Natale, Alessandra Pia (2010) Genotypic and phenotypic flexibility of microbial communities. PhD thesis, University of Warwick.

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Abstract

Paracoccus denitrificans is a facultative anaerobic Gram-negative α-
proteobacterium able to shift to denitrification under anaerobic conditions (John
& Whatley, 1978; Zumft, 1997).
Because of its metabolic versatility, P. denitrificans has been used in this
study as a model organism to investigate the role of environmental heterogeneity
in maintaining metabolic flexibility in bacterial communities. The hypotheses
underlying this study are:
- Metabolic flexibility is maintained in situ by environmental heterogeneity
and, specifically:
- Under constant environmental conditions the metabolic flexibility of the
generalist P. denitrificans will be lost by accumulation of mutations in
unused genes.
Chemostat cultures under constant aerobic conditions revealed how after
~150 generations genetic loci not in use under aerobic conditions (in particular
nirS and nosZ) are subjected to a lower selective pressure that leads to a higher
genetic polymorphism in the population.
The phenotypic analysis of the population resulting from the same
chemostat culture showed a lower specific growth rate and a higher yield
compared to the ancestor population, suggesting a deactivation of concomitant
denitrification and aerobic respiration (Robertson et al., 1988). Furthermore, the
resulting population shows a down-regulation of expression of all three
denitrification genes tested and a lower production of nitrous oxide (N2O).
When cultured in batch cultures for a long period of time under aerobic
conditions, P. denitrificans shows a similar adaptative response. Four parallel
populations, originated from a common ancestor and propagated aerobically for
more than 500 generations undertook some important communal genotypic and
phenotypic changes that suggested that P. denitrificans repetitively adapts to
constant environmental conditions by losing its characteristic metabolic
flexibility.
By following the first steps of loss of metabolic flexibility as an adaptative
response to novel environmental conditions in a generalist model as P.
denitrificans we could empirically witness the important role of the environment
on bacterial evolution and speciation.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Denitrifying bacteria, Microbial metabolism, Bacteria -- Evolution, Bacterial genetics
Official Date:	November 2010
Dates:	Date Event November 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Biological Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Purdy, Kevin
Extent:	xv, 282 leaves : ill., charts
Language:	eng

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