Unbalancing Zur (FurB)‐mediated homeostasis in Anabaena sp. PCC7120: Consequences on metal trafficking, heterocyst development and biofilm formation

Abstract

Zinc is required for the activity of many enzymes and plays an essential role in gene regulation and redox homeostasis. In Anabaena (Nostoc) sp. PCC7120, the genes involved in zinc uptake and transport are controlled by the metalloregulator Zur (FurB). Comparative transcriptomics of a zur mutant (Δzur) with the parent strain unveiled unexpected links between zinc homeostasis and other metabolic pathways. A notable increase in the transcription of numerous desiccation tolerance‐related genes, including genes involved in the synthesis of trehalose and the transference of saccharide moieties, among many others, was detected. Biofilm formation analysis under static conditions revealed a reduced capacity of Δzur filaments to form biofilms compared to the parent strain, and such capacity was enhanced when Zur was overexpressed. Furthermore, microscopy analysis revealed that zur expression is required for the correct formation of the envelope polysaccharide layer in the heterocyst, as Δzur cells showed reduced staining with alcian blue compared to Anabaena sp. PCC7120. We suggest that Zur is an important regulator of the enzymes involved in the synthesis and transport of the envelope polysaccharide layer, influencing heterocyst development and biofilm formation, both relevant processes for cell division and interaction with substrates in its ecological niche.

An ancient bacterial zinc acquisition system identified from a cyanobacterial exoproteome

“…However, we do not rule out that side effects may influence on the abundance of O-proteins. For example, similar to zur mutants from a variety of species, the absence of Zur would provoke a permanent induction of zinc uptake systems and a high level of internal zinc in the Anabaena Δ zur strain [ 45 ], which would impinge on regulators and systems for handling other metals [ 24 , 46 , 47 ] and would alter the cytoplasmic redox state [ 26 , 48 , 49 ]. Side effects associated with this altered status may indirectly influence on the accumulation of proteins in the extracellular space.…”

“…induction of zinc uptake systems and a high level of internal zinc in the Anabaena Δzur strain [45], which would impinge on regulators and systems for handling other metals [24,46,47] and would alter the cytoplasmic redox state [26,48,49]. Side effects associated with this altered status may indirectly influence on the accumulation of proteins in the extracellular space.…”