Visual Detection of Vibrio parahaemolyticus using Combined CRISPR/Cas12a and Recombinase Polymerase Amplification / 生物医学与环境科学（英文）

Objective@#To establish an ultra-sensitive, ultra-fast, visible detection method for Vibrio parahaemolyticus (VP) .@*Methods@#We established a new method for detecting the tdh and trh genes of VP using clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 12a (CRISPR/Cas12a) combined with recombinase polymerase amplification and visual detection (CRISPR/Cas12a-VD).@*Results@#CRISPR/Cas12a-VD accurately detected target DNA at concentrations as low as 10 -18 M (single molecule detection) within 30 min without cross-reactivity against other bacteria. When detecting pure cultures of VP, the consistency of results reached 100% compared with real-time PCR. The method accurately analysed pure cultures and spiked shrimp samples at concentrations as low as 10 2 CFU/g.@*Conclusion@#The novel CRISPR/Cas12a-VD method for detecting VP performed better than traditional detection methods, such as real-time PCR, and has great potential for preventing the spread of pathogens.

Rapid Internal Control Reference Recombinase-Aided Amplification Assays for EBV and CMV Detection / 生物医学与环境科学（英文）

Epstein-Barr virus (EBV) and cytomegalovirus (CMV), two of the most prevalent human herpesviruses, cause a wide spectrum of diseases and symptoms and are associated with serious health problem. In this study, we developed an internal control reference recombinase-aided amplification (ICR-RAA) assay for the rapid detection of EBV and CMV within 30 min. The assay had a sensitivity of 5 and 1 copies/test for EBV and CMV, respectively, with no cross reaction with other pathogens. In comparison with those of the commercial quantitative polymerase chain reaction (qPCR), the sensitivity of the EBV and CMV ICR-RAAs using extracted DNA was 93.33% and 84.84%, respectively; the specificity was 98.75% and 100.00%, respectively; and the Kappa values were 0.930 and 0.892 (

Cloning and high-level expression of Thermus thermophilus RecA in E. coli: purification and novel use in HBV diagnostics

ABSTRACT We studied the role of Thermus thermophilus Recombinase A (RecA) in enhancing the PCR signals of DNA viruses such as Hepatitis B virus (HBV). The RecA gene of a thermophilic eubacterial strain, T. thermophilus, was cloned and hyperexpressed in Escherichia coli. The recombinant RecA protein was purified using a single heat treatment step without the use of any chromatography steps, and the purified protein (>95%) was found to be active. The purified RecA could enhance the polymerase chain reaction (PCR) signals of HBV and improve the detection limit of the HBV diagnosis by real time PCR. The yield of recombinant RecA was ∼35 mg/L, the highest yield reported for a recombinant RecA to date. RecA can be successfully employed to enhance detection sensitivity for the diagnosis of DNA viruses such as HBV, and this methodology could be particularly useful for clinical samples with HBV viral loads of less than 10 IU/mL, which is interesting and novel.

Comparison of activity of OsDmc1A recombinase of rice (Oryza sativa) in presence of Ca2+ and Mg2+ ions.

Recombinases are known to play an important role in the homology search and strand exchange during meiosis as well as homologous recombination (HR)-mediated DNA repair specifically require Mg2+ ion for their activity. The Ca2+ has been shown to stimulate the strand exchange activity of hDmc1 and ScDmc1 by forming the extended filaments on DNA. Oryza sativa disrupted meiotic cDNA1A (OsDmc1A), a homologue of yeast and human Dmc1 from rice shows the hallmark functions of recombinase. Here, we report the effects of Ca2+ and Mg2+ on OsDmc1A activity from rice (Oryza sativa). OsDmc1A showed a concentration-dependent binding with both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) substrates in presence of Mg2+ or Ca2+. The ssDNA and dsDNA binding activities, as well as renaturation activity of OsDmc1A were similar in the presence of Ca2+ or Mg2+. Increasing the Ca2+ or Mg2+ increased the DNA binding, renaturation and strand exchange of OsDmc1A. But, OsDmc1A showed only a slight stimulation of strand exchange activity in presence of Ca2+, when compared the activity in presence of Mg2+. Electron microscopy showed that OsDmc1A formed ring-like structures in presence of Mg2+ or Ca2+. However, OsDmc1A formed filament like structures with both ss and dsDNA in presence of Mg2+ or Ca2+. Taken together, Ca2+ did not affect OsDmc1A recombinase activity significantly.