Applied Soil Ecology 46 (2010) 90–94 Contents lists available at ScienceDirect Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil The evaluation of free and encapsulated Aspergillus awamori for phosphate solubilization in fermentation and soil–plant system Rachana Jain, Jyoti Saxena, Vinay Sharma ∗ Department of Bioscience and Biotechnology, Banasthali University, P.O. Banasthali Vidhyapith, 304022 Rajasthan, Jaipur, India article info Article history: Received 5 October 2009 Received in revised form 25 May 2010 Accepted 20 June 2010 Keywords: Aspergillus awamori S19 Immobilized cells Solubilization Rock phosphate Agar Calcium alginate abstract Aspergillus awamori S19, a phosphate solubilizing filamentous fungi, was immobilized in Ca-alginate and agar. The immobilized microbial cells were applied in a repeated-batch fermentation process in order to test their effect on solubilization of Udaipur rock phosphate (URP) and tricalcium phosphate (TCP). Agar entrapped cells produced 106 mg l -1 whereas Ca-alginate entrapped cells produced 93 mg l -1 soluble P that was significantly higher than freely suspended cells with URP. In the presence of TCP, immobilized cells showed significantly better phosphate solubilization than free cells, viz. 340 and 345 mg l -1 in agar and Ca-alginate entrapment, respectively versus merely 291 mg l -1 with free cells. Further the immobi- lized cells were introduced into the soil supplemented with TCP and URP to analyze their effect on plant growth and P uptake of mung bean plants. The result showed significantly higher plant growth in the presence of fungal inoculates. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Phosphorus (P) is an essential macronutrient for biological growth and development. Despite its wide distribution in nature, it is deficient in most soils due to its high fixation capacity. Majority of the soluble phosphorus applied to soil as a chemical fertilizer is rapidly fixed into insoluble forms (phosphates of iron, aluminum and calcium) and thus becomes unavailable to plants (Altomare et al., 1999). In addition, long term and a large amount of applica- tion of chemical fertilizers are costly. Therefore, there is an obvious necessity to reduce the use of such agrochemicals. Efficient appli- cation of natural materials in agro ecosystem, viz. the use of rock phosphate (RP) as a fertilizer is an attractive alternative (Rajan et al., 1996). However, RP is very insoluble and relatively unavailable for plant uptake (Singh and Kapoor, 1994). Many soil bacteria and fungi have the ability to solubilize phosphate minerals and make them available to plants through acidification, chelation and exchange reaction (Oberson et al., 2001; Egamberdiyeva et al., 2003). They are able to use both inorganic and organic forms of phosphorus (Tarafdar and Jungk, 1987; Chen et al., 2002). A variety of phosphates solubilizing microorganisms (PSMs) have been found in rhizosphere of plants but usually their number is not high enough to solubilize soil bound phosphate in ∗ Corresponding author. Fax: +91 1438 228365. E-mail address: vinaysharma30@yahoo.co.uk (V. Sharma). substantial amounts. Thus there is need for the inoculation of plants by target microorganisms at higher concentrations. Many studies have shown an increase in growth and P uptake by plants through the inoculation of PSMs in pot experiments (Omar, 1998; Vassilev et al., 2006). However, studies often observe that the number of exogenous microorganisms decreases shortly after addition to a site. There are several explanations for the death of introduced microorganisms including extreme fluctuations in temperature, water content, pH, and nutrient availability, along with potentially toxic pollutant levels (heavy metals, pesticides, etc.) in the case of contaminated soils. Biotic factors include competition mainly from indigenous organisms for nutrients and antagonistic inter- actions. It is widely accepted that when applying the inoculant to a harsh environment such as soil, it may be desirable to use a carrier which provide protection. However, very few reports of solubilization of inorganic phosphate (URP and TCP) in soil condi- tions by a microorganism in an immobilized state have yet been made. In general immobilized cells have specific advantages over free cell system such as protection, a higher cell density in small vol- ume as well as cell metabolism, and higher stability (Vassilev and Vassileva, 1992). The objective of this work was to verify the potential applica- tion of a filamentous fungus, Aspergillus awamori S19 in free and entrapped (agar and alginate) forms in in vitro condition. It was also introduced into the soil in the form of free culture and co-entrapped into the carrier in order to evaluate its effect on the plant growth and P uptake. 0929-1393/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2010.06.008