Haikuan Wang

Production and Characterization of Antifungal Compounds Produced by Lactobacillus plantarum IMAU10014

Lactobacillus plantarum IMAU10014 was isolated from koumiss that produces a broad spectrum of antifungal compounds, all of which were active against plant pathogenic fungi in an agar plate assay. Two major antifungal compounds were extracted from the cell-free supernatant broth of L. plantarum IMAU10014. 3-phenyllactic acid and Benzeneacetic acid, 2-propenyl ester were carried out by HPLC, LC-MS, GC-MS, NMR analysis. It is the first report that lactic acid bacteria produce antifungal Benzeneacetic acid, 2-propenyl ester. Of these, the antifungal products also have a broad spectrum of antifungal activity, namely against Botrytis cinerea, Glomerella cingulate, Phytophthora drechsleri Tucker, Penicillium citrinum, Penicillium digitatum and Fusarium oxysporum, which was identified by the overlay and well-diffusion assay. F. oxysporum, P. citrinum and P. drechsleri Tucker were the most sensitive among molds.

Activity against plant pathogenic fungi of Lactobacillus plantarum IMAU10014 isolated from Xinjiang koumiss in China

Thirty-five of the 77 colonies of lactic acid bacteria isolated from koumiss showed antifungal activity against Botrytis cinerea, when tested by the Poison Food Technique. Of these, the most promising isolate having a broad spectrum of antifungal activity, including against Botrytis cinerea, Alternaria solani, Phytophthora drechsleri Tucker, Fusarium oxysporum and Glomerella cingulata, was identified as Lactobacillus plantarum IMAU10014. The effect of pH, temperature and protease on the antifungal activity of L. plantarum IMAU10014 was determined. The activity substance was heat stable. The maximum antifungal activity was observed at pH 4.0. When the supernatant was adjusted to pH 8.0, the activity was lost irreversibly. However, after enzymatic treatment of supernatant with trypsin, neutral protease and proteinase K, loss of part of the antifungal activity was observed which indicated there are other substances in addition to the proteinaceous substance with the antifungal activity.

ACE-Inhibitory Peptide Isolated from Fermented Soybean Meal as Functional Food

Abstract Biologically active peptides as components in functional foods exhibit diverse activities and exert health effects in humans, just as the angiotensin I-converting enzyme (ACE)-inhibitory peptide exerts an antihypertensive effect. The solid-state fermentation of soybean meal was conducted using Bacillus subtilis natto at an appropriate temperature to accelerate proteolytic hydrolysis, and the crude extract containing ACE-inhibitory peptides was sequentially purified by ultrafiltration, gel chromatography and reverse phase-HPLC. A novel ACE-inhibitory peptide was obtained and its ACE-inhibitory activity was 84.1% with an IC50 value of 0.022 mg/ml. The results suggest that these ACE-inhibitory peptides obtained from the solid-state fermentation of soybean meal using B. subtilis natto have good potential for application in the management of hypertension and the fermented soybean meal has good potential for application in the production of a novel physiologically functional food.

A novel alkaline and low-temperature lipase ofBurkholderia cepacia isolated from Bohai in China for detergent formulation

The bacterial strain LP08 was isolated from soil collected from bay of Bohai, China. The sequence of 16S rDNA of strain LP08 showed 99% homology toBurkholderia cepacia. The lipase fromBurkholderia cepacia LP08 was purified by ammonium sulphate precipitation, ion exchange chromatography and Sephadex G-75 chromatography. The characterization of the lipase exhibited maximum activity at 30 °C and pH 9.0. The lipase retained 63, 66, 74, and 95% of its maximum activity at 10, 15, 20 and 25 °C respectively. The lipase activity was promoted in the presence of commercial detergent, sodium cholate, sodium taurocholate, glycerine and NaCl, while was little inhibited in the presence of Triton X-100, Tween-20, Tween-80, SDS, saponin. The present lipase was highly stable towards oxidizing agents and was stable after 1 h at 25 °C in the presence of hydrogen peroxide, sodium hypochlorite and sodium perborate. The results suggest that the lipase fromBurkholderia cepacia LP08 showed good potential for application in the detergent formulation.

Heterologous expression of bovine lactoferricin in Pichia methanolica

According to the bias of codon utilization of Pichia methanolica, a fragment encoding bovine lactoferricin has been cloned and expressed in the P. methanolica under the control of the alcohol oxidase promoter, which was followed by the Saccharomyces cerevisiae α-factor signal peptide. The α-factor signal peptide efficiently directed the secretion of bovine lactoferricin from the recombinant yeast cell. The recombinant bovine lactoferricin appears to be successfully expressed, as it displays antibacterial activity (antibacterial assay). Moreover, the identity of the recombinant product was estimated by Tricine-SDS-PAGE.

A new high phenyl lactic acid‐yielding Lactobacillus plantarum IMAU10124 and a comparative analysis of lactate dehydrogenase gene

Phenyl lactic acid (PLA) has been widely reported as a new natural antimicrobial compound. In this study, 120 Lactobacillus plantarum strains were demonstrated to produce PLA using high-performance liquid chromatography. Lactobacillus plantarum IMAU10124 was screened with a PLA yield of 0.229 g L(-1) . Compared with all previous reports, this is the highest PLA-producing lactic acid bacteria (LAB) when grown in MRS broth without any optimizing conditions. When 3.0 g L(-1) phenyl pyruvic acid (PPA) was added to the medium as substrate, PLA production reached 2.90 g L(-1) , with the highest 96.05% conversion rate. A lowest PLA-yielding L. plantarum IMAU40105 (0.043 g L(-1) ) was also screened. It was shown that the conversion from PPA to PLA by lactic dehydrogenase (LDH) is the key factor in the improvement of PLA production by LAB. Comparing the LDH gene of two strains, four amino acid mutation sites were found in this study in the LDH of L. plantarum IMAU10124.

The efficacy of nematicidal strainSyncephalastrum racemosum

Nematicidal activity using a pure culture ofSyncephalastrum racemosum was studied. The results showed that the metabolites ofS. racemosum have pretty high nematicidal activity. The nematicidal principles were solube in water and had high thermal stability. The major acid metabolites extracted from cultures ofS. racemosum identified from HPLC were oxalic acid dihydrate and tartaric acid. Soil application with culture filtrate ofS. racemosum significantly (P<0.05) reduced nematode population densities and subsequent root-knot development in tomato compared with the controls.

High-level expression of the Streptomyces mobaraense CICC 11018 transglutaminase in Corynebacterium glutamicum ATCC 13032

The transglutaminase (MTG) secreted by Streptomyces mobaraense is a valuable enzyme for the food industry. To optimize the expression system for MTG heterologous expression in Corynebacteriumglutamicum ATCC 13032, we took advantage of the recently identified efficient secretion signal peptide ΔS0949 and the tac-M promoter, a modified version of tac promoter. MTG activity assay showed that the recombinant C. glutamicum ATCC 13032 harboring plasmid pXMJ19-Spromtg which encodes the pro-MTG fused to the signal peptide ΔS0949 secreted pro-MTG to the culture broth with MTG activity of 5.2 U/mL. However, the recombinant strain pXMJ19-MSpromtg/13032 containing both the signal peptide ΔS0949 and the tac-M promoter accumulated pro-MTG up to a level of 6.7 U/mL, that resulted in an increase of 28.8% compared with the pXMJ19-Spromtg/13032 strain. Semi-quantitative RT-PCR demonstrated that transcriptional level of mtg driven by the tac-M promoter was 1.5-fold higher than that driven by the tac promoter, suggesting that, for the expression system used in this study, level of mtg transcription was a limiting factor for high-level MTG production in C. glutamicum ATCC 13032. Thus, further improvement of MTG production in the heterologous host C. glutamicum could be achieved by the use of more powerful promoters.

Characteristics and Application in Food Preservatives of Lactobacillus plantarum TK9 Isolated from Naturally Fermented Congee

Abstract In the present research, a strain of Lactobacillus plantarum TK9 was isolated from the Chinese naturally fermented congee and its characteristics for probiotic and food preservation were investigated. In terms of probiotic, the strain not only survives bile salts and simulated gastric juice but grows well under hypertonic conditions. Besides, the L. plantarum TK9 exhibited a broad antifungal spectrum, including most of the species closely related to food spoilage, like Penicillium roqueforti, Penicillium citrinum, Penicillium oxalicum, Aspergillus fumigatus, Aspergillus flavus and Rhizopus nigricans. But no evident inhibition effect was found on Aspergillus niger. To further evaluate its potential as bio-preservative, L. plantarum TK9 was inoculated into citrus, apples and yogurt prior to the addition of moulds. The results indicated that L. plantarum TK9 could obviously prolong shelf life of the test food for 72–96 h and represent an excellent candidate for food-related bio-preservative.

The Purification of Alkaline and Thermostable Lipase from a Newly Isolated Strain Acinetobacter calcoaceticus 1-7

A newly isolated moderate thermophilic strain 1-7 producing alkaline and thermostable lipase previously was identified as Acinetobacter calcoaceticus, which was isolated from the soil collected from bay of Bohai in China. The lipase showed maximum activity at pH 9.0 and high thermostability. The lipase from Acinetobacter calcoaceticus 1-7 was purified by ammonium sulfate precipitation, ion exchange chromatography and Sephadex G-75 chromatography. The molecular mass (Mr) of the lipase was estimated to be 30 kDa using SDS-PAGE.