Membrane-potential-related fluorescence intensity indicates bacterial injury

PA-1, a novel synthesized pyrrolizidine alkaloid, inhibits the growth of Escherichia coli and Staphylococcus aureus by damaging the cell membrane

In the present study, antimicrobial activity and mode of a novel synthesized pyrrolizidine alkaloid (PA-1) were investigated. PA-1 exhibited predominantly strong antibacterial activity toward six bacteria tested with minimal inhibitory concentration (MIC) values ranging from 0.0039 to 0.025 mg ml(-1). The time-kill assay indicated that PA-1 killed Escherichia coli and Staphylococcus aureus completely at 2MIC (minimum bactericidal concentration) within 8 h. Besides, PA-1-induced death rates of most sensitive strains (E. coli, 97.80% and S. aureus, 96.24%) were analyzed by flow cytometry. A combination of approaches was used to verify the membrane damage of E. coli and S. aureus. Results showed that release of 260 nm absorbing materials quickly increased after PA-1 treatment. PA-1 also rapidly promoted the uptake of crystal violet from 24.52 to 97.12% for E. coli and from 19.68 to 97.63% for S. aureus when the concentrations were changed from MIC to 4MIC. Furthermore, the cellular membrane damages were testified by the significant increase of fluorescence intensity and decrease of membrane potential. Finally, lecithin and phosphate groups were applied to search the possibly targets on the cytoplasmic membrane. Results showed that PA-1 acted on cytoplasmic membrane phospholipids and phosphate groups of S. aureus but not of E. coli. In conclusion, the novel synthesized PA-1 exerted its antibacterial activity by acting on membrane phospholipids and phosphate groups and then damaging the structures of cellular membrane, which finally led to cell death.

Energetics and surface properties of Pseudomonas putida DOT-T1E in a two-phase fermentation system with 1-decanol as second phase

The solvent-tolerant strain Pseudomonas putida DOT-T1E was grown in batch fermentations in a 5-liter bioreactor in the presence and absence of 10% (vol/vol) of the organic solvent 1-decanol. The growth behavior and cellular energetics, such as the cellular ATP content and the energy charge, as well as the cell surface hydrophobicity and charge, were measured in cells growing in the presence and absence of 1-decanol. Although the cells growing in the presence of 1-decanol showed an about 10% reduced growth rate and a 48% reduced growth yield, no significant differences were measured either in the ATP and potassium contents or in the energy charge, indicating that the cells adapted completely at the levels of membrane permeability and energetics. Although the bacteria needed additional energy for adaptation to the presence of the solvent, they were able to maintain or activate electron transport phosphorylation, allowing homeostasis of the ATP level and energy charge in the presence of the solvent, at the price of a reduced growth yield. On the other hand, significantly enhanced cell hydrophobicities and more negative cell surface charges were observed in cells grown in the presence of 1-decanol. Both reactions occurred within about 10 min after the addition of the solvent and were significantly different after killing of the cells with toxic concentrations of HgCl2. This adaptation of the surface properties of the bacterium to the presence of solvents seems to be very similar to previously observed reactions on the level of lipopolysaccharides, with which bacteria adapt to environmental stresses, such as heat shock, antibiotics, or low oxygen content. The results give clear physiological indications that the process with P. putida DOT-T1E as the biocatalyst and 1-decanol as the solvent is a stable system for two-phase biotransformations that will allow the production of fine chemicals in economically sound amounts.

Flow cytometric techniques to characterise physiological states of Acinetobacter calcoaceticus

Monitoring biotechnological processes involves acquiring information about key metabolic events and, ideally, single cell states should be determined to obtain comprehensive data on the physiological status of the surveyed population. In this paper, growth stages of the strain Acinetobacter calcoaceticus 69-V were characterised at the single cell level using flow cytometry. Four methods for analysing bacterial cellular characteristics by fluorescence were compared with respect to their sensitivity to changes in the physiological states induced by changing micro-environmental conditions. DNA analysis was confirmed to be highly informative with regard to the multiplication activity of the population. Measuring the membrane potential related fluorescence intensity (MPRFI) and the rRNA content were found to be useful for describing high-active cell states. A method for the measurement of the fluidity related fluorescence intensity (FRFI) was developed, since it allowed changes in the fluidity of the bacterial membrane to be detected, and thereby provided a valuable means of tracking adaptation of the population to micro-environmental deviations from optimal growth conditions.

Adaptive responses of Ralstonia eutropha to feast and famine conditions analysed by flow cytometry

Results obtained by flow cytometry allow conclusions to be drawn about how the physiological states of Ralstsonia eutropha JMP134 are connected with survival strategies under distinct growth conditions. During both feast and famine conditions the cells were found to proceed through sharply separated phases of life. Two sources of carbon and energy, one poor (0.02% phenol) and one rich (0.2% pyruvate and 0.1% yeast extract) were chosen to study the cellular responses. Despite the major differences in carbon source, when growth stages of the bacteria on the two substrates were characterised in batch growth, only minor differences were found in the time course of the membrane potential related fluorescence intensity (MPRFI). This also applied to the rRNA content and the size-correlated forward scatter (FSC) signal of the cells, both of which increased to high levels during the (early) exponential growth phase. On the rich medium, DNA synthesis initially occurred in an uncoupled manner, then a high rate of PHB formation followed when nutrients began to be limiting. Under famine conditions, the cellular responses were much more complex. PHB was synthesised, then DNA synthesis occurred in a 'eukaryotic' mode, to be succeeded by renewed PHB synthesis. To obtain defined cell physiological states, the chemostat technique was used in addition to batch experiments. The results obtained clearly indicated that key events in cell physiology, including initiation of DNA replication and overflow metabolism, occurred in a hierarchically ordered manner and were tightly correlated with changes in the environmental conditions of the bacterial cells.