Oxidative stress and morphological changes in Blakeslea trispora induced by enhanced aeration during carotene production in a bubble column reactor

Study of the properties of carotenoids and key carotenoid biosynthesis genes from Deinococcus xibeiensis R13

To investigate the properties of carotenoids from the extremophile Deinococcus xibeiensis R13, the factors affecting the stability of carotenoids extracted from D. xibeiensis R13, including temperature, illumination, pH, redox chemicals, metal ions, and food additives, were investigated. The results showed that low temperature, neutral pH, reducing agents, Mn²⁺ , and food additives (xylose and glucose) can effectively improve the stability of Deinococcus carotenoids. The carotenoids of D. xibeiensis R13 exhibited strong antioxidant activity, with the scavenging rate of hydroxyl radicals reaching 71.64%, which was higher than the scavenging efficiency for 1,1-diphenyl-2-picrylhydrazyl free radicals and 2,2'-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) free radicals (44.55 and 27.65%, respectively). In addition, the total antioxidant capacity reached 0.60 U/ml, which was 2.61-fold that of carotenoids from the model strain Deinococcus radiodurans R1. Finally, we predicted the gene clusters encoding carotenoid biosynthesis pathways in the genome of R13 and identified putative homologous genes. The key enzyme genes (crtE, crtB, crtI, crtLm, cruF, crtD, and crtO) in carotenoid synthesis of D. xibeiensis R13 were cloned to construct the multigene coexpression plasmids pET-EBI and pRSF-LmFDO. The carotenoid biosynthesis pathway was heterologously introduced into engineered Escherichia coli EBILmFDO, which exhibited a higher yield (7.14 mg/L) than the original strain. These analysis results can help us to better understand the metabolic synthesis of carotenoids in extremophiles.

Biogenic ZnO Nanoparticles Synthesized Using a Novel Plant Extract: Application to Enhance Physiological and Biochemical Traits in Maize

The need to increase crop productivity and resistance directs interest in nanotechnology. Indeed, biogenic metal oxide nanoparticles can promote beneficial effects in plants, while their synthesis avoids the environmental impacts of conventional synthetic procedures. In this context, this research aimed to synthesize biogenic zinc oxide nanoparticles (ZnO-NPs) using, for the first time, an extract of a wild and spontaneous aquatic species, Lemna minor (duckweed). The effectiveness of this biogenic synthesis was evidenced for comparison with non-biogenic ZnO-NPs (obtained without using the plant extract), which have been synthesized in this research. XRD (X-ray diffraction), FE-SEM (field emission gun electron scanning microscopy), EDX (energy dispersive x-ray spectroscopy), TEM (transmission electron microscope) and UV-vis (ultraviolet-visible spectrophotometry) showed the biogenic approach effectiveness. The duckweed extract was subjected to UHPLC-ESI/QTOF-MS (ultra high-pressure liquid chromatography quadrupole time of flight mass spectrometry) phenolic profiling. This untargeted characterization highlighted a high and chemically diverse content in the duckweed extract of compounds potentially implicated in nanoparticulation. From an application standpoint, the effect of biogenic nanoparticles was investigated on some traits of maize subjected to seed priming with a wide range of biogenic ZnO-NPs concentrations. Inductive effects on the shoot and root biomass development were ascertained concerning the applied dosage. Furthermore, the biogenic ZnO-NPs stimulated the content of chlorophylls, carotenoids, and anthocyanin. Finally, the study of malondialdehyde content (MDA) as a marker of the oxidative status further highlighted the beneficial and positive action of the biogenic ZnO-NPs on maize.

Enhancement of Pneumocandin B0 Production in Glarea lozoyensis by Low-Temperature Adaptive Laboratory Evolution

The production of pneumocandin B0 is limited by feedback inhibition. Here, low-temperature adaptive laboratory evolution (ALE) was used to improve the production capacity of Glarea lozoyensis by enhancing its membrane permeability. After 50 cycles of ALE, the pneumocandin B0 production of the endpoint strain (ALE50) reached 2131 g/L, which was 32% higher than the starting strain (ALE0). ALE50 showed a changed fatty acid composition of the cell membrane, which-+h increased its permeability by 14%, which in turn increased the secretion ratio threefold. Furthermore, ALE50 showed increased intracellular proline and acetyl-CoA concentrations, superoxide dismutase (SOD), and catalase (CAT) activity, as well as total antioxidant capacity. The slight biomass decrease in ALE50 was accompanied by decreased isocitrate dehydrogenase (ICDH) and glucose-6-phosphate dehydrogenase (G6PDH) activity. Finally, a putative model of the accumulation and secretion of pneumocandin B0 in ALE50 was established. ALE is a promising method to release intracellular feedback inhibition.

Novel osmotic stress control strategy for improved pneumocandin B0 production in Glarea lozoyensis combined with a mechanistic analysis at the transcriptome level

Pneumocandin B₀, the precursor of the antifungal drug caspofungin, is a secondary metabolite of the fungus Glarea lozoyensis. In this study, we investigated the effects of mannitol as the sole carbon source on pneumocandin B₀ production by G. lozoyensis. The osmotic pressure is more important in enhancing pneumocandin B₀ production than is the substrate concentration. Based on the kinetic analysis, an osmotic stress control fed-batch strategy was developed. This strategy led to a maximum pneumocandin B₀ concentration of 2711 mg/L with a productivity of 9.05 mg/L/h, representing 34.67 and 6.47% improvements, respectively, over the best result achieved by the one-stage fermentation. Furthermore, G. lozoyensis accumulated glutamate and proline as compatible solutes to resist osmotic stress, and these amino acids also provided the precursors for the enhanced pneumocandin B₀ production. Osmotic stress also activated ROS (reactive oxygen species)-dependent signal transduction by upregulating the levels of related genes and increasing intracellular ROS levels by 20%. We also provided a possible mechanism for pneumocandin B₀ accumulation based on signal transduction. These findings will improve our understanding of the regulatory mechanisms of pneumocandin B₀ biosynthesis and may be applied to improve secondary metabolite production.

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.

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.