Homologous overexpression of NpDps2 and NpDps5 increases the tolerance for oxidative stress in the multicellular cyanobacterium Nostoc punctiforme

Abstract

The filamentous cyanobacterium Nostoc punctiforme has several oxidative stress-managing systems, including Dps proteins. Dps proteins belong to the ferritin superfamily and are involved in abiotic stress management in prokaryotes. Previously, we found that one of the five Dps proteins in Nostoc punctiforme, NpDps2, was critical for H₂O₂ tolerance. Stress induced by high light intensities is aggravated in Nostoc punctiforme strains deficient of either NpDps2, or the bacterioferritin-like NpDps5. Here, we have investigated the capacity of NpDps2 and NpDps5 to enhance stress tolerance by homologous overexpression of these two proteins in Nostoc punctiforme. Both overexpression strains were found to tolerate twice as high concentrations of added H₂O₂ as the control strain, indicating that overexpression of either NpDps2 or NpDps5 will enhance the capacity for H₂O₂ tolerance. Under high light intensities the overexpression of the two NpDps did not enhance the tolerance against general light-induced stress. However, overexpression of the heterocyst-specific NpDps5 in all cells of the filament, led to a higher amount of chlorophyll-binding proteins per cell during diazotrophic growth. The OENpDps5 strain also showed an increased tolerance to ammonium-induced oxidative stress. Our results provide information of how Dps proteins may be utilized for engineering of cyanobacteria with enhanced stress tolerance.