Patterns of protein synthesis in the moderately halophilic bacterium Deleya halophila in response to sudden changes in external salinity

Abstract Exposure of the moderately halophilic bacterium, Deleya halophila , to high NaCl concentrations (2 or 2.5 M) resulted in a transient cessation of cell division. The time taken for the cells to adapt and grow depended on the final salt concentrations. During the initial phases of adaption to high salt both the rate of protein synthesis and amino acid uptake were transiently inhibited. The extent and duration of the inhibition was dependent on the magnitude of the salt shock. Alterations in the patterns of pulse-labelled proteins were observed during adaption to high salt. The response of Deleya halophila cells to decreasing salinity (2.5 to 1 M NaCl) was also characterized by distinct changes in the protein profiles, whereas minor changes in the protein patterns were observed during adaptation from 1 M to 0.5 M NaCl. The labelled protein patterns of cells grown in 1 M or 2.5 M NaCl appear to be similar but not identical.     

High-Salinity-Induced Iron Limitation in Bacillus subtilis

Proteome analysis of Bacillus subtilis cells grown at low and high salinity revealed the induction of 16 protein spots and the repression of 2 protein spots, respectively. Most of these protein spots were identified by mass spectrometry. Four of the 16 high-salinity-induced proteins corresponded to DhbA, DhbB, DhbC, and DhbE, enzymes that are involved in the synthesis of 2,3-dihydroxybenzoate (DHB) and its modification and esterification to the iron siderophore bacillibactin. These proteins are encoded by the dhbACEBF operon, which is negatively controlled by the central iron regulatory protein Fur and is derepressed upon iron limitation. We found that iron limitation and high salinity derepressed dhb expression to a similar extent and that both led to the accumulation of comparable amounts of DHB in the culture supernatant. DHB production increased linearly with the degree of salinity of the growth medium but could still be reduced by an excess of iron. Such an excess of iron also partially reversed the growth defect exhibited by salt-stressed B. subtilis cultures. Taken together, these findings strongly suggest that B. subtilis cells grown at high salinity experience iron limitation. In support of this notion, we found that the expression of several genes and operons encoding putative iron uptake systems was increased upon salt stress. The unexpected finding that high-salinity stress has an iron limitation component might be of special ecophysiological importance for the growth of B. subtilis in natural settings, in which bioavailable iron is usually scarce.     

The response of the filamentous cyanobacterium Spirulina platensis to salt stress

The responses of the filamentous cyanobacterium Spirulina platensis to increased NaCl concentrations (0.25–1.0 M) in addition to the concentration of sodium in the growth medium were studied. A two stage response to the salt stress was observed. This consisted of a relatively short shock stage, followed by adaptation process. It was shown that upon exposure to high salt concentrations of 0.5 M and above, immediate inhibition of photosynthesis and respiration, and complete cessation of growth occurred. After a time lag, the energy-yielding processes exhibited restored activity. At 0.5 and 1.0M NaCl photosynthesis reached 80% and 50% that of the control, while respiration was enhanced by 140 and 200%, respectively. The time lags were longer when the cells were exposed to higher NaCl concentrations. The resumption of growth and the establishment of new steady state growth rates were found to be correlated to the recovery in respiration. The relationship between the growth rates after adaptation and the increased NaCl concentrations was found to be inversely linear. The cellular sodium content was maintained at a constant low level, regardless of the external NaCl concentration, while potassium content declined linearly vs. the external NaCl concentration. The carbohydrate content of the cells rose exponentially with the increase in NaCl concentration.Publication No. 34 from the Micro-Algal Biotechnology Lab.     

Salt stress induction of glutamyl endopeptidase biosynthesis in Bacillus intermedius

Bacteria from the genus Bacillus have evolved complicated regulatory networks to be protected from various environmental stresses, including sudden increase in salinity. Among these regulatory mechanisms is the DegS-DegU signal transduction system, which controls degradative enzyme synthesis and is involved in sensing salt stress in Bacillus subtilis. We report the study of biosynthesis regulation of Bacillus intermedius glutamyl endopeptidase under salt stress conditions. Salt stress during growth in medium containing 1-2.5 M NaCl, KCl or disodium succinate leads to the induction of glutamyl endopeptidase. Analysis of the regulatory region of the gene for B. intermedius glutamyl endopeptidase revealed the presence of a tentative target sequence for DegU control, AGATN10TTGAG. For the expression of the glutamyl endopeptidase gene, functional DegU protein is required. Thus, we suggest that expression of the gene for B. intermedius glutamyl endopeptidase may be controlled by a regulatory system analogous to DegS-DegU two-component system in B. subtilis.     

Electron Flow from NAD(P)H Dehydrogenase to Photosystem I is Required for Adaptation to Salt Shock in the Cyanobacterium Synechocystis sp. PCC 6803

The role of the NAD(P)H-dehydrogenase complex in adaptationto salt stress was examined in an ndhB-inacti-vated mutant ofthe cyanobacterium Synechocystis sp. PCC 6803. Wild-type cellsand ndhB-inactivated mutant cells grew at similar rates underconditions of low salinity (<0.6M NaCl) and high CO² (3%).However, when the concentration of NaCl in the culture mediumwas higher than 0.6 M, the mutant cells grew much more slowlythan the wild-type cells. Upon addition of high concentrationsof NaCl, the oxygen-evolving activity was rapidly inhibitedbut then it recovered, with the rate of recovery depending onthe concentration of NaCl. The recovery of the mutant cellswas significantly delayed when the concentration of NaCl wasabove 0.3 M. At 0.9 M NaCl, wild-type cells recovered with ahalf time of about 40 min, while mutant cells did not recover.The kinetics of changes in Chi fluorescence confirmed theseresults. In wild-type cells, input of electrons from the cytosolto PSI via the NAD(P)H-dehy-drogenase complex increased uponsalt shock. It appears, therefore, that the electron flow fromthe cytosol to PSI via NAD(P)H-dehydrogenase is essential forthe adaptation of cyanobacteria to salt shock. (Received June 11, 1997; Accepted September 24, 1997)     

The groESL operon of the halophilic lactic acid bacterium Tetragenococcus halophila

The groESL operon of the halophilic lactic acid bacterium Tetragenococcus halophila was cloned by a PCR-based method. The molecular masses of GroES and GroEL proteins were calculated to be 10,153 and 56,893 Da, respectively. The amount of groESL mRNA was increased 3.8-fold by heat shock (45 degrees C), and 4-fold by high NaCl (3-4 M). The Bacillus subtilis sigmaA-like constitutive promoter existed in front of groES, and was used under both normal and stress (heat shock and high salinity) conditions.     

Cellular adaptation of Clostridioides difficile to high salinity encompasses a compatible solute-responsive change in cell morphology

Infections by the pathogenic gut bacterium Clostridioides difficile cause severe diarrhoeas up to a toxic megacolon and are currently among the major causes of lethal bacterial infections. Successful bacterial propagation in the gut is strongly associated with the adaptation to changing nutrition-caused environmental conditions; e.g. environmental salt stresses. Concentrations of 350 mM NaCl, the prevailing salinity in the colon, led to significantly reduced growth of C. difficile. Metabolomics of salt-stressed bacteria revealed a major reduction of the central energy generation pathways, including the Stickland-fermentation reactions. No obvious synthesis of compatible solutes was observed up to 24 h of growth. The ensuing limited tolerance to high salinity and absence of compatible solute synthesis might result from an evolutionary adaptation to the exclusive life of C. difficile in the mammalian gut. Addition of the compatible solutes carnitine, glycine-betaine, γ-butyrobetaine, crotonobetaine, homobetaine, proline-betaine and dimethylsulfoniopropionate restored growth (choline and proline failed) under conditions of high salinity. A bioinformatically identified OpuF-type ABC-transporter imported most of the used compatible solutes. A long-term adaptation after 48 h included a shift of the Stickland fermentation-based energy metabolism from the utilization to the accumulation of l -proline and resulted in restored growth. Surprisingly, salt stress resulted in the formation of coccoid C. difficile cells instead of the typical rod-shaped cells, a process reverted by the addition of several compatible solutes. Hence, compatible solute import via OpuF is the major immediate adaptation strategy of C. difficile to high salinity-incurred cellular stress.     

An osmotically induced cytosolic Ca2+ transient activates calcineurin signaling to mediate ion homeostasis and salt tolerance of Saccharomyces cerevisiae

Hyperosmotic stress caused by NaCl, LiCl, or sorbitol induces an immediate and short duration ( approximately 1 min) transient cytosolic Ca(2+) ([Ca(2+)](cyt)) increase (Ca(2+)-dependent aequorin luminescence) in Saccharomyces cerevisiae cells. The amplitude of the osmotically induced [Ca(2+)](cyt) transient was attenuated by the addition of chelating agents EGTA or BAPTA, cation channel pore blockers, competitive inhibitors of Ca(2+) transport, or mutations (cch1Delta or mid1Delta) that reduce Ca(2+) influx, indicating that Ca(ext)(2+) is a source for the transient. An osmotic pretreatment (30 min) administered by inoculating cells into media supplemented with either NaCl (0.4 or 0.5 m) or sorbitol (0.8 or 1.0 m) enhanced the subsequent growth of these cells in media containing 1 m NaCl or 2 m sorbitol. Inclusion of EGTA in the osmotic pretreatment media or the cch1Delta mutation reduced cellular capacity for NaCl but not hyperosmotic adaptation. The stress-adaptive effect of hyperosmotic pretreatment was mimicked by exposing cells briefly to 20 mm CaCl(2). Thus, NaCl- or sorbitol-induced hyperosmotic shock causes a [Ca(2+)](cyt) transient that is facilitated by Ca(2+) influx, which enhances ionic but not osmotic stress adaptation. NaCl-induced ENA1 expression was inhibited by EGTA, cch1Delta mutation, and FK506, indicating that the [Ca(2+)](cyt) transient activates calcineurin signaling to mediate ion homeostasis and salt tolerance.     

Enhancing isoprene production by genetic modification of the 1-deoxy-d-xylulose-5-phosphate pathway in Bacillus subtilis

To enhance the production of isoprene, a volatile 5-carbon hydrocarbon, in the Gram-positive spore-forming rod-shaped bacterium Bacillus subtilis, 1-deoxy-d-xylulose-5-phosphate synthase (Dxs) and 1-deoxy-d-xylulose-5-phosphate reductoisomerase (Dxr) were overexpressed in B. subtilis DSM 10. For the strain that overexpresses Dxs, the yield of isoprene was increased 40% over that by the wild-type strain. In the Dxr overexpression strain, the level of isoprene production was unchanged. Overexpression of Dxr together with Dxs showed an isoprene production level similar to that of the Dxs overproduction strain. The effects of external factors, such as stress factors including heat (48°C), salt (0.3 M NaCl), ethanol (1%), and oxidative (0.005% H(2)O(2)) stress, on isoprene production were further examined. Heat, salt, and H(2)O(2) induced isoprene production; ethanol inhibited isoprene production. In addition, induction and repression effects are independent of SigB, which is the general stress-responsive alternative sigma factor of Gram-positive bacteria.     

Adaptive nature of the transition phases in development: the case of Sorghum bicolor

An increase in tolerance to salinity is induced in Sorghum bicolor by exposure to a sublethal concentration of NaCl during early vegetative development. The phase of competence for induction of this response, termed salt adaptation, is well defined in time and it coincides with the emergence of the first adventitious roots. The link between these events was investigated. Competence for salt adaptation varies among genotypes. It is shown that competence is especially high for genotypes in which the link between the seminal root and the shoot is reduced during emergence of the adventitious root. These data relate the capacity for salt adaptation with development in the absence of NaCl, suggesting that: (i) functional integration of the adventitious roots within the whole plant has an adaptive nature in normal development; (ii) salt adaptation results from an integration of the environmental constraint (NaCl) during this developmental readjustment. It is concluded that perturbations generated by emergence of a new organ are the cause of rapid variations in sensitivity required to open a competence window.