ZN MICROBIAL UPTAKE IN YELLOWSTONE NATIONAL PARK HYDROTHERMAL SPRINGS

Zinc is a crucial micronutrient required by microorganisms as a trace metal cofactor for various cellular processes, and its uptake and bioavailability are influenced by water pH and Zn concentration in aqueous solution [1, 2]. In our study, we calculated Zn uptake rates in hydrothermal springs located in Yellowstone National Park over pH values ranging from 2.14 ± 0.02 to 8.4 ± 0.1, using ⁶⁷Zn as a tracer in in situ bottle incubations, or metal stable isotope probing (MSIP). We collected water samples from six spring sources, incubated for four hours after spiking with ⁶⁷Zn, making ⁶⁷Zn > 99% of the total zinc concentration in the bottles. After field filtration though 0.2-micron filters and acid digestion in 50% v/v nitric acid, we calculated zinc uptake rates from inductively coupled plasma - mass spectrometry (ICP-MS) measurements of ⁶⁷Zn [3]. The lowest Zn uptake rate, 2.34 ± 0.05 nmolL⁻¹d⁻¹, occurred at the acidic spring, pH 2.6 ± 0.1. In contrast, the highest Zn uptake rates occurred at nearly boiling alkaline springs in the Sentinel Meadow and Rabbit Creek areas reaching up to 132 ± 4 and 580 ± 145 nmolL⁻¹d⁻¹ respectively. The most acidic spring, with a pH of 2.14 ± 0.02 and a Zn concentration of 3.59 x10^-7 M, exhibited a Zn uptake rate of 2.11 ± 0.07 nmolL⁻¹d⁻¹. Springs with a pH ≥ 5.4 and zinc concentrations below the ICP-MS detection limit of 1.53 x10^-8 M, on the other hand, exhibited Zn uptake rates at least an order of magnitude higher. A possible explanation is zinc deficiency at higher pH values enhanced uptake of the ⁶⁷Zn spike. The results show that acidic springs exhibited lower Zn uptake rates compared to alkaline springs which is explained by pH effects on short-term Zn uptake rates; the lower the pH, the lower the Zn uptake rates [4]. Samples incubated for 24 hours are currently being analyzed and include a field EDTA wash of the filters to remove adsorbed Zn from the particulate fraction. In conclusion, these results emphasize the influence of pH on particulate Zn uptake rates in hydrothermal springs as elucidated by metal stable isotope probing.

[1] Ting et al. 1991. Biotechnol. Bioeng., 37(5): 445-455. [2] Morel et al. 2003. Science 300(5621): 944-947. [3] Cox et al. 2014. Mar. Chem. 166: 70-81. [4] Xu et al. 2012. Limnol. Oceanogr. 57(1): 293-304.