Present State of Knowledge of AW Effects on Microorganisms

Gould, Glenn

doi:10.1007/978-94-009-5103-7_14

Cited by 21 publications

(14 citation statements)

References 69 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Pyruvate dehydrogenase is a central enzyme of the primary metabolism of S. aureus. Therefore, its apparent induction by osmotic stress brought to mind the common but, with two notable exceptions (16,21), largely untested assumption that osmoadaptation is an energy-consuming process (17,27). The rationale behind this assumption is that the maintenance of very steep humectant and compatible-solute concentration gradients across the cytoplasmic membrane (which is necessary if the cell is to maintain its volume and turgor without accumulating high intracellular concentrations of a humectant that may be disruptive to the cell's metabolism) requires substantial activity of the cell's transport systems, which will, directly or indirectly, consume large quantities of ATP.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Pyruvate Dehydrogenase in Staphylococcus aureus Is Stimulated by Osmotic Stress

Vilhelmsson

Miller

2002

Appl Environ Microbiol

View full text Add to dashboard Cite

The pyruvate dehydrogenase multienzyme complex (PDHC) was found to be upregulated by osmotic stress in the osmotolerant pathogen Staphylococcus aureus. Upregulation was detectable in the levels of both activity and protein and was judged to be about fourfold when sodium chloride was used to adjust the water activity (a w ) of the growth medium to 0.94. The upregulation of the PDHC was also found to be humectant dependent and was greatest when impermeant, nonmetabolizable humectants were used to adjust a w . Further experiments provided evidence that in addition to osmotic upregulation, the PDHC complex is also subject to catabolite repression, thus providing a possible explanation for the observation that high concentrations of carbohydrates are generally more inhibitory to the growth of this bacterial pathogen than are high concentrations of salts.Staphylococcus aureus, an important human pathogen, is considered a highly osmotolerant bacterium and is able to grow at a water activity (a w ) of as low as 0.86 (33). Its osmotolerance may be an important determinant of its ability to grow in foods and on human skin, from where it can spread and/or form toxins and cause disease. Although osmoadaptation of S. aureus has been studied fairly extensively in the past (8,9,29,30,38,42,43,46), it remains unclear why this organism is considerably more osmotolerant than other bacterial pathogens. In fact, thus far, studies have revealed an osmoadaptive process apparently typical for bacteria in general: namely, the accumulation of glycine betaine, proline, or other common compatible solutes through transport from the growth medium (25,29,39) and increased synthesis of stress proteins such as chaperones (31) and alkyl hydroperoxide reductase C (8). However, recent studies have given indications that the regulation of stress gene expression may be somewhat unusual in the staphylococci. For example, expression of the alternative sigma factor B is repressed during osmotic stress in S. aureus (13) while it is strongly induced in Bacillus subtilis under those conditions (11,45). Although a few studies have attempted to identify osmotically upregulated proteins in S. aureus (8,31,44), this field still remains relatively unexplored.A major goal of the present study was to investigate changes in protein composition of this osmotolerant organism in response to osmotic stress and to identify proteins important for its osmoadaptation. Herein, we present evidence that the pyruvate dehydrogenase multienzyme complex (PDHC) of S. aureus, an enzyme of central importance in this organism's primary metabolism, is upregulated by osmotic stress. The implications of this finding with respect to the osmoadaptation of S. aureus and the regulation of its metabolic activity are discussed. MATERIALS AND METHODSStrains and media. S. aureus strain ATCC 12600 was obtained from the American Type Culture Collection (Manassas, Va.) and grown in Trypticase soy broth (TSB; Difco Laboratories, Detroit, Mich.) at 37°C. The a w values of media were measured in d...

show abstract

Section: Resultsmentioning

confidence: 99%

Synthesis of Pyruvate Dehydrogenase in Staphylococcus aureus Is Stimulated by Osmotic Stress

Vilhelmsson

Miller

2002

Appl Environ Microbiol

View full text Add to dashboard Cite

show abstract

“…Thus the intracellular water activity can be reduced and cell volume and turgor can be adapted to the conditions set by the osmotic stress. The compatible solutes known so far belong to the following classes of compounds : inorganic ions, polyols, sugars, betaines and amino acids, and have been extensively reviewed by Mackay et al (1984), Gould (1985), Imhoff (1986) and Triiper & Galinski (1986). The anaerobic heterotrophic eubacteria (Oren, 1985 ;Rengpipat et al, 1988) and halophilic archaeobacteria accumulate inorganic ions such as K+, Na+ and C1-to achieve osmotic equilibrium across the cytoplasmic membrane.…”

Section: Introductionmentioning

confidence: 99%

The spectrum of compatible solutes in heterotrophic halophilic eubacteria of the family Halomonadaceae

Wohlfarth

Severin

Galinski

1990

Journal of General Microbiology

139

101

View full text Add to dashboard Cite

A new family, the Hafomonadaceae, has recently been proposed for members of the genera Deleya and Halornonas. The three strains investigated, Deleya haiuphila, Halomonas elongata and Flavobacterium halmephilum (reclassified as H. hahophila), are aerobic heterotrophic micro-organisms exhibiting an extreme salt tolerance. The major organic osmoregulatory solutes of these organisms were examined using 3C-nuclear magnetic resonance spectroscopy. The relative proportions of the solutes varied with respect to salt concentration, temperature and carbon source. The recently described amino acid ectoine was found to be a dominant solute. For the first time it could be shown for halophilic eubacteria that the intracellular concentration of solutes is sufficient to balance the osmotic pressure of the medium. Thus, there is no need to postulate a hypo-osmotic cytoplasm.

show abstract

“…For example, several authors have reported that the growth boundaries for various genera of microorganisms differ depending on the type of humectant used to depress RH rather than the absolute value of RH (6,8,22,33). The literature on microbial osmoregulation via compatible solutes has also shown that the type of humectant, rather than the absolute value of RH, is critical (14). In recent years, increasing evidence based on glass transition theory has shown that molec-ular mobility (Mm) may be an attribute that deserves further attention, as it is related to many important diffusion-limiting properties of foods (5,36,37,43).…”

mentioning

confidence: 99%

Staphylococcus aureusGrowth Boundaries: Moving towards Mechanistic Predictive Models Based on Solute-Specific Effects

Stewart¹,

Cole²,

Legan³

et al. 2002

Appl Environ Microbiol

View full text Add to dashboard Cite

The formulation of shelf-stable intermediate-moisture products is a critical food safety issue. Therefore, knowing the precise boundary for the growth-no-growth interface of Staphylococcus aureus is necessary for food safety risk assessment. This study was designed to examine the effects of various humectants and to produce growth boundary models as tools for risk assessment. The molecular mobility and the effects of various physical properties of humectants, such as their glass transition temperatures, their membrane permeability, and their ionic and nonionic properties, on S. aureus growth were investigated. The effects of relative humidity (RH; 84 to 95%, adjusted by sucrose plus fructose, glycerol, or NaCl), initial pH (4.5 to 7.0, adjusted by HCl), and potassium sorbate concentration (0 or 1,000 ppm) on the growth of S. aureus were determined. Growth was monitored by turbidity over a 24-week period. Toxin production was determined by enterotoxin assay. The 1,792 data points generated were analyzed by LIFEREG procedures (SAS Institute, Inc., Cary, N.C.), which showed that all parameters studied significantly affected the growth responses of S. aureus. Differences were observed in the growth-no-growth boundary when different humectants were used to achieve the desired RH values in both the absence and the presence of potassium sorbate. Sucrose plus fructose was most inhibitory at neutral pH values, while NaCl was most inhibitory at low pH values. The addition of potassium sorbate greatly increased the no-growth regions, particularly when pH was <6.0. Published kinetic growth and survival models were compared with boundary models developed in this work. The effects of solutes and differences in modeling approaches are discussed.

show abstract

Present State of Knowledge of AW Effects on Microorganisms

Cited by 21 publications

References 69 publications

Synthesis of Pyruvate Dehydrogenase in Staphylococcus aureus Is Stimulated by Osmotic Stress

Synthesis of Pyruvate Dehydrogenase in Staphylococcus aureus Is Stimulated by Osmotic Stress

The spectrum of compatible solutes in heterotrophic halophilic eubacteria of the family Halomonadaceae

Staphylococcus aureusGrowth Boundaries: Moving towards Mechanistic Predictive Models Based on Solute-Specific Effects

Contact Info

Product

Resources

About