Production of added value bacterial lipids through valorisation of hydrocarbon-contaminated cork waste

Yarrowia lipolytica growth, lipids, and protease production in medium with higher alkanes and alkenes

Two strains of Yarrowia lipolytica (CBS 2075 and DSM 8218) were first studied in bioreactor batch cultures, under different controlled dissolved oxygen concentrations (DOC), to assess their ability to assimilate aliphatic hydrocarbons (HC) as a carbon source in a mixture containing 2 g·L-1 of each alkane (dodecane and hexadecane), and 2 g·L-1 hexadecene. Both strains grew in the HC mixture without a lag phase, and for both strains, 30 % DOC was sufficient to reach the maximum values of biomass and lipids. To enhance lipid-rich biomass and enzyme production, a pulse fed-batch strategy was tested, for the first time, with the addition of one or three pulses of concentrated HC medium. The addition of three pulses of the HC mixture (total of 24 g·L-1 HC) did not hinder cell proliferation, and high protease (> 3000 U·L-1) and lipids concentrations of 3.4 g·L-1 and 4.3 g·L-1 were achieved in Y. lipolytica CBS 2075 and DSM 8218 cultures, respectively. Lipids from the CBS 2075 strain are rich in C16:0 and C18:1, resembling the composition of palm oil, considered suitable for the biodiesel industry. Lipids from the DSM 8218 strain were predominantly composed of C16:0 and C16:1, the latter being a valuable monounsaturated fatty acid used in the pharmaceutical industry. Y. lipolytica cells exhibited high intrinsic surface hydrophobicity (> 69 %), which increased in the presence of HC. A reduction in surface tension was observed in both Y. lipolytica cultures, suggesting the production of extracellular biosurfactants, even at low amounts. This study marks a significant advancement in the valorization of HC for producing high-value products by exploring the hydrophobic compounds metabolism of Y. lipolytica.

Corksorb Enhances Alkane Degradation by Hydrocarbonoclastic Bacteria

Biosorbent materials are effective in the removal of spilled oil from water, but their effect on hydrocarbonoclastic bacteria is not known. Here, we show that corksorb, a cork-based biosorbent, enhances growth and alkane degradation by Rhodococcus opacus B4 (Ro) and Alcanivorax borkumensis SK2 (Ab). Ro and Ab degraded 96 ± 1% and 72 ± 2%, respectively, of a mixture of n-alkanes (2 g L-1) in the presence of corksorb. These values represent an increase of 6 and 24%, respectively, relative to the assays without corksorb. The biosorbent also increased the growth of Ab by 51%. However, no significant changes were detected in the expression of genes involved in alkane uptake and degradation in the presence of corksorb relative to the control without the biosorbent. Nevertheless, transcriptomics analysis revealed an increased expression of rRNA and tRNA coding genes, which confirms the higher metabolic activity of Ab in the presence of corksorb. The effect of corksorb is not related to the release of soluble stimulating compounds, but rather to the presence of the biosorbent, which was shown to be essential. Indeed, scanning electron microscopy images and downregulation of pili formation coding genes, which are involved in cell mobility, suggest that cell attachment on corksorb is a determinant for the improved activity. Furthermore, the existence of native alkane-degrading bacteria in corksorb was revealed, which may assist in situ bioremediation. Hence, the use of corksorb in marine oil spills may induce a combined effect of sorption and stimulated biodegradation, with high potential for enhancing in situ bioremediation processes.

Sequencing batch airlift reactors (SBAR): a suitable technology for treatment and valorization of mineral oil wastewaters towards lipids production

Produced water (PW) and spent oil-based wastewaters are some of the largest mineral oil wastewaters produced. Due to the high toxicity of hydrocarbons, several countries set stringent discharge limits and its treatment is compulsory before discharge. In this work, biological treatment of mineral oil wastewaters coupled with the production of bacterial lipids is demonstrated in sequential batch airlift reactors (SBAR). Two SBAR (2 L working volume) were used for treatment of PW and lubricant-based wastewater (LW), inoculated with Alcanivorax borkumensis SK2 (SBAR_Ab+PW) and Rhodococcus opacus B4 (SBAR_R.o+LW), respectively. A total petroleum hydrocarbon removal (TPH) efficiency up to 96% and 80% were achieved for SBAR_Ab+PW and SBAR_R.o+LW, respectively. Intracellular lipids production in SBAR_Ab+PW increased when lower TPH/N ratios and higher feast stage duration were applied (up to 0.74 g g^-1 cell dry weight (CDW)), whereas in SBAR_R.o+LW higher lipids production was observed for higher TPH/N ratios (0.94 g g^-1 in CDW). Triacylglycerols (TAG) were the main intracellular lipid accumulated in both SBAR_Ab+PW and SBAR_R.o+LW operations, while wax ester (WE) production was only observed extracellularly in the SBAR_Ab+PW.

Perspectives on variabilities in biomethane potential test parameters and outcomes: A review of studies published between 2007 and 2018

Biomethane Potential (BMP) test continues to be a useful and inexpensive assay to estimate the digestibility and maximum methane production of various organic substrates in anaerobic digestion or co-digestion processes. Despite its usefulness and several published efforts toward standardizing it, the BMP test still do not follow a universally accepted standard protocol. This makes the comparison of results among studies quite challenging. In this context, this paper analyzes 78 peer-reviewed BMP studies published between 2007 and 2018 that used the BMP test primarily to assess methane potential of commonly digested substrates, such as food waste, wastewater sludge and manure. We focused on the similarities and differences in the methodologies used and, where possible, the results obtained from these studies were compared and discussed. It was observed that many studies do not provide adequate information on salient aspects of the BMP methodology, and results are sometimes reported in different units of measurements. The inoculum to substrate ratio (ISR), substrate concentration and/or load should be clearly indicated in future studies, and positive controls should be included to validate BMP results. It is recommended that more studies assess the impact of nutrient addition, potential effects of continuous and intermittent mixing and mixing intensities and the influence of reactor size and headspace volume on BMP results.