control ecoli growth cell density

control ecoli growth cell density - Microbiol Res(2002 157...

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The transition from the exponential to the stationary phase of Escherichia coli cultures has been investigated regarding nutrient availability. This analysis strongly suggests that the declining of the cell division rate is not caused by mere nutrient limitation but also by an immediate sensing of cell concentration. In addition, both the growth rate and the final biomass achieved by a batch culture can be manipulated by altering its density during the early exponential phase. This result, which has been confirmed by using different experi- mental approaches, supports the hypothesis that the E. coli quorum sensing is not only determined by the release of soluble cell-to-cell communicators. Cell-associated sensing elements might also be involved in modulating the bacterial growth even in the presence of non-limiting (although declin- ing) nutrient concentrations, thus promoting their economical utilisation in dense populations. Key words: quorum sensing – growth rate – autoinducer – cell density – Escherichia coli Introduction Acid production by incomplete oxidation of the carbon sources is often observed in Escherichia coli cultures even when promoting aerobic conditions (Hoffmann et al. 2000). The presence of undesired anaerobic microenvironments, especially at high cell densities, conduces to media acidification and consequent growth inhibition (Nakano et al. 1997). On the other hand, it is known that the maximal biomass concentration reached by a culture is defined by nutrient availability, since the overcoming of nutrient limitation in feed-batch cultures by the controlled nutrient addition permits to achieve progressively higher cell concentrations (Korz et al. 1995; Riesenberg and Guthke 1999). Therefore, both nutrient limitation and acid formation are seen as impor- tant regulators of bacterial growth and cell density in laboratory cultures. Recently, the identification of the bacterial quorum sensing through the release of soluble communicator molecules has revealed a more sophisti- cated mechanism that allows intercellular communica- tion and that can contribute to regulate cell division and density (Whiters and Nordstrom 1998; Hussain et al. 1998). Although this mechanism was initially reported for symbiotic and pathogenic bacteria in natural com- munities (Fuqua et al. 1996), cell density and stress- associated conditions of cultured, non-pathogenic Sal- monella typhimurium and Escherichia coli cells might be also communicated by this mechanism (Surette and Bassler 1998; DeLisa et al. 2001a). For these species, the autoinducer AI-2, which is released to the culture media during the exponential phase, has been identified as responsible for media conditioning and quorum sens- ing (Surette et al. 1999). It is noteworthy that AI-2 activ- ity, despite initially found in cultures growing in Luria Bertani media (LB) supplemented with glucose but not the absence of this sugar (Hussain et al. 1998), it has been also identified as responsible for cell-to-cell com- 0944-5013/02/157/04-257 $15.00/0 Microbiol. Res. 157 (2002) 4 257 Microbiol. Res. (2002) 157, 257–265 http://www.urbanfischer.de/journals/microbiolres
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control ecoli growth cell density - Microbiol Res(2002 157...

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