Electrooptical Determination of Polarizability for On-Line Viability and Vitality Quantification of Lactobacillus plantarum Cultures

Abstract

The rapid assessment of cell viability is crucial for process optimization, e.g., during media selection, determination of optimal environmental growth conditions and for quality control. In the present study, the cells' electric anisotropy of polarizability (AP) as well as the mean cell length in Lactobacillus plantarum batch and fed-batch fermentations were monitored with electrooptical measurements coupled to fully automated sample preparation. It was examined, whether this measurement can be related to the cells' metabolic activity, and thus represents a suitable process analytical technology. It is demonstrated that the AP is an early indicator to distinguish between suitable and unsuitable growth conditions in case of a poor energy regeneration or cell membrane defects in L. plantarum batch and fed-batch cultivations. It was shown that the applied method allowed the monitoring of physiological and morphological changes of cells in various growth phases in response to a low pH-value, substrate concentration changes, temperature alterations, exposure to air and nutrient limitation. An optimal range for growth in batch mode was achieved, if the AP remained above 25·10−28 F·m2 and the mean cell length at ~2.5 μm. It was further investigated, in which way the AP develops after freeze-drying of samples, which were taken in different cultivation phases. It was found that the AP increased most rapidly in resuspended samples from the retardation and late stationary phases, while samples from the early stationary phase recovered slowly. Electrooptical measurements provide valuable information about the physiologic and morphologic state of L. plantarum cells, e.g., when applied as starter cultures or as probiotic compounds.

Monitoring the Physiological State in the Dark Fermentation of Maize/Grass Silage Using Flow Cytometry and Electrooptic Polarizability Measurements

“…FDPA measurements have previously been used as an indicator of the PS of cell suspensions, although most of the cases pertain to monocultures. For instance, FDPA levels have been used to monitor the PS of aerobic Escherichia coli cultivations at different temperatures [33], to follow the acidogenicsolventogenic metabolic shift in Clostridium acetobutylicum [34] and to investigate the performance of Lactobacillus plantarum under different stress conditions, such as non-pH-regulated conditions, different substrate concentrations, nutrient limitations, and suboptimal cultivation temperature [35]. Recently, the applicability of FDPA to monitor the PS of mixed cultures has been tested; Habermann et al [36] measured the FDPA of different AD systems using corn silage as feedstock and obtained decreasing FDPA values under acidification stress, suggesting the PS of the biotic phase in AD systems and sewage sludges can also be monitored through FDPA measurements.…”