Design and characterization of a novel lytic protein against Clostridium difficile

Characterization of a cell wall hydrolase with high activity against vegetative cells, spores and biofilm of Bacillus cereus

Bacillus cereus is a prevalent foodborne pathogen that induces food poisoning symptoms such as vomiting and diarrhea. Its capacity to form spores and biofilm enables it to withstand disinfectants and antimicrobials, leading to persistent contamination during food processing. Consequently, it is necessary to develop novel and efficient antimicrobial agents to control B. cereus, its spores, and biofilms. Peptidoglycan hydrolases have emerged as a promising and eco-friendly alternative owing to their specific lytic activity against pathogenic bacteria. Here, we identified and characterized a Lysozyme-like cell wall hydrolase Lys14579, from the genome of B. cereus ATCC 14579. Recombinant Lys14579 specifically lysed B. cereus without affecting other bacteria. Lys14579 exhibited strong lytic activity against B. cereus, effectively lysing B. cereus cell within 20 min at low concentration (10 μg/mL). It also inhibited the germination of B. cereus spores and prevented biofilm formation at 12.5 μg/mL. Moreover, Lys14579 displayed good antimicrobial stability with negligible hemolysis in mouse red blood cells and no cytotoxicity against RAW264.7 cells. Notably, Lys14579 effectively inhibited B. cereus in boiled rice and minced meat in a dose-dependent manner. Furthermore, bioinformatics analysis and point mutagenesis experiments revealed that Glu-47 was the catalytic site, and Asp-57, Gln-60, Ser-61 and Glu-63 were active-site residues related with the cell wall lytic activity. Taken together, Lys14579 could be a promising biocontrol agent against vegetative cells, spores, and biofilm of B. cereus in food industry.

Engineering of Clostridium tyrobutyricum for butyric acid and butyl butyrate production from cassava starch

Clostridium tyrobutyricum has been successfully engineered to produce butyrate, butanol, butyl butyrate, and γ-aminobutyric acid. It would be interesting to produce bio-chemicals and bio-fuels directly using starch from non-food crop, e.g., cassava, by engineered C. tyrobutyricum. In this study, heterologous α-amylases were screened and expressed in C. tyrobutyricum, resulting in successfully starch hydrolyzation. Furthermore, α-glucosidase (AgluI) was co-expressed with α-amylases, resulting in enhancement in the capacity of starch hydrolyzation and butyrate production. When increasing the cassava starch concentration to 100 g/L, the engineered strain CTAA05 produced 27.0 g/L butyrate. In addition, when introducing butyl butyrate synthetic pathway, strain MU3-AAV produced 26.8 g/L butyl butyrate with 100 g/L cassava starch as substrate. This study showed a generalizable framework to engineered anaerobes for anaerobic production of bio-chemicals and bio-fuels from starchy biomass.

Separation and colorimetric detection of Escherichia coli by phage tail fiber protein combined with nano-magnetic beads

A colorimetric detection method for Escherichia coli (E. coli) in water was established based on a T7 phage tail fiber protein-magnetic separation. Firstly, the tail fiber protein (TFP) was expressed and purified to specifically recognize E. coli, which was verified by using fusion protein GFP-tagged TFP (GFP-TFP) and fluorescence microscopy. Then TFP conjugated with magnetic beads were applied to capture and separate E. coli. The TFP was covalently immobilized on the surface of magnetic beads and captured E. coli as verified by scanning electron microscopy (SEM). Finally, polymyxin B was used to lyse E. coli in solution and the released intracellular β-galactosidase (β-gal) could hydrolyze the colorimetric substrate chlorophenol red-β-D-galactopyranoside (CPRG), causing color change from yellow to purple. The high capture efficiencies of E. coli ranged from 88.70% to 95.65% and E. coli could be detected at a concentration of 10² CFU/mL by naked eyes. The specificity of the chromogenic substrate was evaluated using five different pathogen strains as competitors and tests with four kinds of real water samples showed recoveries of 86.00% to 92.25%. The colorimetric changes determined by visual inspection can be developed as an efficient platform for point-of-care detection of E. coli in resource-limited regions.