For the oxalic acid assay, 5 lL of each cell suspension
was dropped onto LB agar containing 0.1 % CaCl2 (Li
et al. 1999) and incubated either at 30 and 37 C for 24 h.
Oxalic acid was assessed as present when crystals of calcium
oxalate were observed in the medium using light
microscopy (SZ61, Olympus, Tokyo, Japan).