PIRELLAE

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KINGDOM PIRELLAE

INTRODUCTION TO THE KINGDOM PIRELLAE AND ITS SINGLE PHYLUM, PIRELLOBACTERIA

Pirellae (pi-REL-e) is derived from Pirella, a common genus in the kingdom.

Free-living taxa are stalked and superficially similar to the prosthecate alphaproteobacteria (see Figure A). The similarity disappears, however, when the organisms are examined in more detail. Their cell walls are made of protein rather than peptidoglycan, a synapomorphy that separates them from all other Eubacteria. The chlamydias, however, are highly reduced coccoid intracellular parasites (0.2-0.7 µm in diameter; see Figure B). They seem to be unable to make their own ATP and rely on the biochemical machinery of the host cell to make it for them. They cause diseases of human beings that do not require arthropod vectors. One such disease is trachoma, which is common in developing countries and a leading cause of female reproductive problems in the US. Other species cause psittacosis and a chlamydial pneumonia.

A. Planctomyces, a common free-floating prosthecate bacterium in lakes and ponds.

B. Chlamydia, a very small obligate intracellular parasite of humans and other vertebrates. The bacteria are growing within some of the cultured cells and appear to be stipples inside the infected cells.

Images taken from:
A: http://biol-zukan.nara-edu.ac.jp/CompressedPict/Keiso/KeisoHoshi.JPG
B: http://www.bmb.leeds.ac.uk/mbiology/ug/ugteach/icu8/images/std/chlamydia.jpg

SYNOPTIC DESCRIPTION OF THE PIRELLOBACTERIA

The following description comes mainly from Margulis and Schwartz (1998), Barnes (1984), Brock et al. (1994), and Tudge (2000).

I. SYNONYMS: Proteinaceous walled bacteria, stalked bacteria, budding bacteria, Planctomyces.

II. PHYLUM CHARACTERISTICS

A. Structure

Cell Form: Prosthecate, budding or highly reduced unicells.

Cell Wall: Gram+ with proteinaceous walls without peptidoglycan.

Motility: Non-motile or motile.

B. Physiology

O₂ Tolerance: Free-living taxa obligate aerobes.

Substrates:

Products:

C. Other: Stalks are proteinaceous and unlike stalked bacteria of the Proteobacteria phyla. Some grow by budding. One, Gemmata, has a membrane-bound nucleoid region. Chlamydia, a parasitic taxon with a highly reduced genome and physiology.

D. Ecology: Free-floating or attached in freshwater. One group is parasitic.

SYSTEMATICS OF THE PIRELLOBACTERIA

These taxa were once grouped with the other stalked bacteria; however, the Pirellobacteria were separated on the basis of their 16S rRNA. The defining synapomorphy is the type of cell covering. Members of this group are united in having a proteinaceous wall instead of one made of peptidoglycan. I follow the system of Margulis and Schwartz (1998) in which these taxa are grouped together in a single phylum is designated B-11. I have separated the free-living and parasitic taxa into separate classes. Bergey's Manual of Systematic Bacteriology, 2nd edition (Garrity et al. 2001) treats the taxa that I include in the Pirellae as two phyla (Planctomycetes and Chlamydiae) of Bacteria.

HIERARCHICAL CLASSIFICATION OF THE PIRELLOBACTERIA

This system follows Margulis and Schwartz (1998) and modified by the system of Garrity et al. (2001 and 2003).

CLASS PLANCTOMYCETAE

Members of this class are free-living. These grow by polar growth, some with elaborate internal "organelles". With a single order.

ORDER PLANCTOMYCIALES

Gemmatia, Isosphaera, Pirellula, Pirella, Planctomyces.

CLASS CHLAMYDIAE

Members of this class are all parasitic with highly reduced genomes and physiologies.

ORDER CHLAMYDIALES

Chlamydia, Chlamydophila, Parachlamydia, Simkania, Waddlia.

This page is maintained by Jack R. Holt. Last revised: 04/22/2008.