The action in vivo of glycine betaine in enhancement of tolerance of Synechococcus sp. strain PCC 7942 to low temperature

Vulcanimicrobium alpinus gen. nov. sp. nov., the first cultivated representative of the candidate phylum "Eremiobacterota", is a metabolically versatile aerobic anoxygenic phototroph

The previously uncultured phylum "Candidatus Eremiobacterota" is globally distributed and often abundant in oligotrophic environments. Although it includes lineages with the genetic potential for photosynthesis, one of the most important metabolic pathways on Earth, the absence of pure cultures has limited further insights into its ecological and physiological traits. We report the first successful isolation of a "Ca. Eremiobacterota" strain from a fumarolic ice cave on Mt. Erebus volcano (Antarctica). Polyphasic analysis revealed that this organism is an aerobic anoxygenic photoheterotrophic bacterium with a unique lifestyle, including bacteriochlorophyll a production, CO2 fixation, a high CO2 requirement, and phototactic motility using type IV-pili, all of which are highly adapted to polar and fumarolic environments. The cells are rods or filaments with a vesicular type intracytoplasmic membrane system. The genome encodes novel anoxygenic Type II photochemical reaction centers and bacteriochlorophyll synthesis proteins, forming a deeply branched monophyletic clade distinct from known phototrophs. The first cultured strain of the eighth phototrophic bacterial phylum which we name Vulcanimicrobium alpinus gen. nov., sp. nov. advances our understanding of ecology and evolution of photosynthesis.

Overexpression of Choline Oxidase Gene in Three Filial Generations of Rice Transgenic Lines

BACKGROUND

Glycinebetaine (GB) accumulation in many halophytic plants, animals, and microorganisms confers abiotic stress tolerance to salinity, drought, and extreme temperatures. Although there are a few genetic and biochemical pathways to synthesize GB, but isolation of a single gene Choline Oxidase (codA) from Arthrobacter spp. have opened a new hatch to engineer the susceptible plants.

OBJECTIVES

The effects of overexpressed codA gene, through multiple copy insertion and GB accumulation on salinity tolerance in rice were studied.

MATERIALS AND METHODS

Seed-derived embryogenic calli of 'Tarom Molaie' cultivar were targeted with two plasmids pChlCOD and pCytCOD both harboring the codA gene using the biolistic mediated transformation. The regenerated T₀ plants were screened by PCR analysis. A line containing three copies of codA gene and harboring pChlCOD and pCytCOD was identified by Southern blot analysis. The expression of codA gene in this transgenic line was then confirmed by RT-PCR. The Mendelian segregation pattern of the inserted sequences was accomplished by the progeny test using PCR. The effects of overexpression of codA on salinity tolerance were evaluated at germination and seedling stage using T₂-pChl transgenic line and control seeds in the presence of 0, 100, 200, and 300 mM NaCl. Finally, leaf growth dynamics of T₂-pChlCOD transgenic line and control line under hydroponic conditions in the presence of 0, 40, 80, and 120 mM NaCl were assessed.

RESULTS

The seed germination experiment results showed that the transformed seeds had a higher germination rate than the controls under all salinity treatments. But also, the leaf growth dynamics showed that the control plants had a more favorable leaf growth dynamic in all of the treatments. Although, the transgenic lines (T₀, T₁ and T₂) exhibited lower performance than the wild type, the transgenic line varied for GB and choline contents and increasing codA gene copy number led to increased GB content.

CONCLUSION

In a salinity sensitive crop such as rice, GB may not significantly contribute to the plant protection against salt stress. Also, insufficiency of choline resources as GB precursor might have affected the overall growth ability of the transgenic line and resulted in decreased leaf growth dynamics.

Assessment of Synechococcus elongatus PCC 7942 as an option for sustainable wastewater treatment

Industrial wastewaters are recognized as a valuable resource, however, their disposal without proper treatment can result in environmental deterioration. The associated environmental/operational cost of wastewater treatment necessitates upgrade of applied processes towards the goals of sustainability and mitigation of climate change. The implementation of cyanobacteria-based processes can contribute to these goals via resources recovery, production of high-value products, carbon fixation and green-energy production. The present study evaluates the cyanobacterium Synechococcus elongatus PCC 7942 (S7942) as a biological component for novel and sustainable alternatives to typical biological nutrient removal processes. Valuable results regarding cultivation temperature boundaries, applied disinfection techniques and analytical methods, as well as regarding relations between parameters expressing S7942 biomass concentration are presented. The results show that at typical industrial wastewater temperatures, S7942 efficiently grew and removed nitrates from treated snack-industry's wastewater. Moreover, in cultures with treated and relatively saline dairy wastewater, its growth rate slightly decreased, but nevertheless nitrates removal rate remained efficiently high. A comparison between typical denitrification processes and the proposed nutrient removal process indicated that a S7942-based system may constitute an alternative or a supplementary to denitrification process. Thus, Synechococcus elongatus PCC 7942 proved to be a potent candidate towards sustainable industrial wastewater treatment applications.

Molecular and Physiological Adaptations to Low Temperature in Thioalkalivibrio Strains Isolated from Soda Lakes with Different Temperature Regimes

The genus Thioalkalivibrio comprises sulfur-oxidizing bacteria thriving in soda lakes at high pH and salinity. Depending on the geographical location and the season, these lakes can strongly vary in temperature. To obtain a comprehensive understanding of the molecular and physiological adaptations to low temperature, we compared the responses of two Thioalkalivibrio strains to low (10°C) and high (30°C) temperatures. For this, the strains were grown under controlled conditions in chemostats and analyzed for their gene expression (RNA sequencing [RNA-Seq]), membrane lipid composition, and glycine betaine content. The strain Thioalkalivibrio versutus AL2^T originated from a soda lake in southeast Siberia that is exposed to strong seasonal temperature differences, including freezing winters, whereas Thioalkalivibrio nitratis ALJ2 was isolated from an East African Rift Valley soda lake with a constant warm temperature the year round. The strain AL2^T grew faster than ALJ2 at 10°C, likely due to its 3-fold-higher concentration of the osmolyte glycine betaine. Moreover, significant changes in the membrane lipid composition were observed for both strains, leading to an increase in their unsaturated fatty acid content via the Fab pathway to avoid membrane stiffness. Genes for the transcriptional and translational machinery, as well as for counteracting cold-induced hampering of nucleotides and proteins, were upregulated. Oxidative stress was reduced by induction of vitamin B₁₂ biosynthesis genes, and growth at 10°C provoked downregulation of genes involved in the second half of the sulfur oxidation pathway. Genes for intracellular signal transduction were differentially expressed, and interestingly, AL2^T upregulated flagellin expression, whereas ALJ2 downregulated it.

IMPORTANCE In addition to their haloalkaline conditions, soda lakes can also harbor a variety of other extreme parameters, to which their microbial communities need to adapt. However, for most of these supplementary stressors, it is not well known yet how haloalkaliphiles adapt and resist. Here, we studied the strategy for adaptation to low temperature in the haloalkaliphilic genus Thioalkalivibrio by using two strains isolated from soda lakes with different temperature regimes. Even though the strains showed a strong difference in growth rate at 10°C, they exhibited similar molecular and physiological adaptation responses. We hypothesize that they take advantage of resistance mechanisms against other stressors commonly found in soda lakes, which are therefore maintained in the bacteria living in the absence of low-temperature pressure. A major difference, however, was detected for their glycine betaine content at 10°C, highlighting the power of this osmolyte to also act as a key compound in cryoprotection.

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Choline oxidases

Choline oxidase catalyzes the four-electron, two-step, flavin-mediated oxidation of choline to glycine betaine. The enzyme is important both for medical and biotechnological reasons, because glycine betaine is one among a limited number of compatible solutes used by cells to counteract osmotic pressure. From a fundamental standpoint, choline oxidase has emerged as one of the paradigm enzymes for the oxidation of alcohols catalyzed by flavoproteins. Mechanistic, structural, and computational studies have elucidated the mechanism of action of the enzyme from Arthrobacter globiformis at the molecular level. Both choline and oxygen access to the active site cavity are gated and tightly controlled. Amino acid residues involved in substrate binding, and their contribution, have been identified. The mechanism of choline oxidation, with a hydride transfer reaction, an asynchronous transition state, the formation and stabilization of an alkoxide transient species, and a quantum mechanical mode of reaction, has been elucidated. The importance of nonpolar side chains for oxygen localization and of the positive charge harbored on the substrate for activation of oxygen for reaction with the reduced flavin have been recognized. Interesting phenomena, like the formation of a metastable photoinduced flavin-protein adduct, the reversible formation of a bicovalent flavoprotein, and the trapping of the enzyme in inactive conformations, have been described. This review summarizes the current status of our understanding on the structure-function-dynamics of choline oxidase.

Glycine betaine enhances biodegradation of phenol in high saline environments by the halophilic strainOceanobacillussp. PT-20

Glycine betaine enhanced the biodegradation of phenol by halophilic strain PT-20 in high salinity conditions.

Glycinebetaine Biosynthesis in Response to Osmotic Stress Depends on Jasmonate Signaling in Watermelon Suspension Cells

Glycinebetaine is an important non-toxic osmoprotectant, which is accumulated in higher plants under various stresses. The biosynthesis of glycinebetaine achieved via is a two-step oxidation from choline and betaine aldehyde, catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), respectively. Up-regulated gene expression of BADH and CMO induced by stress is clearly observed, but the signal transduction is poorly understood. Here, glycinebetaine accumulation in response to osmotic stress and growth recovery induced by exogenous glycinebetaine were observed in a watermelon cell line. When tracing back to the genome sequence of watermelon, it shows that there exists only one member of ClCMO or ClBADH corresponding to glycinebetaine biosynthesis. Both genes harbor a CGTCA-motif in their promoter region which is involved in methyl jasmonate (MeJA)-responsiveness. Amongst MeJA, Ethephon, abscisic acid (ABA), and salicylic acid (SA), MeJA was most effective in gene inducing the expression of ClCMO and ClBADH, and the accumulation of glycinebetaine could also reach an amount comparable to that after osmotic stress by mannitol. Moreover, when ibuprofen (IBU), a JA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, glycinebetaine accumulation was suppressed significantly. Interestingly, newly grown cells can keep a high content of glycinebetaine when they are sub-cultured from osmotic stressed cells. This study suggests that osmotic stress induced glycinebetaine biosynthesis occurs via JA signal transduction and not only plays a key role in osmotic stress resistance but also contributes to osmotic stress hardening.

Ecology of cold environments: new insights of bacterial metabolic adaptation through an integrated genomic-phenomic approach

Cold environments dominate Earth's biosphere, hosting complex microbial communities with the ability to thrive at low temperatures. However, the underlying molecular mechanisms and the metabolic pathways involved in bacterial cold-adaptation mechanisms are still not fully understood. Herein, we assessed the metabolic features of the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 (PhTAC125), a model organism for cold-adaptation, at both 4 °C and 15 °C, by integrating genomic and phenomic (high-throughput phenotyping) data and comparing the obtained results to the taxonomically related Antarctic bacterium Pseudoalteromonas sp. TB41 (PspTB41). Although the genome size of PspTB41 is considerably larger than PhTAC125, the higher number of genes did not reflect any higher metabolic versatility at 4 °C as compared to PhTAC125. Remarkably, protein S-thiolation regulated by glutathione and glutathionylspermidine appeared to be a new possible mechanism for cold adaptation in PhTAC125. More in general, this study represents an example of how 'multi-omic' information might potentially contribute in filling the gap between genotypic and phenotypic features related to cold-adaptation mechanisms in bacteria.

Quantification of glycine betaine, choline and trimethylamine N-oxide in seawater particulates: Minimisation of seawater associated ion suppression

A liquid chromatography/mass spectrometry (LC/MS, electrospray ionisation) method has been developed for the quantification of nitrogenous osmolytes (N-osmolytes) in the particulate fraction of natural water samples. Full method validation demonstrates the validity of the method for measuring glycine betaine (GBT), choline and trimethylamine N-oxide (TMAO) in particulates from seawater. Limits of detection were calculated as 3.5, 1.2 and 5.9 pg injected onto column (equivalent to 1.5, 0.6 and 3.9 nmol per litre) for GBT, choline and TMAO respectively. Precision of the method was typically 3% for both GBT and choline and 6% for TMAO. Collection of the particulate fraction of natural samples was achieved via in-line filtration. Resulting chromatography and method sensitivity was assessed and compared for the use of both glass fibre and polycarbonate filters during sample collection. Ion suppression was shown to be a significant cause of reduced instrument response to N-osmolytes and was associated with the presence of seawater in the sample matrix.

Revised scheme for the mechanism of photoinhibition and its application to enhance the abiotic stress tolerance of the photosynthetic machinery

When photosynthetic organisms are exposed to abiotic stress, their photosynthetic activity is significantly depressed. In particular, photosystem II (PSII) in the photosynthetic machinery is readily inactivated under strong light and this phenomenon is referred to as photoinhibition of PSII. Other types of abiotic stress act synergistically with light stress to accelerate photoinhibition. Recent studies of photoinhibition have revealed that light stress damages PSII directly, whereas other abiotic stresses act exclusively to inhibit the repair of PSII after light-induced damage (photodamage). Such inhibition of repair is associated with suppression, by reactive oxygen species (ROS), of the synthesis of proteins de novo and, in particular, of the D1 protein, and also with the reduced efficiency of repair under stress conditions. Gene-technological improvements in the tolerance of photosynthetic organisms to various abiotic stresses have been achieved via protection of the repair system from ROS and, also, by enhancing the efficiency of repair via facilitation of the turnover of the D1 protein in PSII. In this review, we summarize the current status of research on photoinhibition as it relates to the effects of abiotic stress and we discuss successful strategies that enhance the activity of the repair machinery. In addition, we propose several potential methods for activating the repair system by gene-technological methods.

Protection of Bacillus subtilis against cold stress via compatible-solute acquisition

Accumulation of compatible solutes is a strategy widely employed by bacteria to achieve cellular protection against high osmolarity. These compounds are also used in some microorganisms as thermostress protectants. We found that Bacillus subtilis uses the compatible solute glycine betaine as an effective cold stress protectant. Glycine betaine strongly stimulated growth at 15°C and permitted cell proliferation at the growth-inhibiting temperature of 13°C. Initial uptake of glycine betaine at 15°C was low but led eventually to the buildup of an intracellular pool whose size was double that found in cells grown at 35°C. Each of the three glycine betaine transporters (OpuA, OpuC, and OpuD) contributed to glycine betaine accumulation in the cold. Protection against cold stress was also accomplished when glycine betaine was synthesized from its precursor choline. Growth of a mutant defective in the osmoadaptive biosynthesis for the compatible solute proline was not impaired at low temperature (15°C). In addition to glycine betaine, the compatible solutes and osmoprotectants l-carnitine, crotonobetaine, butyrobetaine, homobetaine, dimethylsulfonioactetate, and proline betaine all served as cold stress protectants as well and were accumulated via known Opu transport systems. In contrast, the compatible solutes and osmoprotectants choline-O-sulfate, ectoine, proline, and glutamate were not cold protective. Our data highlight an underappreciated facet of the acclimatization of B. subtilis to cold environments and allow a comparison of the characteristics of compatible solutes with respect to their osmotic, heat, and cold stress-protective properties for B. subtilis cells.

Simultaneous expression of choline oxidase, superoxide dismutase and ascorbate peroxidase in potato plant chloroplasts provides synergistically enhanced protection against various abiotic stresses

Plants synthesize compatible solutes such as glycinebetaine (GB) in response to abiotic stresses. To evaluate the synergistic and protective effect of GB, transgenic potato plants expressing superoxide dismutase (SOD) and ascorbate peroxidase (APX) targeting to chloroplasts (referred to as SSA plants) were retransformed with a bacterial choline oxidase (codA) gene to synthesize GB in chloroplast in naturally occurring non-accumulator potato plants (including SSA) under the control of the stress-inducible SWPA2 promoter (referred to as SSAC plants). GB accumulation resulted in enhanced protection of these SSAC plants and lower levels of H(2)O(2) compared with SSA and non-transgenic (NT) plants after methyl viologen (MV)-mediated oxidative stress. Additionally, SSAC plants demonstrated synergistically enhanced tolerance to salt and drought stresses at the whole-plant level. GB accumulation in SSAC plants helped to maintain higher activities of SOD, APX and catalase following oxidative, salt and drought stress treatments than is observed in SSA and NT plants. Conclusively, GB accumulation in SSAC plants along with overexpression of antioxidant genes rendered the plants tolerant to multiple environmental stresses in a synergistic fashion.

Substitution of an active site valine uncovers a kinetically slow equilibrium between competent and incompetent forms of choline oxidase

The enzymatic oxidation of choline to glycine betaine is of interest because organisms accumulate glycine betaine intracellularly in response to stress conditions. This is relevant for the genetic engineering of crops with economic interest that do not naturally possess efficient pathways for the synthesis of glycine betaine and for the potential development of drugs that target the glycine betaine biosynthetic pathway in human pathogens. To date, the best characterized choline-oxidizing enzyme is the flavin-dependent choline oxidase from Arthrobacter globiformis, for which structural, mechanistic, and biochemical data are available. Here, we have replaced a hydrophobic residue (Val464) lining the active site cavity close to the N(5) atom of the flavin with threonine or alanine to investigate its role in the reaction of choline oxidation catalyzed by choline oxidase. The reductive half-reactions of the enzyme variants containing Thr464 or Ala464 were investigated using substrate and solvent kinetic isotope effects, solvent viscosity effects, and proton inventories. Replacement of Val464 with threonine or alanine uncovered a kinetically slow equilibrium between a catalytically incompetent form of enzyme and an active species that can efficiently oxidize choline. In both variants, the active form of enzyme shows a decreased rate of hydroxyl proton abstraction from the alcohol substrate, with minimal changes in the subsequent rate of hydride ion transfer to the flavin. This study therefore establishes that a hydrophobic residue not directly participating in catalysis plays important roles in the reaction of choline oxidation catalyzed by choline oxidase.

Enzymatic characterization of peroxisomal and cytosolic betaine aldehyde dehydrogenases in barley

Betaine aldehyde dehydrogenase (BADH; EC 1.2.1.8) is an important enzyme that catalyzes the last step in the synthesis of glycine betaine, a compatible solute accumulated by many plants under various abiotic stresses. In barley (Hordeum vulgare L.), we reported previously the existence of two BADH genes (BBD1 and BBD2) and their corresponding proteins, peroxisomal BADH (BBD1) and cytosolic BADH (BBD2). To investigate their enzymatic properties, we expressed them in Escherichia coli and purified both proteins. Enzymatic analysis indicated that the affinity of BBD2 for betaine aldehyde was reasonable as other plant BADHs, but BBD1 showed extremely low affinity for betaine aldehyde with apparent K(m) of 18.9 microM and 19.9 mM, respectively. In addition, V(max)/K(m) with betaine aldehyde of BBD2 was about 2000-fold higher than that of BBD1, suggesting that BBD2 plays a main role in glycine betaine synthesis in barley plants. However, BBD1 catalyzed the oxidation of omega-aminoaldehydes such as 4-aminobutyraldehyde and 3-aminopropionaldehyde as efficiently as BBD2. We also found that both BBDs oxidized 4-N-trimethylaminobutyraldehyde and 3-N-trimethylaminopropionaldehyde.

Coordinated regulation of cold-induced changes in fatty acids with cardiolipin and phosphatidylglycerol composition among phospholipid species for the food pathogen Listeria monocytogenes

We present here the structural identification of four phospholipid (Phl) classes in Listeria monocytogenes, the fatty acid (FA) composition for each individual Phl species, and a description of cold-induced FA changes. Cardiolipin (48.5%) and phosphatidylglycerol (18.1%) are dominated by anteiso-FA, and the previously recognized branched FA chain shortening by cold was observed singularly in these Phls. Phosploaminolipid (19.9%) and phosphatidylinositol, (9.1%) are significantly different, containing significant amounts of straight-chain FA. These findings are supported by nuclear magnetic resonance analysis.

Stress-induced expression of choline oxidase in potato plant chloroplasts confers enhanced tolerance to oxidative, salt, and drought stresses

Transgenic potato plants (Solanum tuberosum L. cv. Superior) with the ability to synthesize glycinebetaine (GB) in chloroplasts (referred to as SC plants) were developed via the introduction of the bacterial choline oxidase (codA) gene under the control of an oxidative stress-inducible SWPA2 promoter. SC1 and SC2 plants were selected via the evaluation of methyl viologen (MV)-mediated oxidative stress tolerance, using leaf discs for further characterization. The GB contents in the leaves of SC1 and SC2 plants following MV treatment were found to be 0.9 and 1.43 micromol/g fresh weight by HPLC analysis, respectively. In addition to reduced membrane damage after oxidative stress, the SC plants evidenced enhanced tolerance to NaCl and drought stress on the whole plant level. When the SC plants were subjected to two weeks of 150 mM NaCl stress, the photosynthetic activity of the SC1 and SC2 plants was attenuated by 38 and 27%, respectively, whereas that of non-transgenic (NT) plants was decreased by 58%. Under drought stress conditions, the SC plants maintained higher water contents and accumulated higher levels of vegetative biomass than was observed in the NT plants. These results indicate that stress-induced GB production in the chloroplasts of GB non-accumulating plants may prove useful in the development of industrial transgenic plants with increased tolerance to a variety of environmental stresses for sustainable agriculture applications.

Screening of genes regulated by cold shock in Shewanella piezotolerans WP3 and time course expression of cold-regulated genes

The differential gene transcription of a deep-sea bacterium Shewanella piezotolerans WP3 in response to cold shock was analyzed by RNA arbitrarily primed PCR. Ninety primer sets were used to scan two different RNA pools derived from the culture of cold shock and its control (culture at its optimal grown temperature). Ninety-four putative differentially expressed fragments were identified and cloned. Six out of the 94 fragments were confirmed to be truly differentially transcribed in terms of cold shock by reverse Northern dot blot and then sequenced. Sequence blast analysis showed that the six differentially transcribed genes are putative genes for zonular occludens toxin, chaperon GroEL, efflux transporter, Sua5/YciO/YrdC/YwlC family protein, betaine-aldehyde dehydrogenase, and DEAD box RNA helicase, respectively. The time course expression profiles of these six genes from 0 to 90 min upon cold shock were quantified by real-time PCR. Deletion mutation of the highest induced gene--RNA helicase gene, had no significant impact on the growth of the strain no matter upon cold shock or under permanent low temperature. It is suggested that one or more additional DEAD box RNA helicase genes compensate for the loss of the function of the mutated gene.

Glycinebetaine alleviates the inhibitory effect of moderate heat stress on the repair of photosystem II during photoinhibition

Transformation with the bacterial gene codA for choline oxidase allows Synechococcus sp. PCC 7942 cells to accumulate glycinebetaine when choline is supplemented exogenously. First, we observed two types of protective effect of glycinebetaine against heat-induced inactivation of photosystem II (PSII) in darkness; the codA transgene shifted the temperature range of inactivation of the oxygen-evolving complex from 40-52 degrees C (with half inactivation at 46 degrees C) to 46-60 degrees C (with half inactivation at 54 degrees C) and that of the photochemical reaction center from 44-55 degrees C (with half inactivation at 51 degrees C) to 52-63 degrees C (with half inactivation at 58 degrees C). However, in light, PSII was more sensitive to heat stress; when moderate heat stress, such as 40 degrees C, was combined with light stress, PSII was rapidly inactivated, although these stresses, when applied separately, did not inactivate either the oxygen-evolving complex or the photochemical reaction center. Further our studies demonstrated that the moderate heat stress inhibited the repair of PSII during photoinhibition at the site of synthesis de novo of the D1 protein but did not accelerate the photodamage directly. The codA transgene and, thus, the accumulation of glycinebetaine alleviated such an inhibitory effect of moderate heat stress on the repair of PSII by accelerating the synthesis of the D1 protein. We propose a hypothetical scheme for the cyanobacterial photosynthesis that moderate heat stress inhibits the translation machinery and glycinebetaine protects it against the heat-induced inactivation.

Chlamydomonas reinhardtii, a model system for functional validation of abiotic stress responsive genes

Stress tolerance is a multigenic character and there are many stress responsive genes, which are stress specific. Although many of these have been cloned, their functional significance remains fragmentary. Hence it is important to identify the relevant stress genes involved in altering the metabolism for adaptation. Overexpression is one of the several approaches and Chlamydomonas is a suitable system to study the functional relevance of stress genes. Stress responses can only be assessed on prior exposure to sublethal induction stress. In this study the acclimation response of Chlamydomonas was assessed for different abiotic stresses using physiological screens like chlorophyll stability, membrane damage, cell viability, accumulation of free radicals, survival and recovery growth. We demonstrate that Chlamydomonas responds to diverse stresses and is a potential system to study the relevance of stress genes. The relevance of choline oxidase A (codA), a key enzyme in glycinebetaine biosynthesis, was examined by developing transformants expressing codA gene from Arthrobacter globiformis. Southern positive transformants showed enhanced accumulation of glycinebetaine. The transformants also showed enhanced growth under salinity, high light coupled with methylviologen-induced oxidative stress, high temperature and cold stress. However the transgenics were not tolerant to PEG-mediated simulated osmotic stress, LiCl, menadione and UV stress. Increased cell survival and decreased chlorophyll degradation in transformants under acclimated conditions further confirmed the relevance of codA in imparting stress tolerance. Our results indicated that the relevance of stress responsive genes can be efficiently validated for diverse abiotic stresses using Chlamydomonas system.

Glycinebetaine accumulation is more effective in chloroplasts than in the cytosol for protecting transgenic tomato plants against abiotic stress

Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants were transformed with a gene for choline oxidase (codA) from Arthrobacter globiformis. The gene product (CODA) was targeted to the chloroplasts (Chl-codA), cytosol (Cyt-codA) or both compartments simultaneously (ChlCyt-codA). These three transgenic plant types accumulated different amounts and proportions of glycinebetaine (GB) in their chloroplasts and cytosol. Targeting CODA to either the cytosol or both compartments simultaneously increased total GB content by five- to sixfold over that measured from the chloroplast targeted lines. Accumulation of GB in codA transgenic plants was tissue dependent, with the highest levels being recorded in reproductive organs. Despite accumulating, the lowest amounts of GB, Chl-codA plants exhibited equal or higher degrees of enhanced tolerance to various abiotic stresses. This suggests that chloroplastic GB is more effective than cytosolic GB in protecting plant cells against chilling, high salt and oxidative stresses. Chloroplastic GB levels were positively correlated with the degree of oxidative stress tolerance conferred, whereas cytosolic GB showed no such a correlation. Thus, an increase in total GB content does not necessarily lead to enhanced stress tolerance, but additional accumulation of chloroplastic GB is likely to further raise the level of stress tolerance beyond what we have observed.

The induction of CP43′ by iron-stress in Synechococcus sp. PCC 7942 is associated with carotenoid accumulation and enhanced fatty acid unsaturation

Comparative lipid analysis demonstrated reduced amount of PG (50%) and lower ratio of MGDG/DGDG in iron-stressed Synechococcus sp. PCC 7942 cells compared to cells grown under iron sufficient conditions. In parallel, the monoenoic (C:1) fatty acids in MGDG, DGDG and PG increased from 46.8%, 43.7% and 45.6%, respectively in control cells to 51.6%, 48.8% and 48.7%, respectively in iron-stressed cells. This suggests increased membrane dynamics, which may facilitate the diffusion of PQ and keep the PQ pool in relatively more oxidized state in iron-stressed compared to control cells. This was confirmed by chlorophyll fluorescence and thermoluminescence measurements. Analysis of carotenoid composition demonstrated that the induction of isiA (CP43') protein in response to iron stress is accompanied by significant increase of the relative abundance of all carotenoids. The quantity of carotenoids calculated on a Chl basis increased differentially with nostoxanthin, cryptoxanthin, zeaxanthin and beta-carotene showing 2.6-, 3.1-, 1.9- and 1.9-fold increases, respectively, while the relative amount of caloxanthin was increased only by 30%. HPLC analyses of the pigment composition of Chl-protein complexes separated by non-denaturating SDS-PAGE demonstrated even higher relative carotenoids content, especially of cryptoxanthin, in trimer and monomer PSI Chl-protein complexes co-migrating with CP43' from iron-stressed cells than in PSI complexes from control cells where CP43' is not present. This implies a carotenoid-binding role for the CP43' protein which supports our previous suggestion for effective energy quenching and photoprotective role of CP43' protein in cyanobacteria under iron stress.

Changes in cyclic and respiratory electron transport by the movement of phycobilisomes in the cyanobacterium Synechocystis sp. strain PCC 6803

Phycobilisomes (PBS) are the major accessory light-harvesting complexes in cyanobacteria and their mobility affects the light energy distribution between the two photosystems. We investigated the effect of PBS mobility on state transitions, photosynthetic and respiratory electron transport, and various fluorescence parameters in Synechocystis sp. strain PCC 6803, using glycinebetaine to immobilize and couple PBS to photosystem II (PSII) or photosystem I (PSI) by applying under far-red or green light, respectively. The immobilization of PBS at PSII inhibited the increase in cyclic electron flow, photochemical and non-photochemical quenching, and decrease in respiration that occurred during the movement of PBS from PSII to PSI. In contrast, the immobilization of PBS at PSI inhibited the increase in respiration and photochemical quenching and decrease in cyclic electron flow and non-photochemical quenching that occurred when PBS moved from PSI to PSII. Linear electron transport did not change during PBS movement but increased or decreased significantly during longer illumination with far-red or green light, respectively. This implies that PBS movement is completed in a short time but it takes longer for the overall photosynthetic reactions to be tuned to a new state.

Genetic engineering of the biosynthesis of glycinebetaine enhances thermotolerance of photosystem II in tobacco plants

Genetically engineered tobacco (Nicotiana tabacum L.) with the ability to accumulate glycinebetaine was established. The wild type and transgenic plants were exposed to heat treatment (25-50 degrees C) for 4 h in the dark and under growth light intensity (300 mumol m(-2) s(-1)). The analyses of oxygen-evolving activity and chlorophyll fluorescence demonstrated that photosystem II (PSII) in transgenic plants showed higher thermotolerance than in wild type plants in particular when heat stress was performed in the light, suggesting that the accumulation of glycinebetaine leads to increased tolerance to heat-enhanced photoinhibition. This increased tolerance was associated with an improvement on thermostability of the oxygen-evolving complex and the reaction center of PSII. The enhanced tolerance was caused by acceleration of the repair of PSII from heat-enhanced photoinhibition. Under heat stress, there was a significant accumulation of H(2)O(2), O (2) (-) and catalytic Fe in wild type plants but this accumulation was much less in transgenic plants. Heat stress significantly decreased the activities of catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase in wild type plants whereas the activities of these enzymes either decreased much less or maintained or even increased in transgenic plants. In addition, heat stress increased the activity of superoxide dismutase in wild type plants but this increase was much greater in transgenic plants. Furthermore, transgenic plants also showed higher content of ascorbate and reduced glutathione than that of wild type plants under heat stress. The results suggest that the increased thermotolerance induced by accumulation of glycinebetaine in vivo was associated with the enhancement of the repair of PSII from heat-enhanced photo inhibition, which might be due to less accumulation of reactive oxygen species in transgenic plants.

Photoinhibition of photosystem II under environmental stress

Inhibition of the activity of photosystem II (PSII) under strong light is referred to as photoinhibition. This phenomenon is due to an imbalance between the rate of photodamage to PSII and the rate of the repair of damaged PSII. In the "classical" scheme for the mechanism of photoinhibition, strong light induces the production of reactive oxygen species (ROS), which directly inactivate the photochemical reaction center of PSII. By contrast, in a new scheme, we propose that photodamage is initiated by the direct effect of light on the oxygen-evolving complex and that ROS inhibit the repair of photodamaged PSII by suppressing primarily the synthesis of proteins de novo. The activity of PSII is restricted by a variety of environmental stresses. The effects of environmental stress on damage to and repair of PSII can be examined separately and it appears that environmental stresses, with the exception of strong light, act primarily by inhibiting the repair of PSII. Studies have demonstrated that repair-inhibitory stresses include CO(2) limitation, moderate heat, high concentrations of NaCl, and low temperature, each of which suppresses the synthesis of proteins de novo, which is required for the repair of PSII. We postulate that most types of environmental stress inhibit the fixation of CO(2) with the resultant generation of ROS, which, in turn, inhibit protein synthesis.

Trapping choline oxidase in a nonfunctional conformation by freezing at low pH

Choline oxidase is a flavin-dependent enzyme that catalyzes the oxidation of choline to glycine-betaine, with oxygen as electron acceptor. Storage at pH 6 and -20 degrees C resulted in a change in the conformation of choline oxidase, which was associated with complete loss of catalytic activity when the enzyme was assayed at pH 6. Incubation of the inactive enzyme at pH values > or = 6.5 and 25 degrees C resulted in a fast and partial reactivation of the enzyme, which occurred with slow onset of steady state during enzymatic turnover. The rate of approaching steady state was independent of the concentrations of choline and enzyme, but increased to a limiting value with increasing pH, defining a pKa value of approximately 7.3 for an unprotonated group required for enzyme activation. Prolonged incubation of the inactive enzyme at pH 6 and temperatures > or = 20 degrees C, at which no hysteretic behavior was observed, resulted in the slow and full recovery of activity over 3 h, associated with a conformational change that reverted the enzyme to the native form. Activation of the enzyme at pH 6 was enthalpy-driven with deltaH(double dagger) and TdeltaS(double dagger) values of approximately 112 kJ mol(-1) and approximately 20 kJ mol(-1) determined at 25 degrees C. These data suggest that freezing the enzyme at low pH induces a localized and reversible conformational change that is associated with the complete and reversible loss of catalytic activity.

Iron deficiency in cyanobacteria causes monomerization of photosystem I trimers and reduces the capacity for state transitions and the effective absorption cross section of photosystem I in vivo

The induction of the isiA (CP43') protein in iron-stressed cyanobacteria is accompanied by the formation of a ring of 18 CP43' proteins around the photosystem I (PSI) trimer and is thought to increase the absorption cross section of PSI within the CP43'-PSI supercomplex. In contrast to these in vitro studies, our in vivo measurements failed to demonstrate any increase of the PSI absorption cross section in two strains (Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803) of iron-stressed cells. We report that iron-stressed cells exhibited a reduced capacity for state transitions and limited dark reduction of the plastoquinone pool, which accounts for the increase in PSII-related 685 nm chlorophyll fluorescence under iron deficiency. This was accompanied by lower abundance of the NADP-dehydrogenase complex and the PSI-associated subunit PsaL, as well as a reduced amount of phosphatidylglycerol. Nondenaturating polyacrylamide gel electrophoresis separation of the chlorophyll-protein complexes indicated that the monomeric form of PSI is favored over the trimeric form of PSI under iron stress. Thus, we demonstrate that the induction of CP43' does not increase the PSI functional absorption cross section of whole cells in vivo, but rather, induces monomerization of PSI trimers and reduces the capacity for state transitions. We discuss the role of CP43' as an effective energy quencher to photoprotect PSII and PSI under unfavorable environmental conditions in cyanobacteria in vivo.

Glycinebetaine counteracts the inhibitory effects of salt stress on the degradation and synthesis of D1 protein during photoinhibition in Synechococcus sp. PCC 7942

Glycinebetaine (hereafter referred to as betaine) is a compatible solute that accumulates in certain plants and microorganisms in response to various types of stress. We demonstrated previously that when the cyanobacterium Synechococcus sp. PCC 7942 (hereafter Synechococcus) is transformed with the codA gene for choline oxidase, it can synthesize betaine from exogenously supplied choline, exhibiting enhanced tolerance to salt and cold stress. In this study, we examined the effects of salt stress and betaine synthesis on the photoinhibition of photosystem II (PSII). Salt stress due to 220 mm NaCl enhanced photoinhibition of PSII and betaine protected PSII against photoinhibition under these conditions. However, neither salt stress nor betaine synthesis affected photodamage to PSII. By contrast, salt stress inhibited repair of photodamaged PSII and betaine reversed this inhibitory effect of salt stress. Pulse-chase-labeling experiments revealed that salt stress inhibited degradation of D1 protein in photodamaged PSII and de novo synthesis of D1. By contrast, betaine protected the machinery required for degradation and synthesis of D1 under salt stress. Neither salt stress nor betaine affected levels of psbA transcripts. These observations suggest that betaine counteracts the inhibitory effects of salt stress, with resultant accelerated repair of photodamaged PSII.

Specific RNA binding to ordered phospholipid bilayers

We have studied RNA binding to vesicles bounded by ordered and disordered phospholipid membranes. A positive correlation exists between bilayer order and RNA affinity. In particular, structure-dependent RNA binding appears for rafted (liquid-ordered) domains in sphingomyelin-cholesterol-1,2-dioleoyl-sn-glycero-3-phosphocholine vesicles. Binding to more highly ordered gel phase membranes is stronger, but much less RNA structure-dependent. All modes of RNA-membrane association seem to be electrostatic and headgroup directed. Fluorometry on 1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes indicates that bound RNA broadens the gel-fluid melting transition, and reduces lipid headgroup order, as detected via fluorometric measurement of intramembrane electric fields. RNA preference for rafted lipid was visualized and confirmed using multiple fluorophores that allow fluorescence and fluorescence resonance energy transfer microscopy on RNA molecules closely associated with ordered lipid patches within giant vesicles. Accordingly, both RNA structure and membrane order could modulate biological RNA-membrane interactions.

Chill activation of compatible solute transporters in Corynebacterium glutamicum at the level of transport activity

The gram-positive soil bacterium Corynebacterium glutamicum harbors four osmoregulated secondary uptake systems for compatible solutes, BetP, EctP, LcoP, and ProP. When reconstituted in proteoliposomes, BetP was shown to sense hyperosmotic conditions via the increase in luminal K(+) and to respond by instant activation. To study further putative ways of stimulus perception and signal transduction, we have investigated the responses of EctP, LcoP, and BetP, all belonging to the betaine-carnitine-choline transporter family, to chill stress at the level of activity. When fully activated by hyperosmotic stress, they showed the expected increase of activity at increasing temperature. In the absence of osmotic stress, EctP was not activated by chill and LcoP to only a very low extent, whereas BetP was significantly stimulated at low temperature. BetP was maximally activated at 10 degrees C, reaching the same transport rate as that observed under hyperosmotic conditions at this temperature. A role of cytoplasmic K(+) in chill-dependent activation of BetP was ruled out, since (i) the cytoplasmic K(+) concentration did not change significantly at lower temperatures and (ii) a mutant BetP lacking the C-terminal 25 amino acids, which was previously shown to have lost the ability to be activated by luminal K(+), was fully competent in chill sensing. When heterologously expressed in Escherichia coli, BetP did not respond to chill stress. This may indicate that the membrane in which BetP is inserted plays an important role in chill activation and thus in signal transduction by BetP, different from the previously established K(+)-mediated process.

Glycine betaine as a cryoprotectant for prokaryotes

Osmoprotectants are low molecular weight, hydrophilic, nontoxic molecules that assist a cell under osmotic stress to stabilize its concentration of internal solutes. These properties are similar to compounds used as cryoprotectants for the preservation of prokaryotic cells during freezing. This study tested the ability of a common compatible solute, glycine betaine (GB), to act as a cryoprotectant. In a series of freeze-drying studies using a variety of prokaryotes, GB performed as well, or better than, two commonly used cryoprotectants, sucrose/bovine serum albumin (S/BSA) and trehalose/dextran (T/D). GB did especially well maintaining cell viability after long-term storage (simulated equivalent of 20 years) for microorganisms like Neisseria gonorrhoeae and Streptococcus pneumoniae. GB was tested for its ability to preserve members of the genus Acidothiobacillus, a difficult genus to preserve. For two strains of Acidithiobacillus ferrooxidans that were preserved using liquid drying, GB performed as well as S/BSA. Results were more mixed for two strains of Acidithiobacillus thiooxidans; one strain could be preserved with S/BSA but not GB, the other strain gave low recoveries with both cryoprotectants. GB also proved to be a useful cryoprotectant for liquid nitrogen preservation yielding equivalent results to the cryopreservative, glycerol for halophilic archaea, and neutrophilic Fe-oxidizing bacteria. These results indicate that GB is a simple and useful cryoprotectant that works for a wide range of prokaryotic organisms under different cryopreservation regimens.

Spectroscopic and kinetic properties of recombinant choline oxidase from Arthrobacter globiformis

Choline oxidase catalyzes the four-electron oxidation of choline to glycine betaine, with molecular oxygen acting as primary electron acceptor. Recently, the recombinant enzyme expressed in Escherichia coli was purified to homogeneity and shown to contain FAD in a mixture of oxidized and anionic semiquinone redox states [Fan et al. (2003) Arch. Biochem. Biophys., in press]. In this study, methods have been devised to convert the enzyme-bound flavin semiquinone to oxidized FAD and vice versa, allowing characterization of the resulting forms of choline oxidase. The enzyme-bound oxidized flavin showed typical UV-vis absorbance peaks at 359 and 452 nm (with epsilon(452) = 11.4 M(-1) cm(-1)) and emitted light at 530 nm (with lambda(ex) at 452 nm). The affinity of the enzyme for sulfite was high (with a K(d) value of approximately 50 microM at pH 7 and 15 degrees C), suggesting the presence of a positive charge near the N(1)C(2)=O locus of the flavin. The enzyme-bound anionic flavin semiquinone was unusually insensitive to oxygen or ferricyanide at pH 8 and showed absorbance peaks at 372 and 495 nm (with epsilon(372) = 19.95 M(-1) cm(-1)), maximal fluorescence emission at 454 nm (with lambda(ex) at 372 nm), circular dichroic signals at 370 and 406 nm, and an ESR peak-to-peak line width of 13.9 G. Both UV-vis absorbance studies on the enzyme under turnover with choline and steady-state kinetic data with either choline or betaine aldehyde were consistent with the flavin semiquinone being not involved in catalysis. The pH dependence of the kinetic parameters at varying concentrations of both choline and oxygen indicated that a catalytic base is required for choline oxidation but not for oxygen reduction and that the order of the kinetic steps involving substrate binding and product release is not affected by pH.

Role of the glycine betaine and carnitine transporters in adaptation of Listeria monocytogenes to chill stress in defined medium

The food-borne pathogen Listeria monocytogenes proliferates at refrigeration temperatures, rendering refrigeration ineffective in the preservation of Listeria-contaminated foods. The uptake and intracellular accumulation of the potent compatible solutes glycine betaine and carnitine has been shown to be a key mediator of the pathogen's cold-tolerant phenotype. To date, three compatible solute systems are known to operate in L. monocytogenes: glycine betaine porter I (BetL), glycine betaine porter II (Gbu), and the carnitine transporter OpuC. We investigated the specificity of each transporter towards each compatible solute at 4 degrees C by examining mutant derivatives of L. monocytogenes 10403S that possess each of the transporters in isolation. Kinetic and steady-state compatible solute accumulation data together with growth rate experiments demonstrated that under cold stress glycine betaine transport is primarily mediated by Gbu and that Gbu-mediated betaine uptake results in significant growth stimulation of chill-stressed cells. BetL and OpuC can serve as minor porters for the uptake of betaine, and their action is capable of providing a small degree of cryotolerance. Under cold stress, carnitine transport occurs primarily through OpuC and results in a high level of cryoprotection. Weak carnitine transport occurs via Gbu and BetL, conferring correspondingly weak cryoprotection. No other transporter in L. monocytogenes 10403S appears to be involved in transport of either compatible solute at 4 degrees C, since a triple mutant strain yielded neither transport nor accumulation of glycine betaine or carnitine and could not be rescued by either osmolyte when grown at that temperature.

Nitrogen status modulates the expression of RNA-binding proteins in cyanobacteria

Biochemical responses to cold and osmotic stresses overlap because each decreases the availability of free water. Since RNA-binding proteins are known to accumulate following cold stress and play key roles in regulating transcription termination, the effect of osmotic stress on expression of RNA-binding proteins was examined. The transcript levels of four genes encoding RNA-binding proteins (rbpA, rbpB, rbpC and rbpD) were monitored in Anabaena sp. PCC 7120 cultures supplemented with ammonium ions or growing under nitrogen-fixing conditions. Steady-state transcript levels of all four genes increased transiently in response to a temperature shift from 30 to 20 degrees C under both nitrogen regimes. Osmotic stress also enhanced rbpB, rbpC and rbpD gene expression in ammonium grown cultures. In the absence of a combined nitrogen source, osmotic stress repressed the short-term induction of rbp gene expression. The accumulation of RNA-binding proteins did not follow transcript levels, but remained high 24 h after stress initiation. It is concluded that nitrogen nutrition modulates the stress-responsive regulation of RNA-binding proteins in cyanobacteria, providing a potential mechanism to integrate environmental and developmental signals.

Enhanced formation of flowers in salt-stressed Arabidopsis after genetic engineering of the synthesis of glycine betaine

Previously, we showed that transformation with the codA gene for choline oxidase allows plants to synthesize glycine betaine (GB) and enhances their ability to tolerate various kinds of stress during germination and vegetative growth. In this study, we examined the tolerance of transformed plants to salt stress at the reproductive stage, which is the stage at which plants are most sensitive to environmental stress. Salt-shock treatment of wild-type plants for 3 days resulted in the abortion of flower buds and decreased the number of seeds per silique. These deleterious effects were clearly visible 6 days after the termination of salt-shock treatment. Microscopic examination of floral structures revealed that salt stress inhibited the development of anthers, pistils, and petals. In particular, the production of pollen grains and ovules was dramatically inhibited. These effects of salt stress were significantly reduced by transformation with the codA gene, and our observations suggested that the enhanced tolerance of the transgenic plants was a result of the accumulation of GB in the reproductive organs. Indeed, levels of GB in flowers, siliques, and inflorescence apices were about five times higher than in leaves.

Osmoregulation and its importance to food-borne microorganisms

The control of water activity has been used as a means of preserving foods for thousands of years. This preservation strategy presents food-borne microorganisms with serious problems, many of which relate to the management of water flow. Although the specific details of how each organism deals with these problems are different, several common themes have emerged. Bacteria induce specific responses. both physiological and genetic, to respond to either the loss or the gain of water, triggered by changes in the osmolarity of the environment. Many of the key systems have now been identified and the mechanisms of their regulation are beginning to be understood. Here we review recent developments in the field of bacterial osmoregulation with emphasis on key food-borne genera.

The role of glycine betaine in the protection of plants from stress: clues from transgenic plants

The acclimation of a plant to a constantly changing environment involves the accumulation of certain organic compounds of low molecular mass, known collectively as compatible solutes, in the cytoplasm. The evidence from numerous investigations of the physiology, genetics, biophysics and biochemistry of plants strongly suggests that glycine betaine (GB), an amphoteric quaternary amine, plays an important role as a compatible solute in plants under various types of environmental stress, such as high levels of salts and low temperature. Plant species vary in their capacity to synthesize GB and some plants, such as spinach and barley, accumulate relatively high levels of GB in their chloroplasts while others, such as Arabidopsis and tobacco, do not synthesize this compound. Genetic engineering has allowed the introduction into GB-deficient species of biosynthetic pathways to GB from both micro-organisms and higher plants; this approach has facilitated investigations of the importance of GB in stress protection. In this review, we summarize recent progress in the genetic manipulation of the synthesis of GB, with special emphasis on the relationship between the protective effects of GB in vivo and those documented in vitro.

Unsaturated fatty acids in membrane lipids protect the photosynthetic machinery against salt-induced damage in Synechococcus

In this study, the tolerance to salt stress of the photosynthetic machinery was examined in relation to the effects of the genetic enhancement of the unsaturation of fatty acids in membrane lipids in wild-type and desA+ cells of Synechococcus sp. PCC 7942. Wild-type cells synthesized saturated and mono-unsaturated fatty acids, whereas desA+ cells, which had been transformed with the desA gene for the Delta12 acyl-lipid desaturase of Synechocystis sp. PCC 6803, also synthesized di-unsaturated fatty acids. Incubation of wild-type and desA+ cells with 0.5 M NaCl resulted in the rapid loss of the activities of photosystem I, photosystem II, and the Na+/H+ antiport system both in light and in darkness. However, desA+ cells were more tolerant to salt stress and osmotic stress than the wild-type cells. The extent of the recovery of the various photosynthetic activities from the effects of 0.5 M NaCl was much greater in desA+ cells than in wild-type cells. The photosystem II activity of thylakoid membranes from desA+ cells was more resistant to 0.5 M NaCl than that of membranes from wild-type cells. These results demonstrated that the genetically engineered increase in unsaturation of fatty acids in membrane lipids significantly enhanced the tolerance of the photosynthetic machinery to salt stress. The enhanced tolerance was due both to the increased resistance of the photosynthetic machinery to the salt-induced damage and to the increased ability of desA+ cells to repair the photosynthetic and Na+/H+ antiport systems.

Biotechnological applications of plant freezing associated proteins

Plants use a wide array of proteins to protect themselves against low temperature and freezing conditions. The identification of these freezing tolerance associated proteins and the elucidation of their cryoprotective functions will have important applications in several fields. Genes encoding structural proteins, osmolyte producing enzymes, oxidative stress scavenging enzymes, lipid desaturases and gene regulators have been used to produce transgenic plants. These studies have revealed the potential capacity of different genes to protect against temperature related stresses. In some cases, transgenic plants with significant cold tolerance have been produced. Furthermore, the biochemical characterization of the cold induced antifreeze proteins and dehydrins reveals many applications in the food and the medical industries. These proteins are being considered as food additives to improve the quality and shelf-life of frozen foods, as cryoprotective agents for organ and cell cryopreservation, and as chemical adjuvant in cancer cryosurgery.

Improved tolerance to salinity and low temperature in transgenic tobacco producing glycine betaine

Glycine betaine is an osmoprotectant found in many organisms, including bacteria and higher plants. The bacterium Escherichia coli produces glycine betaine by a two-step pathway where choline dehydrogenase (CDH), encoded by betA, oxidizes choline to betaine aldehyde which is further oxidized to glycine betaine by the same enzyme. The second step, conversion of betaine aldehyde into glycine betaine, can also be performed by the second enzyme in the pathway, betaine aldehyde dehydrogenase (BADH), encoded by betB. Transformation of tobacco (Nicotiana tabacum), a species not accumulating glycine betaine, with the E. coli genes for glycine betaine biosynthesis, resulted in transgenic plants accumulating glycine betaine. Plants producing CDH were found to accumulate glycine betaine as did F1 progeny from crosses between CDH- and BADH-producing lines. Plants producing both CDH and BADH generally accumulated higher amounts of glycine betaine than plants producing CDH alone, as determined by 1H NMR analysis. Transgenic tobacco lines accumulating glycine betaine exhibited increased tolerance to salt stress as measured by biomass production of greenhouse-grown intact plants. Furthermore, experiments conducted with leaf discs from glycine betaine-accumulating plants indicated enhanced recovery from photoinhibition caused by high light and salt stress as well as improved tolerance to photoinhibition under low temperature conditions. In conclusion, introduction of glycine betaine production into tobacco is associated with increased stress tolerance probably partly due to improved protection of the photosynthetic apparatus.

Osmoprotectants and cryoprotectants for Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen that can grow in high osmotic strength environments and at refrigeration temperatures. Glycine betaine, proline betaine, acetylcarnitine, carnitine, gamma-butyrobetaine and 3-dimethylsulphoniopropionate all acted as osmoprotectants, as evidenced by an increase in growth rate of L. monocytogenes 10403S and Scott A when provided with these compounds, while being stressed in defined medium containing 0.7 M NaCl. These same compounds exhibited cryoprotective activity, as evidenced by increasing the growth rate of L. monocytogenes at 5 degrees C. Ectoine, hydroxy ectoine, pipecolic acid and proline were ineffective as osmoprotectants or cryoprotectants under these conditions. The presence of osmoprotectants and cryoprotectants in foods may provide compounds assisting L. monocytogenes to overcome the barriers of high osmotic strength and low temperature that otherwise control microbial growth.

Iron superoxide dismutase protects against chilling damage in the cyanobacterium synechococcus species PCC7942

A strain of Synechococcus sp. PCC7942 lacking functional Fe superoxide dismutase (SOD), designated sodB-, was characterized by its growth rate, photosynthetic pigments, inhibition of photosynthetic electron transport activity, and total SOD activity at 0 degrees C, 10 degrees C, 17 degrees C, and 27 degrees C in moderate light. At 27 degrees C, the sodB- and wild-type strains had similar growth rates, chlorophyll and carotenoid contents, and cyclic photosynthetic electron transport activity. The sodB- strain was more sensitive to chilling stress at 17 degrees C than the wild type, indicating a role for FeSOD in protection against photooxidative damage during moderate chilling in light. However, both the wild-type and sodB- strains exhibited similar chilling damage at 0 degrees C and 10 degrees C, indicating that the FeSOD does not provide protection against severe chilling stress in light. Total SOD activity was lower in the sodB- strain than in the wild type at 17 degrees C and 27 degrees C. Total SOD activity decreased with decreasing temperature in both strains but more so in the wild type. Total SOD activity was equal in the two strains when assayed at 0 degrees C.

Enhanced tolerance to light stress of transgenic Arabidopsis plants that express the codA gene for a bacterial choline oxidase

Arabidopsis thaliana was transformed with the codA gene from Arthrobacter globiformis. This gene encodes choline oxidase, an enzyme that converts choline to glycinebetaine. The photosynthetic activity, monitored in terms of chlorophyll fluorescence, of transformed plants was more tolerant to light stress than that of wild-type plants. This enhanced tolerance to light stress was caused by acceleration of the recovery of the photosystem II (PS II) complex from the photo-inactivated state. The transformed plants synthesized glycinebetaine, but no changes were detected in the relative levels of membrane lipids or in the relative levels of fatty acids in the various membrane lipids. Transformation with the codA gene increased levels of H2O2, a by-product of the reaction catalyzed by choline oxidase, by only 50% to 100% under stress or non-stress conditions. The activity of ascorbate peroxidase and, to a lesser extent, that of catalase in transformed plants were significantly higher than in the wild-type plants. These observations suggest that H2O2 produced by choline oxidase in the transformed plants might have stimulated the expression of H2O2 scavenging enzymes, with resultant maintenance of the level of H2O2 within a certain limited range. It appears that glycinebetaine produced in vivo, but not changes in membrane lipids or in the level of H2O2, protected the PS II complex in transformed plants from damage due to light stress.

Osmosensing by bacteria: signals and membrane-based sensors

Bacteria can survive dramatic osmotic shifts. Osmoregulatory responses mitigate the passive adjustments in cell structure and the growth inhibition that may ensue. The levels of certain cytoplasmic solutes rise and fall in response to increases and decreases, respectively, in extracellular osmolality. Certain organic compounds are favored over ions as osmoregulatory solutes, although K+ fluxes are intrinsic to the osmoregulatory response for at least some organisms. Osmosensors must undergo transitions between "off" and "on" conformations in response to changes in extracellular water activity (direct osmosensing) or resulting changes in cell structure (indirect osmosensing). Those located in the cytoplasmic membranes and nucleoids of bacteria are positioned for indirect osmosensing. Cytoplasmic membrane-based osmosensors may detect changes in the periplasmic and/or cytoplasmic solvent by experiencing changes in preferential interactions with particular solvent constituents, cosolvent-induced hydration changes, and/or macromolecular crowding. Alternatively, the membrane may act as an antenna and osmosensors may detect changes in membrane structure. Cosolvents may modulate intrinsic biomembrane strain and/or topologically closed membrane systems may experience changes in mechanical strain in response to imposed osmotic shifts. The osmosensory mechanisms controlling membrane-based K+ transporters, transcriptional regulators, osmoprotectant transporters, and mechanosensitive channels intrinsic to the cytoplasmic membrane of Escherichia coli are under intensive investigation. The osmoprotectant transporter ProP and channel MscL act as osmosensors after purification and reconstitution in proteoliposomes. Evidence that sensor kinase KdpD receives multiple sensory inputs is consistent with the effects of K+ fluxes on nucleoid structure, cellular energetics, cytoplasmic ionic strength, and ion composition as well as on cytoplasmic osmolality. Thus, osmoregulatory responses accommodate and exploit the effects of individual cosolvents on cell structure and function as well as the collective contribution of cosolvents to intracellular osmolality.

Metabolic engineering of rice leading to biosynthesis of glycinebetaine and tolerance to salt and cold

Genetically engineered rice (Oryza sativa L.) with the ability to synthesize glycinebetaine was established by introducing the codA gene for choline oxidase from the soil bacterium Arthrobacter globiformis. Levels of glycinebetaine were as high as 1 and 5 micromol per gram fresh weight of leaves in two types of transgenic plant in which choline oxidase was targeted to the chloroplasts (ChlCOD plants) and to the cytosol (CytCOD plants), respectively. Although treatment with 0.15 M NaCl [corrected] inhibited the growth of both wild-type and transgenic plants, the transgenic plants began to grow again at the normal rate after a significantly less time than the wild-type plants after elimination of the salt stress. Inactivation of photosynthesis, used as a measure of cellular damage, indicated that ChlCOD plants were more tolerant than CytCOD plants to photoinhibition under salt stress and low-temperature stress. These results indicated that the subcellular compartmentalization of the biosynthesis of glycinebetaine was a critical element in the efficient enhancement of tolerance to stress in the engineered plants.

Enhancement of the tolerance of Arabidopsis to high temperatures by genetic engineering of the synthesis of glycinebetaine

Arabidopsis thaliana was transformed with the codA gene for choline oxidase from Arthrobacter globiformis under control of the 35S RNA promoter of cauliflower mosaic virus. As a result, high levels of glycinebetaine accumulated in the seeds of transformed plants. Transformation with the codA gene significantly enhanced the tolerance to high temperatures during the imbibition and germination of seeds, as well as during growth of young seedlings. The extent of enhancement of the tolerance to high temperature was correlated with levels of choline oxidase expressed and of glycinebetine accumulated in the transformed plants. The induction of homologues of heat shock protein 70 at high temperature was less conspicuous in the transformed plants than in the wild-type plants, suggesting that the transformation alleviated the high-temperature stress.