESIS

Upon cooling, alkanes can form intermediate phases between liquid and crystal. They are called "rotator" or "plastic" phases and have long-range positional order with rotational freedom around the long molecular axis which gives them non-trivial and useful visco-plastic properties. We expect that the formation and structure of rotator phases formed in freezing alkanes can be understood much deeper by tracking the process at molecular level with atomistic molecular dynamics.

SIMULATIONS

We defined an appropriate CHARMM36-based computational protocol for simulating the freezing of hexadecane, which contained a sufficiently long (500 ns) equilibrium sampling of the frozen states. We employed it to simulate successfully the freezing of bulk and interface-contacting hexadecane and to provide a pioneering clarification of the effect of surfactant on the crystallization mechanism and on the type of intermolecular ordering in the crystallites.

FINDINGS

The devised computational protocol was able to reproduce the experimentally observed polycrystalline structure formed upon cooling. However, different crystallization mechanisms were established for the two types of models. Crystallites nucleate at random locations in the bulk and start growing rapidly within tens of nanoseconds. In contrast, the surfactants freeze first during the fast cooling (<1 ns), followed by rapid hexadecane freezing, with nucleation starting along the entire surfactant adsorption layer. Thereby, the hexadecane molecules form rotator phases which transition into a more stable ordered phase. This collective transition is first-time visualized directly. The developed robust computational protocol creates a foundation for future in-depth modelling and analysis of solid-state alkane-containing, incl. lipid, structures.

Effective removal of hydrogen sulfide from landfill gases using a modified iron pentacarbonyl desulfurization agent and the desulfurization mechanism

High-efficiency desulfurization is key to the recovery and use of landfill gases. In this study, a nano‑iron oxide desulfurization agent modified from iron pentacarbonyl was prepared in n-decane (DE) and hexadecane (HE) by ultrasonic disruption without any supporting materials and its hydrogen sulfide removal ability and desulfurization mechanism were studied. The yield of the desulfurization agent was higher when HE was used as the solvent; however, the products generated by both solvents had the same crystal type and similar properties. The efficiency of the desulfurization agent was significantly improved at 150-200 °C, exceeding 90% at 150 °C with single sulfur production. The maximum sulfur adsorption capacity of the desulfurization agent produced after 3 h of DE ultrasonic treatment at 200 °C (DE3) was 492 mg/g (desulfurization efficiency = 97.33%), while that of the agent produced after 3 h of HE ultrasonic treatment at 250 °C (HE3) was 522 mg/g (desulfurization efficiency = 99.30%). The desulfurization reaction involved both chemical adsorption and catalytic decomposition and the catalytic decomposition reaction rate was lower than that of chemical adsorption. Therefore, the more Fe_xS_y produced in the chemical adsorption process, the better catalytic performance was.

Permeability of Olmesartan Medoxomil from Lipid Based and Suspension Formulations using an Optimized HDM-PAMPA Model

Hexadecane membrane-parallel artificial membrane permeability assay (HDM-PAMPA) is based on an artificial hexadecane membrane that separates the two compartments (donor and acceptor compartment). This model is used to predict the permeability of drugs in gastrointestinal tract and to simulate the passive absorption. In vivo behaviour of the drugs can be estimated with these systems in drug development studies. In our study we optimized HDM-PAMPA model to determine permeability of olmesartan medoxomil (OM) lipid based drug delivery system (OM-LBDDS). In order to prove that LBDDS formulation facilitates the weak permeability of OM, permeation rates were compared with the OM suspension formula (containing 0.25% v/w CMC). The experiment was performed on a 96-well MultiScreen® PAMPA filter plate (MAIPN4510). The permeability of olmesartan formulations from the donor to acceptor compartment separated by a HDM membrane were determined by the previous validated HPLC method. We created positive control series without coating hexadecane membrane to present the LBDDS and suspension formulation permeability from uncoated plates. The effective permeability constant (P_e) was calculated by the formula and improvement of permeability of OM-LBDDS formulation from hexadecane membrane was confirmed. On the contrary there was no permeation of OM-Suspension in the hexadecane coated plates. As a result, the intestinal permeability of OM-LBDDS was calculated to be at least 100 times more than the suspension. OM-Suspension permeation was only observed in the hexadecane uncoated positive control plates. This was also manifestation of HDM-PAMPA mimicking permeability of intestines because of its lipidic construction.

Unravelling the process of petroleum hydrocarbon biodegradation in different filter materials of constructed wetlands by stable isotope fractionation and labelling studies

Maintaining and supporting complete biodegradation during remediation of petroleum hydrocarbon contaminated groundwater in constructed wetlands is vital for the final destruction and removal of contaminants. We aimed to compare and gain insight into biodegradation and explore possible limitations in different filter materials (sand, sand amended with biochar, expanded clay). These filters were collected from constructed wetlands after two years of operation and batch experiments were conducted using two stable isotope techniques; (i) carbon isotope labelling of hexadecane and (ii) hydrogen isotope fractionation of decane. Both hydrocarbon compounds hexadecane and decane were biodegraded. The mineralization rate of hexadecane was higher in the sandy filter material (3.6 µg CO2 g-1 day-1) than in the expanded clay (1.0 µg CO2 g-1 day-1). The microbial community of the constructed wetland microcosms was dominated by Gram negative bacteria and fungi and was specific for the different filter materials while hexadecane was primarily anabolized by bacteria. Adsorption / desorption of petroleum hydrocarbons in expanded clay was observed, which might not hinder but delay biodegradation. Very few cases of hydrogen isotope fractionation were recorded in expanded clay and sand & biochar filters during decane biodegradation. In sand filters, decane was biodegraded more slowly and hydrogen isotope fractionation was visible. Still, the range of observed apparent kinetic hydrogen isotope effects (AKIEH = 1.072-1.500) and apparent decane biodegradation rates (k = - 0.017 to - 0.067 day-1) of the sand filter were low. To conclude, low biodegradation rates, small hydrogen isotope fractionation, zero order mineralization kinetics and lack of microbial biomass growth indicated that mass transfer controlled biodegradation.

Biofilm mediated synergistic degradation of hexadecane by a naturally formed community comprising Aspergillus flavus complex and Bacillus cereus group

BACKGROUND

The hydrophobic nature of hydrocarbons make them less bioavailable to microbes, generally leading to low efficiency in biodegradation. Current bioremediation strategies for hydrocarbon contamination, uses induced mixed microbial cultures. This in-vitro study demonstrates the utilization of naturally occurring communities in suitable habitats for achieving highly efficient, synergistic degradation of hydrocarbons in a simple community structure without additives.

METHODS

Enrichment media supplemented with 1% (7652.53 mg/L) hexadecane (HXD) as the sole carbon source were inoculated with samples of soil with waste polythene, collected from a municipal landfill in order to isolate microbial communities. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed on HXD grown co-cultures and individual counterparts after 14 days incubation and percentage degradation was calculated. Microbes were identified using 16S rRNA gene and Internal Transcribed Spacer region sequencing. Biofilm formation was confirmed through scanning electron microscopy, in the most efficient community.

RESULTS

Three mixed communities (C1, C2 and C3) that demonstrated efficient visual disintegration of the HXD layer in the static liquid cultures were isolated. The C1 community showed the highest activity, degrading > 99% HXD within 14 days. C1 comprised of a single fungus and a bacterium and they were identified as a Bacillus sp. MM1 and an Apsergillus sp. MM1. The co-culture and individual counterparts of the C1 community were assayed for HXD degradation by GC-MS. Degradation by the fungal and bacterial monocultures were 52.92 ± 8.81% and 9.62 ± 0.71% respectively, compared to 99.42 ± 0.38% by the co-culture in 14 days. This proved the synergistic behavior of the community. Further, this community demonstrated the formation of a biofilm in oil-water interface in the liquid medium. This was evidenced from scanning electron microscopy (SEM) showing the Bacillus cells attached on to Aspergillus mycelia.

CONCLUSIONS

This study demonstrates the utilization of naturally formed fungal-bacterial communities for enhanced biodegradation of hydrocarbons such as hexadecane and reports for the first time, synergistic degradation of hexadecane through biofilm formation, by a community comprising of Bacillus cereus group and Aspergillus flavus complex.

Evidences of extracellular abiotic degradation of hexadecane through free radical mechanism induced by the secreted phenazine compounds of P. aeruginosa NY3

The aim of this work was to investigate the effects of secreted extracellular phenazine compounds (PHCs) on the degradation efficiency of alkanes by P. aeruginosa NY3. Under aerobic conditions, the PHCs secreted by P. aeruginosa NY3 initiate the oxidation of alkanes outside cells, in coupling with some reducing agents, such as β-Nicotinamide adenine dinucleotide, reduced disodium salt (NADH) or reduced glutathione (GSH). This reaction might be via free radical reactions similar to Fenton Oxidation Reaction (FOR). P. aeruginosa NY3 secretes pyocyanin (Pyo), 1-hydroxyphenazine (HPE), phenazine-1-carboxylic acid (PCA), and phenazine-1-amide (PCN) simultaneously. The cell-free extracellular fluid containing these four PHCs degrades hexadecane effectively. The observation of Electron Spin Resonance (EPR) signals of superoxide anion radical (O₂^-), hydroxyl radical (OH) and/or carbon free radicals (R) both in vivo and in vitro suggested the degradation of hexadecane could be via a free radical pathway. Secretion of PHCs has been found to be characteristic of Pseudomonas which is often involved in or related to the degradation of organic pollutants. Our work suggested that certain organic contaminants may be oxidized through ubiquitously extracellular abiotic degradation by the free radicals produced during bio-remediation and bio-treatment.

Potential microbial consortium involved in the biodegradation of diesel, hexadecane and phenanthrene in mangrove sediment explored by metagenomics analysis

Hydrocarbon contamination is a serious problem that degrades the quality of mangrove ecosystems, and bioremediation using autochthonous bacteria is a promising technology to recover an impacted environment. This research investigates the biodegradation rates of diesel, hexadecane and phenanthrene, by conducting a microcosm study and survey of the autochthonous microbial community in contaminated mangrove sediment, using an Illumina MiSeq platform. The biodegradation rates of diesel, hexadecane and phenanthrene were 82, 86 and 8 mg kg^-1 sediment day^-1, respectively. The removal efficiencies of hexadecane and phenanthrene were >99%, whereas the removal efficiency of diesel was 88%. A 16S rRNA gene amplicon sequence analysis revealed that the major bacterial assemblages detected were Gammaproteobacteria, Deltaproteobacteria, Alphaproteobacteria. The bacterial compositions were relatively constant, while reductions of the supplemented hydrocarbons were observed. The results imply that the autochthonous microorganisms in the mangrove sediment were responsible for the degradation of the respective hydrocarbons. Diesel-, hexadecane- and phenanthrene-degrading bacteria, namely Bacillus sp., Pseudomonas sp., Acinetobacter sp. and Staphylococcus sp., were also isolated from the mangrove sediment. The mangrove sediment provides a potential resource of effective hydrocarbon-degrading bacteria that can be used as an inoculum or further developed as a ready-to-use microbial consortium for the purpose of bioremediation.

Biodegradation of hexadecane using sediments from rivers and lagoons of the Southern Gulf of Mexico

The Southern Gulf of Mexico is an area highly impacted by crude oil extraction, refining activities and the presence of natural petroleum seepage. Oceanic currents in the Gulf of Mexico continually facilitate the transport of hydrocarbons to lagoons and rivers. This research evaluated hexadecane (HXD) degradation in marine sediment samples from lagoons and rivers that are fed by the Southern Gulf of Mexico, specifically six samples from rivers, three samples from lagoons, and one sample from a marine outfall. The highest rates of biodegradation were observed in sediments from the mouths of the Gonzalez River and the Champotón Lagoon. The lowest consumption rate was found in sediment from the mouth of the Coatzacoalcos River. With regards to the Ostión Lagoon and the Grijalva River, there was a low rate of consumption, but a high efficiency of degradation which took place at the end of the experiments. No correlation was found between the consumption rate and the environmental physicochemical parameters.

Rhodococcus opacus B4: a promising bacterium for production of biofuels and biobased chemicals

Bacterial lipids have relevant applications in the production of renewable fuels and biobased oleochemicals. The genus Rhodococcus is one of the most relevant lipid producers due to its capability to accumulate those compounds, mainly triacylglycerols (TAG), when cultivated on different defined substrates, namely sugars, organic acids and hydrocarbons but also on complex carbon sources present in industrial wastes. In this work, the production of storage lipids by Rhodococcus opacus B4 using glucose, acetate and hexadecane is reported for the first time and its productivity compared with Rhodococcus opacus PD630, the best TAG producer bacterium reported. Both strains accumulated mainly TAG from all carbon sources, being influenced by the carbon source itself and by the duration of the accumulation period. R. opacus B4 produced 0.09 and 0.14 g L(-1) at 24 and 72 h, with hexadecane as carbon source, which was 2 and 3.3 fold higher than the volumetric production obtained by R. opacus PD630. Both strains presented similar fatty acids (FA) profiles in intact cells while in TAG produced fraction, R. opacus B4 revealed a higher variability in fatty acid composition than R. opacus PD630, when both strains were cultivated on hexadecane. The obtained results open new perspectives for the use of R. opacus B4 to produce TAG, in particular using oily (alkane-contaminated) waste and wastewater as cheap raw-materials. Combining TAG production with hydrocarbons degradation is a promising strategy to achieve environmental remediation while producing added value compounds.

Diffusional behavior and guest conformational analysis of hexadecane-1,16-diol and hexadecane in urea crystal model via molecular dynamics simulation approach

Diffusion at the atomic or molecular level is a source of many physical, chemical, and biological processes taking place in plentiful materials. This work is an endeavor toward investigating the diffusional behavior of two different type of guests, hexadecane-1,16-diol and hexadecane enclathration in urea tunnel architecture, whereby the correlation of the diffusion mechanism with the guest's structural and conformational properties is explored. To carry out this study, molecular dynamics simulation approach is adopted. It is found that hexadecane-1,16-diol exhibit slower diffusion with an average diffusion coefficient value [Formula: see text], where hexadecane diffuse more rapidly with an average diffusion coefficient value [Formula: see text]. It is also observed that the structural properties influence the guest's travel distance and torsion angle distribution of the trans and gauche conformational proportion. Furthermore, the observed high energy barrier accounted for hexadecane-1,16-diol and low energy barrier for hexadecane along urea tunnel systems was analyzed. The comparison of our obtained results are in close agreement with the available experimental measurements, i.e., gauche proportion properties between two different guest molecules correlate well with Raman spectroscopy investigation on α,ω-dihalogenoalkane/urea inclusion compounds. Our calculations also successfully endorse the structure-property relation between the two systems.

Comparison of (14)C liquid scintillation counting at NIST and NRC Canada

An informal bilateral comparison of (14)C liquid scintillation (LS) counting at the National Research Council of Canada (NRC) and the National Institute of Standards and Technology (NIST) has been completed. Two solutions, one containing (14)C-labeled sodium benzoate and one containing (14)C-labeled n-hexadecane, were measured at both laboratories. Despite observed LS cocktail instabilities, the two laboratories achieved accord in their standardizations of both solutions. At the conclusion of the comparison, the beta spectrum used for efficiency calculations was identified as inadequate and the data were reanalyzed with different inputs, improving accord.

Culturable populations of Acinetobacter can promptly respond to contamination by alkanes in mangrove sediments

This study evaluated the potential of bacterial isolates from mangrove sediments to degrade hexadecane, an paraffin hydrocarbon that is a large constituent of diesel and automobile lubricants. From a total of 18 oil-degrading isolates obtained by an enrichment technique, four isolates showed a great potential to degrade hexadecane. The strain MSIC01, which was identified by 16S rRNA gene sequencing as Acinetobacter sp., showed the best performance in degrading this hydrocarbon, being capable of completely degrading 1% (v/v) hexadecane within 48 h without releasing biosurfactants. Its hydrophobic surface probably justifies its potential to degrade high concentrations of hexadecane. Thus, the sediments from the studied mangrove harbour bacterial communities that are able to use oil as a carbon source, which is a particularly interesting feature due to the risk of oil spills in coastal areas. Moreover, Acinetobacter sp. MSIC01 emerged as a promising candidate for applications in bioremediation of contaminated mangrove sediments.

Functional gene expression of oil-degrading bacteria resistant to hexadecane toxicity

Contamination with oil poses a threat to the environment and to human health worldwide. Biological methodologies have proved to be economical, versatile and efficient for the remediation of pollutants. In this paper, a highly efficient oil-degrading bacterial strain USTB-2 was isolated from an oil production well of Dagang oil field in Tianjin, China. The 16S rRNA sequence of USTB-2 showed 100% similarity with that of Bacillus subtilis BSn5. Hexadecane is one of the most important components in petroleum. The half inhibitory ratio (IC₅₀) of hexadecane inhibited organisms, determined by microcalorimetry, was lower in USTB-2 than in B. BSn5. The results indicate that the strain USTB-2 degrades hexadecane to make it less toxic compared with the normal strain. RT-PCR was used to evaluate the expression of oil-degrading enzymes, specifically 4-hydroxyphenylacetate 3-monooxygenase genes (HPMO). A sharp increase in the expression of HPMO genes was observed for USTB-2, while the expression of HPMO genes in reference strain B. BSn5 remained relatively stable. These methods can be used to study the metabolic potential of microorganisms for in situ oil decontamination.