Effect of Temperature and Salinity Stress on Growth and Lipid Composition of Shewanella gelidimarina

Abstract

The maximum growth temperature, the optimal growth temperature, and the estimated normal physiological range for growth of Shewanella gelidimarina are functions of water activity (a w ), which can be manipulated by changing the concentration of sodium chloride. The growth temperatures at the boundaries of the normal physiological range for growth were characterized by increased variability in fatty acid composition. Under hyper-and hypoosmotic stress conditions at an a w of 0.993 (1.0% [wt/vol] NaCl) and at an a w of 0.977 (4.0% [wt/vol] NaCl) the proportion of certain fatty acids (monounsaturated and branched-chain fatty acids) was highly regulated and was inversely related to the growth rate over the entire temperature range. The physical states of lipids extracted from samples grown at stressful a w values at the boundaries of the normal physiological range exhibited no abrupt gel-liquid phase transitions when the lipids were analyzed as liposomes. Lipid packing and adaptational fatty acid composition responses are clearly influenced by differences in the temperature-salinity regime, which are reflected in overall cell function characteristics, such as the growth rate and the normal physiological range for growth.Antarctic sea ice is characterized by the presence of a unique bacterial community that is dominated by psychrophilic bacteria (2,3,12). Nichols et al. (25) have discussed the potential role of the temperature-salinity regime in selecting psychrophilic bacteria in sea ice. It has been suggested that understanding the physiological response of psychrophilic bacteria to combined temperature-salinity stress is very important for understanding the bacterial sea ice community. The importance of fluctuations in salinity that affect the composition of microbial populations in estuarine and brackish water ecosystems has been recognized (7, 30), and such fluctuations are very important when the survival and viability of psychrophilic marine bacteria are considered (12,20,21,34). Changes in salinity similar to those observed in estuarine and brackish water environments also occur in Antarctic coastal waters and sea ice and are associated with the annual ice formation and melting cycle. However, researchers have attempted to relate changes in physicochemical parameters to a physiological mechanism for growth in only a few studies of psychrophilic bacteria (8,11,21,26,35).Workers have proposed a number of models to describe the effect of temperature and/or salinity on bacterial growth. Most of these models are empirical and seek solely to summarize observations of bacterial growth under various conditions. Many are based on the Arrhenius equation and utilize Arrhenius kinetics to describe bacterial growth in response to temperature. The concept of a normal physiological range (NPR) for bacterial growth is derived from modelling of the bacterial growth rate by using Arrhenius models. Over a defined range of temperature, the growth rates of all bacteria obey Arrhenius kinetics, and this temperature range is desig...

Impact of Seawater Salinity on Ultrastructure of Chloroplasts and Oleosomes in Relation to Fat Metabolism in Flag Leaf of Two Wheat Cultivars During Grain-filling

“…Seawater caused an increase in the stroma and damaged of chloroplast membranes. The rounding of chloroplasts was attributed to the increase in the volume of the stroma and disorganization of the thylakoid membranes [13].The same observations were also reported by some authors (Liu et al [26], Mitsuya et al [27]). The concentrations of 10% or 25% seawater at 21 days post-anthesis in Gemmieza-9 caused pronounced swelling of the thylakoid membranes in chloroplasts.…”

“…In this connection, Torzilli [12] found that, salt stress increased the cellular concentrations of glycerol in Aureobasidium pullulans. Nichols et al [13] found that in Shewanella gelidimarina, under hyper-osmotic and hypo-osmotic stress conditions, an increase in the proportion of saturated fatty acids was accompanied with increasing salinity level.…”

Environmental Stress and Antibiotic Resistance in Food-Related Pathogens

“…Alterations in environmental temperature adversely change membrane fluidity, leading bacteria to make compensatory alterations in the degree of saturation of membrane fatty acids (4,20,27,28) to reestablish ideal states of membrane fluidity. Loss of ideal states of membrane fluidity may have an impact on membrane receptor and signaling activities, reducing the rates and efficacy of binding of antibiotics (29,35) and their import or export through bacterial membranes (27).…”

“…Alterations in environmental temperature adversely change membrane fluidity, leading bacteria to make compensatory alterations in the degree of saturation of membrane fatty acids (4,20,27,28) to reestablish ideal states of membrane fluidity. Loss of ideal states of membrane fluidity may have an impact on membrane receptor and signaling activities, reducing the rates and efficacy of binding of antibiotics (29,35) and their import or export through bacterial membranes (27). On their return to optimum temperature conditions (i.e., removal of temperature stress), bacteria may rebalance the degree of saturation of membrane fatty acids (4,20,27,28) to nonstress conditions, reestablishing optimum membrane structure and function, with a concomitant return to previously observed rates of ABR binding, import, and export.…”

“…Loss of ideal states of membrane fluidity may have an impact on membrane receptor and signaling activities, reducing the rates and efficacy of binding of antibiotics (29,35) and their import or export through bacterial membranes (27). On their return to optimum temperature conditions (i.e., removal of temperature stress), bacteria may rebalance the degree of saturation of membrane fatty acids (4,20,27,28) to nonstress conditions, reestablishing optimum membrane structure and function, with a concomitant return to previously observed rates of ABR binding, import, and export. However, further work will be required to elucidate the processes by which thermal stress can induce persistent increases in antibiotic susceptibility.…”