The (oxalato)aluminate complex as an antimicrobial substance protecting the “shiro” of Tricholoma matsutake from soil micro-organisms

Figures & data

Fig. 1. The antimicrobial activity against B. subtilis. (a) The mycorrhiza from the shiro front, (b): Paper discs containing the extract from the shiro front.

Note: The center disc contained totarol as a standard antimicrobial compound in B.

Fig. 2. The steric structure and ²⁷Al NMR spectrum of the extract from the shiro front of shiro No. 32. (a): Tris(oxalato)aluminate, (b): Bis(oxalato)aluminate, (c): (Oxalato)aluminate.

Table 1. The antimicrobial activity of oxalic acid and the (oxalato)aluminate complex.

Compound	µmol	DIZ (mm)
Oxalic acid	0.1	ND
	0.3	ND
	1.0	14
(Oxalato)aluminate complex	0.1	10
	0.3	16
	1.0	24

Notes: DIZ, Diameter of inhibitory zone; ND, Not detected.

Fig. 3. The antimicrobial activities of the mixtures of aluminum chloride and disodium oxalate with molar ratios of 1:1 (○), 1:2 (●), and 1:3 (△).

Fig. 4. The antimicrobial activity of oxalic acid against B. subtilis in the absence (a) and presence (b) of aluminum phosphate (5.5 mM).

Note: The discs contained 1 μmol of oxalic acid.

Table 2. The antimicrobial activity of organic acids (1 μmol) against B. subtilis in the presence or absence of aluminum phosphate (5.5 mM).

Organic acid	AlPO4 in media	DIZ (mm)
Lactic acid	—	20
	+	29
Malic acid	—	9
	+	11
Succinic acid	—	9
	+	11
Malonic acid	—	ND
	+	ND
Citric acid	—	11
	+	11

Notes: DIZ, Diameter of inhibitory zone; ND, Not detected.

Fig. 5. The effect of the (oxalato)aluminate complex on the mycelia growth of T. matsutake.

Note: Ratio means magnification of the colony size on the medium containing the oxalato(aluminate) complex on comparison with the control. Colony size of the control was 4.0 ± 0.16 cm².

Table 3. The antimicrobial activity of the (oxalato)aluminate complex.

Micro-organism	MIC (ppm) or inhibitory rate (%) at 300 ppm
Bacillus subtilis FKU101	30 ppm
B. subtilis JCM1465	300 ppm
Arthrobacter chlorophenolicus	300 ppm
Pseudomonas aeruginosa	300 ppm
Rhizobium radiobacter	300 ppm
Escherichia coli JCM18426	300 ppm
E. coli JCM20135	300 ppm
Saccharomyces cerevisiae	30 ppm
Penicillium citrinum	81%
Aspergillus niger	59%
Trichoderma reesei	>300 ppm
Rhizopus oryzae	>300 ppm

Note: MIC, Minimum inhibitory concentration.

Fig. 6. The distribution of T. matsutake mycelium (a), the (oxalato)aluminate complex (b), oxalic acid (c), pH (d), antimicrobial activity (e), bacteria (f), fungi (g), and phosphorus (h) inside the shiro front (SI), at the shiro front (SF), and outside the shiro front (SO) of No.32 and 7.

Note: DIZ, diameter of inhibitory zone.

Fig. 7. Three functions of oxalic acid secreted from the mycorrhiza. A: Release of soluble phosphorus from aluminum phosphate, B: Detoxification of aluminum in acidic soil, C: Formation of the antimicrobial (oxalato)aluminate complex.

Note: Al(oxalate) complex, the (oxalato)aluminate complex.