Effects of salinity level on the activity of chloride cell and mucus secreting cell in the gill of the female Shortfin molly, Poecilia mexicana Steindachner, 1863

Ovoviviparous poeciliid fishes have been relatively well studied in the unique reproductive strategy, but their osmoregulatory system largely remains unknown. In this study, we conducted a short-term (7 days) lab experiment to investigate the effect of different salinity levels from 0 (freshwater) to 50 ppt (mesosaline) on the number of chloride cells and mucus secreting cells of female Poecilia mexicana. The density of chloride cells and mucus secreting cell were also arranged along the epithelial lamellae in wild fish. More interestingly, the average density of chloride cells and the mucus secreting cell were mostly differed between these levels (P < 0.05). Integrative data from our study suggested that the potential function of the osmoregulatory mechanism/strategy was supported by chloride and mucus secreting cells of female P. mexicana gill.

Cell culture-based shark karyotyping as a resource for chromosome-scale genome analysis

Karyotyping is indispensable for validating genome assemblies whose sequence lengths can be scaled up to chromosome sizes using modern methods and is traditionally performed using cytogenetic techniques. Karyotype reports of chondrichthyans are scarce, mainly because of their unique osmoregulatory mechanism, which hinders cell culture. Here, we focused on carpet shark species and the culture conditions for fibroblasts and lymphocytes. Using this method, we performed high-fidelity characterization of their karyotypes, namely 2n = 102 for the whale shark (Rhincodon typus) and zebra shark (Stegostoma fasciatum), and 2n = 106 for the brownbanded bamboo shark (Chiloscyllium punctatum) and whitespotted bamboo shark (C. plagiosum). We identified heteromorphic XX/XY sex chromosomes for the two latter species and demonstrated the first-ever fluorescence in situ hybridization of shark chromosomes prepared from cultured cells. Our technical solution is applicable to diverse chondrichthyan species and will deepen the understanding of early vertebrate evolution at the molecular level.

An Osmoregulatory Mechanism Operating through OmpR and LrhA Controls the Motile-Sessile Switch in the Plant Growth-Promoting BacteriumPantoea alhagi

ABSTRACTAdaptation to osmotic stress is crucial for bacterial growth and survival in changing environments. Although a large number of osmotic stress response genes have been identified in various bacterial species, how osmotic changes affect bacterial motility, biofilm formation, and colonization of host niches remains largely unknown. In this study, we report that the LrhA regulator is an osmoregulated transcription factor that directly binds to the promoters of theflhDC,eps, andopgGHoperons and differentially regulates their expression, thus inhibiting motility and promoting exopolysaccharide (EPS) production, synthesis of osmoregulated periplasmic glucans (OPGs), biofilm formation, and root colonization of the plant growth-promoting bacteriumPantoea alhagiLTYR-11Z. Further, we observed that the LrhA-regulated OPGs control RcsCD-RcsB activation in a concentration-dependent manner, and a high concentration of OPGs induced by increased medium osmolarity is maintained to achieve the high level of activation of the Rcs phosphorelay, which results in enhanced EPS synthesis and decreased motility inP. alhagi. Moreover, we showed that the osmosensing regulator OmpR directly binds to the promoter oflrhAand promotes its expression, whilelrhAexpression is feedback inhibited by the activated Rcs phosphorelay system. Overall, our data support a model wherebyP. alhagisenses environmental osmolarity changes through the EnvZ-OmpR two-component system and LrhA to regulate the synthesis of OPGs, EPS production, and flagellum-dependent motility, thereby employing a hierarchical signaling cascade to control the transition between a motile lifestyle and a biofilm lifestyle.IMPORTANCEMany motile bacterial populations form surface-attached biofilms in response to specific environmental cues, including osmotic stress in a range of natural and host-related systems. However, cross talk between bacterial osmosensing, swimming, and biofilm formation regulatory networks is not fully understood. Here, we report that the pleiotropic regulator LrhA inPantoea alhagiis involved in the regulation of flagellar motility, biofilm formation, and host colonization and responds to osmotic upshift. We further show that this sensing relies on the EnvZ-OmpR two-component system that was known to detect changes in external osmotic stress. The EnvZ-OmpR-LrhA osmosensing signal transduction cascade is proposed to increase bacterial fitness under hyperosmotic conditions inside the host. Our work proposes a novel regulatory mechanism that links osmosensing and motile-sessile lifestyle transitions, which may provide new approaches to prevent or promote the formation of biofilms and host colonization inP. alhagiand other bacteria possessing a similar osmoregulatory mechanism.

Water Activity Relationships for Selected Mesophiles and Psychrotrophs at Refrigeration Temperature

The growth rate and lag phase of Pseudomonas fluorescens, Brochothrix thermosphacta, Salmonella typhlmurium, Enterococcus faecalis, and Staphylococcus aureus were studied in liquid media as a function of temperature, water activity (aw) and solute type. The lag phase lengthened and the growth rate decreased when the temperature was lowered or the aw reduced, and these variations depended on the aw-controlling solute. In general, the magnitude order of the solute effect on the growth rate parameters was glycerol &lt; NaCl &lt; sucrose. This effect can be related to the ability of the solutes to permeate the cell and can be explained by the osmoregulatory mechanism. The specific growth rate was not as sensitive to the aw-controlling solute as the lag phase. A linear extrapolation method was a reliable and convenient method to estimate the minimum aw for microbial growth.

Lack of osmoregulation in Aplysia brasiliana: correlation with response of neuron R15 to osphradial stimulation

The exposure of Aplysia brasiliana to dilute seawater (90 and 80%) caused an increase of the relative weight, which returned to the original values after a few hours. Both osmotic and chloride concentrations of the hemolymph decreased on exposure to 80 and 90% dilute seawater, and after 3-h exposure there were no differences between the hemolymph and external media osmotic and chloride concentrations. In contrast to the clear regulatory capabilities reported for A. californica, A. brasiliana cannot maintain the osmolality of its body fluid in dilute media. In A. californica, osphradial receptors and neuron R15 are apparently involved in this regulatory mechanism. Perfusion of osphradium of A. brasiliana with dilute seawater (95-80%) did not affect electrical activity of the bursting neuron R15; perfusion with 70 and 60% seawater caused a transient increase in the duration of the quiescent period. In contrast to the model established for A. californica, in A. brasiliana no relationship was found between exposure of the osphradium to dilute media and electrical activity in neuron R15, which is in accordance with the lack of an osmoregulatory mechanism in this species. Such differences may reflect inherent differences in salinity tolerance between the two species.

Blood Composition and Osmoregulation in Ammocoete Larvae

Ammocoetes of all species are typical stenohaline freshwater animals which are able to regulate their blood and tissue ions very efficiently although they live in a very dilute environment. They excrete osmotic water by a well-developed kidney, and water turnover is high. Nephron units are sequentially arranged and have similar differentiated segments to those of other freshwater vertebrates. Total ion loss is low so the kidney must conserve ions efficiently. Ion loss is compensated by an ion-uptake mechanism, probably located in the interplatelet area of the gills. Here, the cells contain a sodium carrier whose transport rate is regulated by internal and external sodium levels; also they have mechanisms for potassium and chloride uptake. Both the gills and kidney have ion transport type cells, but the skin does not. The gills are probably the main access route for water, ions, and lampricides. The freshwater mechanism of osmoregulation persists beyond metamorphosis and thereafter many lampreys become euryhaline, but ammocoetes are unable to osmoregulate in hypertonic solutions and show passive responses. The adults of anadromous species like Lampetra fluviatilis and Petromyzon marinus develop a marine osmoregulatory mechanism which is similar to that of marine teleosts, whilst freshwater species like the landlocked P. marinus of the Great Lakes and the dwarf brook lamprey, Lampetra planeri, show reduced capacities for osmoregulation in seawater.Key words: ammocoetes, lampreys, osmoregulation, blood composition, gills, ion fluxes, kidney, urine, water fluxes, ion compartments

Osmotic and ionic regulation in different populations of the new zealand freshwater crayfish Paranephrops zealandicus

1. Some features of the osmoregulatory mechanism are compared in four populations of Paranephrops zeal andicus White collected form freshwaters of different ionic concentrations. 2. Crayfish from freshwaters of ca, 2-0 mM-NaCl concentration show a sustained decrease in blood concentration of ca. 8% when placed in 0-2 mM-NaCl. 3. Populations from freshwaters of ca. 0-2-0-4 mM-NaCl show lower rates of net salt loss in distilled water and higher rates of net salt uptake form dilute NaCl solutions than do populations from freshwaters of ca. 0-8-2-0 mM-NaCl. 4. Renal salt losses over the first 24 h in distilled water account for ca. 18% of the total salt loss. 5. It is suggested that P. zealandicus from environments of lowest concentration shows a similar degree of adaptation to freshwater as do crayfish of the northern hemisphere. It differs in possessing a substantially higher blood concentration.

Isoosmotic Transport of Fluid Across the Hamster Small Intestine in the Presence of Phlorizin-Induced Inhibition of Sugar Transport

Experiments were performed to investigate whether the fluid transported across the small intestine is isoosmotic with the mucosal solution when the active transport of glucose is partially inhibited. Everted hamster mid small intestine was incubated in one of the following four mucosal solutions: (1) Isotonic control, Krebs–Ringer bicarbonate solution containing 10 mM glucose (KRBSG); (2) Isotonic with phlorizin, KRBSG + 5 × 10−5 M phlorizin; (3) Hypertonic control, KRBSG + 50 mM mannitol; (4) Hypertonic with phlorizin, KRBSG + 50 mM mannitol + 5 × 10−5 M phlorizin. The serosal surface of the intestine was not bathed. Results indicate that the transported fluid was always isoosmotic with any of the mucosal solutions used. When the mucosal solution was made hypertonic with mannitol, the concentration of glucose and electrolytes in the absorbate increased, and as a result, the absorbate became hypertonic and isoosmotic with the mucosal solution. The presence of phlorizin either in the isotonic or in the hypertonic mucosal solution decreased the glucose concentration of the absorbate, but the transported fluid became isoosmotic with the mucosal solution due to a higher concentration of Na, K, and their associated anions. Phlorizin caused a decrease in the transmural potential difference. In spite of this, the presence of this glucoside in the mucosal solution increased the transport of sodium in relation to glucose transport. It is suggested that, at the concentrations used, phlorizin inhibits sodium movement through the electrogenic pathway, but increases the transport of this ion through the non-electrogenic route. This increase in neutral sodium transport seems to compensate for the low concentration of glucose in the absorbate, so that the absorbate becomes isoosmotic with the mucosal solution whether the latter is isotonic or hypertonic. It is suggested further that isoosmotic transport of fluid is an inherent property of the small intestine and that there may be an osmoregulatory mechanism in the gut which controls this process.