Biodegradation of hexadecane in liquid and solid-state fermentations by Aspergillus niger

Comparative Bioremediation of Tetradecane, Cyclohexanone and Cyclohexane by Filamentous Fungi from Polluted Habitats in Kazakhstan

Studying the fates of oil components and their interactions with ecological systems is essential for developing comprehensive management strategies and enhancing restoration following oil spill incidents. The potential expansion of Kazakhstan's role in the global oil market necessitates the existence of land-specific studies that contribute to the field of bioremediation. In this study, a set of experiments was designed to assess the growth and biodegradation capacities of eight fungal strains sourced from Kazakhstan soil when exposed to the hydrocarbon substrates from which they were initially isolated. The strains were identified as Aspergillus sp. SBUG-M1743, Penicillium javanicum SBUG-M1744, SBUG-M1770, Trichoderma harzianum SBUG-M1750 and Fusarium oxysporum SBUG-1746, SBUG-M1748, SBUG-M1768 and SBUG-M1769 using the internal transcribed spacer (ITS) region. Furthermore, microscopic and macroscopic evaluations agreed with the sequence-based identification. Aspergillus sp. SBUG-M1743 and P. javanicum SBUG-M1744 displayed remarkable biodegradation capabilities in the presence of tetradecane with up to a 9-fold biomass increase in the static cultures. T. harzianum SBUG-M1750 exhibited poor growth, which was a consequence of its low efficiency of tetradecane degradation. Monocarboxylic acids were the main degradation products by SBUG-M1743, SBUG-M1744, SBUG-M1750, and SBUG-M1770 indicating the monoterminal degradation pathway through β-oxidation, while the additional detection of dicarboxylic acid in SBUG-M1768 and SBUG-M1769 cultures was indicative of the fungus' ability to undertake both monoterminal and diterminal degradation pathways. F. oxysporum SBUG-M1746 and SBUG-M1748 in the presence of cyclohexanone showed a doubling of the biomass with the ability to degrade the substrate almost completely in shake cultures. F. oxysporum SBUG-M1746 was also able to degrade cyclohexane completely and excreted all possible metabolites of the degradation pathway. Understanding the degradation potential of these fungal isolates to different hydrocarbon substrates will help in developing effective bioremediation strategies tailored to local conditions.

Spatial distribution characteristics and degradation mechanism of microorganisms in n-hexadecane contaminated vadose zone

The damage caused by petroleum hydrocarbon pollution to soil and groundwater environment is becoming increasingly significant. The vadose zone is the only way for petroleum hydrocarbon pollutants to leak from surface into groundwater. The spatial distribution characteristics of indigenous microorganisms in vadose zone, considering presence of capillary zones, have rarely been reported. To explore the spatial distribution characteristics of indigenous microorganisms in vadose zone contaminated by petroleum hydrocarbons, a one-dimensional column migration experiment was conducted using n-hexadecane as characteristic pollutant. Soil samples were collected periodically from different heights during experiment. Corresponding environmental factors were monitored online. The microbial community structure and spatial distribution characteristics of the cumulative relative abundance were systematically analyzed using 16S rRNA sequencing. In addition, the microbial degradation mechanism of n-hexadecane was analyzed using metabolomics. The results showed that presence of capillary zone had a strong retarding effect on n-hexadecane infiltration. Leaked pollutants were mainly concentrated in areas with strong capillary action. Infiltration and displacement of NAPL-phase pollutants were major driving force for change in moisture content (θ) and electric conductivity (EC) in vadose zone. The degradation by microorganisms results in a downward trend in potential of hydrogen (pH) and oxidation-reduction potential (ORP). Five petroleum hydrocarbon-degrading bacterial phyla and 11 degradable straight-chain alkane bacterial genera were detected. Microbial degradation was strong in the area near edge of capillary zone and locations of pollutant accumulation. Mainly Sphingomonas and Nocardioides bacteria were involved in microbial degradation of n-hexadecane. Single-end oxidation involved microbial degradation of n-hexadecane (C16H34). The oxygen consumed, hexadecanoic acid (C16H32O2) produced during this process, and release of hydrogen ions (H+) were the driving factors for reduction of ORP and pH. The vadose zone in this study considered presence of capillary zone, which was more in line with actual contaminated site conditions compared with previous studies. This study systematically elucidated vertical distribution characteristics of petroleum hydrocarbon pollutants and spatiotemporal variation characteristics of indigenous microorganisms in vadose zone considered presence of capillary zone. In addition, the n-hexadecane degradation mechanism was elucidated using metabolomics. This study provides theoretical support for development of natural attenuation remediation measures for petroleum-hydrocarbon-contaminated soil and groundwater.

Exploiting fungi in bioremediation for cleaning-up emerging pollutants in aquatic ecosystems

Aquatic pollution negatively affects water bodies, marine ecosystems, public health, and economy. Restoration of contaminated habitats has attracted global interest since protecting the health of marine ecosystems is crucial. Bioremediation is a cost-effective and eco-friendly way of transforming hazardous, resistant contaminants into environmentally benign products using diverse biological treatments. Because of their robust morphology and broad metabolic capabilities, fungi play an important role in bioremediation. This review summarizes the features employed by aquatic fungi for detoxification and subsequent bioremediation of different toxic and recalcitrant compounds in aquatic ecosystems. It also details how mycoremediation may convert chemically-suspended matters, microbial, nutritional, and oxygen-depleting aquatic contaminants into ecologically less hazardous products using multiple modes of action. Mycoremediation can also be considered in future research studies on aquatic, including marine, ecosystems as a possible tool for sustainable management, providing a foundation for selecting and utilizing fungi either independently or in microbial consortia.

Biodegradation half-lives of biodiesel fuels in aquatic and terrestrial systems: A review

Information on biodegradation kinetics of biodiesel fuels is a key aspect in risk and impact assessment practice and in selection of appropriate remediation strategies. Unfortunately, this information is scattered, while factors influencing variability in biodegradation rates are still not fully understood. Therefore, we systematically reviewed 32 scientific literature sources providing 142 biodegradation and 56 mineralization half-lives of diesel and biodiesel fuels in various experimental systems. The analysis focused on the variability in half-lives across fuels and experimental conditions, reporting sets of averaged half-life values and their statistical uncertainty. Across all data points, biodegradation half-lives ranged from 9 to 62 days, and were 2-5.5 times shorter than mineralization half-lives. Across all fuels, biodegradation and mineralization half-lives were 2.5-8.5 times longer in terrestrial systems when compared to aquatic systems. The half-lives were generally shorter for blends with increasing biodiesel content, although differences in number of data points from various experiments masked differences in half-lives between different fuels. This in most cases resulted in lack of statistically significant effects of the type of blends and experimental system on biodegradation half-lives. Our data can be used for improved characterization of risks and impacts of biodiesel fuels in aerobic aquatic and terrestrial environments, while more experiments are required to quantify biodegradation kinetics in anaerobic conditions. Relatively high biodegradability of biodiesel may suggest that passive approaches to degrade and dissipate contaminants in situ, like monitored natural attenuation, may be appropriate remediation strategies for biodiesel fuels.

Modelling of n-Hexadecane bioremediation from soil by slurry bioreactors using artificial neural network method

Diesel oil is known to be one of the major petroleum products that can pollute water and soil. Soil pollution caused by petroleum hydrocarbons has substantially impacted the environment, especially in the Middle East. In this study, modeling and optimization of hexadecane removal from soil was performed using two pure cultures of Acinetobacter and Acromobacter and consortium culture of both bacterial species using artificial neural network (ANN) method. Then the best ANN structure was proposed based on mean square error (MSE) as well as correlation coefficient (R) for pure cultures of Acinetobacter and Acromobacter as well as their consortium. The results showed that the correlations between the actual data and the data predicted by ANN (R2) in Acromobacter, Acinetobacter and consortium of both cultures were 0.50, 0.47 and 0.63, respectively. Despite the low correlation between the experimental data and the data predicted by the ANN, the correlation coefficient and the precision of ANN for the consortium was higher. As a result, ANN had desirable precision to predict hexadecan removal by the cobsertium culture of Ochromobater and Acintobacter.

Cultivable fungi from deep-sea oil reserves in the Gulf of Mexico: Genetic signatures in response to hydrocarbons

The estimation of oil spill effects on marine ecosystems is limited to the extent of our knowledge on the autochthonous biota. Fungi are involved in key ecological marine processes, representing a major component of post-spill communities. However, information on their functional capacities remains lacking. Herein we analyzed cultivable fungi from sediments in two oil-drilling regions of the Gulf of Mexico for their ability to tolerate and use hexadecane and 1-hexadecene as the sole carbon sources; and to evaluate gene expression profiles of key hydrocarbonoclastic taxa during utilization of these hydrocarbons. The isolated fungi showed differential sensitivity patterns towards the tested hydrocarbons under three different concentrations. Remarkably, six OTUs (Aureobasidium sp., Penicillium brevicompactum, Penicillium sp., Phialocephala sp., Cladosporium sp. 1 and 2) metabolized the tested alkane and alkene as the sole carbon sources, confirming that deep-sea fungal taxa are valuable genetic resources with potential use in bioremediation. RNA-seq results revealed distinctive gene expression profiles in the hydrocarbonoclastic fungus Penicillium sp. when using hexadecane and 1-hexadecene as the sole carbon sources, with up-regulation of genes involved in transmembrane transport, metabolism of six-carbons carbohydrates, and nitric oxide pathways.

Biodegradation of n-hexadecane by Aspergillus sp. RFC-1 and its mechanism

Fungi can use n-hexadecane (HXD) as a sole carbon source. But the mechanism of HXD degradation remains unclear. This work mainly aimed to study the degradation of HXD by Aspergillus sp. RFC-1 obtained from oil-contaminated soil. The HXD content, medium acidification and presence of hexadecanoic acid in the medium were determined by gas chromatography-mass spectrometry, and fungal growth was observed. Enzyme and gene expression assays suggested the involvement of an alkane hydroxylase, an alcohol dehydrogenase, and a P450 enzyme system in HXD degradation. A biosurfactant produced by the strain RFC-1 was also characterized. During 10 days of incubation, 86.3% of HXD was degraded by RFC-1. The highest activities of alkane hydroxylase (125.4 µmol mg^-1 protein) and alcohol dehydrogenase (12.5 µmol mg^-1 proteins) were recorded. The expression level of cytochrome P450 gene associated with oxidation was induced (from 0.94-fold to 5.45-fold) under the HXD condition by Real-time PCR analysis. In addition, HXD accumulated in inclusion bodies of RFC-1with the maximum of 5.1 g L^-1. Results of blood agar plate and thin-layer chromatography analysis showed RFC-1 released high lipid and emulsification activity in the fungal culture. Induced cell surface hydrophobicity and reduced surface tension also indicated the RFC-1-mediated biosurfactant production, which facilitated the HXD degradation and supported the degradation process.

Critical Values of Porosity in Rice Cultures of Isaria fumosorosea by Adding Water Hyacinth: Effect on Conidial Yields and Quality

Conidia of the entomopathogenic fungus Isaria fumosorosea are used to control insect pests in crops. Commercially available mycoinsecticides manufactured with this fungus are produced on a large scale via solid-state cultures (SSC). In order to favour gaseous exchange in SCC, texturizers can be added to increase porosity fraction (ε). This work presents results of water hyacinth (Eichhornia crassipes) as a novel texturizer. A mixture of parboiled rice (PR), with a ε = 0.23, was used as a substrate, which was then mixed with water hyacinth (WH amendment) as a texturizer at different proportions affecting ε. Strains CNRCB1 and ARSEF3302 of I. fumosorosea yielded 1.6 (1.49-1.71) × 10(9) and 7.3 (7.02-7.58) × 10(9) conidia per gram of initial dry rice after 8 days, at ε values of 0.34 and 0.36, respectively. Improvement of conidial yields corresponded to 1.33 and 1.55 times, respectively, compared to rice alone using WH amendment in the mixtures PR:WH (%) at 90-10 and 80-20. In addition, infectivity against Galleria mellonella larvae was maintained. This is the first report of the use of water hyacinth as a texturizer in SSC, affecting ε, which is proposed a key parameter in conidia production by I. fumosorosea, without affecting conidial infectivity.

Modeling of an aerobic bioprocess based on gas exchange and dynamics: a novel approach

Monitoring of the biological degradation of a substrate by microorganisms is a key issue, especially in the soil bioremediation area. Respiration measurement is the easiest way to obtain online information on the biological activity. Nevertheless, it is indirectly related to substrate consumption and microbial growth. To be able to link these phenomena, a robust and descriptive model has been developed. Both biological and gas/liquid transfer dynamics must be taken into account to link the online measurement with the actual biological respiration. For that, experimental evolution of the respiratory ouotient (RQ) during a biodegradation has been compared against general biodegradation knowledge. To obtain a reliable model, practical and structural sensitivity analyses have been conducted. The model can describe the evolution of both online measurable and non-measurable states. It also gives a new definition of the apparent RQ, measured in the gas phase, compared to the actual biological RQ.

Biodegradation of toluene in a two-phase partitioning bioreactor--impact of activated sludge acclimation

A two-phase partitioning bioreactor was considered to remove toluene contained in a biodegradable organic phase by activated sludge (AS). The selected solvent was hexadecane. In a first step, the biodegradation of toluene dissolved in hexadecane by AS was examined. In a second step, acclimation of the AS was carried out in order to improve the biodegradation rate. Acclimation improved toluene removal, since biodegradation yield increased from 72% to more than 91%. A total consumption was observed after only 4 days culture with acclimated AS, since the rest of the toluene corresponded to gas leak; while in the case of non-acclimated sludge, losses cannot account for all non-degraded toluene. Regarding hexadecane, acclimation also improved its degradation, from 43% to 79% after 6 days culture for non-acclimated and acclimated AS, respectively.

Carbon content reduction in a model reluctant clayey soil: slurry phase n-hexadecane bioremediation

Clayey soils contaminated with organic pollutants are nowadays one of the important environmental issues as they are highly reluctant to conventional bioremediation techniques. In this study, biodegradability of n-hexadecane as a model contaminant in oil polluted clayey soil by an indigenous bacterium was investigated. Maximal bacterial growth was achieved at 8% (v/v) n-hexadecane as sole carbon and energy sources in aqueous phase. The predominant n-hexadecane uptake mechanism was identified to be biosurfactant-mediated using bacterial adhesion to hydrocarbon (BATH) test and surface tension measurements. The effect of n-hexadecane concentration, soil to water ratio, inoculum concentration and pH on total organic carbon (TOC) reduction from kaolin soil in slurry phase was investigated at two levels in shake flasks using full factorial experimental design method where 10,000 (mg n-hexadecane)(kg soil)(-1), soil-water ratio of 1:3, 10% (v/w) inoculum and pH of 7 resulted in the highest TOC reduction of 70% within 20 days. Additionally, slurry bioreactor experiments were performed to study the effect of various aeration rates on n-hexadecane biodegradation during 9 days where 2.5 vvm was found as an appropriate aeration rate leading to 54% TOC reduction. Slurry phase bioremediation is shown to be a successful method for remediation of clayey reluctant soils.

Degradation of procyanidins by Aspergillus fumigatus: Identification of a novel aromatic ring cleavage product

Aspergillus fumigatus was able to grow on apple-purified procyanidins (PCs). PCs concentration decreased 30% over the first 60 h of liquid fermentation. The mean degree of polymerization (DPn) of apple-purified PCs increased from 8 to 15 during the fermentation. A fungal enzyme extract from the liquid fermentation was used to study procyanidin B2 [(-)-epicatechin-(4beta-8)-(-)-epicatechin] degradation. The major degradation product (PB2-X) had a retention time of 10.5 min and a molecular mass at m/z 609. High-performance liquid chromatography/multiple fragment mass spectrometry (HPLC/MS(n)) was used for the structural characterization of PB2-X as well as that of thiolysis-treated PB2-X. Twelve fragment ions at m/z 565, 547, 457, 439 (two fragment ions), 421, 413, 377, 395, 351, 287 and 277 were completely identified. It was therefore deduced that the terminal unit of procyanidin B2 dimer was modified by an oxygenase from A. fumigatus leaving the extension unit intact. In addition, FT-IR analysis confirmed a lactone formation in (-)-epicatechin moiety involved in oxidative degradation. Two reaction schemes were postulated for the interpretation of the results.

Biodegradation of high concentrations of hexadecane by Aspergillus niger in a solid-state system: kinetic analysis

Solid-state microcosms were used to assess the influence of constant and variable C/N ratios on the biodegradation efficiency by Aspergillus niger at high hexadecane (HXD) concentrations (180-717 mg g-1). With a constant C/N ratio, 100% biodegradation (33-44% mineralization) was achieved after 15 days, at rates increasing as the HXD concentration increased. Biomass yields (YX/S) remained almost independent (approximately 0.77) of the carbon-source amount, while the specific growth rates (mu) decreased with increasing concentrations of HXD. With C/N ratios ranging from 29 to 115, complete degradation was only attained at 180 mg g-1, corresponding to 46% mineralization. YX/S diminished (approximately 0.50 units) as the C/N ratio increased. The highest values of mu (1.08 day-1) were obtained at low C/N values. Our results demonstrate that, under balanced nutritional conditions, high HXD concentrations can be completely degraded in solid-state microcosms, with a negligible (<10%) formation of by-products.

Proteoglycan isolated from Phellinus linteus induces toll-like receptors 2- and 4-mediated maturation of murine dendritic cells via activation of ERK, p38, and NF-kappaB

Mushroom polysaccharides are increasingly being utilized to treat a wide variety of diseases. Phellinus linteus proteoglycan (PL) has been reported to have anti-tumor and immunomodulatory properties. However, the cellular and molecular mechanism underlying its therapeutic effect is poorly understood. In this study, we investigated whether PL induces the phenotypic and functional maturation of murine bone marrow-derived dendritic cells (DC) and the possibility that Toll-like receptors (TLRs), which are known to be involved in immune-related responses, may be the receptor(s) of PL. The expression of surface molecules, including major histocompatibility complex (MHC) class II and CD86, increased on DC that were stimulated in a dose-dependent manner with PL, in comparison with unstimulated DC. Furthermore, PL increases the production of IL-12 by DC, as well as the IL-2 secretion and proliferation of allogeneic T cells. In addition, the activities of PL on DC were significantly reduced by treating the cells with anti-TLR2 or anti-TLR4 antibody (Ab) prior to PL, suggesting that both of them are possible receptors of PL. Also, maturation of DC by PL was able to directly activate mitogen-activated protein kinases (MAPKs), such as ERK1/2 and p38, and the nuclear transcription factor NF-kappaB p65. Also, the pretreatment of DC with inhibitors of NF-kappaB p65, and ERK and p38 MAPK signal pathways inhibited PL-induced up-regulation of surface molecules, such as MHC class II and CD86, and IL-12 production. Our results demonstrated that PL stimulation could induce the phenotypic and functional maturation of DC via TLR2 and/or TLR4 mediated-NF-kappaB, ERK and p38 MAPK signal pathways.

Microbiological degradation of pentane by immobilized cells of Arthrobacter sp

The increasing production of several plastics such as expanded polystyrene, widely used as packaging and building materials, has caused the release of considerable amounts of pentane employed as an expanding agent. Today many microorganisms are used to degrade hydrocarbons in order to minimize contamination caused by several industrial activities. The aim of our work was to identify a suitable microorganism to degrade pentane. We focused our attention on a strain of Arthrobacter sp. which in a shake-flask culture produced 95% degradation of a 10% mixture of pentane in a minimal medium after 42 days of incubation at 20 degrees C. Arthrobacter sp. cells were immobilized on a macroporous polystyrene particle matrix that provides a promising novel support for cell immobilization. The method involved culturing cells with the expanded polystyrene in shake-flasks, followed by in situ growth within the column. Scanning electron microscopy analysis showed extensive growth of Arthrobacter sp. on the polymeric surface. The immobilized microorganism was able to actively degrade a 10% mixture of pentane, allowing us to obtain a bioconversion yield of 90% after 36 h. Moreover, in repeated-batch operations, immobilized Arthrobacter sp. cells were able to maintain 85-95% pentane degradation during a 2 month period. Our results suggest that this type of bioreactor could be used in pentane environmental decontamination.

Alleviation of experimental septic shock in mice by acidic polysaccharide isolated from the medicinal mushroom Phellinus linteus

This study reports that acidic polysaccharide (PL) isolated from Phellinus linteus alleviated the septic shock induced by high dose lipopolysaccharide (LPS) injection in mice. To examine the origin of this effect, we investigated cytokine production in serum and the expression of MHC II in B cells and macrophages in areas of inflammation. Pretreatment with PL 24 h before LPS administration resulted in a significant inhibition of up to 68% of circulating tumor necrosis factor (TNF)-alpha, a moderate reduction of 45% of interleukine (IL)-12 and 23% of IL-1beta, but no significant reduction in IL-6. In addition, the expression of MHC II in B cells and macrophages was examined. Our results show that LPS-stimulated cytokine release and the level of MHC II can be modulated by in vivo administration of soluble PL in mice. The decrease of IL-1beta, IL-12 and TNF-alpha in sera and the down-modulation of MHC II during septic shock may contribute to the long survival of mice by PL. Administration of PL in vivo decreases IL-2, IFN-gamma and TNF-alpha production in splencotyes and enhances spontaneous cell apoptosis in macrophages and lymphocytes stimulated with LPS in vitro. Thus, part of the anti-inflammatory effects of PL treatment in vivo may result from the enhanced apoptosis of a portion of the activated macrophages and lymphocytes. The ability of PL to significantly reduce the TNF-alpha production indicates the potential of the polysaccharides in possible therapeutic strategies that are based on down-regulation of TNF-alpha.

An optimized method for Aspergillus niger spore production on natural carrier substrates

Aspergillus niger spores have wide ranging applications in the fermentation industry as well as in wastewater treatment. We present an optimized method for production of A. niger spores on natural substrates such as rice, split pea, and millet. The specific productivity (number of spores per gram of dry substrate) was 31-fold greater and volumetric productivity was 750-fold greater compared to agar slopes. The important process variables were incubation temperature, moisture content, and inoculum quantity. We find that the optimal condition for total spore count is different from the viable spore count for millet. The optimum lies in a narrow region defined by the process parameters. Of the three substrates tested split pea gave the highest specific spore productivity of 3.1 x 10(10) spores per gram of dry substrate. This is the first report of systematic study on the effect of process parameters on spore viability. The method of A. niger spore production on natural substrate appears advantageous as compared to the currently practiced method in terms of scale-up, cost, and ease of operation.