Regulation of pH on inflation and deflation of biosynthetic gas vesicles used as ultrasound molecular imaging probes / 生物工程学报

Gas vesicles (GVs) are gas-filled protein nanostructures that can regulate the buoyancy of microorganisms such as cyanobacteria and archaea. Recent studies have shown that GVs have the potential to be used as ultrasound molecular imaging probes in disease diagnosis and treatment. However, the mechanism of the inflation and deflation of GVs remains unclear, which hampers the preservation of GVs and gas replacement. In the present study, the environmental pH value was found to be an important factor in regulating the inflation and deflation of GVs. It can not only regulate the inflation and deflation of GVs in vivo to make Microcystis sp. cells present distinct levitation state, but also regulate the inflation and deflation of purified GVs in vitro, and the regulation process is reversible. Our results may provide a technical support for the large-scale production and preservation of biosynthetic ultrasound molecular imaging probes, especially for gas replacement to meet different diagnostic and therapeutic needs, and would facilitate the application of biosynthetic ultrasound molecular imaging probes.

A new method for isolating gas vesicles from Microcystis for ultrasound contrast / 生物工程学报

Gas vesicles are a unique class of gas-filled protein nanostructures which are commonly found in cyanobacteria and Halobacterium. The gas vesicles may scatter sound waves and generate harmonic signals, which enabled them to have the potential to become a novel ultrasound contrast agent. However, the current hypertonic cracking method for isolating gas vesicles contains tedious operational procedures and is of low yield, thus not suitable for large-scale application. To overcome these technical challenges, we developed a rapid and efficient method for isolating gas vesicles from Microcystis. The new H2O2-based method increased the yield by three times and shortened the operation time from 24 hours to 7 hours. The H2O2 method is not only suitable for isolation of gas vesicles from laboratory-cultured Microcystis, but also suitable for colonial Microcystis covered with gelatinous sheath. The gas vesicles isolated by H2O2 method showed good performance in ultrasound contrast imaging. In conclusion, this new method shows great potential for large-scale application due to its high efficiency and wide adaptability, and provides technical support for developing gas vesicles into a biosynthetic ultrasonic contrast agent.

Screening for hyper-accumulating lipid mutants in Aurantiochytrium limacinum using high-throughput fluorescence-based method / 生物工程学报

Docosahexaenoic acid (DHA) has many unique physiological functions such as promoting the development of brain and retina in infants. Therefore, it is widely applied to food, pharmacy, breeding and other industries. To obtain engineered strains of Aurantiochytrium limacinum SR21 suitable for industrial application with increased lipid and DHA production, we designed a simple, fast, accurate and high-throughput screening method based on Nile red staining of oil droplets. First, ultraviolet C (UVC) mutagenesis was used to generate a random mutant library of A. limacinum. Second, screening conditions were optimized including staining conditions of Nile red and the sorting criterion. Thereby, three putative high-lipid mutants (D03432, D05106 and D01521) were selected from the mutant library containing 3 648 mutated clones. The three mutants grew faster and produced higher amounts of lipids and DHA compared to wild type (WT). In 100 mL cultures, the lipid content of D03432 and D05106 mutants reached 64.74% and 63.13% of dry cell weight respectively, whereas the wild strain exhibited only 43.19%. DHA yield in these two mutants were even 2.26-fold and 2.37-fold higher than that of the wild strain. Experiment with 5 L fermentor further confirmed that D03432 and D05106 mutants had better performance than the wild strain on DHA yield (45.51% and 66.46% more than that of the wild strain, respectively), and demonstrated their high potential for industrial application. This work not only generated several high-DHA content mutants with high potential for industrial use, but also provided vital guidance for high-throughput screening of lipid hyper-accumulating mutants in other oil-producing microorganisms.