Current Microbiology

Lactobacillus plantarum là loài chủ yếu trong số các chủng vi khuẩn axit lactic được tách chiết từ sữa lên men truyền thống của người Maasai ở Kenya. Các chủng được chọn đã được đặc trưng hóa về các tính chất chức năng thông qua các quy trình tiêu chuẩn in vitro. Tất cả các chủng đều thể hiện khả năng chịu axit ở pH 2.0 sau 2 giờ tiếp xúc với giá trị dao động từ 1% đến 100%, trong khi khả năng chịu mật của các tế bào bị căng thẳng axit ở 0.3% oxgal thay đổi từ 30% đến 80%. Khả năng bám dính in vitro vào dòng tế bào tiết nhầy HT 29 MTX và khả năng gắn kết với các ma trận protein ngoài tế bào đã được chứng minh ở một số chủng. Bốn chủng được thử nghiệm trong quá trình giả lập đoạn dạ dày-tá tràng đã sống sót với tỷ lệ phục hồi dao động từ 17% đến 100%. Các chủng này có khả năng kháng lại một số kháng sinh đã được thử nghiệm. Từ những nghiên cứu in vitro này, một số chủng Lb. plantarum tách chiết từ sữa lên men truyền thống của người Maasai cho thấy tiềm năng probiotic. Các chủng này là những ứng viên tốt cho việc phát triển chế phẩm khởi đầu đa chức năng.

The Campylobacter coli 72Dz/92 cjaA gene (orthologue of cj0982c of C. jejuni NCTC 11168) product is a highly immunogenic, amino acid–binding protein. CjaA was palmitic acid-modified when processed in E. coli. In addition, site-directed mutagenesis of the Cys residue of the LAAC motif of its signal sequence confirmed that CjaA is a lipoprotein when processed in Campylobacter. Localization of the protein appeared to be host dependent. In Campylobacter, CjaA was recovered mainly as an inner-membrane protein, whereas in E. coli most of the protein was present in the periplasmic space. Interestingly, antiserum raised against Campylobacter glycine-extracted material also recognized CjaA produced by Campylobacter and Escherichia coli, indicating that at least part of the protein may be surface exposed. Site-directed mutagenesis of the Asn residues of two putative N-linked glycosylation sites (NIS and NFT) showed that CjaA is glycosylated and that only the first N-X-S/T sequeon serves as a glycan acceptor.

The present study investigated the use of two-phase olive mill waste (TPOMW) as substrate for the production of exopolysaccharide (EPS) by the endospore-forming bacilli Paenibacillus jamilae. This microorganism was able to grow and produce EPS in aqueous extracts of TPOMW as a unique source of carbon. The effects of substrate concentration and the addition of inorganic nutrients were investigated. Maximal polymer yield in 100-ml batch-culture experiments (2 g l−1) was obtained in cultures prepared with an aqueous extract of 20% TPOMW (w/v). An inhibitory effect was observed on growth and EPS production when TPOMW concentration was increased. Nutrient supplementation (nitrate, phosphate, and other inorganic nutrients) did not increase yield. Finally, an adsorption experiment of Pb (II), Cd (II), Cu (II), Zn (II), Co (II), and Ni (II) by EPS is reported. Lead was preferentially complexed by the polymer, with a maximal uptake of 230 mg/g EPS.

In order to improve the thermostability of Escherichia coli AppA phytase, Error-prone PCR was used to randomize mutagenesis appA gene, and a gene mutation library was constructed. A mutant I408L was selected from the library by the method of high-throughput screening with 4-methyl-umbelliferylphosphate (4-MUP). The appA gene of the mutant was cloned and expressed in E. coli Origami (DE3). The recombinant protein was purified by Ni-affinity chromatography, and the enzymatic features were analyzed. The results indicated that AppA phytase activities of mutant I408L and wild-type (WT) strain remained at 51.3 and 28%, respectively, after treatment at 85°C for 5 min. It means that the thermostability enhancement of AppA phytase I408L was 23.3% more as compared with WT. The K m of both phytase were 0.18 and 0.25 mM, respectively, which indicated that the catalyzing efficiency of I408L was improved. AppA phytase of mutant I408L showed a significant enhancement against trypsin, which was nearly three times compared with WT. In addition, AppA phytase of mutant could be activated by Mg2+ and Mn2+; in contrast, it could be inhibited by Ca2+, Co2+, Cu2+, and K+ in varying degrees, and the enzymatic activity was almost lost the presence of Fe3+ and Zn2+. It appears that screening thermotolerant phytase of E. coli by high throughput screening with a fluorescence substrate is a fast, simple, and effective method. The mutant I408L obtained in this study could be used for the large-scale commercial production of phytase.

A bacterial strain, designated TRPH29T, was isolated from saline-alkaline soil, collected from the southern edge of the Gurbantunggut desert, Xinjiang, People’s Republic of China. The isolate was Gram-staining positive, facultatively anaerobic, straight rods. Growth occurred at 15–40 °C (optimum, 28 °C), pH 8.0–13.0 (optimum, 10.0), and in the presence of 0–15% (w/v) NaCl (optimum, 2%). Phylogenetic analysis using 16S rRNA gene sequence indicated that strain TRPH29T showed the highest sequence similarities to Alkalihalobacillus krulwichiae (98.31%), Alkalihalobacillus wakoensis (98.04%), and Alkalihalobacillus akibai (97.69%). Average nucleotide identity (ANI) and digital DNA-DNA hybridization values between strain TRPH29T and Alkalihalobacillus krulwichiae, Alkalihalobacillus wakoensis, Alkalihalobacillus akibai were in the range of 73.62–75.52% and 15.0–21.20%, respectively. Results of genome analyses indicated that the genome size of strain TRPH29T was 5.05 Mb, with a genomic DNA G + C content of 37.30%. Analysis of the cellular component of strain TRPH29T revealed that the primary fatty acids were anteiso-C15:0 and iso-C15:0, and the polar lipids included diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unidentified glycolipid, and an unidentified phospholipid. The predominant respiratory quinone was MK-7. Based on the genomic, phylogenetic, phenotypic and chemotaxonomic analyses, strain TRPH29T represents a novel species of the genus Alkalihalobacillus, for which the name Alkalihalobacillus deserti sp. nov. is proposed. The type strain is TRPH29T (= CGMCC 1.19067T = NBRC 115475T).

Six monoclonal antibodies to Θ toxin ofClostridium perfringens were characterized. Four antibodies, 1C3, 2D4, 1B9, and 3F11, were nonneutralizing for Θ toxin and were non-cross-reacting with streptolysin O (SLO). The other two antibodies, 3H10 and 2C5, were cross-binding and cross-neutralizing with SLO. Neutralizing activity of 3H10 was higher than that of 2C5 on the basis of the binding activity with Θ toxin and SLO. Both antibodies could inhibit hemolysis even after binding of the toxins to sheep red blood cells and inhibited cardiotoxicity of the toxins in cultured heart cells.

Quorum sensing in Serratia marcescens, which uses two types of signaling molecules–N-acyl homoserine lactones and furanosyl borate diester–play important regulatory roles in the synthesis of 2,3-butanediol and prodigiosin. In the hope of understanding the effect of quorum sensing on physiologic metabolism, we established two molecular strategies, one to express acyl-homoserine lactone hydrolase to inactivate AI-1 signaling molecule using an expression vector with lactose as the inducer and the other to mutate luxS gene with a suicide plasmid pUTKm2 to inhibit the synthesis of AI-2 signaling molecule.

AphA and OpaR are the master regulators of quorum sensing in Vibrio parahaemolyticus and there is reciprocal negative regulation between AphA and OpaR. The histone-like nucleoid structure (H-NS) protein is a global transcriptional repressor of horizontally transferred genes, but a few prokaryotic genes, for example flagella genes, are stimulated by H-NS. The regulation of opaR by H-NS was investigated using the following methods: primer extension, LacZ fusion, quantitative RT-PCR, and electrophoretic mobility shift assay. One transcription start site located at 74 bp upstream of opaR was detected and its activity was induced by H-NS. Therefore, a single H-NS-dependent promoter was transcribed for opaR in V. parahaemolyticus. Because the H-NS protein could not bind to the upstream region of opaR and H-NS does not regulate aphA, indirect activation of the transcription of opaR by H-NS cannot be mediated by the AphA repressor.

The high sensitivity of probiotic bacteria (PB) to many environmental factors limits the number of food products where they can be incorporated. This study aimed to examine the capability of a unique three-layered microcapsule structure to protect PB against extremely elevated temperatures and low pHs to allow their incorporation into bakery goods. The microcapsules were prepared first by granulation of a Bifidobacterium lactis (BL) strain, as a model PB, to form a core, and then coating the core with three consecutive protective layers. The physical features and the shape of the microcapsules obtained from three sequential preparations were characterized using various methods. A viable cell count was utilized to evaluate the efficiency of the microcapsule structure to protect the bacteria during a bread-baking process carried out at 180 °C for 40 min and also during the exposure to simulated gastric fluid (pH 1.2) for up to 1 h. The results showed that whereas the free bacteria (unprotected BL) encountered a significant viability loss under these conditions, the microencapsulated BL presented superior resistance.