THESIS
2015
x, 132 pages : illustrations (some color) ; 30 cm
Abstract
Escherichia coli, a constitutive microflora of mammalian guts, was originally thought to
be able to live only in the enteric environment. As such, the occurrence of E. coli in water and
food has been used as an indicator of fecal contamination, signaling the possible presence of
fecal pathogens. However, recent reports have indicated that E. coli can be found in many
different types of external habitats (e.g. seawater, sediment and soil) independent of fecal
input. Once exposed to the external environment, E. coli will encounter various stresses that
are not present in the animal hosts. One of immediate impact to E. coli cells entering the
marine environment is the high salinity of seawater. Although the physiology, genetics and
biochemistry of E. coli have been intensively stud...[
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Escherichia coli, a constitutive microflora of mammalian guts, was originally thought to
be able to live only in the enteric environment. As such, the occurrence of E. coli in water and
food has been used as an indicator of fecal contamination, signaling the possible presence of
fecal pathogens. However, recent reports have indicated that E. coli can be found in many
different types of external habitats (e.g. seawater, sediment and soil) independent of fecal
input. Once exposed to the external environment, E. coli will encounter various stresses that
are not present in the animal hosts. One of immediate impact to E. coli cells entering the
marine environment is the high salinity of seawater. Although the physiology, genetics and
biochemistry of E. coli have been intensively studied, it remains unknown that how the
bacterium survive in the external habitats. Previous studies also showed that E. coli exhibited
considerable intraspecies genomic variation, which suggested that the organism was capable
of adapting to different ecological niches. In this study, we investigate the tolerance of 160
fecal E. coli isolates to different salinity levels so as to understand the intra-specific variations
in such stress resistance. After that, we used transcriptomic and proteomic analysis to unravel
the methods that E. coli isolates of different genetic background use to overcome salinity
stress. Different proteomic and transcriptomic profiles of different E. coli isolates revealed
that during growth under different salinity conditions, several metabolic processes were
involved in overcoming osmosis stress. Elucidating the global adaptive response of different
E. coli isolates during exposure to different salinity stress has provided more information of
the physiology of this bacterium when facing high salinity stress of marine environment.
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