Genetic analysis of DMSP metabolism in the marine Roseobacter clade

Kirkwood, Mark (2012) Genetic analysis of DMSP metabolism in the marine Roseobacter clade. Doctoral thesis, University of East Anglia.

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Genetic, biochemical, bioinformatic and molecular approaches were used to analyse
microbial catabolism of dimethylsulfoniopropionate (DMSP), an abundant anti-stress
compound made by marine phytoplankton.
Members of the Roseobacter clade of marine α-proteobacteria may catabolise DMSP by two
different routes; demethylation to form methylmercaptopropionate (MMPA), and cleavage by
DMSP-lyases, yielding volatile dimethylsulfide (DMS) plus acrylate.
The DMSP-lyase, DddP, was purified from Roseovarius nubinhibens ISM and characterised
in vitro. Nuclear magnetic resonance spectroscopy and gas chromatography confirmed bona
fide DMSP lyase activity and mutation of predicted active-site residues abolished DMS
DddP was also detected in the fungal coral pathogen Aspergillus sydowii, likely acquired
from bacteria by inter-Domain horizontal-gene-transfer.
A new DMSP-lyase, DddW, was identified in another Roseobacter species, Ruegeria
pomeroyi DSS-3, initially by microarray-based demonstrations that transcription of dddW
was induced in cells grown with DMSP. An adjacent gene encoded the cognate
transcriptional regulator. Escherichia coli cells that over-expressed DddW cleaved DMSP
into DMS plus acrylate. Thus, Ruegeria pomeroyi has three DMSP-lyases, with DddP and
DddQ being known already; mutational analyses showed that all three contributed to its
DMSP-dependent DMS (Ddd+) phenotype.
Moran’s laboratory had shown that the DMSP demethylase was encoded by R. pomeroyi
dmdA. I unveiled intimate links between the demethylation and the cleavage pathway(s). A
key player is acuI, which is co-transcribed with dmdA, both genes being induced by DMSP
and, more markedly, the DMSP-catabolite, acrylate. Furthermore, AcuI- mutants failed to
grow on acrylate as sole carbon source and were more sensitive to its toxic effects. AcuI-
mutants failed to grow on DMSP so, surprisingly, Ruegeria likely uses lyase pathway(s) to
grow on this compound. A potential regulatory gene, transcribed divergently from dmdA, was
also identified.
The microarray also, wholly unexpectedly, revealed a suite of cox genes involved in carbon
monoxide oxidation that was up-regulated in response to DMS.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Mia Reeves
Date Deposited: 16 May 2013 12:11
Last Modified: 16 May 2013 12:11

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