This paper omits clearly to cite (Blanvillain S, Meyer D, Boulanger A, Lautier M, Guynet C, et al. (2007) Plant Carbohydrate Scavenging through TonB-Dependent Receptors: A Feature Shared by Phytopathogenic and Aquatic Bacteria. PLoS ONE 2(2): e224 doi:10.1371/journal.pone.0000224).
Blanvillain et al, were the first to describe the characterization and functional study of TonB-dependent receptors (TBDRs) in the plant pathogenic bacterium Xanthomonas campestris pv. campestris (Xcc), which is recognized as a model pathogen in phytopathology. They also analyzed the distribution and conservation of these outer membrane proteins in the genomes of 226 Gramnegative bacteria.
They showed that:
- TBDRs are over represented in Xanthomonas species and in a small fraction of the studied bacteria, most of which are living in aquatic habitats and have the capacity to degrade plant carbohydrates.
- One Xcc TBDR is involved in the active transport of sucrose. This TBDR belongs to a novel type of sucrose utilization locus which is required for full virulence on plants.
- Genome context analysis combined with expression studies suggest that the sucrose locus is not unique and that Xcc possesses several carbohydrate utilization loci which depend on TBDRs for the active transport of plant molecules across the outer membrane. These loci, designated CUT, and several Xcc TBDRs are conserved in aquatic bacteria such as Caulobacter crescentus, Colwellia psychrerythraea, Saccharophagus degradans, Shewanella spp., Sphingomonas spp. or Pseudoalteromonas spp., which share the ability to degrade a wide variety of complex carbohydrates and display TBDR overrepresentation.
They concluded that Xanthomonas species, aquatic bacteria and other bacteria having TBDR overrepresentation employ TBDRs not only for iron uptake but also for the scavenging of plant carbohydrates. As these compounds are widespread in nature, TBDRs might play a key role in bacterial adaptation in a wide range of environments.
This study was the first example showing the functionality of such loci. It was also the first work proposing the existence of a panel of CUT loci in bacteria allowing the exploitation
of various plant molecules.
Moreover, as other phytopathogenic or plant-associated
bacteria have an intermediate overrepresentation of TBDRs, Blanvillain and colleagues proposed that TBDRs may
play a very general role in the interaction with plants.
Their work not only has an impact in phytopathology, but concerns also a range of bacteria living in different environments including aquatic habitats. Therefore, this work
represents a new and emerging theme in bacteriology. The detailed study of TBDRs and CUT loci will probably give a new picture about bacterial adaptation and evolution. Furthermore,
it may also help to better understand the cycling of organic nutriments.

Based on these data, I totally disagree with the paper of Weiner et al. when it is told that " Not only is this an extraordinary range of catabolic capability, many of the enzymes exhibit unusual architecture including novel combinations of catalytic and substrate-binding modules. "
Their analysis on the genome content on carbohydrate-degradating enzymes among other bacteria is completely biased as they focused on certain categories of enzymes (eg polysaccharide lyases) and they did not consider the total number of carbohydrate degradative enzymes in one given genome. Indeed Blanvillain and colleagues showed that "The analysis of carbohydrate active enzymes identified in the predicted proteomes of 209 Gram negative bacteria and referenced in the CAZy database (http://afmb.cnrs-mrs.fr/C...) showed that, after Bacteroides sp. and S. degradans, which are well known specialists for polysaccharide degradation, Xcc has one of the highest number of genes involved in polysaccharide metabolism per megabase (29.9, total 152) (Table S2). These genes encode 82 predicted glycosyl hydrolases, 45 glycosyl transferases, 5 polysaccharide lyases, 18 carbohydrate esterases and 2 carbohydrate binding proteins. Interestingly, 46 of these proteins are encoded in the vicinity of 24 TBDR genes."
It is sad that such details are totally absent in the paper of Weiner et al.
The topic of carbohydrates degradation should be taken in its globality (rather than viewed by the prisma of particular enzymes) and replaced in the context of complex bacterial lifestyles.