Oxidative Stress Response and Morphological Changes of Blakeslea trispora Induced by Butylated Hydroxytoluene During Carotene Production

Approach to an answer to "How dangerous microplastics are to the human body": A systematic review of the quantification of MPs and simultaneously exposed chemicals

This review aims to facilitate future research on microplastics (MPs) in the environment using systematic and analytical protocols, ultimately contributing to assessment of the risk to human health due to continuous daily exposure to MPs. Despite extensive studies on MP abundance in environment, identification, and treatment, their negative effects on human health remain unknown due to the lack of proof from clinical studies and limited technology on the MP identification. To assess the risk of MPs to human health, the first step is to estimate MP intake via ingestion, inhalation, and dermal contact under standardized exposure conditions in daily life. Furthermore, rather than focusing on the sole MPs, migrating chemicals from plastic products should be quantified and their health risk be assessed concurrently with MP release. The critical factors influencing MP release and simultaneously exposed chemicals (SECs) must be investigated using a standardized identification method. This review summarises release sources, factors, and possible routes of MPs from the environment to the human body, and the quantification methods used in risk assessment. We also discussed the issues encountered in MP release and SEC migration. Consequently, this review provides directions for future MP studies that can answer questions about MP toxicity to human health.

Bacillus cereus WL08 immobilized on tobacco stem charcoal eliminates butylated hydroxytoluene in soils and alleviates the continuous cropping obstacle of Pinellia ternata

Butylated hydroxytoluene (BHT), as an emerging contaminant in ecosystems, has potential influences on animals, aquatic organisms, and public health, and has been proven to be a major allelochemical of Pinellia ternata. In this study, Bacillus cereus WL08 was used to rapidly degrade BHT in liquid culture. Strain WL08 immobilized on tobacco stem charcoal (TSC) particles notably accelerated BHT removal in contract to its free cells, and exhibited excellent reutilization and storage capacities. The optimal removal parameters of TSC WL08 were ascertained to be pH 7.0, 30 °C, 50 mg L^-1 BHT and 0.14 mg L^-1 TSC WL08. Moreover, TSC WL08 significantly accelerated the degradation of 50 mg L^-1 BHT in sterile and non-sterile soils compared to that of free WL08 or natural dissipation, and notably shortened their half-lives by 2.47- or 362.14- fold, and 2.20- or 14.99- fold, respectively. Simultaneously, TSC WL08 was introduced into the continuous cropping soils of P. ternata, which accelerated the elimination of allelochemical BHT, and notably enhanced the photosynthesis, growth, yield, and quality of P. ternata. This study provides new insights and strategies for the rapid in situ remediation of BHT-polluted soils and effective alleviation of P. ternata cropping obstacles.

Advances in engineering the production of the natural red pigment lycopene: A systematic review from a biotechnology perspective

BACKGROUND

Lycopene is a natural red compound with potent antioxidant activity that can be utilized both as pigment and as a raw material in functional food, and so possesses good commercial prospects. The biosynthetic pathway has already been documented, which provides the foundation for lycopene production using biotechnology.

AIM OF REVIEW

Although lycopene production has begun to take shape, there is still an urgent need to alleviate the yield of lycopene. Progress in this area can provide useful reference for metabolic engineering of lycopene production utilizing multiple approaches.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Using conventional microbial fermentation approaches, biotechnologists have enhanced the yield of lycopene by selecting suitable host strains, utilizing various additives, and optimizing culture conditions. With the development of modern biotechnology, genetic engineering, protein engineering, and metabolic engineering have been applied for lycopene production. Extraction from natural plants is the main way for lycopene production at present. Based on the molecular mechanism of lycopene accumulation, the production of lycopene by plant bioreactor through genetic engineering has a good prospect. Here we summarized common strategies for optimizing lycopene production engineering from a biotechnology perspective, which are mainly carried out by microbial cultivation. We reviewed the challenges and limitations of this approach, summarized the critical aspects, and provided suggestions with the aim of potential future breakthroughs for lycopene production in plants.

Microbubble ozonation of the antioxidant butylated hydroxytoluene: Degradation kinetics and toxicity reduction

Butylated hydroxytoluene (BHT) is recognized as a crucial pollutant in aquatic environments, but efforts to achieve its complete removal are without success. The aim of this study was to investigate the degradation efficiency of BHT in water using ozone microbubbles (OMB), coupled with toxicity change assessment at sub-lethal BHT concentrations (0.34, 0.45 and 0.90 μM) based on oxidative stress biomarkers in Daphnia magna. The efficiency of OMB on ozone gas mass transfer was assessed and the contribution of hydroxyl radicals (·OH) in the degradation of BHT was determined using p-chlorobenzoic acid (pCBA) probe compound and a ·OH radical scavenger (sodium carbonate, Na₂CO₃). The ozone gas mass transfer coefficient (k_La = 1.02 × 10^-2 s^-1) was much larger than the ozone self-decomposition rate (k_d = 8 × 10^-4 s^-1) implying little influence of self-decomposing ozone in the volumetric ozone transfer during OMB generation. Generally, OMB improved ozone gas mass transfer (1.3-19-fold) relative to conventional ozone techniques, while indirect reaction of BHT with ·OH was dominant (82%) over the direct reaction with molecular ozone. Addition of 15, 25 and 35 mM Na₂CO₃ reduced BHT degradation by 30, 50 and 65%, respectively, indicating the significance of ·OH in the degradation of BHT. Increase in initial BHT concentration correspondingly reduced its removal rate by OMB possibly due to increase in metabolites produced during ozonation. Post BHT treatment exposure tests recorded significant (p < 0.05) reductions in oxidative stress (according to enzyme activities changes) in D. magna compared to pretreatment tests, demonstrating the effectiveness of OMB in detoxification of BHT. Overall, the results of the study indicate that OMB is extremely efficient in complete degradation of BHT in water and, consequently, significantly (p < 0.05) reducing its toxicity.

Rhodotorula mucilaginosa C2.5t1 Modulates Carotenoid Content and CAR Genes Transcript Levels to Counteract the Pro-Oxidant Effect of Hydrogen Peroxide

In order to contribute to the elucidation of the biological role of carotenoids, the cellular response to hydrogen peroxide was analyzed in the red yeast R. mucilaginosa. For that, the wild strain C2.5t1, that produces β-carotene, torulene, and torularhodin, and the albino mutant 200A6 that is incapable of producing detectable amounts of these carotenoids, were grown in the presence of increasing concentrations of hydrogen peroxide. In spite of the difference in carotenoid content, the two strains presented comparable resistance to the pro-oxidant that showed a minimum inhibitory concentration of 6 mM. When subject to 1 h treatment with 16 mM hydrogen peroxide the two strains increased catalase but not superoxide activity, suggesting that catalase plays a major role in cell protection in both the wild strain and the albino mutant. Moreover, C2.5t1 reduced its carotenoid content by about 40% upon hydrogen peroxide treatment. This reduction in carotenoids was in agreement with a significant decrease of the transcript levels of genes involved in carotenoid biosynthesis. Since an excess of β-carotene may enhance reactive oxygen species toxicity, these results suggest that C2.5t1 modulates carotenoid content to counteract the pro-oxidant effect of hydrogen peroxide.

Effect of SDS on release of intracellular pneumocandin B0 in extractive batch fermentation of Glarea lozoyensis

Pneumocandin B₀ is a hydrophobic secondary metabolite that accumulates in the mycelia of Glarea lozoyensis and inhibits fungal 1,3-β-glucan synthase. Extractive batch fermentation can promote the release of intracellular secondary metabolites into the fermentation broth and is often used in industry. The addition of extractants has been proven as an effective method to attain higher accumulation of hydrophobic secondary metabolites and circumvent troublesome solvent extraction. Various extractants exerted significant but different influences on the biomass and pneumocandin B₀ yields. The maximum pneumocandin B₀ yield (2528.67 mg/L) and highest extracellular pneumocandin B₀ yield (580.33 mg/L) were achieved when 1.0 g/L SDS was added on the 13th day of extractive batch fermentation, corresponding to significant increases of 37.63 and 154% compared with the conventional batch fermentation, respectively. The mechanism behind this phenomenon is partly attributed to the release of intracellular pneumocandin B₀ into the fermentation broth and the enhanced biosynthesis of pneumocandin B₀ in the mycelia.

Waste cooking oil: A new substrate for carotene production by Blakeslea trispora in submerged fermentation

The objective of this study was to evaluate a waste, waste cooking oil (WCO) as substrate for carotene production by Blakeslea trispora in shake flask culture. WCO was found to be a useful substrate for carotene production. B. trispora formed only pellets during fermentation. The oxidative stress in B. trispora induced by hydroperoxides and BHT as evidenced by increase of the specific activities of superoxide dismutase (SOD) and catalase (CAT) increased significantly the production of carotenes. The highest concentration of carotenes (2021 ± 75 mg/l or 49.3 ± 0.2 mg/g dry biomass) was obtained in culture grown in WCO (50.0 g/l) supplemented with CSL (80.0 g/l) and BHT (4.0 g/l). In this case the carotenes produced consisted of β-carotene (74.2%), γ-carotene (23.2%), and lycopene (2.6%). The external addition in the above medium glucose, Span 80, yeast extract, casein acid hydrolysate, l-asparagine, thiamine. HCl, KH2PO4, and MgSO4·7H2O did not improve the production of carotenes.

The role of oxidative stress on carotene production by Blakeslea trispora in submerged fermentation

In aerobic metabolism, reactive oxygen species (ROS) are formed during the fermentation that can cause oxidative stress in microorganisms. Microbial cells possess both enzymatic and non-enzymatic defensive systems that may protect cells from oxidative damage. The antioxidant enzymes superoxide dismutase and catalase are the two key defensive enzymes to oxidative stress. The factors that induce oxidative stress in microorganisms include butylated hydroxytoluene (BHT), hydrogen peroxide, metal ions, dissolved oxygen tension, elevated temperature, menadione, junglone, paraquat, liquid paraffin, introduction to bioreactors of shake flask inocula and synthetic medium sterilized at initial pH 11.0. Carotenes are highly unsaturated isoprene derivatives. They are used as antioxidants and as coloring agents for food products. In fungi, carotenes are derived via the mevalonate biosynthesis pathway. The key genes in carotene biosynthesis are hmgR, ipi, isoA, carG, carRA and carB. Among microorganisms, Βlakeslea trispora is the main microorganism used for the production of carotenes on the industrial scale. Currently, the synthetic medium is considered the superior substrate for the production of carotenes in a pilot plant scale. The fermentation systems used for the production of carotenes include shake flasks, stirred tank fermentor, bubble column reactor and flat panel photobioreactor. This review summarizes the oxidative stresses in microorganisms and it is focused on the current status of carotene production by B. trispora including oxidative stress induced by BHT, enhanced dissolved oxygen levels, iron ions, liquid paraffin and synthetic medium sterilized at an initial pH 11.0. The oxidative stress induced by the above factors increases significantly the production of carotenes. However, to further reduce the cost of carotene production, new biotechnological methods with higher productivity still need to be explored.

2,6-Di-Tert-Butyl-Hydroxytoluene and Its Metabolites in Foods

2,6-Di-tert-butyl-hydroxytoluene (BHT, E-321) is a synthetic phenolic antioxidant which has been widely used as an additive in the food, cosmetic, and plastic industries for the last 70 y. Although it is considered safe for human health at authorized levels, its ubiquitous presence and the controversial toxicological data reported are of great concern for consumers. In recent years, special attention has been paid to these 14 metabolites or degradation products: BHT-CH₂ OH, BHT-CHO, BHT-COOH, BHT-Q, BHT-QM, DBP, BHT-OH, BHT-OOH, TBP, BHQ, BHT-OH(t), BHT-OH(t)QM, 2-BHT, and 2-BHT-QM. These derived compounds could pose a human health risk from a food safety point of view, but they have been little studied. In this context, this review deals with the occurrence, origin, and fate of BHT in foodstuffs, its biotransformation into metabolites, their toxicological implications, their antioxidant and prooxidant properties, the analytical determination of metabolites in foods, and human dietary exposure. Moreover, noncontrolled additional sources of exposure to BHT and its metabolites are highlighted. These include their carryover from feed to fish, poultry and eggs, their presence in smoke flavorings, their migration from plastic pipelines and packaging to water and food, and their presence in natural environments, from which they can reach the food chain.

Biological roles of fungal carotenoids

Carotenoids are terpenoid pigments widespread in nature, produced by bacteria, fungi, algae and plants. They are also found in animals, which usually obtain them through the diet. Carotenoids in plants provide striking yellow, orange or red colors to fruits and flowers, and play important metabolic and physiological functions, especially relevant in photosynthesis. Their functions are less clear in non-photosynthetic microorganisms. Different fungi produce diverse carotenoids, but the mutants unable to produce them do not exhibit phenotypic alterations in the laboratory, apart of lack of pigmentation. This review summarizes the current knowledge on the functional basis for carotenoid production in fungi. Different lines of evidence support a protective role of carotenoids against oxidative stress and exposure to visible light or UV irradiation. In addition, the carotenoids are intermediary products in the biosynthesis of physiologically active apocarotenoids or derived compounds. This is the case of retinal, obtained from the symmetrical oxidative cleavage of β-carotene. Retinal is the light-absorbing prosthetic group of the rhodopsins, membrane-bound photoreceptors present also in many fungal species. In Mucorales, β-carotene is an intermediary in the synthesis of trisporoids, apocarotenoid derivatives that include the sexual hormones the trisporic acids, and they are also presumably used in the synthesis of sporopollenin polymers. In conclusion, fungi have adapted their ability to produce carotenoids for different non-essential functions, related with stress tolerance or with the synthesis of physiologically active by-products.

Oxidative stress protection and glutathione metabolism in response to hydrogen peroxide and menadione in riboflavinogenic fungus Ashbya gossypii

Ashbya gossypii is a plant pathogen and a natural overproducer of riboflavin and is used for industrial riboflavin production. A few literature reports depict a link between riboflavin overproduction and stress in this fungus. However, the stress protection mechanisms and glutathione metabolism are not much explored in A. gossypii. In the present study, an increase in the activity of catalase and superoxide dismutase was observed in response to hydrogen peroxide and menadione. The lipid peroxide and membrane lipid peroxide levels were increased by H2O2 and menadione, indicating oxidative damage. The glutathione metabolism was altered with a significant increase in oxidized glutathione (GSSG), glutathione peroxidase (GPX), glutathione S transferase (GST), and glutathione reductase (GR) and a decrease in reduced glutathione (GSH) levels in the presence of H2O2 and menadione. Expression of the genes involved in stress mechanism was analyzed in response to the stressors by semiquantitative RT-PCR. The messenger RNA (mRNA) levels of CTT1, SOD1, GSH1, YAP1, and RIB3 were increased by H2O2 and menadione, indicating the effect of stress at the transcriptional level. A preliminary bioinformatics study for the presence of stress response elements (STRE)/Yap response elements (YRE) depicted that the glutathione metabolic genes, stress genes, and the RIB genes hosted either STRE/YRE, which may enable induction of these genes during stress.

Oxidative stress response of Blakeslea trispora induced by H2O2 during β-carotene biosynthesis

The cellular response of Blakeslea trispora to oxidative stress induced by H2O2 in shake flask culture was investigated in this study. A mild oxidative stress was created by adding 40 μm of H2O2 into the medium after 3 days of the fermentation. The production of β-carotene increased nearly 38 % after a 6-day culture. Under the oxidative stress induced by H2O2, the expressions of hmgr, ipi, carG, carRA, and carB involving the β-carotene biosynthetic pathway all increased in 3 h. The aerobic metabolism of glucose remarkably accelerated within 24 h. In addition, the specific activities of superoxide dismutase and catalase were significantly increased. These changes of B. trispora were responses for reducing cell injury, and the reasons for increasing β-carotene production caused by H2O2.

Improved β-carotene production by oxidative stress in Blakeslea trispora induced by liquid paraffin

When 3 % (v/v) liquid paraffin was added to the medium, β-carotene production increased from 397 to 715 mg l(-1) in mated cultures of Blakeslea trispora. Liquid paraffin also enhanced the oxygen concentration and induce high oxidative stress, as observed by the increase in activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). After 84 h of cultivation in the presence of liquid paraffin, the activities of SOD, CAT and POD in B. trispora increased 77, 52.5 and 76.6 %, respectively.

Stimulation of the biosynthesis of carotenes by oxidative stress in Blakeslea trispora induced by elevated dissolved oxygen levels in the culture medium

The adaptive response of the fungus Blakeslea trispora to the oxidative stress induced by elevated dissolved oxygen concentrations during carotene production was investigated by measuring the specific activities of catalase (CAT) and superoxide dismutase (SOD) and the micromorphology of the fungus using a computerized image analysis system. Changes in the ratio of the volume of air (V(a)) over the medium and the volume of medium (V(m)) in the flask caused changes of the morphology of microorganism from clumps to pellets and increases in the specific activities of CAT and SOD. The oxidative stress in B. trispora resulted in a significant increase in carotene production, and a maximum proportion of β-carotene (60%), γ-carotene (50%), and lycopene (10%) (as percentages of total carotenes) was observed at a ratio V(a)/V(m) of 15.7, 4.0 and 1.5, respectively. The highest concentration of carotenes (115.0mg/g dry biomass) was obtained in V(a)/V(m) ratio of 9.0.