Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

Record number 456526
Title Physiological and molecular adaptations of Lactococcus lactis to near-zero growth conditions
Author(s) Ercan, O.
Source Wageningen University. Promotor(en): Michiel Kleerebezem, co-promotor(en): Eddy Smid. - Wageningen : Wageningen University - ISBN 9789462570719 - 206
Department(s) Microbiology
Host-Microbe Interactomics
Food Microbiology
VLAG
Publication type Dissertation, internally prepared
Publication year 2014
Keyword(s) lactococcus lactis - adaptatiefysiologie - voedselmicrobiologie - groeitempo - groeispanning - transcriptomica - metabolomica - lactococcus lactis - adaptation physiology - food microbiology - growth rate - growth stress - transcriptomics - metabolomics
Categories Food Microbiology
Abstract

Lactococcus lactis is an important lactic acid bacteria (LAB) species that is used for the manufacture of dairy products, such as cheese, buttermilk, and other fermented products. The predominant function of this bacterium in dairy fermentation is the production of lactic acid, as its major fermentation end-product that contributes to preservation and microbial safety of the product. Moreover, L. lactis is frequently encountered in natural ecosystems such as in (rotting) plant material.

Due to restricted energy source availability, natural microbial communities commonly live in a situation that can be characterized as ‘hunger’, which is different from strict nutrient-starvation. As a consequence, environmental microbes commonly grow at very low-growth rates as compared to laboratory cultures. Analogously, microorganisms can experience such nutrient-poor conditions in diverse industrial fermentation applications. For example, LAB encounter extreme low or no energy source availability during the extended ripening process of cheeses or dry sausages, which can take months. Despite these harsh environmental conditions, many LAB are able to remain viable in these processes for months and sustain a low-level metabolic activity, which plays an important role in their contribution to flavor and aroma formation in the product matrix.

In this thesis, the quantitative physiology of L. lactis at near-zero specific growth rates was studies, employing both metabolic and genome-wide transcriptome studies in an experimental set-up of carbon-limited retentostat cultivation. Chapter 2 describes how retentostat cultivation enables uncoupling of growth and non-growth related processes in L. lactis, allowing the quantitative analysis of the physiological adaptations of this bacterium to near-zero growth rates. In chapter 3, transcriptome and metabolome analyses were integrated to understand the molecular adaptation of L. lactis to near-zero specific growth rate, and expand the studies in chapter 2 towards gene regulations patterns that play a profound role in zero-growth adaptation. Chapter 4 describes the enhanced robustness to several stress conditions of L. lactis after its adaptation to extremely low-specific growth rate by carbon-limited retentostat cultivation. In this chapter correlations were modelled that quantitatively and accurately describe the relationships between growth-rate, stress-robustness, and stress-gene expression levels, revealing correlation coefficients for each of the varieties involved. Chapter 5 evaluates the distinction between the transcriptome responses to extended carbon-limited growth and severe starvation conditions, where the latter condition was elicited by switching off the medium supply of the retentostat cultures described in chapter 1. Chapter 6 highlights the comparison of the physiological and molecular adaptations of industrially important microorganisms towards carbon-limited retentostat conditions. In conclusion, this thesis describes the quantitative physiological, metabolic, and genome-wide transcriptional adaptations of L. lactis at near-zero specific growth rates induced by carbon source limited retentostat cultivation, and compares these molecular adaptations to those elicited by strict carbon-starvation conditions.

Comments
There are no comments yet. You can post the first one!
Post a comment
 
Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.