Protists are Key Players in Protein Nitrogen Utilization

Anukool Vaishnav, Martin Rozmoš, Michala Kotianová, Hana Hršelová, Petra Bukovská, Jan Jansa Laboratory of Fungal Biology, Institute of Microbiology, Czech Academy of Sciences Protists are Key Players in Protein Nitrogen Utilization Institute of Microbiology Academy of Sciences of the Czech Republic WP4 RO4-2 This research has been supported by the Ministry of Education, Youth and Sports of the Czech Republic grant Talking microbes-understanding microbial interactions within One Health framework (CZ.02.01.01/00/22_008/0004597) Why Nitrogen Matters •Nitrogen (N) is the most limiting nutrient for plants. •Agriculture depends on inorganic fertilizers. •Up to 50% of fertilizer N is lost, polluting soil and water (Coskun et al., 2017). •Most soil N (80% to 90%) is organic (protein, chitin, residues) Liu et al., 2018). •How do plants access organic N? Created with BioRender.com Arbuscular Mycorrhizal Fungi (AMF) •Symbiotic fungi living in plant roots and help in nutrients uptake. •They cannot break down organic matter on their own (Tisserant et al. 2013). •They rely on microbes in the hyphosphere to access organic N (Jansa et al. 2018; Rozmoš et al. 2022). •Who are their helpers? Faghihinia et al. 2023 Hypothesis: The Missing Players •Bacteria release nutrients from organic matter. •Protists graze on bacteria and recycle nutrients (microbial loop). •We asked: •Can bacteria + protists help AMF access chitin and protein N? •Do AMF influence these microbes in return? Experimental Design •Compartmented microcosm with chicory roots. •3 nitrogen sources in hyphosphere compartments: ammonium, chitin, protein •Two treatments: with AMF (Rhizophagus irregularis) vs without AMF •With bacteria (Paenibacillus chitinolyticus) ± protists (Polysphondylium pallidum). •Traced N flow using 15N isotope labeling. •Seven replicate microcosms for each treatment combination. Results •Rapid proliferation with finely branched AMF hyphae and some spores on NH4Cl. •Slower, thinner growth on chitin and protein. (a) outside the root compartment, (b) NH4Cl, (c) chitin, and (d) protein. Results •Mycorrhizal system (M+) transfer organic N into roots. •Non-mycorrhizal (NM) showed less transfer. •N Source Matters •Highest transfer from ammonium and chitin, not-dependent on protist presence (P+). •Protein: less transfer, dependent on protist presence. Results •AMF and types of N sources influenced bacteria and protists growth. •Chitin boosted bacterial abundance the most. •Presence of protists reduced bacterial abundance, except when AMF present. •AMF increased abundance of the protists on protein (showing AMF priming effect). •On ammonium, both protist and bacteria suppressed in the presence of AMF (showing competition). Conclusion: Ammonium •AMF directly take up ammonium. •Compete strongly with bacteria and protists. •Efficient transfer of N to plants.