Wang Tao, Persson Per, Tunlid Anders
Department of Biology, Microbial Ecology Group, Lund University, Ecology Building, Lund, SE-223 62, Sweden.
CAS Key Laboratory of Mountain Surface Processes and Ecological Regulation, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, 610041, China.
Environ Microbiol. 2021 Oct;23(10):5837-5849. doi: 10.1111/1462-2920.15539. Epub 2021 May 4.
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.
森林土壤中很大一部分氮（N）以与矿物结合的蛋白质化合物形式存在。蛋白质与矿物之间的紧密结合限制了微生物对该氮源的利用，而这是土壤氮相对稳定的储存库。我们已经表明，外生菌根（ECM）真菌卷缘桩菇能够从与氧化铁结合的蛋白质中获取氮。通过严格控制的同位素、光谱和色谱实验，我们证明了从与氧化铁结合的牛血清白蛋白（BSA）中获取氮的能力也存在于ECM真菌柱孢疣柄牛肝菌和橄榄皮盘菌中。尽管它们在进化历史、生长速率、探索类型和有机物分解机制方面存在差异，但其氮获取机制与卷缘桩菇所描述的机制相似。这些真菌通过细胞外天冬氨酸蛋白酶对与矿物结合的BSA的直接作用，从与矿物结合的BSA中释放氮，而无需蛋白质先解吸。蛋白酶吸附到矿物上会抑制水解，但这种不利影响会被调节矿物表面的化合物分泌所抵消。这些数据表明，在多个谱系和探索类型的ECM真菌中都存在通过酶渗出物驱动从与矿物结合的蛋白质中获取氮的机制。
