Decrypting the effect of sulfate stress on the cyanobacterium Anabaena sp. PCC 7120 using physiological, proteome and transcript analysis in conjunction with bioinformatics

Sulfate limitation affects growth and various metabolic processes in cyanobacteria. However, there is little understanding of the underlying mechanism of these processes. Hence, the study investigated the effects of sulfate limitation in the cyanobacterium, Anabaena sp. PCC 7120. Results showed that sulfate stress affected photo- pigment contents in the test cyanobacterium delineating reduced growth. Proteome profile showed that differential expression profiles of different proteins involved in the various metabolic pathways suggested sulfur- dependent pathways were altered due to sulfate limitation. The most damaging effect was observed on the proteins belonging to the photosynthesis pathway, affirming the relationship between sulfur and carbon metabolism. Expression of proteins involved in the pathways such as nitrogen, protein synthesis, chaperone category, amino acid biosynthesis, and redox-responsive proteins were down-regulated. Moreover, forty-seven hypothetical proteins were also influenced by sulfate limitation. Molecular chaperones act as a physical barrier to prevent the aggregation of housekeeping proteins. Down expression of these proteins might affect the sustainability of the other proteins. Besides, transcript levels of the selected proteins were in concordance with physiological as well as proteome data. Additionally, template-based modeling and ab initio full atomic relaxation were performed via bioinformatic analysis through different tools to gain deeper insight into the structural and functional attributes of hypothetical proteins. Based on study, it could be concluded that mostly the proteins were downregulated which may lead to PCD in the cyanobacterium and also suggested that sulfur is a central hub and crucial for various sulfur-dependent pathways.