Biology Reference
In-Depth Information
Cellular Interactions with the Environment--Stress
Carbon Storage
Poly-hydroxyalkanoates (PHAs) store carbon energy, are synthesized from the ca-
tabolism of lipids, and constitute up to almost 90% of the dry weight of the Beta-
proteobacteria species Comamonas testosteroni [63]. These lipid-like carbon/energy
storage polymers are found in granular inclusions. The PhaR candidate VIMSS583509
is likely to be a regulatory protein for PHA synthesis, and is found near other pro-
teins associated with PHA granule biosynthesis and utilization in D. aromatica
(VIMSS583511-583513).
Phasins are relatively small proteins (180-200 aas) that have been shown to associ-
ate with PHA inclusions [64]. There are six copies of phasin-type proteins, with indica-
tions of recent gene duplication for three of the phasin-type proteins (VIMSS581881,
582264, and 3337571 (formerly 583582)). There are also three homologs of the active
subunit poly-B-hydroxybutyrate polymerase (PhaC orthologs) and two PHA reductase
candidates present in a direct repeat, which is also found in Legionella pneumophila .
Interestingly, one PhaC-like protein, VIMSS583511, is 70% identical to NodG of
Azospirillum brasilense , a nodulation protein [65]. No PhaA-like ketothiolase ortho-
log is present. The presence of an amplifi ed gene pool for carbon storage granules
in D. aromatica may confer the ability to survive under low nutrient conditions, and
poly-3-hydroxybutyrate accumulation has recently been observed in A. aromaticum
EbN1 cultures displaying reduced growth [66].
Phosphate
Inorganic polyphosphate storage appears likely, as both polyphosphate kinase (Ppk,
VIMSS582444) and exopolyphosphatase (Ppx, VIMSS583870) are present. These
genes are similar to those encoded in Pseudomonas aeruginosa , in that they are in
disparate regions of the chromosome [67]. Polyphosphate has been implicated in
stress response due to low nutrients in the environment [68], and also in DNA uptake
[69].
Phosphate transport appears to be encoded in a large cluster of genes
(VIMSS581746-581752), and response to phosphate starvation is likely supported by
the PhoH homolog VIMSS583854.
Biofilm Formation
There is a large cluster of eps export associated genes, including a proposed exo-
sortase (epsH, VIMSS582792). Presence of the eps family proteins (VIMSS582786,
VIMSS582790-582801) indicates capsular eps production, associated with either host
cell interactions (including root colonization [70]) or biofilm production in soil sedi-
ments [71]. Dechloromonas aromatica is one of a small number of species (19 out
of 280 genomes assessed by Haft et al. [71]) that also encodes the PEP-CTERM ex-
port system. The PEP-CTERM signal, present in 16 proteins in this genome, is pro-
posed to be exported via a potential exportase, represented in this genome by epsH
(VIMSS582792). Additionally, the presence of proteins encoding this putative expor-
tase is seen only in genomes also encoding the eps genes.
 
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