Pichia Caribbica Research Articles

Insight into the mechanisms involved in the improved antagonistic efficacy of Pichia caribbica against postharvest black spot of tomato fruits by combined application with oligochitosan

Our previous study demonstrated that the combined application with oligochitosan (OCH) improved the biocontrol efficacy of Pichia caribbica against postharvest black spot of tomato fruits. The involved mechanisms were elucidated based on the induction of fruit resistance. However, the mechanisms needed to be further explored from the antagonistic yeast perspective. The current study determined the effects of OCH on P. caribbica growth in vitro and the effects of combined application with OCH on the colonization ability, the reactive oxygen species (ROS) accumulation, especially the gene expression levels of P. caribbica in fruit wounds. The findings revealed that OCH increased the viable cell number of P. caribbica in NYDB and in tomato fruit wounds. Additionally, combined application with OCH could alleviate ROS accumulation in P. caribbica inoculated in fruit wounds. Transcriptome analysis revealed that the genes related to MAPK signal transduction, meiosis – yeast, DNA replication, tryptophan metabolism and glutathione metabolism of P. caribbica were induced by the combined application with OCH in fruit wounds, which triggered its MAPK signal transduction, promoted its growth and reproduction, and improved its antioxidant capability. Therefore, the capability of P. caribbica to survive and colonize fruit wounds were raised and its antagonistic efficacy against postharvest black spot pathogen was heightened by combined application with OCH. This study will open up new possibilities for improving the biocontrol efficacy of antagonists against postharvest pathogens of fruits and vegetables.

Combined application of oligochitosan and Pichia carrbbica improves the disease resistance of postharvest tomato fruits

Our previous study showed that postharvest treatment of tomato with Pichia caribbica along with oligochitosan (OCH) significantly alleviated postharvest black spot of tomato fruit compared with P. caribbica alone. This study was to explore the effect of combined application of OCH and P. caribbica on disease resistance of tomato fruits through analyzing the activities of disease resistance-related enzymes, as well as transcriptome analysis of the fruit gene expression. Our findings indicated that P. caribbica, together with OCH, improved the activities of key enzymes associated with disease resistance in tomato fruit. Moreover, the combined application further upregulated the expression of genes involved in α-linolenic acid metabolism, the signal transduction pathways such as Ca2+, MAPK and plant hormone signaling pathways, resistant substance synthesis, and ROS metabolism, which improved the fruit disease resistance. Considering the significance of these results, OCH hold great potential for use in microbial biocontrol strategies against postharvest tomato diseases.

Food-grade xylitol production from corncob biomass with acute oral toxicity studies

Xylitol, a sugar substitute, is widely used in various food formulations and finds a steady global market. In this study, xylitol crystals were produced from corncob by fermentation (as an alternative to the chemical catalytic process) by a GRAS yeast Pichia caribbica MTCC 5703 and characterized in detail for their purity and presence of any possible contaminant that may adversely affect mammalian cell growth and proliferation. The acute and chronic oral toxicity trials demonstrated no gross pathological changes with average weekly weight gain in female Wistar rats at high xylitol loading (LD50 > 10,000mg/kg body weight). The clinical chemistry analysis supported the evidence of no dose-dependent effect by analyzing blood biochemical parameters. The finding suggests the possible application of the crystals (> 98% purity) as a food-grade ingredient for commercial manufacture pending human trials.

Pichia caribbica combined with oligochitosan controlling black spot of tomatoes and the regulation on ROS metabolism of the fruits

Black spot caused by Alternaria alternata is one of the main postharvest diseases of tomato fruits. This research aimed to investigate biocontrol efficacy of Pichia caribbica combined with oligochitosan (OCH) against black spot of tomato fruits and explore the mechanisms involved in improved disease resistance of the fruits by yeast combined with OCH based on analysis of reactive oxygen species (ROS) metabolism. The results indicated that in comparison with P. caribbica alone, yeast combined with OCH (2000 μg/mL) could further reduce black spot of tomato fruits. P. caribbica combined with OCH increased NADPH oxidase (NOX) activity in the fruits compared with the control and the group treated with yeast alone. The activities of enzymatic system for ROS scavenging including antioxidant enzymes, enzymes involved in ascorbate–glutathione (AsA-GSH) and GPX (glutathione peroxidase) cycles, and glutathione S-transferase (GST) in the fruits were induced by yeast combined with OCH. Additionally, the contents of ascorbic acid (AsA) and glutathione (GSH) belonging to non-enzymatic system for ROS scavenging were enhanced in the fruits. Collectively, the induction of NOX and the improvement of enzymatic and non-enzymatic systems for ROS scavenging resulted in the decrease in O2–·, H2O2 and malondialdehyde (MDA) production in the fruits, thus promoting the disease resistance of tomato fruits. This research will provide new ideas for the control of postharvest diseases of tomato fruits.

Crystalline xylitol production from corncob biomass with oral toxicity analysis

Xylitol, a five-carbon sugar alcohol, has a steady global market and finds application as a natural sugar substitute in various food and confectionery products. Biocatalytic xylitol production, although touted as a greener alternative to conventional chemical catalysis, suffers from certain challenges, the primary being high cost of production. This study demonstrates a process for food-grade xylitol production from corncob biomass with energy reduction through two major process modifications. A non-conventional fermentation strategy was adopted whereby adjusting aeration without agitation, xylitol with high yield (0.86 ± 0.015 g/g), and productivity (0.74 gL-1h-1) could be produced by a GRAS Pichia caribbica MTCC 5703 strain. Xylitol was recovered from the broth in the form of crystals using a combination of membrane-based filtration and crystallization. The crystals demonstrated ~98 % purity when quantified with 1H NMR. Oral toxicity analysis of the crystals demonstrated no adverse effect in female Winstar rats (at a loading of 2000 mg/kg body weight of animals). Overall process statistics showed that 0.584 kg of food-grade xylitol crystals could be produced from 3.5 kg of corncob biomass. The two-process modifications during fermentation and xylitol recovery enabled an energy saving of ~20.842 kW/kg of crystals, providing tremendous advantages for biorefinery-based large-scale xylitol production from corncob biomass.

Insights into the defense mechanisms involved in the induction of resistance against black spot of cherry tomatoes by Pichia caribbica

Our previous study showed that Pichia caribbica could alleviate black spot of cherry tomatoes. This study aimed to explore the comprehensive mechanisms involved in the induced disease resistance of cherry tomatoes by this yeast. The results indicated that P. caribbica increased the activities of defense-related enzymes and enzymes of phenylpropanoid pathway including polyphenol oxidase, chitinase, β-1,3-glucanase, phenylalanine ammonia-lyase and cinnamate-4-hydroxylase in the fruits. Considering together with transcriptome analysis results, it was suggested that P. caribbica triggered mitogen-activated protein kinase, Ca2+ and plant hormone signaling pathways, up-regulated genes related to reactive oxygen species scavenging, induced defense-related genes and enzyme activities, and stimulated genes and the activities of enzymes involved in secondary metabolite synthesis to accumulate total phenols, lignin and flavonoids, thus enhancing the resistance of cherry tomatoes against black spot. This study will provide new insights into the underlying mechanisms involved in induced disease resistance of cherry tomatoes by antagonistic yeast.

Pichia caribbica improves disease resistance of cherry tomatoes by regulating ROS metabolism

Black spot caused by Alternaria alternata is one of major diseases of postharvest cherry tomatoes. This study intends to investigate biocontrol efficacy of Pichia caribbica against black spot and explore the mechanisms involved in improved disease resistance of cherry tomatoes through analyzing reactive oxygen species (ROS) metabolism. The results demonstrated that P. caribbica significantly decreased the occurrence of black spot in cherry tomatoes. P. caribbica improved the activities of enzymatic system for ROS scavenging in cherry tomatoes, including some antioxidant enzymes, the enzymes in ascorbic acid-glutathione (AsA-GSH) and glutathione peroxidase (GPX) cycles, and glutathione S-transferase (GST). Furthermore, P. caribbica maintained the high level of the key antioxidant substances and then decreased the production rate of O2¯·, the contents of H2O2 and malondialdehyde (MDA). These results revealed that P. caribbica induced the enzymatic and non-enzymatic systems to remove ROS, and then improved the disease resistance of cherry tomatoes against pathogen. This study will provide new strategy for controlling postharvest disease of fruits and vegetables by improving the ability of ROS scavenging to defense against pathogens.

Process development for crystalline xylitol production from corncob biomass by Pichia caribbica

Xylitol, a commodity chemical, is widely used in nutraceutical and pharmaceutical formulations. Microbial xylitol production is a promising alternative to mitigate current industrial practice issues and offers an environment-friendly sustainable conversion route. This study demonstrates a bioprocess for xylitol production from corncob using a mesophilic yeast Pichia caribbica. Corncob was hydrolyzed by dilute acid and steam explosion to recover fermentable xylose and used as the feed for xylitol production. Activated carbon treatment (3% w/v) completely removed the biomass-derived inhibitors furfural and hydroxymethyl furfural from the liquid hydrolysate. The fermenting yeast Pichia caribbica produced 124.1 ± 0.45 g/L xylitol from the detoxified and concentrated corncob hydrolysate with a high yield of 0.80 ± 0.02 g/g. The crystallized xylitol with 96.5% purity demonstrated no harmful effects on the cell line used as a control for the in-vitro toxicity studies. This proof of concept can be applied to help scale up for bio-refinery-based large-scale production of xylitol from corncob biomass.

Process development for detoxification of corncob hydrolysate using activated charcoal for xylitol production

The work describes process development for detoxification of corncob hydrolysate using activated carbon for microbial xylitol production. Activated carbon was used as an adsorbent to completely remove the major fermentation inhibitors obtained during dilute acid and steam explosion of biomass. A xylitol yield of 0.78 g/g was achieved from the detoxified hydrolysate in a 5 L fermenter by Pichia caribbica. The spent carbon was effectively regenerated and used for three consecutive cycles of operation. The successive regeneration and reuse of carbon could reduce the operational cost by ~ 38% and be used as a reference dataset for process scale-up and cost-effective xylitol production.

Novel Effective Yeast Strains and Their Performance in High Gravity and Very High Gravity Ethanol Fermentations from Sweet Sorghum Juice

Yeasts were isolated from four potential sources, sweet sorghum juice, sugar cane juice, grapes and rambutan. The 27 yeast isolates were tested for their ethanol tolerance (15% v/v of ethanol) and ethanol fermentation performance in a synthetic ethanol production medium (200 g/L of total sugar). Only five isolates, SCJ04KKU, SCJ07KKU, SCJ09KKU, SCJ14KKU and SSJ01KKU could tolerate 15% ethanol and produce ethanol at levels higher than 55 g/L. The ethanol production efficiency from sweet sorghum juice under high gravity (HG, 200 and 240 g/L of total sugar) and very high gravity (VHG, 280 g/L of total sugar) conditions of the five isolates was tested. Saccharomyces cerevisiae NP01 and S. cerevisiae ATCC4132 were used as reference strains. The results showed that the SSJ01KKU isolate gave the highest ethanol production efficiency under all conditions. Ethanol concentration (PE), yield (YP/S) and productivity (QP) values were 98.89 g/L, 0.50 and 1.18 g/L·h, respectively, with sugar consumption (SC) of 98.96% under the HG condition at 200 g/L of total sugar. Under the HG condition at 240 g/L of total sugar, the PE, YP/S and QP values were 118.12 g/L, 0.51 and 1.41 g/L·h, respectively, with the SC of 95.79%. These values were 82.29 g/L, 0.34 and 0.98 g/L·h, respectively, with the SC of 85.59% under the VHG condition. Addition of urea into the sweet sorghum juice under all conditions significantly shortened the fermentation time, resulting in increased QP values. Based on molecular taxonomic analysis of the five isolates using sequence analysis of the D1/D2 domain and the ITS1 and ITS2 regions, SSJ01KKU is S. cerevisiae, whereas SCJ04KKU, SCJ07KKU, SCJ09KKU and SCJ14KKU are Pichia caribbica.

In vitro control of Botrytis cinerea and Penicillium italicum by antagonistic yeasts

Gray mold in grapes (caused by Botrytis cinerea) and blue mold in citrus (caused by Penicillium italicum) are post-harvest diseases that cause major losses in these crops. The control of these diseases is based on the use of synthetic chemical fungicides. The increase in regulatory policies and demand to reduce the application of pesticides, due to harmful effects on the environment and humans, have led to the search for more ecofriendly alternatives, such as biological control agents. Thus, the present work aims to verify the antagonistic potential of four yeast strains, Pichia caribbica (CCMA 0759), Hanseniaspora opuntiae (CCMA 0760), Pichia manshurica (CCMA 0762), and Lachancea thermotolerans (CCMA 0763), against of B cinerea and P. italicum. To assess the antagonism of volatile compounds, Petri plates with two divisions containing potato-dextrose-agar (PDA) were used by placing a fungal mycelial disc and yeast suspension (3.0 × 106 cells mL-1) on opposite sides of the plate. The colony diameter and mycelial growth rate index of the fungi were evaluated via comparisons with the control plate without yeast. For the evaluation of the antagonism of diffusible substances in the medium, yeasts were striated 3 cm from the center of the plates containing PDA. After 48 h, a mycelial disc of each phytopathogen was placed in the center of the plates. The colony growth, inhibition halo, and mycelial growth rate index were evaluated via comparisons with the control plate. All yeast strains showed an antagonistic effect on the mycelial growth of B. cinerea in both tests. In the volatile compounds test, H. opuntiae, L. thermotolerans, P. caribbica, and P. manshurica inhibited mycelial growth by approximately 82%, 75%, 72%, and 50%, respectively. In the antagonism test of the diffusible substances in the medium, P. caribbica and P. manshurica inhibited mycelial growth by 58% and 33%, respectively. However, these yeast strains did not show an antagonistic effect against P. italicum. Thus, all isolates demonstrated potential to be tested as biocontrol agents of gray mold in post-harvest grape fruits.

Effects of yeast fermentation broths on the Meloidogyne incognita population in soybean

Root-knot nematodes are pathogenic to a wide range of plants worldwide and can reduce the yield potential of important crops. The objective of this study was to investigate the potential effects of yeast fermentation broths (YFBs) on the hatching of Meloidogyne incognita second-stage juveniles (J2s) in vitro. In addition, application methods of the yeasts for the control of the nematode in soybean were evaluated. Fermentation broths (FBs) of Pichia manshurica CCMA0762, Pichia caribbica CCMA0759, Lachancea thermotolerans CCMA0763, Hanseniaspora opuntiae CCMA0760 and Kodamaea (Pichia) ohmeri CCMA0758 were evaluated in the hatching test in vitro. The same treatments were separately applied to the soil, soil+shoot and shoots of plants inoculated with M. incognita, and the results were compared with those of the control and those from a yeast-based commercial product. L. thermotolerans CCMA0763 and P. caribbica CCMA0759 FBs were selected for evaluation of nematode infection. All YFBs inhibited J2 hatching. The L. thermotolerans FB reduced the number of nematodes in one experiment when applied to soil. The most effective application mode differed by FB type. L. thermotolerans and P. caribbica FBs, when applied to shoots, decreased the number of J2s, sausage-shaped juveniles, adult females and total nematodes at different evaluation times.

The protein expression profile and transcriptome characterization of Pichia caribbica induced by ascorbic acid under the oxidative stress

Ascorbic acid (vitamin C, Vc) is a well-known antioxidant, which can eliminate reactive oxygen species (ROS) in order to protect yeasts subjected oxidative stress. In our previous research, Pichia caribbica, one of the antagonistic yeasts showed an activity against postharvest diseases of apples, and Vc enhanced the tolerance to oxidative stress of P. caribbica, and improved its biocontrol efficacy to postharvest blue mold decay of apples. However, the mechanisms, especially the molecular mechanisms of the tolerance of P. caribbica improved by Vc under oxidative stress are not sufficiently clear. The purpose of this research was to investigate the protein expression profile and transcriptome characterization of P. caribbica induced by Vc under oxidative stress. The proteomics results showed that there were 31 differentially expressed proteins (DEPs), among them 25 DEPs were up-regulated and 6 DEPs were down-regulated. These up-regulated DEPs were associated with the energy metabolism and glucose metabolism, including fructose – bisphosphate aldolase, malate dehydrogenase, peroxisomal catalase and so on. Transcriptomics analysis showed that 68 genes were differentially expressed, among them 38 genes were up-regulated and 30 genes were down-regulated. These up-regulated genes were found to be related to cell wall, energy synthesis, polysaccharides hydrolysis and antioxidant activity.

Investigating possible mechanisms of Pichia caribbica induced with ascorbic acid against postharvest blue mold of apples

The present study investigated the effect of ascorbic acid (Vitamin C, VC) at 250 μg/mL in the enhancement of biocontrol efficacy of Pichia caribbica against blue mold decay caused by Penicillium expansum on apples. Compared to the performance of the yeast without treatment, P. caribbica induced by 250 μg/mL of VC potentially enhanced biocontrol activity against P. expansum and high growth rate on the apple surface when stored at 20 °C and 4 °C. The mechanisms underlying this improvement in biocontrol efficiency were probed by investigating the protein expression profile and transcriptome characterization of P. caribbica induced by VC. From the proteomics results, 46 proteins were identified as differentially expressed proteins (DEPs), among them 18 proteins were up-regulated and 28 proteins were significantly down-regulated. These up-regulated DEPs including glyceraldehyde-3-phosphate dehydrogenase and alcohol dehydrogenase were associated with the glucose metabolism. From the transcriptomic analysis, 292 genes were found to be differentially expressed genes (DEGs), among them 137 genes were up-regulated and 155 genes were down-regulated. These up-regulated genes were involved in pyruvate metabolism, amino sugar and nucleotide sugar metabolism. These molecular studies suggest that VC treatment significantly induces the metabolic pathways of P. caribbica, thereby VC potentially enhances the biocontrol efficacy of P. caribbica to postharvest diseases of apples.

S-Adenosylmethionine-Dependent Methyltransferase Helps Pichia caribbica Degrade Patulin.

Patulin contamination not only is a menace to human health but also causes serious environmental problems worldwide due to the synthetic fungicides that are used to control it. This study focused on investigating the patulin degradation mechanism in Pichia caribbica at the molecular level. According to the results, P. caribbica (2 × 106 cells/mL) was able to degrade patulin from 20 μg/mL to an undetectable level in 72 h. The RNA-seq data showed patulin-induced oxidative stress and responses in P. caribbica. The deletion of PcCRG1 led to a significant decrease in patulin degradation by P. caribbica, whereas the overexpression of PcCRG1 accelerated the degradation of patulin. The study identified that PcCRG1 protein had the ability to degrade patulin in vitro. Overall, we demonstrated that the patulin degradation process in P. caribbica was more than one way; PcCRG1 was an S-adenosylmethionine-dependent methyltransferase and played an important role in the patulin degradation process in P. caribbica.

Development of air-blast dried non-Saccharomyces yeast starter for improving quality of Korean persimmon wine and apple cider

A total of 512 yeasts, including 422 non-Saccharomyces yeasts, were isolated from various fruits including apple, aronia, Muscat Bailey A grapes, and persimmon. These were used to prepare persimmon wine and apple cider starters that produced high levels of aromatic compounds, which contribute to high-quality fermented products. Environmental tolerance testing with 20% glucose and 8% EtOH, alongside a sniffing test, led to the selection of Wickerhamomyces anomalus (Synonym Pichia anomala) SJ20, Meyerozyma caribbica (Synonym Pichia caribbica) YP1, Pichia kluyveri CD34, Hanseniaspora uvarum SJ69 (for persimmon wine), W. anomalus CS7-16 (for apple cider), and Starmerella bacillaris (Synonym Candida zemplinina) CD80 (for both wines) as wine starters. These strains had high environmental stress tolerance and the highest sniffing test scores. Persimmon wine and apple cider were fermented using these strains in single- or mixed-culture with S. cerevisiae W-3 to determine the improved effect on wine aroma. In accordance with the results of volatile ester compounds and sensory evaluation, W. anomalus SJ20, H. uvarum SJ69, and W. anomalus CS7-16 had an excellent potential as persimmon wine and apple cider starters. Moreover, other strains also showed a good potential for a distinctive persimmon wine and apple cider because of the different compositions of the various volatile ester compounds. Six types of sugars (fructose, glucose, maltose, sucrose, raffinose, sucrose, and trehalose), four types of rehydration solutions (distilled water, 1× phosphate buffered saline, 0.85% NaCl, and 1% peptone water), and two types of antioxidants (l-ascorbic acid and glutathione) were examined to improve the survival rate of air-blast dried non-Saccharomyces yeast cells. Optimal sugar and rehydration conditions for each strain were validated, and scanning electron microscopy showed that each cell was surrounded by protectants, including sugar, skim milk, and lactomil. Storability assessment of air-blast dried yeast cells maintained at 4 °C for two months indicated that at least one condition in each strain had a higher survival rate than the control, regardless of the concentration or type of antioxidant treatment, except for M. caribbica YP1. These results suggest that antioxidant treatment contributes to maintaining the viability of air-blast dried cells in hostile environments.

Identification and toxicological analysis of products of patulin degradation by Pichia caribbica

Increasing patulin contamination in fruits and fruit-derived products has become a major challenge for the food industry. Biological methods of patulin control have an important role to play owing to their safety and efficiency. In this study, we used the yeast Pichia caribbica to degrade patulin effectively. The intermediate degradation products of patulin by P. caribbica were identified as (E)- and (Z)-ascladiol using high performance liquid chromatography and liquid chromatography-tandem mass spectroscopy. Only (E)-ascladiol was detected in the products of patulin degradation by intracellular enzymes. Toxic analyses on Escherichia coli Top10 cells, Arabidopsis thaliana, and human esophageal epithelial cells (Het-1a) showed that the intermediate degradation product ascladiol and the final degradation products were significantly less toxic and almost non-toxic compared to patulin (p < 0.05), respectively. Furthermore, toxicological analysis revealed that ascladiol and the final degradation products induced very little reactive oxygen species accumulation in Het-1a cells. Further toxicological analysis revealed that ascladiol and the final degradation products induced cell apoptosis to a lesser extent and did not significantly inhibit cell proliferation (p > 0.05) compared to patulin. Analysis of the characteristics and toxicity of the degradation products of patulin by P. caribbica demonstrate that ascladiol is less toxic and the final degradation products are not poisonous, therefore patulin detoxification strategies using P. caribbica are good approaches to limit the patulin risks.

Bamboo leaf flavonoid enhances the control effect of Pichia caribbica against Penicillium expansum growth and patulin accumulation in apples

Patulin (PAT) mainly produced by Penicillium expansum is a very problematic mycotoxin, and its presence is often reported in different foods and food products. The prevention of these products from initial contamination and/or degradation is therefore of foremost importance in protecting consumer health. In this report, Pichia caribbica (1 × 108 cells mL−1) antagonistic yeasts incorporated with bamboo leaf flavonoid (0.01% w/v) were assessed for PAT degradation capabilities in in-vitro and in-vivo. Also the effects of treatments on wound lesion diameter, lignification and pH level were investigated. Clearly, the combined biocontrol agent (P. caribbica and bamboo leaf flavonoid) had the ability to degrade PAT in vitro with undetected level at 96 h of incubation in NYDB media. In apple fruits, PAT accumulation was significantly lower at 20 d (at 20 °C) of storage. Wound lignification was significantly enhanced from 0.31 to 0.27 after 15 d of storage, whereas pH was modified (>4.0) in host; which might lead to an increase in PAT breakdown. P. caribbica combined with bamboo leaf flavonoid could be a promising biocontrol agent for PAT degradation processes in apple fruits.

Bioprospection of cold-adapted yeasts with biotechnological potential from Antarctica.

The aim of this study was to investigate the ability to produce extracellular hydrolytic enzymes at low temperature of yeasts isolated from 25 de Mayo island, Antarctica, and to identify those exhibiting one or more of the evaluated enzymatic activities. A total of 105 yeast isolates were obtained from different samples and 66 were identified. They belonged to 12 basidiomycetous and four ascomycetous genera. Most of the isolates were ascribed to the genera Cryptococcus, Mrakia, Cystobasidium, Rhodotorula, Gueomyces, Phenoliferia, Leucosporidium, and Pichia. Results from enzymes production at low temperatures revealed that the Antarctic environment contains metabolically diverse cultivable yeasts, which represent potential tools for biotechnological applications. While most the isolates proved to produce 2-4 of the investigated exoenzymes, two of them evidenced the six evaluated enzymatic activities: Pichia caribbica and Guehomyces pullulans, which were characterized as psycrotolerant and psycrophilic, respectively. In addition, P. caribbica could assimilate several n-alkanes and diesel fuel. The enzyme production profile and hydrocarbons assimilation capacity, combined with its high level of biomass production and the extended exponential growth phase make P. caribbica a promising tool for cold environments biotechnological purposes in the field of cold-enzymes production and oil spills bioremediation as well.

Mechanisms of glycine betaine enhancing oxidative stress tolerance and biocontrol efficacy of Pichia caribbica against blue mold on apples

The effects of glycine betaine (GB) treatment on biocontrol efficacy of Pichia caribbica against blue mold decay of apples and oxidative stress tolerance were investigated. To reveal the mechanism of GB enhancing oxidative stress tolerance and biological control efficacy of P. caribbica, the accumulation of intracellular reactive oxygen species (ROS), protein carbonylation, lipid oxidation and differentially expressed proteins were analyzed. Compared with P. caribbica treated without GB, P. caribbica treated with GB exhibited enhanced biocontrol activity (disease incidence decreased from 48.81% to 32.14%) and oxidative stress tolerance when exposed to oxidative stress (survival ability increased from 60.1% to 77.7%), as well as improved growth in wounds of apples. GB treatment reduced accumulation of ROS, levels of oxidative damage to cellular proteins and lipids in P. caribbica. The proteomic analysis showed that 51 proteins were differentially expressed in P. caribbica after GB treatment, 33 proteins of which were successfully identified by MALDI-TOF-MS and database Queries. The up-regulation of some identified proteins related to carbohydrate transport and metabolism (enolase, pyruvate kinase and isocitrate lyase), stress response and regulation (peroxisomal catalase and Serine/threonine protein kinase) were involved in the enhancement of oxidative stress tolerance and biocontrol efficacy of P. caribbica.