Characterization of Planctomyces limnophilus and development of genetic tools for its manipulation establish it as a model species for the phylum Planctomycetes

Abstract

Planctomycetes represent a remarkable clade in the domain Bacteria because they play crucial roles in global carbon and nitrogen cycles and display cellular structures that closely parallel those of eukaryotic cells. Studies on Planctomycetes have been hampered by the lack of genetic tools, which we developed for Planctomyces limnophilus.

Fig. 1.

TEM analysis of negative-stained P. limnophilus cells in either sessile (A and B) or swarmer (C and D) state of the life cycle, which is similar to yet distinct from that previously reported (12a). (A) The holdfast substance (hs) is positioned at the end of the multifiber stalk (st) and attaches cells to a surface. Attachment is further supported by fibrous structures (fi). (B) High-resolution micrographs of the stalk attachment at the cell pole and of the holdfast structure. (C) Swarmer cell with flagellum (fl) and so-called large crateriform structures (lcs) dispersed all over the cell surface. Further magnification (D) reveals in addition small crateriform structures (scs) at the pole of the cell, where the flagellar hook (flh) is attached.

Fig. 2.

TEM analysis of thin sections from P. limnophilus cells revealed an intracytoplasmic membrane (ICM) that divides the cytoplasm into a paryphoplasm (Py) and a pirellulosome (Pi). Within the ICM of the Pi, the nucleoid is not covered by a further membrane but is always condensed, while the size and organization of Py and Pi differ between individual cells (A to C). (A′ to C′) Colors of cell compartments are false (for illustration only).

Fig. 3.

P. limnophilus genome map with highlighted positions of Tn5 transposon insertions as revealed by modified arbitrary PCR. The distribution appears random, although the sample number of nine does not allow statistical analysis.