The spores of A. niger were counted in a Neubauer chamber and cells of the B. cepacia were quantified using a spectrophotometer (600 nm), using a previously established growth curve. Serial dilutions of the suspensions were made to obtain 22.3 × 106 spores mL−1 and 4.6 × 109 bacteria mL−1, and these were used as inoculum for the growth assays. The inocula concentrations were based on previous works (Barroso & Nahas, 2006; Park et al., 2010). The spore suspension (0.5 mL) and the cell suspension (0.75 mL) were inoculated into 50 mL sterile liquid media in Petri dishes (150 mm diameter) and incubated at 30 °C for 9 days without agitation. Both spore and cell suspensions were inoculated into co-cultures. Cultures were harvested

at 3-day Ceritinib intervals by filtration or centrifugation. The mycelia were filtrated using Whatman No. 1 filter paper, preweighed, and dried; the filtrate was used for subsequent chemical analysis. The mycelium retained on the filter

paper was washed see more with 50 mL of 1 M HCl to remove any undissolved CaP, followed by 50 mL of water and subsequently weighed; after which, the mycelia were dried in an oven at 105 °C for 24 h. The B. cepacia culture was centrifuged for 15 min at 10 000 r.p.m., and the supernatant was removed for chemical analysis. After removing the supernatant, the cells were washed with 10 mL of HCl 1 M. The pellet was resuspended in 10 mL of water; the dry weight of cell was assayed after drying at 105 °C for 24 h. The dry weight of a co-culture of A. niger–B. cepacia was obtained after centrifugation, using the same protocol described previously for the bacterial culture. Each treatment was replicated three times. The cell-free filtrates were used for chemical analysis. Soluble phosphate was determined using the Ames

(1966) method and quantified spectrophotometrically at 820 nm based on a standard curve. Titratable acidity and pH values were determined by titration of 10 mL of culture Thymidine kinase medium with 0.02 M NaOH using an automatic Titration Manager. Residual sugar was determined spectrophotometrically at 607 nm using anthrone solution. The efficiency of solubilization (ES) of CaPO4 (expressed as a percentage) was determined by the relationship between the amount of phosphate solubilized and the amount added to the culture medium. Acid phosphatase activity was determined using 4 mM p-nitrophenylphosphate in 0.1 M acetate buffer (pH 5.4) as substrate (Nahas et al., 1982). The reaction mixture contained 0.2 mL of culture medium and 1.8 mL of substrate solution. The mixture was stirred and incubated for 20 min at 37 °C. The p-nitrophenol released was measured using a spectrophotometer at 405 nm. One unit of phosphatase activity was defined as the amount of enzyme required to liberate 1 μmol p-nitrophenol per hour under the assay conditions. Specific activity was expressed as units per mg dry biomass. All chemical analysis was performed in duplicate.