Plant-type and bacterial-type ferredoxins in a nitrogen-fixing cyanobacterium: Nostoc sp. strain PCC 73102

Abstract

The cyanobacterium Nostoc sp. strain PCC 73102, cultured under nitrogen‐fixing conditions, was investigated for the occurrence of ferrodoxins by SDS‐PAGE/Western immunoblots using antisera directed against both a major plant‐type and a bacterial‐type ferredoxin purified from Anabaena variabilis. Immunocytological labelling and transmission electron microscopy were used to study the distribution of both types of ferredoxins in the Nostoc cells. SDS‐PAGE/Western immunoblots revealed two proteins/polypeptides in the Nostoc strain, immunologically related to two soluble ferredoxins purified from Anabaena variabilis: the major plant‐type ferredoxin (Fd I) and a bacterial‐type ferredoxin (Fd III). Immunolocalization showed a uniform distribution of the plant‐type and the bacterial‐type ferredoxin in both the photosynthetic vegetative cells and in the nitrogen‐fixing heterocysts, with no specific association with any subcellular inclusions. Using the particle analysis of an image processor, the labelling associated with the vegetative cells, expressed as number of gold particles per cell area, was found to be only slightly higher (1.2x) or almost twice as high (1.9x) compared to the heterocysts for the major plant‐type and the bacterial‐type ferredoxin, respectively.