Characterization of Physa acuta expressed sequence tags and transcript mining following cadmium exposure

Abstract

Freshwater molluscs have found strategic applications in public and veterinary health. Additionally, they have been used as bioindicator organisms towards environmental biomonitoring of polluted waters. The freshwater pulmonate, Physa acuta has been extensively studied as a potential biomarker in aquatic habitats with heavy metal, chemical, and microbial stressors. Lack of genomic resources is the bottleneck towards the study of candidate genes responsible for the unique adaptation of the mollusc to contaminated aquatic habitats. We have reported an EST survey of functionally relevant stress and defense related genes from P. acuta in our earlier study. In continuation of the same, we generated 1108 high-quality ESTs from a normalized cDNA library, pooled from the RNA isolated from the whole body tissue of CdCl2 exposed specimens of P. acuta. After clustering and assembly, we finally obtained 730 unique sequences representing 114 contigs and 616 singletons. Annotation of EST sequences revealed that 65.2, 62.8, and 35.9 % show significant homology to NCBI non-redundant database, Molluscs amino acid database, and NCBI KOG database, respectively. The functional characterization of the ESTs in Cd treated P. acuta group showed a greater proportion of signal transduction, cytoskeleton, and extracellular structure relevant genes compared with the control group. A large proportion of transcripts of cadmium treated P. acuta fell under the poorly characterized group of genes. These EST resources provide valuable information on Cd-specific transcript expression of P. acuta and could be utilized by scientists for developing new biomonitoring markers.