Adenine deficient yeast : a unicellular model organism for tracing Zn(II) and untra-small AgNPs in intra/extracellular environment

Abstract

The biosensor is gradually becoming a potential sensor to monitor the environmental pollution, especially their effects on organisms. The autofluorescence intensity (FITC channel) of an adenine deficient yeast (Ade(-) yeast) was enhanced in the presence of Zn. The biosensor could accurately quantify the extracellular concentrations of labile Zn ranging from 0.01 to 0.5 μM in complex medium. As Ade(-) yeast responds to intracellular Zn, we employed it as a model eukaryote to quantify the Zn influx, transportation between labile and storage pools, and efflux under different Zn exposure levels (< 1 μM). Yeast regulated Zn uptake from the extracellular source by controlling the Zn influx at the bio-interface. Under exposure of such low dose of Zn, transportation between labile Zn and storage Zn pools or Zn efflux to the extracellular environment was not obvious. As dissolved Ag decreased the Zn directed fluorescence increase of Ade(-) yeast, we used Ade(-) yeast loaded with Zn to quantify the concentration of extracellular ultra-small AgNPs. The lowest detectable concentration of AgNPs (7 nm) was 8.9 μg/L, while the bio-response induced by larger AgNPs (20 nm) did not change with increasing AgNPs concentration. Ade(-) yeast selectively collected the ambient ultra-small AgNPs and acted as a screener to differentiate small AgNPs and large ones. Despite the newborn bud could act as an outlet to spit out the invasive AgNPs, the depuration of total Ag from yeast could be inhibited by the continuously growing daughter bud. The secreted complex was defined as exosome escaped by vesicle related exocytosis and composed of organic corona. Numerous AgNPs were evenly distributed in the complex and shrinks to as small as half of the originally synthesized AgNPs after cellular transformation. Based on the specific response of model yeast to intracellular labile Zn, contents of Zn(II) and AgNPs in the environment are quantified and the intracellular behavior of both Zn(II) and AgNPs can be simultaneously revealed.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Karl Wah Keung TSIM (Supervisor) & Wenxiong Wang (Supervisor)