---
_id: '820'
abstract:
- lang: eng
text: "The lac operon is a classic model system for bacterial gene regulation, and
has been studied extensively in E. coli, a classic model organism. However, not
much is known about E. coli’s ecology and life outside the laboratory, in particular
in soil and water environments. The natural diversity of the lac operon outside
the laboratory, its role in the ecology of E. coli and the selection pressures
it is exposed to, are similarly unknown.\r\nIn Chapter Two of this thesis, I explore
the genetic diversity, phylogenetic history and signatures of selection of the
lac operon across 20 natural isolates of E. coli and divergent clades of Escherichia.
I found that complete lac operons were present in all isolates examined, which
in all but one case were functional. The lac operon phylogeny conformed to the
whole-genome phylogeny of the divergent Escherichia clades, which excludes horizontal
gene transfer as an explanation for the presence of functional lac operons in
these clades. All lac operon genes showed a signature of purifying selection;
this signature was strongest for the lacY gene. Lac operon genes of human and
environmental isolates showed similar signatures of selection, except the lacZ
gene, which showed a stronger signature of selection in environmental isolates.\r\nIn
Chapter Three, I try to identify the natural genetic variation relevant for phenotype
and fitness in the lac operon, comparing growth rate on lactose and LacZ activity
of the lac operons of these wild isolates in a common genetic background. Sequence
variation in the lac promoter region, upstream of the -10 and -35 RNA polymerase
binding motif, predicted variation in LacZ activity at full induction, using a
thermodynamic model of polymerase binding (Tugrul, 2016). However, neither variation
in LacZ activity, nor RNA polymerase binding predicted by the model correlated
with variation in growth rate. Lac operons of human and environmental isolates
did not differ systematically in either growth rate on lactose or LacZ protein
activity, suggesting that these lac operons have been exposed to similar selection
pressures. We thus have no evidence that the phenotypic variation we measured
is relevant for fitness.\r\nTo start assessing the effect of genomic background
on the growth phenotype conferred by the lac operon, I compared growth on minimal
medium with lactose between lac operon constructs and the corresponding original
isolates, I found that maximal growth rate was determined by genomic background,
with almost all backgrounds conferring higher growth rates than lab strain K12
MG1655. However, I found no evidence that the lactose concentration at which growth
was half maximal depended on genomic background."
acknowledgement: "ERC H2020 programme (grant agreement no. 648440)\r\nThanks to Jon
Bollback for giving me the chance to do this work, for sharing the ideas that lay
at the basis of this work, for his honesty and openness, showing himself to me as
a person and not just as a boss. Thanks to Nick Barton for his guidance at the last
stage, reading and commenting extensively on several versions of this manuscript,
and for his encouragement; thanks to both Jon and Nick for their kindness and patience.
Thanks to Erik van Nimwegen and Calin Guet for their time and willingness to be
in my thesis committee, and to Erik van Nimwegen especially for agreeing to enter
my thesis committee at the last moment, and for his very sharp, helpful and relevant
comments during and after the defense. Thanks to my collaborators and discussion
partners: Anne Kupczok, for her guidance, ideas and discussions during the construction
of the manuscript of Chapter Two, and her comments on the manuscript; Georg Rieckh
for making me aware of the issue of parameter identifiability, suggesting how to
solve it, and for his unfortunate idea to start the plasmid enterprise in the first
place; Murat Tugrul for sharing his model, for his enthusiasm, and his comments
on Chapter Three; Srdjan Sarikas for his collaboration on the Monod model fitting,
fast forwarding the analysis to turbo speed and making beautiful figures, and making
the discussion fun on top of it all; Vanessa Barone for her last minute comments,
especially on Chapter Three, providing a sharp and very helpful experimentalist
perspective at the last moment; Maros Pleska and Marjon de Vos for their comments
on the manuscript of Chapter Two; Gasper Tkacik for his crucial input on the relation
between growth rate and lactose concentration; Bor Kavcic for his input on growth
rate modeling and error propagation. Thanks to the Bollback, Bollenbach, Barton,
Guet and Tkacik group members for both pro- viding an inspiring and supportive scientific
environment to work in, as well as a lot of warmth and colour to everyday life.
And thanks to the friends I found here, to the people who were there for me and
to the people who changed my life, making it stranger and more beautiful than I
could have imagined, Maros, Vanessa, Tade, Suzi, Andrej, Peter, Tiago, Kristof,
Karin, Irene, Misha, Mato, Guillaume and Zanin. "
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Fabienne
full_name: Jesse, Fabienne
id: 4C8C26A4-F248-11E8-B48F-1D18A9856A87
last_name: Jesse
citation:
ama: Jesse F. The lac operon in the wild. 2017. doi:10.15479/AT:ISTA:th_857
apa: Jesse, F. (2017). The lac operon in the wild. Institute of Science and
Technology Austria. https://doi.org/10.15479/AT:ISTA:th_857
chicago: Jesse, Fabienne. “The Lac Operon in the Wild.” Institute of Science and
Technology Austria, 2017. https://doi.org/10.15479/AT:ISTA:th_857.
ieee: F. Jesse, “The lac operon in the wild,” Institute of Science and Technology
Austria, 2017.
ista: Jesse F. 2017. The lac operon in the wild. Institute of Science and Technology
Austria.
mla: Jesse, Fabienne. The Lac Operon in the Wild. Institute of Science and
Technology Austria, 2017, doi:10.15479/AT:ISTA:th_857.
short: F. Jesse, The Lac Operon in the Wild, Institute of Science and Technology
Austria, 2017.
date_created: 2018-12-11T11:48:41Z
date_published: 2017-08-25T00:00:00Z
date_updated: 2023-09-07T12:01:21Z
day: '25'
ddc:
- '576'
- '577'
- '579'
degree_awarded: PhD
department:
- _id: JoBo
doi: 10.15479/AT:ISTA:th_857
ec_funded: 1
file:
- access_level: open_access
checksum: c62257a7bff0c5f39e1abffc6bfcca5c
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date_created: 2018-12-12T10:17:00Z
date_updated: 2020-07-14T12:48:10Z
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content_type: application/x-tex
creator: dernst
date_created: 2019-04-05T08:51:59Z
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file_name: 2017_thesis_Jesse_source.tex
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language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
month: '08'
oa: 1
oa_version: Published Version
page: '87'
project:
- _id: 2578D616-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '648440'
name: Selective Barriers to Horizontal Gene Transfer
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
publist_id: '6829'
pubrep_id: '857'
status: public
supervisor:
- first_name: Jonathan P
full_name: Bollback, Jonathan P
id: 2C6FA9CC-F248-11E8-B48F-1D18A9856A87
last_name: Bollback
orcid: 0000-0002-4624-4612
title: The lac operon in the wild
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2017'
...
---
_id: '6291'
abstract:
- lang: eng
text: Bacteria and their pathogens – phages – are the most abundant living entities
on Earth. Throughout their coevolution, bacteria have evolved multiple immune
systems to overcome the ubiquitous threat from the phages. Although the molecu-
lar details of these immune systems’ functions are relatively well understood,
their epidemiological consequences for the phage-bacterial communities have been
largely neglected. In this thesis we employed both experimental and theoretical
methods to explore whether herd and social immunity may arise in bacterial popu-
lations. Using our experimental system consisting of Escherichia coli strains
with a CRISPR based immunity to the T7 phage we show that herd immunity arises
in phage-bacterial communities and that it is accentuated when the populations
are spatially structured. By fitting a mathematical model, we inferred expressions
for the herd immunity threshold and the velocity of spread of a phage epidemic
in partially resistant bacterial populations, which both depend on the bacterial
growth rate, phage burst size and phage latent period. We also investigated the
poten- tial for social immunity in Streptococcus thermophilus and its phage 2972
using a bioinformatic analysis of potentially coding short open reading frames
with a signalling signature, encoded within the CRISPR associated genes. Subsequently,
we tested one identified potentially signalling peptide and found that its addition
to a phage-challenged culture increases probability of survival of bacteria two
fold, although the results were only marginally significant. Together, these results
demonstrate that the ubiquitous arms races between bacteria and phages have further
consequences at the level of the population.
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Pavel
full_name: Payne, Pavel
id: 35F78294-F248-11E8-B48F-1D18A9856A87
last_name: Payne
orcid: 0000-0002-2711-9453
citation:
ama: Payne P. Bacterial herd and social immunity to phages. 2017.
apa: Payne, P. (2017). Bacterial herd and social immunity to phages. Institute
of Science and Technology Austria.
chicago: Payne, Pavel. “Bacterial Herd and Social Immunity to Phages.” Institute
of Science and Technology Austria, 2017.
ieee: P. Payne, “Bacterial herd and social immunity to phages,” Institute of Science
and Technology Austria, 2017.
ista: Payne P. 2017. Bacterial herd and social immunity to phages. Institute of
Science and Technology Austria.
mla: Payne, Pavel. Bacterial Herd and Social Immunity to Phages. Institute
of Science and Technology Austria, 2017.
short: P. Payne, Bacterial Herd and Social Immunity to Phages, Institute of Science
and Technology Austria, 2017.
date_created: 2019-04-09T15:16:45Z
date_published: 2017-02-01T00:00:00Z
date_updated: 2023-09-07T12:00:00Z
day: '01'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: NiBa
- _id: JoBo
file:
- access_level: closed
checksum: a0fc5c26a89c0ea759947ffba87d0d8f
content_type: application/pdf
creator: dernst
date_created: 2019-04-09T15:15:32Z
date_updated: 2020-07-14T12:47:27Z
file_id: '6292'
file_name: thesis_pavel_payne_final_w_signature_page.pdf
file_size: 3025175
relation: main_file
- access_level: open_access
checksum: af531e921a7f64a9e0af4cd8783b2226
content_type: application/pdf
creator: dernst
date_created: 2021-02-22T13:45:59Z
date_updated: 2021-02-22T13:45:59Z
file_id: '9187'
file_name: 2017_Payne_Thesis.pdf
file_size: 3111536
relation: main_file
success: 1
file_date_updated: 2021-02-22T13:45:59Z
has_accepted_license: '1'
language:
- iso: eng
month: '02'
oa: 1
oa_version: Published Version
page: '83'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
status: public
supervisor:
- first_name: Jonathan P
full_name: Bollback, Jonathan P
id: 2C6FA9CC-F248-11E8-B48F-1D18A9856A87
last_name: Bollback
orcid: 0000-0002-4624-4612
- first_name: Nicholas H
full_name: Barton, Nicholas H
id: 4880FE40-F248-11E8-B48F-1D18A9856A87
last_name: Barton
orcid: 0000-0002-8548-5240
title: Bacterial herd and social immunity to phages
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2017'
...
---
_id: '1121'
abstract:
- lang: eng
text: "Horizontal gene transfer (HGT), the lateral acquisition of genes across existing
species\r\nboundaries, is a major evolutionary force shaping microbial genomes
that facilitates\r\nadaptation to new environments as well as resistance to antimicrobial
drugs. As such,\r\nunderstanding the mechanisms and constraints that determine
the outcomes of HGT\r\nevents is crucial to understand the dynamics of HGT and
to design better strategies to\r\novercome the challenges that originate from
it.\r\nFollowing the insertion and expression of a newly transferred gene, the
success of an\r\nHGT event will depend on the fitness effect it has on the recipient
(host) cell. Therefore,\r\npredicting the impact of HGT on the genetic composition
of a population critically\r\ndepends on the distribution of fitness effects (DFE)
of horizontally transferred genes.\r\nHowever, to date, we have little knowledge
of the DFE of newly transferred genes, and\r\nhence little is known about the
shape and scale of this distribution.\r\nIt is particularly important to better
understand the selective barriers that determine\r\nthe fitness effects of newly
transferred genes. In spite of substantial bioinformatics\r\nefforts to identify
horizontally transferred genes and selective barriers, a systematic\r\nexperimental
approach to elucidate the roles of different selective barriers in defining\r\nthe
fate of a transfer event has largely been absent. Similarly, although the fact
that\r\nenvironment might alter the fitness effect of a horizontally transferred
gene may seem\r\nobvious, little attention has been given to it in a systematic
experimental manner.\r\nIn this study, we developed a systematic experimental
approach that consists of\r\ntransferring 44 arbitrarily selected Salmonella typhimurium
orthologous genes into an\r\nEscherichia coli host, and estimating the fitness
effects of these transferred genes at a\r\nconstant expression level by performing
competition assays against the wild type.\r\nIn chapter 2, we performed one-to-one
competition assays between a mutant strain\r\ncarrying a transferred gene and
the wild type strain. By using flow cytometry we\r\nestimated selection coefficients
for the transferred genes with a precision level of 10-3,and obtained the DFE
of horizontally transferred genes. We then investigated if these\r\nfitness effects
could be predicted by any of the intrinsic properties of the genes, namely,\r\nfunctional
category, degree of complexity (protein-protein interactions), GC content,\r\ncodon
usage and length. Our analyses revealed that the functional category and length\r\nof
the genes act as potential selective barriers. Finally, using the same procedure
with\r\nthe endogenous E. coli orthologs of these 44 genes, we demonstrated that
gene dosage is\r\nthe most prominent selective barrier to HGT.\r\nIn chapter 3,
using the same set of genes we investigated the role of environment on the\r\nsuccess
of HGT events. Under six different environments with different levels of stress\r\nwe
performed more complex competition assays, where we mixed all 44 mutant strains\r\ncarrying
transferred genes with the wild type strain. To estimate the fitness effects of\r\ngenes
relative to wild type we used next generation sequencing. We found that the DFEs\r\nof
horizontally transferred genes are highly dependent on the environment, with\r\nabundant
gene–by-environment interactions. Furthermore, we demonstrated a\r\nrelationship
between average fitness effect of a gene across all environments and its\r\nenvironmental
variance, and thus its predictability. Finally, in spite of the fitness effects\r\nof
genes being highly environment-dependent, we still observed a common shape of\r\nDFEs
across all tested environments."
acknowledgement: "This study was supported by European Research Council ERC CoG 2014
– EVOLHGT,\r\nunder the grant number 648440.\r\n\r\nIt is a pleasure to thank the
many people who made this thesis possible.\r\nI would like to first thank my advisor,
Jonathan Paul Bollback for providing guidance in\r\nall aspects of my life, encouragement,
sound advice, and good teaching over the last six\r\nyears.\r\nI would also like
to thank the members of my dissertation committee – Călin C. Guet\r\nand John F.
Baines – not only for their time and guidance, but for their intellectual\r\ncontributions
to my development as a scientist.\r\nI would like to thank Flavia Gama and Rodrigo
Redondo who have taught me all the\r\nskills in the laboratory with their graciousness
and friendship. Also special thanks to\r\nBollback group for their support and for
providing a stimulating and fun environment:\r\nIsabella Tomanek, Fabienne Jesse,
Claudia Igler, and Pavel Payne.\r\nJerneja Beslagic is not only an amazing assistant,
she also has a smile brighter and\r\nwarmer than the sunshine, bringing happiness
to every moment. Always keep your light\r\nNeja, I will miss our invaluable chatters
a lot."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Hande
full_name: Acar, Hande
id: 2DDF136A-F248-11E8-B48F-1D18A9856A87
last_name: Acar
orcid: 0000-0003-1986-9753
citation:
ama: Acar H. Selective barriers to horizontal gene transfer. 2016.
apa: Acar, H. (2016). Selective barriers to horizontal gene transfer. Institute
of Science and Technology Austria.
chicago: Acar, Hande. “Selective Barriers to Horizontal Gene Transfer.” Institute
of Science and Technology Austria, 2016.
ieee: H. Acar, “Selective barriers to horizontal gene transfer,” Institute of Science
and Technology Austria, 2016.
ista: Acar H. 2016. Selective barriers to horizontal gene transfer. Institute of
Science and Technology Austria.
mla: Acar, Hande. Selective Barriers to Horizontal Gene Transfer. Institute
of Science and Technology Austria, 2016.
short: H. Acar, Selective Barriers to Horizontal Gene Transfer, Institute of Science
and Technology Austria, 2016.
date_created: 2018-12-11T11:50:16Z
date_published: 2016-12-01T00:00:00Z
date_updated: 2023-09-07T11:42:26Z
day: '01'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: JoBo
ec_funded: 1
file:
- access_level: closed
checksum: 94bbbc754c36115bf37f8fc11fad43c4
content_type: application/pdf
creator: dernst
date_created: 2019-08-13T11:17:50Z
date_updated: 2019-08-13T11:17:50Z
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creator: dernst
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success: 1
file_date_updated: 2021-02-22T11:51:13Z
has_accepted_license: '1'
language:
- iso: eng
month: '12'
oa: 1
oa_version: Published Version
page: '75'
project:
- _id: 2578D616-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '648440'
name: Selective Barriers to Horizontal Gene Transfer
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
publist_id: '6239'
status: public
supervisor:
- first_name: Jonathan P
full_name: Bollback, Jonathan P
id: 2C6FA9CC-F248-11E8-B48F-1D18A9856A87
last_name: Bollback
orcid: 0000-0002-4624-4612
title: Selective barriers to horizontal gene transfer
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2016'
...