OXALIC ACID SYNTHESIS BY THE MYCORRHIZAL FUNGUS PAXILLUS INVOLUTUS (BATSCH. EX FR.) FR.

Abstract

SUMMARYOxalic acid produced by an isolate of the mycorrhizal fungus Paxillus involutus (Batsch. ex Fr.) Fr. in still broth culture was assayed using high-performance liquid chromatography. Production of oxalic acid per unit of mycelium was influenced by nitrogen source and concentrations of exogenous calcium and bicarbonate ions. Nitrate-grown mycelia produced large quantities of oxalic acid; ammonium-grown mycelia produced small quantities regardless of what other ions were present. Calcium concentrations between 10 and 50 meq T^ slightly enhanced oxalic acid production in the presence of nitrate; concentrations between 250 and 500 meq 1"^ depressed production. Small additions of bicarbonate ions substantially increased oxalic acids production when nitrate was present. When calcium was present, most of the oxalic acid was associated with the mycelium, probably as calcium oxalate. In the absence of calcium, most of the oxalic acid occurred free in the culture medium. It is concluded that in calcareous soils, bicarbonate and nitrate are more important than calcium in stimulating oxalate production. The significance and underlying mechanisms of oxalate production are discussed.

Mobilisation of potassium and phosphorus from iron ore by ectomycorrhizal fungi

“…Oxalate chelation of these cations results in structural imbalance and therefore, may lead to the dissolution and release of other elements embedded in minerals such as K and P (Yuan et al 2004;Delvasto et al 2009). Secondly, both protons (from organic acids) and K (from minerals such as muscovite) are monovalent, but the size of the protons (0.32 9 10 -10 m) is much smaller than that of K (2.03 9 10 -10 m) (Lapeyrie et al 1987;Yuan et al 2004). The size, therefore, gives an advantage to protons to replace interlayer K contained in layer minerals such as muscovite associated with iron ores investigated in this study.…”

“…However, this tendency could not be linked to other isolates. Numerous studies (Paris et al 1995;Lapeyrie et al 1987;Parks 1990;Wallander and Wickman 1999;Rosling et al 2004; had successfully linked biological weathering and leaching of minerals to the effects of organic acids. These acids act in two major ways that involve the contribution of metal complexing organic acid anion and protons (Gadd 1999).…”

Diversity in phosphorus mobilisation and uptake in ectomycorrhizal fungi

“…However, exposure to Al and Fe generally did not stimulate oxalate production by the fungal species used. In contrast to metal exposure, nitrogen source appears to be a major factor as in vitro studies carried out in pure culture show a consistent stimulation of oxalic acid production in the presence of nitrate and inhibition by ammonium for P. involutus (Gharieb and Gadd 1999;Lapeyrie et al 1987;. We can hypothesise that it is Barber 1984) the NH 4 + ion per se which has an inhibitory effect on oxalate synthesis as organic nitrogen did not inhibit organic acid release in R. roseolus, contrary to ammonium (Plassard, unpublished data).…”

“…In particular, Paxillus involutus, Suillus sp. and Rhizopogon roseolus were strong oxalate producers Lapeyrie et al 1987). Now, approximately 30 species of ECM fungi belonging to the genera Cortinarius, Lactarius, Paxillus, Piloderma, Pisolithus and Suillus were found to be able to release substantial amounts of LMWOAs, with oxalate being the predominant form (Courty et al 2010).…”

“…The first studies on the capacity of ectomycorrhizal fungi to produce LMWOAs were carried out by Lapeyrie and colleagues (Lapeyrie 1988;Lapeyrie et al 1987Lapeyrie et al , 1991. Lapeyrie et al (1991) used 11 different ectomycorrhizal strains and found that oxalate production ranged from 27 to 120 μg mg −1 fungal dry weight, whereas other LMWOAs could not be detected.…”