Development of a recombinase polymerase based isothermal amplification combined with lateral flow assay (HLB-RPA-LFA) for rapid detection of "Candidatus Liberibacter asiaticus".

Huanglongbing (HLB) or citrus greening is highly destructive disease that is affecting the citrus industry worldwide and it has killed millions of citrus plants globally. HLB is caused by the phloem limited, Gram negative, non-culturable, alpha-proteobacterium, 'Candidatus Liberibacter asiaticus'. Currently, polymerase chain reaction (PCR) and real time PCR have been the gold standard techniques used for detection of 'Ca. L. asiaticus'. These diagnostic methods are expensive, require well equipped laboratories, not user-friendly and not suitable for on-site detection of the pathogen. In this study, a sensitive, reliable, quick and low cost recombinase polymerase based isothermal amplification combined with lateral flow assay (HLB-RPA-LFA) technique has been developed as a diagnostic tool for detection of 'Ca. L. asiaticus'. The assay was standardized by designing the specific primer pair and probe based on the conserved 16S rRNA gene of 'Ca. L. asiaticus'. The assay was optimized for temperature and reaction time by using purified DNA and crude plant extracts and the best HLB-RPA-LFA was achieved at the isothermal temperature of 38°C for 20 to 30 min. The efficacy and sensitivity of the assay was carried out by using field grown, HLB-infected, HLB-doubtful and healthy citrus cultivars including mandarin, sweet orange cv. mosambi, and acid lime. The HLB-RPA-LFA did not show cross-reactivity with other citrus pathogens and is simple, cost-effective, rapid, user-friendly and sensitive. Thus, the HLB-RPA-LFA method has great potential to provide an improved diagnostic tool for detection of 'Ca. L. asiaticus' for the farmers, nurserymen, disease surveyors, mobile plant pathology laboratories, bud-wood certification and quarantine programs.

Purification and physicochemical characterization of a serine protease with fibrinolytic activity from latex of a medicinal herb Euphorbia hirta.

A 34 kDa serine protease, designated as hirtin, with fibrinolytic activity was purified to homogeneity from the latex of Euphorbia hirta by the combination of ion exchange and gel filtration chromatography. The N-terminal sequence of hirtin was found to be YAVYIGLILETAA/NNE. Hirtin exhibited esterase and amidase activities along with azocaseinolytic, gelatinolytic, fibrinogenolytic and fibrinolytic activities. It preferentially hydrolyzed Aα and α-chains, followed by Bß and ß, and γ and γ-γ chains of fibrinogen and fibrin clot respectively. The optimum pH and temperature for enzyme activity was found to be pH 7.2 and 50 °C respectively. Enzymatic activity of hirtin was significantly inhibited by PMSF and AEBSF. It showed higher specificity for synthetic substrate p-tos-GPRNA for thrombin. The CD spectra of hirtin showed a high content of ß-sheets as compared to α-helix. The results indicate that hirtin is a thrombin-like serine protease and may have potential industrial and therapeutic applications.