Soil aminopeptidase induction is unaffected by inorganic nitrogen availability

• Published in: Soil biology & biochemistry 2020-10, Vol.149 (C), p.107952, Article 107952
• Main Authors: Norman, J.S., Smercina, D.N., Hileman, J.T., Tiemann, L.K., Friesen, M.L.
• Format: Article
• Language: English
• Subjects: Aminopeptidase; Exoenzyme; Fertilization; Induction; Microbe; Nitrogen
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2020.107952

Soil microbes release a variety of aminopeptidase enzymes to degrade proteins into their constituent amino acid monomers, thereby increasing amino acid availability in the near-cell environment. We investigated how inorganic N availability controls the substrate induction response of aminopeptidase enzymes by conducting protein amendment experiments via gelatin addition to fertilized and unfertilized soil from a long-term N addition study. Protein addition triggered a measurable increase in enzyme activity, which we interpreted as an induction response, in all five of the aminopeptidase enzymes we investigated. The magnitude of these induction responses did not differ by fertilization regime even when unamended aminopeptidase activity differed between long-term fertilization treatments. Though soil microbes are thought to release aminopeptidase enzymes as a means of cellular N acquisition at steady-state concentrations, our results suggest that they use the same enzymes to access protein-derived C as an energetic resource at non-steady-state conditions, such as those triggered by the substrate induction response. The substrate induction response of aminopeptidase enzymes is therefore best viewed as a means of microbial competition for the substantial energetic resources available in protein subsidies. •We investigated controls on five different soil aminopeptidase enzymes.•Long term fertilization repressed activity for some aminopeptidase enzymes.•Gelatin addition caused induction responses in all aminopeptidase enzymes.•Induction responses were of equal magnitude in fertilized and unfertilized soil.•Microbes use protein subsidies as energy sources regardless of N availability.