Effects of Different Preservation Methods on Activity of Recombinant E. coli

[ Objective] To explore different preservation methods of recombinant E. coli and find out the optimal conditions for preservation. [ Method] The recombinant E. coli DH5cx transformed pcDNA.3 were respectively preserved at 4℃ and -70 ℃, and the activity was determined after dif- ferent time. [ Result] The number of living E. coll with high dilutions preserved at 4 ℃ was gradually increased within the first 7 d, peaked on Day 7, and then gradually decreased. The number of living E. coli, which were preserved in 8% glycerol at -70℃ when OD800 at 0.8, were significantly higher than that of other groups after different preservation time. [ Conclusion] The optimal storage time was 7 d for recombinant E. coli at 4 ℃. For preservation at -70 ℃, the bacteria should be in logarithmic growth phase and preserved in 8% glycerol.

Fluorescent aptasensor for detection of live foodborne pathogens based on multicolor perovskite-quantum-dot-encoded DNA probes and dual-stirring-bar-assisted signal amplification

In this study,a fluorescent(FL)aptasensor was developed for on-site detection of live Salmonella typhimurium(S.T.)and Vibrio parahaemolyticus(V.P.).Complementary DNA(cDNA)of aptamer(Apt)-functionalized multicolor polyhedral oligomeric silsesquioxane-perovskite quantum dots(cDNA-POSSPQDs)were used as encoded probes and combined with dual-stirring-bar-assisted signal amplification for pathogen quantification.In this system,bar 1 was labeled with the S.T.and V.P.Apts,and then bar 2 was functionalized with cDNA-POSS-PQDs.When S.T.and V.P.were introduced,pathogen-Apt complexes would form and be released into the supernatant from bar 1.Under agitation,the two complexes reached bar 2 and subsequently reacted with cDNA-POSS-PQDs,which were immobilized on MXene.Then,the encoded probes would be detached from bar 2 to generate FL signals in the supernatant.Notably,the pathogens can resume their free state and initiate next cycle.They swim between the two bars,and the FL signals can be gradually enhanced to maximum after several cycles.The FL signals from released encoded probes can be used to detect the analytes.In particular,live pathogens can be distinguished from dead ones by using an assay.The detection limits and linear range for S.T.and V.P.were 30 and 10 CFU/mL and 10^(2) -10^(6) CFU/mL,respectively.Therefore,this assay has broad application potential for simultaneous on-site detection of various live pathogenic bacteria in water.

Trojan nanobacteria hybridized with prodrug nanocapsules for efficient combined tumor therapy

Live bacteria-based drug delivery systems have been raised as promising tools for enhancing drug delivery into tumors due to their active tumor targeting and easy surface modifiability.In this work,a“Trojan nanobacteria hybrid”,E.coli@highly integrated nanocapsules(HINCs)hybrid(HINE-Hybrid),was successfully constructed with HINCs of prodrug based on covalent selfassembly and the facultative anaerobic bacterium E.coli MG 1655 for combined chemotherapy,photothermal therapy(PTT),and chemodynamic therapy(CDT).HINCs were constructed by covalent cross-linking of pillar[5]arene derivatives and cisplatin prodrug linker,which can be endocytosed and lysed to release therapeutic agents.Under the near-infrared(NIR)light(at 808 nm)irradiation,the system temperature can be significantly increased by HINCs,which further leads to the highly efficient generation of reactive oxygen species(ROS).In addition,HINE-Hybrid shows significant antitumor effects in in vitro and in vivo studies and also promotes immune cell infiltration and antitumor cytokine expression in the tumor microenvironment(TME).HINEHybrid exerts its anticancer properties efficiently due to selective enrichment and multiplication of E.coli at tumor sites,which is important for the construction of bacterial-assisted antitumor platforms.

Bacterial viability assessment by flow cytometry analysis in soil

Soil microhabitats and their heterogeneity are often considered to be among the most important factors affecting soil biotic communities.The microbial commu-nity has become one of the most important links in soil nutrient cycles and trophic components due to its role in biological processes,spatial and temporal dynamics,and physiological adaptation.Sandy-soil desert systems are characterized by fast water infiltration during the rainy season,high salinity,and low moisture availability in the upper soil layers.Plants have developed different ecophy-siological adaptations in order to cope with this harsh environment.The Tamarix aphylla is known to be one of the most commonly adapted plants,exhibiting a mechan-ism for secretion of excess salts as aggregates through its leaves.These leaves aggregate beneath the plant,creating'islands of salinity'.Soil biotic components are,therefore,exposed to extreme abiotic stress conditions in this niche.The goal of this study was to examine the effect of T.aphylla on the live/dead bacterial population ratio on a spatial and temporal scale.The results emphasize the effect of abiotic factors,which changed on temporal as well as spatial scales,and also on the size of the active soil bacterial community,which fluctuated between 1.44%and 25.4%in summer and winter,respectively.The results of this study elucidate the importance of moisture availability and the'island-of-salinity'effect on the active microbial community in a sandy desert system.