Persistence of catalytic activity of fungal phosphatases incubated in tropical soils Brice Kedi a, b , Joseph Sei b , Hervé Quiquampoix a , Siobhán Staunton a, * a INRA, UMR Eco&Sols, INRA-IRD-Cirad-Montpellier SupAgro, 2 place Viala, 34060 Montpellier, France b LCMI, UFR SSMT, Université de Cocody, 22 BP 582 Abidjan 22, Côte d’Ivoire, France article info Article history: Received 5 September 2011 Received in revised form 2 February 2012 Accepted 5 February 2012 Available online 17 February 2012 Keywords: Phosphatase Protection Degradation Vertisol Acrisol Ferralsol Oxisol Adsorption Suillus collinitus Hebeloma cylindrosporum Sterilization Incubation abstract Catalytic activity of extracellular enzymes in soil controls many biogeochemical cycles. The efficiency of extracellular enzymes depends on their interaction with soil organo-mineral surfaces and their resis- tance to degradation and inactivation. Little is known about the factors that control the time dependence of enzyme activity in soil. We have monitored catalytic activity of native and added phosphatase incu- bated for up to one month in moist soil. Two fungal phosphatases and three tropical soils (two acrisols with contrasting organic matter content and a vertisol) were compared and the effect of soil sterilisation measured. The enzymes had different stabilities in solution. Activity of Hebeloma cylindrosporum phos- phatase was protected in acrisols, but not in contact with the vertisol. In contrast, the decline of activity of Suillus collinitus phosphatase followed the same trend in solution and in the presence of each of the soils. Sterilisation decreased native phosphatase activity. The rate of decline of added phosphatase activity was identical in sterile and non-sterile soils. We discuss the effects of degradation of the enzyme in soil and changing relative activity in the adsorbed state. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The contribution of extracellular enzymes to biogeochemical cycles in soil is determined in part by the persistence of activity with time. As for most proteins, extracellular enzymes interact with soil organo-mineral surfaces and are often strongly and irreversibly adsorbed (Quiquampoix, 1987a,b; Norde and Lyklema, 1991; Quiquampoix and Burns, 2007). Adsorption may contribute to the protection of enzymes against microbial degradation and thus enhance their long-term survival (Carter et al., 2007; George et al., 2005). There are several possible reasons for this enhanced stability over time. Changes in conformation and the imposition of a more rigid conformation may afford some degree of protection. Immo- bilised enzymes in soil may also be physically protected against proteases by their location in fine pores or clay interlayers where they remain accessible to substrates (Nannipieri et al., 1996). In a few cases the opposite has been observed, with immobilised enzymes having less stability and less resistance to protease attack than free enzymes (Carrasco et al., 1995). Soil enzymes may resist temperature shock and even autoclaving, but the protection appears to be more effective in smectitic soils than kaolinitic soils (Carter et al., 2007). Phosphatases are of particular interest in soil since a large proportion of soil phosphorus may be in organic forms and so catalytic hydrolysis may play an important role in the acquisition of phosphorus, especially in highly weathered tropical soils (Turner and Engelbrecht, 2011; Vance et al., 2003). Phosphatases are produced and secreted in soil by plants (Coello, 2002), bacteria (Palacios et al., 2005) and fungi including ectomycorrhizal fungi (Cairney, 2011; Quiquampoix and Mousain, 2005). The aim of this paper is to test the widely held belief that adsorption on soil always protects enzymes and confers them a longer effective life-span than in solution. Information on the life- span of enzymes in soil is also important when considering enzyme activity as a probe of soil quality. There may be a time lag between a change in soil microbial activity, due to land use change or the introduction of a stress and visible changes in enzymatic activity. We studied extracellular enzymes obtained from two ectomycor- rhizal fungi (Suillus collinitus and Hebeloma cylindrosporum) that have different stabilities in solution. They were incubated under * Corresponding author. Tel.: þ33 (0) 499 61 23 31; fax: þ33 (0) 499 61 30 88. E-mail address: staunton@montpellier.inra.fr (S. Staunton). Contents lists available at SciVerse ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2012.02.005 Soil Biology & Biochemistry 56 (2013) 69e74