Cell concentration,viability and culture composition of airborne bacteria during a dust event in Beijing

Airborne bacteria were measured when a dust storm passed Beijing in spring 2012 with a focus on cell concentration, viability and TSA- and R2A-cultured strain composition. The concentration varied at an order of 10^7 cells/m3 with dust loading （demonstrated with PM10） and they had a very close correlation （RT2 = 0.91, p 〈 0.01）. At the time of highest PM10 of 652 μg/m3, the bacterial concentration reached 1.4 × 10^8 cells/m3, which was larger than that before and after the dust event by one order. Bacterial viability, the ratio of number concentration of viable cells to total cells, was 32%-64% and smaller in the dust plume than that before the dust arrival. Bacterial strains from the culture ranged between 2.5 × 10^4 and 4.6 × 10^5 CFU/m3 and no correlation with PM10 was determined. Their composition was different before and after the dust arrival according to 16S rRNA gene sequences and strains belong to Actinomycetes and Firmicutes were the majority in the dust samples.

The role of glutathione-mediated triacylglycerol synthesis in the response to ultra-high cadmium stress in Auxenochlorella protothecoides

Under ultra-high cadmium(Cd)stress,large amounts of glutathione are produced in Auxenochlorella protothecoides UTEX 2341,and the lipid content increases significantly.Glutathione is the best reductant that can effectively remove Cd,but the relationship between lipid accumulation and the cellular response to Cd stress has not been ascertained.Integrating analyses of the transcriptomes and lipidomes,the mechanism of lipid accumulation to Cd tolerance were studied from the perspectives of metabolism,transcriptional regulation and protein glutathionylation.Under Cd stress,basic metabolic pathways,such as purine metabolism,translation and pre-m RNA splicing process,were inhibited,while the lipid accumulation pathway was significantly activated.Further analysis revealed that the transcription factors(TFs)and genes related to lipid accumulation were also activated.Analysis of the TF interaction sites showed that ABI5,MYBrel and NF-YB could further regulate the expression of diacylglycerol acyltransferase through glutathionylation/deglutathionylation,which led to increase of the triacylglycerol(TAG)content.Lipidomes analysis showed that TAG could help maintain lipid homeostasis by adjusting its saturation/unsaturation levels.This study for the first time indicated that glutathione could activate TAG synthesis in microalga A.protothecoides,leading to TAG accumulation and glutathione accumulation under Cd stress.Therefore,the accumulation of TAG and glutathione can confer resistance to high Cd stress.This study provided insights into a new operation mode of TAG accumulation under heavy metal stress.