1. ¹School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China
2. ²Department of Civil and Environmental Engineering, University of Vermont, Burlington, VT, USA

Correspondence: BL Lim, School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China. E-mail: bllim@hku.hk

Received 16 February 2007; Accepted 27 April 2007; Published online 7 June 2007.

Abstract

Phytate, the most abundant organic phosphorus compound in soil, dominates the biotic phosphorus input from terrestrial runoffs into aquatic systems. Microbial mineralization of phytate by phytases is a key process for recycling phosphorus in the biosphere. Bioinformatic studies were carried out on microbial genomes and environmental metagenomes in the NCBI and the CAMERA databases to determine the distribution of the four known classes of phytase in the microbial world. The -propeller phytase is the only phytase family that can be found in aquatic environments and it is also distributed in soil and plant bacteria. The -propeller phytase-like genes can be classified into several subgroups based on their domain structure and the positions of their conserved cysteine residues. Analysis of the genetic contexts of these subgroups showed that -propeller phytase genes exist either as an independent gene or are closely associated with a TonB-dependent receptor-like gene in operons, suggesting that these two genes are functionally linked and thus may play an important role in the cycles of phosphorus and iron. Our work suggests that -propeller phytases play a major role in phytate-phosphorus cycling in both soil and aquatic microbial communities.