Transient self‐inhibition of the growth of Lactobacillus delbrueckii subsp. bulgaricus in a pH‐regulated fermentor

Abstract

An industrial strain of Lactobacillus delbrueckii subsp. bulgaricus was grown in a synthetic medium on lactose as carbon substrate, in a pH-regulated fermentor. Growth proceeded in two distinct phases separated by a transient stationary phase. Various experimental approaches were used to identify the cause of this growth arrest. Growth experiments in L. bulgaricus culture supernatant fluids collected at different cultivation times in fermentor, and supplemented or not with various nutritional solutions, enabled us to discard the possibility of a nutritional limitation. Tube cultures of L. bulgaricus in medium supplemented with various lactic acid concentrations showed a potential inhibition by this metabolic end product but confirmed that this inhibition was not responsible for the cessation of growth. It was concluded that at least one inhibitory compound was produced during the growth phase of the strain, and this compound disappeared from the medium in the transient stationary phase, enabling the growth to start again later in the culture. Indeed, the stoichiometric analysis of the culture showed, firstly, that unidentified carbon compounds were produced from lactose during growth, which were probably converted in lactic acid during the transient stationary phase and, secondly, that part of the amino acids consumed gave catabolic end products. Finally, bacteriocin-like compounds were not considered to be responsible for this growth arrest.

Enhancement of lactate and succinate formation in adhE or pta-ackA mutants of NADH dehydrogenase-deficient Escherichia coli

“…Lactic acid can be produced at high level (210 g l −1 ) in glucose‐fed batch readers of lactic acid bacteria (Bai et al. 2003) and in pH‐regulated fermentors Lactobacillus bulgaricus Ext 2·215 converted lactose and amino acids in the media to galactose which was excreted to the media and the glucose was converted to lactate in a highly efficient process 1·97 mol mol −1 (Mercade et al. 2003).…”

Article

“…Growth proceeded in two distinct phases separated by a stationary phase of about 20 h. Catabolic activity continued during this stationary phase, albeit at a slower rate, as shown by the slower increase in lactate accumulation. This transient stop of growth was due to the production during the first phase of growth of toxic compounds, which disappeared later in the culture, as proposed by Mercade et al [17].…”

“…Since in a more complex medium the maximal growth rate is higher than in mMPL medium (µ max = 0.94 h -1 in MRS medium, [20]. After this short exponential growth phase, the decrease in the growth rate is considered to be due to an inhibition of anabolism linked to the accumulation of toxic compounds [17]. This growth decrease is accompanied by a slowing-down of the energy-producing catabolic flux converting the sugar into lactic acid, leading to a linear relationship linking the specific rate of ATP production (q ATP ) and the growth rate (Fig.…”

“…bulgaricus / analyse énergétique / catabolisme / anabolisme / coefficient de maintenance Energetic analysis of L. bulgaricus 41 Growth was studied in a synthetic medium [17], modified from the MPL medium described by Chervaux et al [4]. This medium, mMPL medium, was prepared from freshly prepared concentrated solutions, and sterilized by filtration through cellulose nitrate membranes (0.22 µm pore size; Sartorius, Gottingen, Germany) directly into the sterilized (20 min at 121°C) culture vessel.…”

“…bulgaricus cultivated in synthetic media, for which in addition, growth sometimes stops early on the fermentation, before sugar exhaustion [8,9,17,22]. After an exhaustive analysis of all the possible hypotheses to explain this phenotype, Mercade et al [17] proposed that this growth arrest was due to the production of one (or more) toxic compound which was inhibitory against anabolic reactions. These results illustrate that lactic acid is far from being either the only or the major toxic compound produced by lactic acid bacteria.…”