Ultrasound contrast agents from microbubbles to biogenic gas vesicles

Microbubbles have been the earliest and most widely used ultrasound contrast agents by virtue of their unique features:such as non-toxicity,intravenous inject-ability,ability to cross the pulmonary capillary bed,and significant enhancement of echo signals for the duration of the examination,resulting in essential preclinical and clinical applications.The use of microbubbles functional-ized with targeting ligands to bind to specific targets in the bloodstream has further enabled ultrasound molecular imaging.Nevertheless,it is very challenging to utilize targeted microbubbles for molecular imaging of extra-vascular targets due to their size.A series of acoustic nanomaterials have been developed for breaking free from this constraint.Especially,biogenic gas vesicles,gas-filled protein nanostructures from microorganisms,were engineered as thefirst biomolecular ultrasound contrast agents,opening the door for more direct visual-ization of cellular and molecular function by ultrasound imaging.The ordered protein shell structure and unique gasfilling mechanism of biogenic gas vesicles endow them with excellent stability and attractive acoustic responses.What’s more,their genetic encodability enables them to act as acoustic reporter genes.This article reviews the upgrading progresses of ultrasound contrast agents from microbubbles to biogenic gas vesicles,and the opportu-nities and challenges for the commercial and clinical translation of the nascentfield of biomolecular ultrasound.

Measurement of Gas Vesicle in Cyanobacteria and Its Pretreatment Methods

[Objective]The aim was to measure gas vesicle in cyanobacteria and discuss its pretreatment methods.[Method]The capillary pressure method to determine gas vesicle in cyanobacteria was modified firstly,and then the lower detection limit and precision of modified apparatus were tested,finally the effects of two concentration methods and preservation methods on cell quantity and gas vesicle content of three cyanobacterias were studied.[Result]The lower detection limit and precision of modified apparatus to measure gas vesicle in three cyanobacterias were 0.001 8 μl/ml and 1% respectively.Unicellular Microcystis couldn＇t be concentrated effectively by filtration or centrifugation method,and the loss rate reached 50%.However,the colony of Microcystis and filamentous Planktothrix mougeotii could be effectively concentrated by centrifugation and filtration method respectively,with low loss rate.Besides,the effects of filtration and centrifugation on the content of gas vesicle in cells could be neglected.After preserved by direct refrigeration and adding Lugol＇s iodine solution for 7 d,there was no obvious change in cell concentration and gas vesicle content per cell,and the loss of gas vesicle under direct refrigeration was small,while the preservation of natural water samples should add Lugol＇s iodine solution.[Conclusion]The study could provide theoretical foundation for the researches on buoyancy regulation mechanism and blooming mechanism of cyanobacteria.

Floating Escherichia coli by Expressing Cyanobacterial Gas Vesicle Genes

Gas vesicles are hollow, air-filled polyprotein structures that provide the buoyancy to cells. They are found in a variety of prokaryotes. In this study, we isolated a partial gas vesicle protein gene cluster containing gvpA and gvpC20ψ from Planktothrix rubescens, and inserted it into an expression vector and expressed it in E. coli. The gas vesicle was developed in bacterial cells, which made bacterial cells to float on medium surface. We also amplified gvpA and gvpC20ψ separately and synthesized an artificial operon by fusing these two genes with the standardized gene expression controlling elements of E. coli. The artificial operon was expressed in E. coli, forming gas vesicles and floating bacteria cells. Our findings verified that the whole set of genes and the overall structure of gas vesicle gene cluster are not necessary for developing gas vesicles in bacteria cells. Two genes, gvpA and gvpC20ψ, of the gas vesicle gene cluster are sufficient for synthesizing an artificial operon that can develop gas vesicles in bacteria cells. Our findings provided a wide range of applications including easing the harvest of cultured microalgae and bacteria, as well as enriching and remediating aquatic pollutants by constructing gas vesicles in their ceils.

Construction of vesicle CdSe nano-semiconductors photocatalysts with improved photocatalytic activity:Enhanced photo induced carriers separation efficiency and mechanism insight

Visible-light-driven photocatalysis as a green technology has attracted a lot of attention due to its potential applications in environmental remediation. Vesicle Cd Se nano-semiconductor photocatalyst are successfully prepared by a gas template method and characterized by a variety of methods. The vesicle Cd Se nano-semiconductors display enhanced photocatalytic performance for the degradation of tetracycline hydrochloride, the photodegradation rate of78.824% was achieved by vesicle Cd Se, which exhibited an increase of 31.779% compared to granular Cd Se. Such an exceptional photocatalytic capability can be attributed to the unique structure of the vesicle Cd Se nano-semiconductor with enhanced light absorption ability and excellent carrier transport capability. Meanwhile, the large surface area of the vesicle Cd Se nano-semiconductor can increase the contact probability between catalyst and target and provide more surface-active centers. The photocatalytic mechanisms are analyzed by active species quenching. It indicates that h＋and UO2^-are the main active species which play a major role in catalyzing environmental toxic pollutants. Simultaneously, the vesicle Cd Se nano-semiconductor had high efficiency and stability.