3 and 3.2 times higher in the co-culture and B. cepacia culture medium than the fungal culture on the third day. The peak enzymatic see more activity was observed on the sixth day. Subsequently, the acid phosphatase activity of the medium grown with A. niger and co-culture did not change, and the activity of the medium grown with bacteria declined enough. In general, a significant correlation was observed between the variables studied (Table 2). Solubilized phosphate showed a significant positive correlation with titratable acidity and a significant negative correlation with pH and glucose content. Significant negative correlations were also observed between titratable acidity and pH, as well as between glucose and pH. CaP was

more efficiently solubilized in media wherein A. niger–B. cepacia were co-cultivated, in comparison with single cultures. This is the first report of joint utilization of CaP by two PSM in vitro. The results presented here clearly

depict that co-culture of these microorganisms is mutually beneficial and results in enhanced quantities of soluble P produced in the growth medium. Extent of phosphate solubilization by A. niger and B. cepacia Daporinad mouse have previously been reported as 1394 μg P2O5 mL−1 (Rinu & Pandey, 2010) and 200 μg mL−1 (Lin et al., 2006) or 346 μg mL−1 (Song et al., 2008), respectively. The quantity of phosphate solubilized on the ninth day by B. cepacia was 0.86 mg   mL−1 and by A. niger was 10.07 mg  mL−1. These results demonstrate that both microorganisms were highly efficient at solubilizing phosphate with ES rates of 78% and 91%, respectively. Previous results have demonstrated ES rates ranging from 42 (Vassileva et al., 1998), 47 (Rinu & Pandey, 2010), and 54% (Omar, 1998) using A. niger in culture media. However, our results demonstrate that the A. niger–B. cepacia co-culture solubilized 1.10 mg  mL−1 and yielded ES rates of 100%, higher than that obtained by either single culture. A plausible hypothesis is that synergism between the fungus and bacteria may have caused considerable improvement in growth and phosphate solubilization.

The activity of PSM in vitro generally correlates with various factors, most importantly, the release Nintedanib (BIBF 1120) of organic acids, which subsequently decreases the pH of the growth medium (El-Azouni, 2008; Kang et al., 2008; Song et al., 2008; Park et al., 2010). Similar trends were observed in this study. In addition, we observed that differences in growth rate influenced the production of acid, the reduction in pH, and consequently, the solubilization of phosphate. Rapid growth was observed during the initial period of incubation; for B. cepacia and the co-culture, this was 3 days and for A. niger, 6 days. High rates of bacterial and fungal growth in phosphate solubilization assays have also been reported in other studies (Lin et al., 2006; Saber et al., 2009). Phosphate solubilization by both single cultures as well as the co-culture correlated significantly with production of acid (0.