Abstract
Population heterogeneity occurring in industrial microbial bioprocesses
is regarded as a putative effector causing performance loss in large
scale. While the existence of subpopulations is a commonly accepted
fact, their appearance and impact on process performance still remains
rather unclear. During cell cycling, distinct subpopulations differing
in cell division state and DNA content appear which contribute
individually to the efficiency of the bioprocess. To identify stressed
or impaired subpopulations, we analyzed the interplay of growth rate,
cell cycle and phenotypic profile of subpopulations by using flow
cytometry and cell sorting in conjunction with mass spectrometry based
global proteomics. Adjusting distinct growth rates in chemostats with
the model strain Pseudomonas putida KT2440, cells were differentiated by
DNA content reflecting different cell cycle stages. The proteome of
separated subpopulations at given growth rates was found to be highly
similar, while different growth rates caused major changes of the
protein inventory with respect to e.g. carbon storage, motility, lipid
metabolism and the translational machinery.
In conclusion, cells in various cell cycle stages at the same growth
rate were found to have similar to identical proteome profiles showing
no significant population heterogeneity on the proteome level. In
contrast, the growth rate clearly determines the protein composition and
therefore the metabolic strategy of the cells.
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