signature=ee77ceee708494dd78ef09a68b76113a,The Planctomycetes, Verrucomicrobia, Chlamydiae and siste...

The Planctomycetes,Verrucomicrobia,Chlamydiae and sister phyla comprise a superphylum with biotechnological and medical relevance

Michael Wagner and Matthias Horn

In the rRNA-based tree of life four bacterial phyla,comprising

the Planctomycetes,Verrucomicrobia,Chlamydiae and

Lentisphaerae,form together with the candidate phyla

Poribacteria and OP3a monophyletic group referred to as the

PVC superphylum.This assemblage contains organisms that

possess dramatically different lifestyles and which colonize

sharply contrasting habitats.Some members of this group are

among the most successful human pathogens,others are

abundant soil microbes,and others still are of major

importance for the marine nitrogen cycle and hold much

promise for sustainable wastewater treatment.Recent

comparative genomic and metagenomic analyses of a few

representatives of this group revealed many unusual features

and generated unexpected hypotheses regarding their

physiology,some of which have already been con?rmed

experimentally.Furthermore,the availability of these genome

sequences offered new insights into the evolutionary history of

this peculiar group of microbes with major medical,ecological

and biotechnological relevance.

Addresses

Department of Microbial Ecology,University of Vienna,1090Vienna,

Austria

Corresponding author:Wagner,Michael(wagner@microbial-

http://www.doczj.com/doc/df34dc76c8d376eeaeaa3189.html)

Current Opinion in Biotechnology2006,17:241–249

This review comes from a themed issue on

Environmental biotechnology

Edited by David A Stahl and Michael Wagner

Available online15th May2006

0958-1669/$–see front matter

#2006Elsevier Ltd.All rights reserved.

DOI10.1016/j.copbio.2006.05.005

Introduction

The most recent version of the bacterial tree of life

consists of at least50phyla[1].Owing to dif?culties in

the reconstruction of ancient relationships among bacter-

ial phyla,however,their branching order in this tree

remains largely unresolved.An interesting exception to

this mistiness is the PVC superphylum—an assemblage

of four bacterial phyla together with the Poribacteria and

OP3candidate phyla(which contain no cultured rela-

tives),which is consistently recovered as a monophyletic

group in16S rRNA trees with different treeing methods

(Figure1).At?rst glance,this grouping is unexpected

because no obvious similarities between the different

phyla,which would re?ect their shared evolutionary

history,are apparent.Furthermore,bootstrap support

for this superphylum is not very high(Figure1)and there

are a few reports in which some of its members do not

cluster together[2–4].However,owing to limited data at

the time of their publication,these reports did not include

all postulated phyla of the PVC superphylum,which

might have resulted in biased tree topologies.Further-

more,a closer inspection of the available literature,

including all recently published genome sequences of

members of the PVC superphylum,reveals several unex-

pected similarities which lend additional support to the

monophyly of this group.A better understanding of the

evolution and biology of the bacteria of the PVC super-

phylum is of particular importance,because it encom-

passes organisms of major medical or environmental

relevance.Furthermore,this grouping includes the

recently discovered anaerobic ammonia oxidizers,which

are increasingly exploited for the cost-effective removal

of nitrogen compounds in sewage treatment.

The?rst part of this review summarizes separately for

each phylum selected research highlights published since

January2004(some earlier publications are also cited if

required to provide context),while the second part aims

to provide a synthesis of these?ndings in an evolutionary

context.

Planctomycetes

Of all phyla grouped in the PVC superphylum,the

Planctomycetes are most frequently represented in the

current16S rRNA Ribosomal Database Project(RDP)

database(release9.38)and make up 0.8%of all depos-

ited sequences.This relatively low number has to be

interpreted with caution,because the16S rRNA genes of

Planctomycetes do have mismatches to some PCR primers

that are widely used in environmental diversity surveys

[5].Although this feature might lead to underrepresenta-

tion of the Planctomycetes in environmental16S rRNA

libraries,the past few years have nonetheless seen a?ood

of papers reporting the detection of Planctomycetes in

aquatic and terrestrial ecosystems.For example,the

Planctomycetes was the most numerous bacterial group

in an acidic Sphagnum peat bog detectable by?uorescence

in situ hybridization[6]and they were also found in

hot springs[7].As for the other phyla within the PVC

superphylum,some Planctomycetes live together with