Deciphering the mechanisms of zinc tolerance in the cyanobacterium Anabaena sphaerica and its zinc bioremediation potential.

Abstract

Cyanobacteria adopt a variety of changes at proteomic and metabolic levels for surviving under harmful environmental conditions including heavy metal stress. The current study investigates the impact of zinc stress on the proteome of Anabaena sphaerica to get an insight into its molecular mechanisms of zinc tolerance. The study revealed three different aspects that were associated with the zinc tolerance in A. sphaerica: (i) the reduced expression of photosynthesis, nitrogen fixation, energy metabolism, respiratory, and transcriptional/translational proteins probably to conserve energy and utilizing it to sustain growth; (ii) the enhanced expression of metallothionein and ferritin domain protein All 3940 to chelate free zinc ions whereas upregulation of antioxidative proteins for detoxifying reactive oxygen species; and (iii) the expression of large numbers of hypothetical proteins to maintain the important cellular functions. Furthermore, over expressions of sulfate adenylyl transferase and cystathionine beta synthase along with the increased synthesis of peptidases and thiolated antioxidant proteins were also noticed which denoted cysteine synthesis under sulfur deprivation possibly by mobilizing the sulfur from dead cells and its channelization towards the production of thiolated antioxidants. Besides tolerating excess amount of zinc, A. sphaerica exhibited high zinc biosorption efficiency which confirmed its outstanding zinc bioremediation potential.