scholarly journals Life at low water activity

2004 ◽  
Vol 359 (1448) ◽  
pp. 1249-1267 ◽  
Author(s):  
W. D. Grant
Keyword(s):  
Osmotic Stress ◽  
Water Activity ◽  
Water Availability ◽  
Osmotic Potential ◽  
Compatible Solutes ◽  
Restricted Range ◽  
High Concentration ◽  
Geological Time ◽  
Time Periods ◽  
Sugar Levels

Two major types of environment provide habitats for the most xerophilic organisms known: foods preserved by some form of dehydration or enhanced sugar levels, and hypersaline sites where water availability is limited by a high concentration of salts (usually NaCl). These environments are essentially microbial habitats, with high–sugar foods being dominated by xerophilic (sometimes called osmophilic) filamentous fungi and yeasts, some of which are capable of growth at a water activity ( a w ) of 0.61, the lowest a w value for growth recorded to date. By contrast, high–salt environments are almost exclusively populated by prokaryotes, notably the haloarchaea, capable of growing in saturated NaCl ( a w 0.75). Different strategies are employed for combating the osmotic stress imposed by high levels of solutes in the environment. Eukaryotes and most prokaryotes synthesize or accumulate organic so–called ‘compatible solutes’ (osmolytes) that have counterbalancing osmotic potential. A restricted range of bacteria and the haloarchaea counterbalance osmotic stress imposed by NaCl by accumulating equivalent amounts of KCl. Haloarchaea become entrapped and survive for long periods inside halite (NaCl) crystals. They are also found in ancient subterranean halite (NaCl) deposits, leading to speculation about survival over geological time periods.

Humectant Permeability Influences Growth and Compatible Solute Uptake by Staphylococcus aureus Subjected to Osmotic Stress

2002 ◽  
Vol 65 (6) ◽  
pp. 1008-1015 ◽  
Author(s):  
ODDUR VILHELMSSON ◽  
KAREN J. MILLER
Keyword(s):  
Staphylococcus Aureus ◽  
Sodium Chloride ◽  
Water Activity ◽  
Glycine Betaine ◽  
Compatible Solutes ◽  
Foodborne Pathogen ◽  
Compatible Solute ◽  
Solute Uptake ◽  
Stressed Cells ◽  
Carnitine Uptake

The effects of different humectants (sodium chloride, sucrose, and glycerol) on the growth of and compatible solute (glycine betaine, proline, and carnitine) uptake by the osmotolerant foodborne pathogen Staphylococcus aureus were investigated. While growth in the presence of the impermeant humectants sodium chloride and sucrose induced the accumulation of proline and glycine betaine by cells, growth in the presence of the permeant humectant glycerol did not. When compatible solutes were omitted from low-water-activity media, growth was very poor in the presence of impermeant humectants. In contrast, the addition of compatible solutes had essentially no effect on growth when cells were grown in low-water-activity media containing glycerol as the humectant. Carnitine was found to accumulate to high intracellular levels in osmotically stressed cells when proline and glycine betaine were absent, making it a potentially important compatible solute for this organism.

scholarly journals Effect of Seed Inoculation on Alfalfa Tolerance to Water Deficit Stress

2017 ◽  
Vol 45 (1) ◽  
pp. 82-88
Author(s):  
Mahnaz ZAFARI ◽  
Ali EBADI ◽  
Sodabeh JAHANBAKHSH GODEHKAHRIZ
Keyword(s):  
Water Deficit ◽  
Osmotic Potential ◽  
Mycorrhizal Fungi ◽  
Soluble Sugars ◽  
Compatible Solutes ◽  
Membrane Stability ◽  
Forage Yield ◽  
Water Deficit Stress ◽  
Cell Membrane Stability ◽  
Seed Inoculation

Water deficit is one of the most important environmental stresses that adversely affect crop growth and production and mycorrhizal fungi and symbiotic bacteria have important role in resistance to drought stress. The effect of biofertilizers on alfalfa stress tolerance was studied at the greenhouse condition. Treatments comprised three water-deficit stresses (35%, 55% and 75% of field capacity) and four seeds inoculations (Glomus mosseae, Sinorhizobium meliloti, G. mosseae + S. meliloti and non-inoculated). Water-deficit stress decrease cell membrane stability (39%), total Chl (24.05%), carotenoid (35.55%), quantum yield (50.64%) and forage yield (28.20%), while increased the proline and soluble sugars content (68.55 and 46.53% respectively) and osmotic potential (45.84%). The inoculation of seeds increased the capability of the plants in counteracting the stress, so that the production of compatible solutes was increased and the photosynthetic indices, proline, osmotic potential, membrane stability and forage yield were improved by seed inoculation. Mycorrhiza improved photosynthetic indexes and proline, but bacteria had more efficacy on membrane stability and forage yield. However, double inoculation due to the synergistic effect of mycorrhiza and Sinorhizobium, had the greatest effect than Solitary inoculation. Our results suggest that biofertilized alfalfa plants were better adapted than non- biofertilized ones to cope with water deficit.

Major Compatible Solutes and Structural Adaptation of Proteins in Extremophiles

2022 ◽  
pp. 161-186
Author(s):  
Hardik Shah ◽  
Khushbu Panchal ◽  
Amisha Panchal
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Osmotic Stress ◽  
Amino Acid Composition ◽  
Scientific Community ◽  
Compatible Solutes ◽  
Organic Solutes ◽  
Structural Adaptation ◽  
Extreme Habitats

Extremophiles are the most ancient microbes on the Earth and also a center of attraction for the scientific community for research because of their ability to adapt to extreme habitats. Compatible solutes are among those factors which enable these microorganisms to thrive in such extreme habitats. Under osmotic stress, the majority of extremophiles accumulate specific organic solutes such as amino acids, sugars, polyols, and their derivatives. In addition, proteins in extremophiles are found to be evolved by changing their amino acid composition to alter the hydrophobicity of its core and surface charge to maintain activity. This chapter encompasses a comprehensive study about the role of various compatible solutes in the endurance of microorganisms under extremophilic conditions, synthesis of compatible solutes, nature of extremophilic proteins, and their applications. Furthermore, an attempt has been made to cover various strategies adopted by the scientific community while pursuing research on compatible solutes.

Proline Analogues in Melaleuca Species: Response of Melaleuca lanceolata and M. uncinata to Water Stress and Salinity

1987 ◽  
Vol 14 (6) ◽  
pp. 669 ◽  
Author(s):  
BP Naidu ◽  
GP Jones ◽  
LG Paleg ◽  
A Poljakoff-Mayber
Keyword(s):  
Water Stress ◽  
Osmotic Adjustment ◽  
Osmotic Potential ◽  
Compatible Solutes ◽  
Species Response ◽  
Laboratory Conditions ◽  
Relative Water ◽  
Response To Water ◽  
First Time

Fifteen species of Melaleuca and two species of Callistemon from the field were examined to determine whether they accumulated nitrogen-containing compatible solutes and, if so, which. In addition to L-proline, N-methyl-L-proline (MP) (isolated for the first time from plants), trans-4-hydroxy-N-methyl- L-proline (MHP), and N, N'-dimethyl-trans-4-hydroxy-L-proline (DHP) were found in various combinations in the 15 Melaleuca species. M. lanceolata seedlings were subjected to water or salinity stress and M. uncinata to water stress under laboratory conditions. In both species significant reductions in leaf water potential (Ψw), osmotic potential (Ψs), turgor potential (Ψp), and relative water content (RWC) were observed in response to water stress. Salinised M. lanceolata plants showed considerable osmotic adjustment and maintained Ψp comparable to that of control plants; salinity, however, decreased RWC. In response to the imposed stresses under laboratory conditions, proline and MHP levels in M. lanceolata, and MHP and DHP levels in M. uncinata, increased. In addition to possible protective or osmotic roles in vivo, these proline analogues may be useful in chemotaxonomic investigations of Melaleuca species.

Effects of long-term ionic and osmotic stress conditions on photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803

2005 ◽  
Vol 32 (9) ◽  
pp. 807 ◽  
Author(s):  
Saowarath Jantaro ◽  
Paula Mulo ◽  
Tove Jansén ◽  
Aran Incharoensakdi ◽  
Pirkko Mäenpää
Keyword(s):  
Osmotic Stress ◽  
Stress Component ◽  
D1 Protein ◽  
Long Term Effects ◽  
High Concentration ◽  
High Concentrations ◽  
Synechocystis Sp ◽  
Halotolerant Cyanobacterium ◽  
Pcc 6803

Salinity is considered to be one of the most severe problems in worldwide agricultural production, but the published investigations give contradictory results of the effect of ionic and osmotic stresses on photosynthesis. In the present study, long-term effects of both ionic and osmotic stresses, especially on photosynthesis, were investigated using the moderately halotolerant cyanobacterium Synechocystis sp. PCC 6803. Our results show that the PSII activity and the photosynthetic capacity tolerated NaCl but a high concentration of sorbitol completely inhibited both activities. In line with these results, we show that the amount of the D1 protein of PSII was decreased under severe osmotic stress, whereas the levels of PsaA / B and NdhF3 proteins remained unchanged. However, high concentrations of sorbitol stress led to a drastic decrease of both psbA (encoding D1) and psaA (encoding PsaA) transcripts, suggesting that severe osmotic stress may abolish the tight coordination of transcription and translation normally present in bacteria, at least in the case of the psaA gene. Taken together, our results indicate that the osmotic stress component is more detrimental to photosynthesis than the ionic one and, furthermore, under osmotic stress, the D1 protein appears to be the target of this stress treatment.

Influence of Water Activity on Foodborne Bacteria — A Review1

1983 ◽  
Vol 46 (2) ◽  
pp. 142-150 ◽  
Author(s):  
WILLIAM H. SPERBER
Keyword(s):  
Glutamic Acid ◽  
Water Activity ◽  
Bacterial Growth ◽  
Food Systems ◽  
New Technologies ◽  
Compatible Solutes ◽  
Food Products ◽  
Influence Of Water ◽  
Chemical Preservatives ◽  
Reduced Water

The influence of water activity on some characteristics of bacterial growth is presented. Bacteria are able to overcome the plasmolytic effect of reduced water activity by intracellularly accumulating compatible solutes such as glutamic acid or proline. In food systems, water activity is one of several preservative factors which interact to form a preservative system. Other preservative factors considered in this review are temperature, pH, O/R potential and chemical preservatives. Control of water activity in foods is receiving more attention as new food products and new technologies are developed.

Retention of Viability of Salmonella in Sucrose as Affected by Type of Inoculum, Water Activity, and Storage Temperature

2017 ◽  
Vol 80 (9) ◽  
pp. 1408-1414 ◽  
Author(s):  
Larry R. Beuchat ◽  
David A. Mann ◽  
Christine A. Kelly ◽  
Ynes R. Ortega
Keyword(s):  
Osmotic Stress ◽  
Water Activity ◽  
Storage Temperature ◽  
Low Level ◽  
High Sugar ◽  
High Inoculum ◽  
Stress Survival ◽  
Low Levels ◽  
Survival Patterns ◽  
And Storage

ABSTRACT Outbreaks of salmonellosis have been associated with consumption of high-sugar, low–water activity (aw) foods. The study reported here was focused on determining the effect of storage temperature (5 and 25°C) on survival of initially high and low levels of Salmonella in dry-inoculated sucrose (aw 0.26 ± 0.01 to 0.54 ± 0.01) and wet-inoculated sucrose (aw 0.24 ± 0.01 to 0.44 ± 0.04) over a 52-week period. With the exception of dry-inoculated sucrose at aw 0.26, Salmonella survived for 52 weeks in dry- and wet-inoculated sucrose stored at 5 and 25°C. Retention of viability was clearly favored in sucrose stored at 5°C compared with 25°C, regardless of level or type of inoculum or aw. Survival at 5°C was not affected by aw. Initial high-inoculum counts of 5.18 and 5.25 log CFU/g of dry-inoculated sucrose (aw 0.26 and 0.54, respectively) stored for 52 weeks at 5°C decreased by 0.56 and 0.53 log CFU/g; counts decreased by >4.18 and >4.25 log CFU/g in samples stored at 25°C. Inactivation rates in wet-inoculated sucrose were similar to those in dry-inoculated sucrose; however, a trend toward higher persistence of Salmonella in dry- versus wet-inoculated sucrose suggests there was a higher proportion of cells in the wet inoculum with low tolerance to osmotic stress. Survival patterns were similar in sucrose initially containing a low level of Salmonella (2.26 to 2.91 log CFU/g). The pathogen was recovered from low-inoculated sucrose stored at 5°C for 52 weeks regardless of type of inoculum or aw and from dry-inoculated sucrose (aw 0.54) and wet-inoculated sucrose (aw 0.24) stored at 25°C for 12 and 26 weeks, respectively. Results emphasize the importance of preventing contamination of sucrose intended for use as an ingredient in foods not subjected to a treatment that would be lethal to Salmonella.

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