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The use of multi‐parameter flow cytometry to study the impact of limiting substrate, agitation intensity, and dilution rate on cell aggregation during Bacillus licheniformis CCMI 1034 aerobic continuous culture fermentations
Author(s) -
da Silva Teresa Lopes,
Reis Alberto,
Kent Christopher A.,
Roseiro J. Carlos,
Hewitt Christopher J.
Publication year - 2005
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.20622
Subject(s) - dilution , bacillus licheniformis , chemistry , chemostat , substrate (aquarium) , chromatography , biofilm , sonication , extracellular polymeric substance , biophysics , chemical engineering , bacteria , biology , bacillus subtilis , ecology , physics , genetics , thermodynamics , engineering
Abstract The main objective of this work was to establish those factors either physical (power input) or chemical (limiting substrate or dilution rate) that enhance cell aggregation (biofilm or floc formation) and cell physiological state during aerobic continuous cultures of Bacillus licheniformis. Glucose‐limited steady‐state continuous cultures growing at a dilution rate between 0.64 and 0.87/h and 1,000 rpm (mean specific energy dissipation rate ( $\bar {\varepsilon} _T$ ) = 6.5 W/kg), led to the formation of a thin biofilm on the vessel wall characterized by the presence of a high proportion of healthy cells in the broth (after aggregate disruption by sonication) defined as having intact polarized cytoplasmic membranes. An increased $\bar {\varepsilon} _T$ (from 6.5 W/kg to 38 W/kg) was found to hinder cell aggregation under carbon limitation. The carbon recovery calculated from glucose indicated that additional extracellular polymer was being produced at dilution rates >0.87/h. B. licheniformis growth under nitrogen limitation led to floc formation which increased in size with dilution rate. Counter‐intuitively the flocs became more substantial with an increase in $\bar {\varepsilon} _T$ from 6.5 W/kg to 38 W/kg under nitrogen limitation. Indeed the best culture conditions for enhanced metabolically active cell aggregate formation was under nitrogen limitation at $\bar {\varepsilon} _T$ = 6.5 W/kg (leading to floc formation), and under carbon limitation at a dilution rate of between 0.64 and 0.87/h, at $\bar {\varepsilon} _T$ = 6.5 W/kg (leading to vessel wall biofilm formation). This information could be used to optimize culture conditions for improved cell aggregation and hence biomass separation, during thermophilic aerobic bioremediation processes. © 2005 Wiley Periodicals, Inc.