Influence of Complex Nutrient Source on Growth of and Curvacin A Production by Sausage Isolate
            <i>Lactobacillus curvatus</i>
            LTH 1174

Flow cytometry (FC) has been introduced to characterize and to assess the physiological states of microorganisms in conjunction with the classical plate-counting method. To show the applicability of the technique, in particular for the development of kinetic models, pure culture fermentation experiments were followed over time, using both prokaryotic (Lactobacillus hilgardii) and eukaryotic (Saccharomyces cerevisiae) microorganisms growing in standard culture media (MRS and YPD). The differences observed between the active and viable cells determined by FC and CFU, respectively, allowed us to determine that a large number of cells were in a viable but nonculturable (VBNC) state, which resulted in a subpopulation much larger than the damaged-cell (double-stained) subpopulation. Finally, the determination of the evolution of viable, the VBNC, and the dead cells allowed us to develop a segregated kinetic model to describe the yeast and the bacteria population dynamics and glucose consumption in batch cultures. This model, more complete than that which is traditionally used, based only on viable cell measurements, describes better the behavior and the functionality of the cultures, giving a deeper knowledge in real time about the status and the course of the bioprocesses.

Section: Resultsmentioning

confidence: 99%

Application of Flow Cytometry to Segregated Kinetic Modeling Based on the Physiological States of Microorganisms

Quirós

Herrero

Garcı́a

et al. 2007

“…The max , , and K d of LIS R were determined independently; the other parameters were set as for the Listeria monoculture and LIS S . Upon repetition, the coefficients of variation of the parameters are generally lower than 10%, with the exception of k inact for which 25% can be observed (13,17,(20)(21)(22).…”

mentioning

confidence: 99%

Modeling Bacteriocin Resistance and Inactivation of Listeria innocua LMG 13568 by Lactobacillus sakei CTC 494 under Sausage Fermentation Conditions

Leroy

Lievens

Vuyst

2005

Self Cite

In mixed cultures, bacteriocin production by the sausage isolate Lactobacillus sakei CTC 494 rapidly inactivated sensitive Listeria innocua LMG 13568 cells, even at low bacteriocin activity levels. A small fraction of the listerial population was bacteriocin resistant. However, sausage fermentation conditions inhibited regrowth of resistant cells.Lactobacillus sakei CTC 494, producer of the bacteriocin sakacin K, inhibits Listeria spp. during sausage fermentation (12). Bacteriocins are small peptides or proteins with antibacterial activity (5). The resistance of the target strain may compromise bacteriocin efficacy (6,7,11,23). This study focuses on in vitro interaction kinetics between Lactobacillus sakei CTC 494 and Listeria innocua LMG 13568 and on listerial sakacin K resistance as a function of key sausage fermentation conditions (temperature, pH, salt, and nitrite) that may affect both bacteriocin production (13,14,17,21,22) and activity (9, 10). Listeria innocua, being more competitive (2) and resistant to sakacin K (12) than Listeria monocytogenes, offered a worst-case approach. An industrial, nonbacteriocinogenic Lactobacillus sakei I strain was used for comparison.Fermentations were done in a Biostat C fermentor (B. Braun Biotech International, Melsungen, Germany) in 10 liters of customized MRS medium (3). Modifications involved the addition of 40 g of sodium chloride per liter (VWR International, Darmstadt, Germany) and 200 ppm of sodium nitrite (VWR International). Some experiments, being highly reproducible (13, 17, 21-23), were repeated. Culture preparation, fermentor setup, and on-line control were as described previously (13). Bacteriocin-free Lactobacillus sakei CTC 494 inocula (10%) were prepared in 100 ml MRS medium (Oxoid, Basingstoke, United Kingdom) at 37°C overnight, since no sakacin K is produced above 33°C (13).Listeria innocua LMG 13568 inocula (1%) were prepared in 100 ml of brain heart infusion (Oxoid) at 30°C overnight. Lactobacilli were enumerated on MRS agar (Oxoid) after incubation at 30°C; Listeria innocua LMG 13568 did not grow on this medium during the first days. Listeriae were enumerated on Palcam agar (Oxoid) after incubation at 30°C. The standard deviation on both measurements equaled 0.07 log CFU ml Ϫ1 . Bacteriocin activity in the cell-free culture supernatant was estimated by a twofold critical dilution method (4, 13). A variation coefficient of 20% on bacteriocin measurement occurs, but activity curves are reproducible (13,14). Salt and nitrite did not interfere with the assay (14).The bacterial population was regarded as an association of subpopulations (in CFU per ml) of Lactobacillus sakei CTC 494 (LAC) and both bacteriocin-sensitive (LIS S ) and bacteriocin-resistant (LIS R ) Listeria innocua LMG 13568. The equations used for the model shown in Table 1 (13-15) were solved by Euler integration in Microsoft Excel by minimizing residual sums of squares. The max , , and K d of LIS R were determined independently; the other parameters were set as for the Listeria monocult...

“…Compared with the results of Lobas et al and Kanari et al, the period of the fermentation process was shortened, and higher gellan gum production (14.75 g liter Ϫ1 ) was obtained in a 30-liter fermentor under optimal conditions. Various mathematical models have been proposed for the kinetics of microbial growth and product formation with other strains (2,6,31). For extracellular polysaccharide production, the logistic and Luedeking-Piret equations, developed originally for the formation of lactic acid (20), have been proposed to describe the time courses of product formation, substrate consumption, and cell growth (7,18,32), because those models are substantially more accurate and convenient than other models that have been reported.…”

mentioning

confidence: 99%

Modeling for Gellan Gum Production by Sphingomonas paucimobilis ATCC 31461 in a Simplified Medium

Wang

Yuan

et al. 2006

Gellan gum production was carried out by Sphingomonas paucimobilis ATCC 31461 in a simplified medium with a short incubation time, and a kinetic model for understanding, controlling, and optimizing the fermentation process was proposed. The results revealed that glucose was the best carbon source and that the optimal concentration was 30 g liter ؊1 . As for the fermenting parameters, considerably large amounts of gellan gum were yielded by an 8-h-old culture and a 4% inoculum at 200 rpm on a rotary shaker. Under the optimized conditions, the maximum level of gellan gum (14.75 g liter ؊1 ) and the highest conversion efficiency (49.17%) were obtained in a 30-liter fermentor in batch fermentation. Logistic and Luedeking-Piret models were confirmed to provide a good description of gellan gum fermentation, which gave some support for the study of gellan gum fermentation kinetics. Additionally, this study is the first demonstration that gellan gum production is largely growth associated by analysis of kinetics in its batch fermentation process. Based on model prediction, higher gellan gum production (17.71 g liter ؊1 ) and higher conversion efficiency (57.12%) were obtained in fed-batch fermentation at the same total glucose concentration (30 g liter ؊1 ).