Osmosensing and osmoregulatory compatible solute accumulation by bacteria Wood, J.M.; Bremer, Erhard; Csonka, L.N.; Kraemer, R; Poolman, B.; van der Heide, Tiemen; Smith, L.T. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. AbstractBacteria inhabit natural and artificial environments with diverse and fluctuating osmolalities, salinities and temperatures. Many maintain cytoplasmic hydration, growth and survival most effectively by accumulating kosmotropic organic Ž . Ž . solutes compatible solutes when medium osmolality is high or temperature is low above freezing . They release these solutes into their environment when the medium osmolality drops. Solutes accumulate either by synthesis or by transport from the extracellular medium. Responses to growth in high osmolality medium, including biosynthetic accumulation of trehalose, also protect Salmonella typhimurium from heat shock. Osmotically regulated transporters and mechanosensitive channels modulate cytoplasmic solute levels in Bacillus subtilis, Corynebacterium glutamicum, Escherichia coli, Lactobacillus plantarum, Lactococcus lactis, Listeria monocytogenes and Salmonella typhimurium. Each organism harbours multiple osmoregulatory transporters with overlapping substrate specificities. Membrane proteins Ž that can act as both osmosensors and osmoregulatory transporters have been identified secondary transporters ProP of . E. coli and BetP of C. glutamicum as well as ABC transporter OpuA of L. lactis . The molecular bases for the modulation of gene expression and transport activity by temperature and medium osmolality are under intensive investigation with emphasis on the role of the membrane as an antenna for osmo-andror thermosensors. ᮊ 2001 Elsevier Science Inc. All rights reserved. Wood et al. r Comparati¨e Biochemistry and Physiology Part A 130 2001 437᎐460 438

The drought of 1983 resulted in some 10 billion dollars in agricultural losses and has focused attention on the vulnerability of our major crops to this devastating form of environmental stress. This article is concerned with the molecular biology of a new class of genes, called osm (osmotic tolerance) genes, that protect bacteria like Escherichia coli against osmotic stress and may work in a similar manner in plants and animals. Osm genes govern the production of a class of molecules, such as betaine and proline, that protect the cell and its constituents against dehydration. These osmoprotectant molecules have been known for many years to accumulate in plants but have only recently been shown to have potent antistress activity for bacteria.

No abstract

Listeria monocytogenes is a gram-positive food-borne pathogen that is notably resistant to osmotic stress and can grow at refrigerator temperatures. These two characteristics make it an insidious threat to public health. Like several other organisms, L. monocytogenes accumulates glycine betaine, a ubiquitous and effective osmolyte, intracellularly when grown under osmotic stress. However, it also accumulates glycine betaine when grown under chill stress at refrigerator temperatures. Exogenously added glycine betaine enhances the growth rate of stressed but not unstressed cells, i.e., it confers both osmotolerance and cryotolerance. Both salt-stimulated and cold-stimulated accumulation of glycine betaine occur by transport from the medium rather than by biosynthesis. Direct measurement of glycine betaine uptake shows that cells transport betaine 200-fold faster at high salt concentration (4% NaCl) than without added salt and 15-fold faster at 7 than at 30 degrees C. The kinetics of glycine betaine transport suggest that the two transport systems are indistinguishable in terms of affinity for betaine and may be the same. Hyperosmotic shock and cold shock experiments suggest the transport system(s) to be constitutive; activation was not blocked by chloramphenicol. A cold-activated transport system is a novel observation and has intriguing implications concerning the physical state of the cell membrane at low temperature.

Numerical approximations to the dynamic equations &re given which allow basin-size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines. Emphasis is placed on computational economy through the use of a splitexplicit time integration scheme, on the proper formulation of the advection and Coriolis terms in the momentum equation in case of strongly varying layer thickness, and on the correct estimation of the horizontal pressure gradient force in grid boxes truncatcd by steep bottom slopes. The algorithms are tested in a series of two-and three-layer double-gyre experiments. In cases of steady forcing leading to a steady circulation, we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing. This includes layers intersecting topographic obstacles. A long-term (25-30 year) vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyc!mfic gyre in a steadily forced model is documented. The paper forms the basis for a subsequent s• udy in which circulation features obtained in a realistic North Atlantic setting will be discussed. INTRODUCTORY REMARKS Numerical modeling of geophysical fluid systems using electronic computers began approximately four decades ago.Until the middle to late 1960s, ocean model development lagged significantly behind that of atmospheric models. A number of reasons (apart from societal needs) can be cited for this lag, among them the inherently greater comp!exity of circu!ation systems confined to closed basins, a highly nonlinear equation of state for seawater, and the lack of threedimensional synoptic observations for ocean model initialization and verification. Furthermore, the computing power required to resolve the relevant hydrodynamic instability processes in grid-point space is far greater in the ocean than in the atmosphere because of the much smaller radius of deformation. The above factors, taken together, imply that a major commitment of institutional resources was required in the past to mount a credible oceanic modeling effort. Thus oceanic modeling has never become a "cottage industry" like atmospheric modeling. Fiscal constraints often prohibited duplication of efforts -real or perceived -, and thus steered second paper will be the actual results obtained from the Atlantic model. In isopycnic coordinate representation, the ocean is viewed as a stack of immiscible layers, each of which is characterized by a constant value of density and is governed by dynamic equations resembling the shallow-water equations. The layers interact through hydrostatically transmitted pressure forces. The analytic models of Welander [1966] and Parsons [1969], in which the vertical structure of the ocean is represented in terms of!ayers of constant density, can be considered as prototypes of the model employed in this study. Huang [1986] has recently extended the work of Welander and Parsons in numerical models with ...