Lu Huang,Weilai Lu,Yunkai Yu,Haoning Qiu,Yan Zeng,Lida Wang,Ying Liu,Lei Yan,Yu Vincent Fu,Yanning Zheng
Ammonium (NH 4 + ) transport across cell membranes plays an important role in assimilation or removal of the environmental nitrogen. The membrane protein AmtB has been considered to be the NH 4 + transporter that is responsible for the NH 4 + uptake. The phototrophic diazotroph Rhodopseudomonas palustris harboring two amtB genes has been widely used in wastewater treatment and bioremediation. However, the role of AmtB in NH 4 + uptake remains unclear in R. palustris . Here, we employed an innovative approach combining stable isotope probing (SIP) with Raman spectroscopy to determine the physiological functions of AmtB1 and AmtB2 in R. palustris. This powerful technique allowed us to investigate NH 4 + uptake at the single-cell level. The generated R. palustris Δ amtB1 Δ amtB2 mutant lacking AmtB1 and AmtB2 proteins was still capable of utilizing 15 NH 4 + even the 15 NH 4 + concentration was as low as 5 μM. These data demonstrate that both of the AmtB proteins are not essential for R. palustris to take up NH 4 + regardless of environmental NH 4 + levels. However, both AmtB1 and AmtB2 can contribute to NH 4 + uptake under nitrogen-limiting conditions. Given that R. palustris primarily expresses AmtB2 in these conditions, AmtB2 plays a more important role in NH 4 + uptake compared to AmtB1. In addition, transcriptomic analysis showed that the deletion of the amtB1 and amtB2 genes resulted in the upregulation of many transporter genes, providing potential targets for future investigation of alternative NH 4 + uptake systems.
The abnormal concentration of anthrax spore biomarker 2,6-pyridinedicarboxylic acid (2,6-DPA) will seriously affect public health. Therefore, a sensitive and rapid assay for 2,6-DPA monitoring is of vital importance. In this work, novel nano-sized amorphous Eu-NH 2 BDC (amEu-NH 2 BDC) and amorphous Tb-NH 2 BDC (amTb-NH 2 BDC) metal organic frameworks are prepared by adjusting the ratio of metal and ligand, respectively. Both of them exhibit highly sensitive and selective ratiometric fluorescence detection for 2,6-DPA with wider linear range and lower detection limit in aqueous solutions and human serum. Attributed to the coordination effect of 2,6-DPA in triggering the characteristic fluorescence emissions of Eu 3+ or Tb 3+ by replacing coordinated solvent molecules, as evidenced by ultraviolet–visible spectroscopy, the fluorescence lifetimes analysis, thermal gravimetric analysis , Fourier-transform infrared spectroscopy, density functional theory (DFT) simulations and X-ray photoelectron spectroscopy. In addition, the amEu-NH 2 BDC or amTb-NH 2 BDC loaded paper-based microsensors are constructed for real-time and sensitive detection of 2,6-DPA and coupled with a smartphone-assisted visual portable device.
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