A rapid method for an offline glycerol determination during microbial fermentation

Towards controlled and simple design of non-enzymatic amperometric sensor for glycerol determination in yeast fermentation medium

Glycerol is a widely used signaling bioanalyte in biotechnology. Glycerol can serve as a substrate or product of many metabolic processes in cells. Therefore, quantification of glycerol in fermentation samples with inexpensive, reliable, and rapid sensing systems is of great importance. In this work, an amperometric assay based on one-step designed electroplated functional Pd layers with controlled design was proposed for a rapid and selective measurement of glycerol in yeast fermentation medium. A novel assay utilizing electroplated Pd-sensing layers allows the quantification of glycerol in yeast fermentation medium in the presence of interfering species with RSD below 3% and recoveries ranged from 99 to 103%. The assay requires minimal sample preparation, viz. adjusting of sample pH to 12. The time taken to complete the electrochemical analysis was 3 min. Remarkably, during investigations, it was revealed that sensitivity and selectivity of glycerol determination on Pd sensors were significantly affected by its adsorption and did not depend on the surface structure of sensing layers. This study is expected to contribute to both fundamental and practical research fields related to a preliminary choice of functional sensing layers for specific biotechnology and life science applications in the future.

Regulation of dye-decolorizing peroxidase gene expression in Pleurotus ostreatus grown on glycerol as the carbon source

Dye-decolorizing peroxidases (DyPs) (E.C. 1.11.1.19) are heme peroxidases that catalyze oxygen transfer reactions similarly to oxygenases. DyPs utilize hydrogen peroxide (H2O2) both as an electron acceptor co-substrate and as an electron donor when oxidized to their respective radicals. The production of both DyPs and lignin-modifying enzymes (LMEs) is regulated by the carbon source, although less readily metabolizable carbon sources do improve LME production. The present study analyzed the effect of glycerol on Pleurotus ostreatus growth, total DyP activity, and the expression of three Pleos-dyp genes (Pleos-dyp1, Pleos-dyp2 and Pleos-dyp4), via real-time RT-qPCR, monitoring the time course of P. ostreatus cultures supplemented with either glycerol or glucose and Acetyl Yellow G (AYG) dye. The results obtained indicate that glycerol negatively affects P. ostreatus growth, giving a biomass production of 5.31 and 5.62 g/L with respective growth rates (micra; m) of 0.027 and 0.023 h-1 for fermentations in the absence and presence of AYG dye. In contrast, respective biomass production levels of 7.09 and 7.20 g/L and growth rates (μ) of 0.033 and 0.047 h-1 were observed in equivalent control fermentations conducted with glucose in the absence and presence of AYG dye. Higher DyP activity levels, 4,043 and 4,902 IU/L, were obtained for fermentations conducted on glycerol, equivalent to 2.6-fold and 3.16-fold higher than the activity observed when glucose is used as the carbon source. The differential regulation of the DyP-encoding genes in P. ostreatus were explored, evaluating the carbon source, the growth phase, and the influence of the dye. The global analysis of the expression patterns throughout the fermentation showed the up- and down- regulation of the three Pleos-dyp genes evaluated. The highest induction observed for the control media was that found for the Pleos-dyp1 gene, which is equivalent to an 11.1-fold increase in relative expression (log2) during the stationary phase of the culture (360 h), and for the glucose/AYG media was Pleos-dyp-4 with 8.28-fold increase after 168 h. In addition, glycerol preferentially induced the Pleos-dyp1 and Pleos-dyp2 genes, leading to respective 11.61 and 4.28-fold increases after 144 h. After 360 and 504 h of culture, 12.86 and 4.02-fold increases were observed in the induction levels presented by Pleos-dyp1 and Pleos-dyp2, respectively, in the presence of AYG. When transcription levels were referred to those found in the control media, adding AYG led to up-regulation of the three dyp genes throughout the fermentation. Contrary to the fermentation with glycerol, where up- and down-regulation was observed. The present study is the first report describing the effect of a less-metabolizable carbon source, such as glycerol, on the differential expression of DyP-encoding genes and their corresponding activity.

Development of a portable optical device with a multi-channel spectrometer sensor for quantification of glycerol in wine: a maker approach for on-site analysis

In this work we present a novel and environmentally friendly approach for quantifying glycerol in wine samples using a portable optical device based on the maker concept and do-it-yourself (DIY) principles. This method offers significant advantages, including cost-effectiveness, reduced sample and reagent consumption, and the potential for integrating IoT (Internet of Things) technology. The chemical strategy involves the oxidation of glycerol using periodate, followed by the formation of the 3,5-diacetyl-1,4-dihydrolutidine (DDL) compound through a reaction with acetylacetone. The utilization of a cost-effective AS7341 color sensor as a detector enables accurate and sensitive detection of glycerol levels in wine samples. The optimized procedure demonstrates adequate analytical performance for glycerol determination in wine samples, encompassing a wide linear range (0.5 mg L-1 to 40.0 mg L-1), high correlation coefficient (r = 0.998), and low limits of detection (0.050 mg L-1). The method exhibits excellent precision, with the coefficient of variation estimated to be 0.1% for 10 independent measurements of a 20 mg L-1 solution. These features render it suitable not only for routine glycerol analysis in the wine industry, but also for addressing challenges related to wine adulteration and counterfeiting.

Mycobacterial Populations Partly Change the Proportions of the Cells Undergoing Asymmetric/Symmetric Divisions in Response to Glycerol Levels in Growth Medium

Twenty to thirty percent of the septating mycobacterial cells of the mid-log phase population showed highly deviated asymmetric constriction during division (ACD), while the remaining underwent symmetric constriction during division (SCD). The ACD produced short-sized cells (SCs) and normal/long-sized cells (NCs) as the sister-daughter cells, but with significant differential susceptibility to antibiotic/oxidative/nitrite stress. Here we report that, at 0.2% glycerol, formulated in the Middlebrook 7H9 medium, a significantly high proportion of the cells were divided by SCD. When the glycerol concentration decreased to 0.1% due to cell-growth/division, the ACD proportion gradually increased until the ACD:SCD ratio reached ~50:50. With further decrease in the glycerol levels, the SCD proportion increased with concomitant decrease in the ACD proportion. Maintenance of glycerol at 0.1%, through replenishment, held the ACD:SCD proportion at ~50:50. Transfer of the cells from one culture with a specific glycerol level to the supernatant from another culture, with a different glycerol level, made the cells change the ACD:SCD proportion to that of the culture from which the supernatant was taken. RT-qPCR data showed the possibility of diadenosine tetraphosphate phosphorylase (MSMEG_2932), phosphatidylinositol synthase (MSMEG_2933), and a Nudix family hydrolase (MSMEG_2936) involved in the ACD:SCD proportion-change in response to glycerol levels. We also discussed its physiological significance.

Augmenting the biodegradation of recalcitrant ethinylestradiol using Rhodopseudomonas palustris in a hybrid photo-assisted microbial fuel cell with enhanced bio-hydrogen production

This study presents the biodegradation potential of ethinylestradiol (EE2) in anaerobic environments using exoelectrogenic activity of Rhodopseudomonas palustris. EE2, a basic ingredient in oral contraceptives, is a significant estrogenic micropollutant in various wastewaters and is considered highly recalcitrant. This recalcitrance of EE2 has caused anoxic areas to become repositories for these pollutants. Thus, it is essential to find the microorganisms and suitable methods to degrade this compound. An initial EE2 concentration of 1 mg/L, used in an anaerobic photobioreactor, resulted in 70% EE2 degradation over a period of 16 days with an increase of 63% in hydrogen production when EE2 was used with glycerol as the main carbon source in the culture medium. Furthermore, in the novel setup of hybrid photo-assisted microbial fuel cell (h-PMFC) employed here, EE2 degradation enhanced to 89.82% with a maximum power density of 0.633 ± 0.04 mW/m². The hybrid MFC employed here could metabolize EE2 and sustained the bio-hydrogen production for 14 days to run the hydrogen fuel cell which otherwise could not be sustained with glycerol only and thus increased the overall power output. The current work highlights the use of R. palustris and the significance of co-metabolism in bioremediation of pollutants and bioenergy generation.

Multiple biosurfactant production by Aureobasidium pullulans strain YTP6-14 in aqueous and heavy oil layers

Aureobasidium pullulans YTP6-14 was demonstrated to be an excellent multiple biosurfactant producer utilizing cheap carbon sources available in Thailand, including glycerol and cassava flour hydrolysate. A. pullulans YTP6-14 maximally produced 1.81 g/l biosurfactant in an aqueous layer (BS-AQ) in a medium containing glycerol, and 7.37 or 6.37 g/l biosurfactant in a heavy oil layer (BS-HO) in cassava flour hydrolysate or a glucose containing medium, respectively. Each BS-AQ and BS-HO had critical micelle concentration values of 41.32 mg/l and 13.51 mg/l, and both biosurfactants formed a stable food oil emulsion and reduced the amount of biofilms formed by Streptococcus sobrinus and Streptococcus mutans. BS-AQ and BS-HO were mainly composed of liamocins or exophilins and massoia lactone, respectively.

The Genome-Wide Mutation Shows the Importance of Cell Wall Integrity in Growth of the Psychrophilic Yeast Metschnikowia australis W7-5 at Different Temperatures

In this study, it was found that a Cre/loxP system could be successfully used as a tool for editing the genome of the psychrophilic yeast Metschnikowia australis W7-5 isolated from Antarctica. The deletion and over-expression of the TPS1 gene for trehalose biosynthesis, the GSY gene for glycogen biosynthesis, and the GPD1 and GPP genes for glycerol biosynthesis had no influence on cell growth of the mutants and transformants compared to cell growth of their wild-type strain M. australis W7-5, indicating that trehalose, glycogen, and glycerol had no function in growth of the psychrophilic yeast at different temperatures. However, removal of the SLT2 gene encoding the mitogen-activated protein kinase in the cell wall integrity (CWI) signaling pathway and the SWI4 and SWI6 genes encoding the transcriptional activators Swi4/6 had the crucial influence on cell growth of the psychrophilic yeast at the low temperature, especially at 25 °C and expression of the genes related to cell wall and lipid biosynthesis. Therefore, the cell wall could play an important role in growth of the psychrophilic yeast at different temperatures and biosynthesis of cell wall was actively regulated by the CWI signaling pathway. This was the first time to show that the genome of the psychrophilic yeast was successfully edited and the molecular evidences were obtained to elucidate mechanisms of low temperature growth of the psychrophilic yeast from Antarctica.

Glycerol, trehalose and vacuoles had relations to pullulan synthesis and osmotic tolerance by the whole genome duplicated strain Aureobasidium melanogenum TN3-1 isolated from natural honey

In our previous study, it was found that Aureobasidium melanogenum TN3-1 was a high pullulan producing and osmotic tolerant yeast-like fungal strain. In this study, the HOG1 signaling pathway controlling glycerol synthesis, glycerol, trehalose and vacuoles were found to be closely related to its pullulan biosynthesis and high osmotic tolerance. Therefore, deletion of the key genes for the HOG1 signaling pathway, glycerol and trehalose biosynthesis and vacuole formation made all the mutants reduce pullulan biosynthesis and increase sensitivity of the growth of the mutants to high glucose concentration. Especially, abolishment of both the VSP11 and VSP12 genes which controlled the fission/fusion balance of vacuoles could cause big reduction in pullulan production (less than 7.4 ± 0.4 g/L) by the double mutant ΔDV-5 and increased sensitivity to high concentration glucose, while expression of the VSP11 gene in the double mutant ΔDV-5 made the transformants EV-2 restore pullulan production and tolerance to high concentration glucose. But cell growth of them were the similar. The double mutant ΔDV-5 had much bigger vacuoles and less numbers of vacuoles than the transformant EV-2 and its wild type strain TN3-1 while it grew weakly on the plate with 40% (w/v) glucose while the transformant EV-2 and its wild type strain TN3-1 could grow normally on the plate even with 60% (w/v) glucose. The double mutant ΔDV-5 also had high level of pigment and its cells were swollen. This was the first time to give the evidence that glycerol, trehalose and vacuoles were closely related to pullulan biosynthesis and high osmotic tolerance by A. melanogenum.

Exogenous l-proline improved Rhodosporidium toruloides lipid production on crude glycerol

BACKGROUND

Crude glycerol as a promising feedstock for microbial lipid production contains several impurities that make it toxic stress inducer at high amount. Under stress conditions, microorganisms can accumulate l-proline as a safeguard. Herein, l-proline was assessed as an anti-stress agent in crude glycerol media.

RESULTS

Crude glycerol was converted to microbial lipids by the oleaginous yeast Rhodosporidium toruloides CGMCC 2.1389 in a two-staged culture mode. The media was supplied with exogenous l-proline to improve lipid production efficiency in high crude glycerol stress. An optimal amount of 0.5 g/L l-proline increased lipid titer and lipid yield by 34% and 28%, respectively. The lipid titer of 12.2 g/L and lipid content of 64.5% with a highest lipid yield of 0.26 g/g were achieved with l-proline addition, which were far higher than those of the control, i.e., lipid titer of 9.1 g/L, lipid content of 58% and lipid yield of 0.21 g/g. Similarly, l-proline also improved cell growth and glycerol consumption. Moreover, fatty acid compositional profiles of the lipid products was found suitable as a potential feedstock for biodiesel production.

CONCLUSION

Our study suggested that exogenous l-proline improved cell growth and lipid production on crude glycerol by R. toruloides. The fact that higher lipid yield as well as glycerol consumption indicated that l-proline might act as a potential anti-stress agent for the oleaginous yeast strain.

Enhancement of glycerol production by UV-mutagenesis of the marine yeast Wickerhamomyces anomalus HH16: kinetics and optimization of the fermentation process

The current study aims to enhance glycerol production using UV-mutagenesis of the marine yeast Wickerhamomyces anomalus HH16 isolated from marine sediment collected from South Sinai Governorate, Egypt. Besides optimization of the culture conditions and analyzing the kinetic parameters of growth and glycerol biosynthesis by the mutant strain were studied. The marine yeast isolate HH16 was selected as the front runner glycerol-producer among all tested isolates, with glycerol yield recorded as 66.55 gl^-1. The isolate was identified based on the phenotypic and genotypic characteristics of W. anomalus. The genotypic characterization based on the internal transcribed spacer (ITS) sequence was deposited in the GenBank database with the accession number MK182824. UV-mutagenesis of W. anomalus HH16 by its exposure to UV radiation (254 nm, 200 mW cm^-2) for 5 min; increased its capability in the glycerol production rate with 16.97% (80.15 g l^-1). Based on the kinetic and Monod equations, the maximum specific growth rate (μ _max) and maximum specific glycerol production rate (v _max) by the mutant strain W. anomalus HH16MU5 were 0.21 h^-1 and 0.103 g g^-1, respectively. Optimization of the fermentation parameters such as nitrogen source, salinity and pH has been achieved. The maximum glycerol production 86.55 g l^-1 has been attained in a fermentation medium composed of 200 g l^-1 glucose, 1 g l^-1 peptone, 3 g l^-1 yeast extract, and 58.44 g l^-1 NaCl, this medium was adjusted at pH 8 and incubated for 3 days at 30° C. Moreover, results indicated the ability of this yeast to produce glycerol (73.33 g l^-1) using a seawater based medium. These findings suggest the applicability of using the yeast isolate W. anomalus HH16MU5 as a potential producer of glycerol for industrial purposes.

Recombinant O-mannosylated protein production (PstS-1) from Mycobacterium tuberculosis in Pichia pastoris (Komagataella phaffii) as a tool to study tuberculosis infection

Background

Pichia pastoris (syn. Komagataella phaffii) is one of the most highly utilized eukaryotic expression systems for the production of heterologous glycoproteins, being able to perform both N- and O-mannosylation. In this study, we present the expression in P. pastoris of an O-mannosylated recombinant version of the 38 kDa glycolipoprotein PstS-1 from Mycobacterium tuberculosis (Mtb), that is similar in primary structure to the native secreted protein.

Results

The recombinant PstS-1 (rPstS-1) was produced without the native lipidation signal. Glycoprotein expression was under the control of the methanol-inducible promoter pAOX1, with secretion being directed by the α-mating factor secretion signal. Production of rPstS-1 was carried out in baffled shake flasks (BSFs) and controlled bioreactors. A production up to ~ 46 mg/L of the recombinant protein was achieved in both the BSFs and the bioreactors. The recombinant protein was recovered from the supernatant and purified in three steps, achieving a preparation with 98% electrophoretic purity. The primary and secondary structures of the recombinant protein were characterized, as well as its O-mannosylation pattern. Furthermore, a cross-reactivity analysis using serum antibodies from patients with active tuberculosis demonstrated recognition of the recombinant glycoprotein, indirectly indicating the similarity between the recombinant PstS-1 and the native protein from Mtb.

Conclusions

rPstS-1 (98.9% sequence identity, O-mannosylated, and without tags) was produced and secreted by P. pastoris, demonstrating that this yeast is a useful cell factory that could also be used to produce other glycosylated Mtb antigens. The rPstS-1 could be used as a tool for studying the role of this molecule during Mtb infection, and to develop and improve vaccines or kits based on the recombinant protein for serodiagnosis.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1059-3) contains supplementary material, which is available to authorized users.

The ejector loop reactor: Application for microbial fermentation and comparison with a stirred-tank bioreactor

Ejector loop reactors (ELR) are successfully used in industrial chemical processes for gas/liquid reactions. They achieve higher mass transfer rates compared to the stirred-tank reactor (STR) at comparable specific power input. Insufficient oxygen transport and shear stress induced growth inhibition are limiting parameters during microbial fermentation. Due to its better mass transfer characteristics, the ELR was expected to have beneficial effects on biomass and recombinant protein production. One concern, however, was whether the ELR's shear stress characteristics would have a negative effect. This study evaluated the suitability of using the Buss-Loop® Reactor (BLR), one of the most advanced ELR technologies, as a bioreactor. The well-studied STR was used as a reference. A lab scale BLR was adapted for microbial fermentation. Mass transfer rates and specific power inputs were within the same order of magnitude in the ELR and the reference STR. Maximum k L a values of 207 and 205 h^-1 at power inputs of 6.9 and 9.7 W/L were measured in the ELR and STR, respectively. During batch fermentation of Escherichia coli K12 MG1655, maximum cell densities were higher in the ELR (OD600 of 22) than in the STR (OD600 of 18). Green fluorescence protein (GFP) production with pGS1 was comparable; however, more GFP was released into the media in the ELR. This indicates higher cell disruption compared to the STR. Despite this drawback of the first prototype, our work clearly demonstrates the potential of the ELR as a system for microbial fermentations.

Morphological and Transcriptomic Analysis Reveals the Osmoadaptive Response of Endophytic Fungus Aspergillus montevidensis ZYD4 to High Salt Stress

Halophilic fungi have evolved unique osmoadaptive strategies, enabling them to thrive in hypersaline habitats. Here, we conduct morphological and transcriptomic response of endophytic fungus (Aspergillus montevidensis ZYD4) in both the presence and absence of salt stress. Under salt stress, the colony morphology of the A. montevidensis ZYD4 changed drastically and exhibited decreased colony pigmentation. Extensive conidiophores development was observed under salt stress; conidiophores rarely developed in the absence of salt stress. Under salt stress, yellow cleistothecium formation was inhibited, while glycerol and compatible sugars continued to accumulate. Among differentially expressed unigenes (DEGs), 733 of them were up-regulated while 1,619 unigenes were down-regulated. We discovered that genes involved in the accumulation of glycerol, the storage of compatible sugars, organic acids, pigment production, and asexual sporulation were differentially regulated under salt stress. These results provide further understanding of the molecular basis of osmoadaptive mechanisms of halophilic endophytic fungi.

Metabolic networks to generate pyruvate, PEP and ATP from glycerol in Pseudomonas fluorescens

Glycerol is a major by-product of the biodiesel industry. In this study we report on the metabolic networks involved in its transformation into pyruvate, phosphoenolpyruvate (PEP) and ATP. When the nutritionally-versatile Pseudomonas fluorescens was exposed to hydrogen peroxide (H2O2) in a mineral medium with glycerol as the sole carbon source, the microbe reconfigured its metabolism to generate adenosine triphosphate (ATP) primarily via substrate-level phosphorylation (SLP). This alternative ATP-producing stratagem resulted in the synthesis of copious amounts of PEP and pyruvate. The production of these metabolites was mediated via the enhanced activities of such enzymes as pyruvate carboxylase (PC) and phosphoenolpyruvate carboxylase (PEPC). The high energy PEP was subsequently converted into ATP with the aid of pyruvate phosphate dikinase (PPDK), phosphoenolpyruvate synthase (PEPS) and pyruvate kinase (PK) with the concomitant formation of pyruvate. The participation of the phospho-transfer enzymes like adenylate kinase (AK) and acetate kinase (ACK) ensured the efficiency of this O2-independent energy-generating machinery. The increased activity of glycerol dehydrogenase (GDH) in the stressed bacteria provided the necessary precursors to fuel this process. This H2O2-induced anaerobic life-style fortuitously evokes metabolic networks to an effective pathway that can be harnessed into the synthesis of ATP, PEP and pyruvate. The bioconversion of glycerol to pyruvate will offer interesting economic benefit.