Abstract EANA2025-113

Microbial growth depends on environmental conditions and these are often far from
optimum. Different factors can affect the growth of microorganisms such as nutrient
availability, temperature, pH, salinity, etc. Nevertheless, most studies have been carried
out exclusively under optimum growth conditions (González & Aranda, 2023). As a
consequence, our knowledge on the behavior of microorganisms, and specifically of
extremophiles, under changing conditions is quite limited.
In this study we will analyze the functional response of the extreme thermophilic bacterium
Thermus thermophilus through comparative analysis of gene expression at different
growth rates, from optimum growth (doubling time, approx. 30 min) to near-zero growth
rates (doubling time, approx 66 days). To obtain procariotic cells at near-zero growth rate
we used a system called retentostat, a modification of a continous culture system
(chemostat) in which cells return to the vessel so that an increasing numbers of cells must
share the same nutrient resources.
We analyzed different parameters such as membrane potential and ARN/ADN ratio using
fluorescent indicators, DiOC2(3) and SYTO13 respectively. Global gene expression was
analized by RNA-seq (Illumina). Cells of Thermus thermophilus maintain activity and cell
integrity over a very broad range of growth rates and these cells functional response will
be presented in this study.

Keywords: Thermophile, nutrient availability, near-zero growth, retentostat, gene
expression, transcriptomics.

References
González, J. M., & Aranda, B. (2023). Microbial growth under limiting conditions – future perspectives. Microorganisms 11, 1641. doi: 10.3390/microorganisms11071641