African Journal of Biotechnology Vol. 5 (8), pp. 653-658, 18 April 2006   

ISSN 1684–5315 © 2006 Academic Journals        

Full Length Research Paper

Response of planktonic bacteria of New Calabar River to zinc stress

C. O. Nweke¹*, J.C. Okolo¹, C. E. Nwanyanwu¹ and C. S. Alisi²

¹Department of Microbiology, Federal University of Technology, P.M.B.1526, Owerri, Nigeria.

²Department of Biochemistry, Federal University of Technology, P.M.B. 1526, Owerri, Nigeria.

*Corresponding author: Email: xrisokey@yahoo.com.

Accepted 18 March, 2006

Toxicity of Zn²⁺ on four planktonic bacteria isolated from New Calabar River water was assessed via dehydrogenase assay. Pure cultures of the bacterial strains were exposed to various Zn²⁺ concentrations (0.2 - 2.0 mM) in a nutrient broth amended with glucose and TTC. The responses of the bacterial strains to Zn²⁺ is concentration-dependent. At 0.2 mM, Zn²⁺ stimulated dehydrogenase activity in Proteus sp. PLK2 and Micrococcus sp. PLK4. In all strains, dehydrogenase activity was progressively inhibited at concentrations greater than 0.2 mM.  The IC₅₀ ranges from 0.236 ± 0.044 to 0.864 ± 0.138 mM. Total inhibition occurred at concentrations ranging from 1.283 ± 0.068 to 2.469 ± 0.045 mM. The order of zinc tolerance is: Micrococcus sp. PLK4 > Proteus sp. PLK2 > Pseudomonas sp. PLK5 > Escherichia sp. PLK1. The  result of the in vitro study indicated that the bacterial strains are sensitive to Zn²⁺ stress. Therefore, Zn²⁺contamination would pose serious threat to their metabolism in natural environments.

Key words: New Calabar River, zinc toxicity, planktonic bacteria, dehydrogenase.