L.sp.HXQ 001 菌在小鼠肠道定植的实验研究

研究Ｌ·ｓｐ．ＨＸＱ００１菌株对小鼠的有益作用。通过对口服该菌液使之定植于小鼠肠道,分离小鼠粪便、肠段匀浆中该菌菌落及作肠段切片ＨＥ染色,肠道的正常防御机制不能杀灭该菌,并能在小鼠肠道定植,且以结肠为主。该菌定植肠段有淋巴细胞浸润,但无变性坏死等变化,显示生理性炎症反应。Ｌ．ｓｐ．ＨＸＱ００１菌株不是小鼠肠道正常菌群但仍可定植于肠道、激发机体免疫应答。有望成为新的肠道微生态调节剂。     

Enzymatic synthesis of l-DOPA α-glycosides by reaction with sucrose catalyzed by four different glucansucrases from four strains of Leuconostoc mesenteroides

l-DOPA α-glycosides were synthesized by reaction of l-DOPA with sucrose, catalyzed by four different glucansucrases from Leuconostoc mesenteroides B-512FMC, B-742CB, B-1299A, and B-1355C. The glucansucrases catalyzed the transfer of d-glucose from sucrose to the phenolic hydroxyl position-3 and -4 of l-DOPA. The glycosides were fractionated and purified by Bio-Gel P-2 column chromatography, and the structures were determined by ¹H NMR spectroscopy. The major glycoside was 4-O-α-d-glucopyranosyl l-DOPA, and the minor glycoside was 3-O-α-d-glucopyranosyl l-DOPA. The two glycosides were formed by all four of the glucansucrases. The ratio of the 4-O-α-glycoside to the 3-O-α-glycoside produced by the B-512FMC dextransucrase was higher than that for the other three glucansucrases. The glycosylation of l-DOPA significantly reduced the oxidation of the phenolic hydroxyl groups, which prevents their methylation, potentially increasing the use of l-DOPA in the treatment of Parkinson’s disease. The use of one enzyme, glucansucrase, and sucrose as the d-glucosyl donor makes the synthesis considerably simpler and cheaper than the formerly published procedure using cyclomaltodextrin and cyclomaltodextrin glucanyltransferase, followed by glucoamylase, and β-amylase hydrolysis.     

Cloning, expression and characterization of an extracellular enolase from Leuconostoc mesenteroides

Enolase on the surface of streptococci putatively facilitates pathogenic invasion of the host organisms. The related Leuconostoc mesenteroides 512FMCM is nonpathogenic, but it too has an extracellular enolase. Purified isolates of extracellular dextransucrase from cultures of L. mesenteroides contain minute amounts of enolase, which separate as small crystals. Expression of L. mesenteroides enolase in Escherichia coli provides a protein (calculated subunit mass of 47 546 Da) catalyzing the conversion of 2-phsopho-D-glycerate to phosphoenolpyruvate. The pH optimum is 6.8, with Km and kcat values of 2.61 mM and 27.5 s(-1), respectively. At phosphate concentrations of 1 mM and below, fluoride is a noncompetitive inhibitor with respect to 2-phospho-D-glycerate, but in the presence of 20 mM phosphate, fluoride becomes a competitive inhibitor. Recombinant enolase significantly inhibits the activity of purified dextransucrase, and does not bind human plasminogen. Results here suggest that in some organisms enolase may participate in protein interactions that have no direct relevance to pathogenic invasion.     

Microbial population dynamics and temperature changes during fermentation of kimjang kimchi

A distinct subset of lactic acid bacteria that are greatly influenced by temperature play an important role during kimchi fermentation. However, microbial population dynamics and temperature control during kimjang kimchi fermentation, which is traditionally fermented underground, are not known. Here we show that Lactobacillus sakei predominates in kimjang kimchi, perhaps due to suitable fermentation (5∼9°C) and storage (−2°C) temperatures. The temperature of this kimchi gradually decreased to 3.2°C during the first 20 days of fermentation (−0.3°C/day) and then was stably maintained around 1.6°C, indicating that this simple approach is very efficient both for fermentation and storage. These findings provide important information towards the development of temperature controlling systems for kimchi fermentation.     

Quenching Effect of Tocopherols on the Methyl Linoleate Photooxidation and Their Oxidation Products

The quenching effect of α-, γ- and δ-tocopherols on the methylene blue sensitized photo- oxidation of methyl linoleate was investigated, and the ¹O₂. quenching ability of tocopherols was determined. The ¹O₂ quenching rate constants for α-, γ- and δ-tocopherols in ethanol were estimated to be 2.6 × 10⁸ m^?1 sec^?1, 1.8 × 10⁸ m^?1 sec^?1 and 1.0 × 10⁸ m^?1 sec^?1, respectively. And the rate constants for the chemical reaction between each tocopherol and ¹O₂ were 6.6 × 10⁶ m^?1 sec^?1, 2.6 × 10⁶ m^?1 sec^?1 and 0.7 × 10⁶ m^?1 sec^?1 for α-, γ- and δ-tocopherols, respectively. The results show that α-tocopherol is the most effective compound toward ¹O₂ among the three tocopherols. The photooxidation of each tocopherol produced two peroxides which, after chemical reduction, were identified to be tocopherol hydroquinone by gas chromatography-mass spectrometry analysis. The photooxidation mechanism of these tocopherols was assumed to be different from that of autoxidation.     

Insoluble glucans from planktonic and biofilm cultures of mutants of <Emphasis Type="Italic">Leuconostoc mesenteroides</Emphasis> NRRL B-1355

Leuconostoc mesenteroides strain NRRL B-1355 produces the soluble exopolysaccharides alternan and dextran in planktonic cultures. Mutants of this strain are available that are deficient in the production of alternan, dextran, or both. Our recent work demonstrated that biofilms from mutant strains contained insoluble polysaccharides. We now find that the insoluble polysaccharides are composed of d-glucose polymers with contiguous sequences of α(1→3) and α(1→6) linkages. In addition, planktonic cultures of the wild type also produce this insoluble mixture in association with the cell mass. This material is similar to the insoluble glucan matrix known as mutan formed by cariogenic strains of streptococci. The production of insoluble mutan-like glucans may be more widespread among Leuconostoc spp. than previously recognized. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.