Biochemische und molekularbiologische Untersuchung der Magnetosomenmembran in Magnetospirillum gryphiswaldense

Abstract

Magnetosomes in magnetotactic bacteria (MTB) are among the most intriguing examples of subcellular structures in prokaryotes. The magnetosome particles consist of the magnetic iron mineral magnetite (or rarely greigite), which is enclosed within membrane vesicles.So far, the biomineralization process is poorly understood, but the magnetosome membrane (MM) seemed to be crucial in the biological control of magnetite formation.This work displays the first comprehensive biochemical and molecular investigations of the magnetosomes in Magnetospirillum gryphiswaldense. The biochemical characteristics of the MM were investigated by using various proteomic approaches to analyze the protein composition. In total, a number of 17 magnetosome membrane-associated proteins were found to constitute the magnetosome subproteome, and most of these proteins are novel for Magnetospirillum gryphiswaldense. Except of one, all MMPs were encoded by open reading frames in the mms6-cluster, mamGFDC-cluster and mamAB-cluster. These three gene clusters are arranged within the magnetosome island, which comprises approximately 150 genes. At least 25 of the genes are involved in magnetosome formation. Most of the mam-genes were found to be conserved, in respect of nucleotide sequence and gene arrangement, in different magnetotactic strains. Based on the amino acid sequences of the identified MMPs, special functions in magnetosome formation like in iron accumulation, nucleation, crystal growth and in the arrangement and shape of the magnetosome particles within the cell are discussed.Initial deletion experiments of the mamGFDC-cluster revealed an effect on size and shape of single magnetosome particles.This is the first time GFP-fusions of MMPs were employed to study protein localization in Magnetospirillum gryphiswaldense. Preliminary results indicate that the most abundant MMP (MamC) is localized exclusively in the MM.