Influence of Ammonium on Formation of Mineral-Associated Organic Carbon by an Ectomycorrhizal Fungus

Investigating removal mechanisms of long- and short-chain per- and polyfluoroalkyl substances using specialty adsorbents in a field-scale surface water filtration system

This study assessed the application of two specialty adsorbents, also known as green sorption media (GSM), including clay-perlite and sand sorption media (CPS) and zero-valent iron and perlite green environmental media (ZIPGEM) to remove long- and short-chain per- and polyfluoroalkyl substances (PFAS) at field scale. The field-scale demonstration employed four GSM filter cells installed near the C-23 Canal (St. Lucie County, FL), which discharges water to the ecologically sensitive St. Lucie River estuary and to the Atlantic Ocean finally. Although prior lab-scale experiments had demonstrated the effectiveness of CPS and ZIPGEM in treating long-chain PFAS, their performance in field-scale application warranted further investigation. The study reveals the critical roles of divalent cations such as Ca2+ and monovalent cations such as ammonium and hydronium ions, as well as other water quality parameters, on PFAS removal efficacy. Ammonia, most likely resulting from photo- and bacterial ammonification, gives rise to elevated ammonium ion formation in the wet season due to the decrease in pH, which ultimately worsens PFAS adsorption. Moreover, there is a strong negative correlation between pH and PFAS removal efficiency in the presence of ammonia, as evidenced by the reduced removal of PFAS during events associated with low pH.

A widespread mechanism in ectomycorrhizal fungi to access nitrogen from mineral-associated proteins

A large fraction of nitrogen (N) in forest soils is present in mineral-associated proteinaceous compounds. The strong association between proteins and minerals limits microbial accessibility to this source, which is a relatively stable reservoir of soil N. We have shown that the ectomycorrhizal (ECM) fungus Paxillus involutus can acquire N from iron oxide-associated proteins. Using tightly controlled isotopic, spectroscopic and chromatographic experiments, we demonstrated that the capacity to access N from iron oxide-associated bovine serum albumin (BSA) is shared with the ECM fungi Hebeloma cylindrosporum and Piloderma olivaceum. Despite differences in evolutionary history, growth rates, exploration types and the decomposition mechanisms of organic matter, their N acquisition mechanisms were similar to those described for P. involutus. The fungi released N from mineral-associated BSA by direct action of extracellular aspartic proteases on the mineral-associated BSA, without initial desorption of the protein. Hydrolysis was suppressed by the adsorption of proteases to minerals, but this adverse effect was counteracted by the secretion of compounds that conditioned the mineral surface. These data suggest that the enzymatic exudate-driven mechanism to access N from mineral-associated proteins is found in ECM fungi of multiple lineages and exploration types.

Nitrogen acquisition from mineral-associated proteins by an ectomycorrhizal fungus

In nitrogen (N)-limited boreal forests, trees depend on the decomposing activity of their ectomycorrhizal (ECM) fungal symbionts to access soil N. A large fraction of this N exists as proteinaceous compounds associated with mineral particles. However, it is not known if ECM fungi can access these mineral-associated proteins; accordingly, possible acquisition mechanisms have not been investigated. With tightly controlled isotopic, spectroscopic, and chromatographic experiments, we quantified and analyzed the mechanisms of N acquisition from iron oxide mineral-associated proteins by Paxillus involutus, a widespread ECM fungus in boreal forests. The fungus acquired N from the mineral-associated proteins. The collective results indicated a proteolytic mechanism involving formation of the crucial enzyme-substrate complexes at the mineral surfaces. Hence, the enzymes hydrolyzed the mineral-associated proteins without initial desorption of the proteins. The proteolytic activity was suppressed by adsorption of proteases to the mineral particles. This process was counteracted by fungal secretion of mineral-surface-reactive compounds that decreased the protease-mineral interactions and thereby promoted the formation of enzyme-substrate complexes. The ability of ECM fungi to simultaneously generate extracellular proteases and surface-reactive metabolites suggests that they can play an important role in unlocking the large N pool of mineral-associated proteins to trees in boreal forests.