Magnetosomes of magnetotactic bacteria (MTB) consist of structurally perfect, nano-sized magnetite crystals enclosed within vesicles of a proteo-lipid membrane. In the well-studied model M. gryph. biosynthesis of its isotropic cuboctahedral-shaped crystals is controlled by more than 30 genes comprised within compact magnetosome gene clusters [1]. Similar, yet distinct gene clusters were also identified in many diverse MTB in which they likely account for the biomineralization of magnetosome crystals with a variety of more complex, genetically encoded morphologies such as anisotropic elongated shapes. However, since most of these MTB are inaccessible to genetic and biochemical approaches, their functional analysis requires the expression of magnetosome genes in a foreign host [2]. Here, we investigated whether biosynthetic multi-gene clusters from various magnetotactic Alphaproteobacteria can be functionally expressed in the tractable M. gryph. To this end, DNA fragments from various donors were PCR amplified and cloned by multi-fragment hot fusion assembly or yeast-based transformation-associated recombination (TAR) cloning into large expression cassettes up to 40 kb in size. Upon transfer and chromosomal integration in M. gryph., gene clusters were stably maintained and restored the magnetosome phenotypes of donor MTB to different degrees. Expression of certain parts of some of the gene clusters led to the biomineralization of magnetite particles with aberrant sizes and shapes. This suggests that the transferred genes may control the morphology of magnetosomes, which is currently explored in more detail. In conclusion, our results confirm that M. gryph. is a useful host for the expression and functional elucidation of morphogenic magnetosome genes from foreign MTB.

[1] R. Uebe, D. Schüler

2016. Magnetosome biogenesis in magnetotactic bacteria. Nat Rev Microbiol 14:621–637.

[2] R.P. Awal, C.T. Lefevre, D. Schüler

2023, Functional expression of foreign magnetosome genes in the alphaproteobacterium Magnetospirillum gryphiswaldense., mBio 14: e0328222.