Intermediary metabolism and shell growth in the brachiopod Terebratalia transversa

Juvenile Terebratalia transversa (Brachiopoda) metabolize carbohydrates in the anterior-most marginal mantle at a rate of 0.46 μM glucose/g/hr (in vitro incubation of mantle in C¹⁴-glucose in a carrying medium of 10^-3 M non-radioactive glucose). The rate declines to 0.18μM glucose/g/hr in full-grown specimens. Carbohydrate metabolism in the marginal (anterior-most) mantle averages approximately 3.7 times greater than metabolism in (a portion of the ‘posterior’) mantle situated between the coelomic canals and the marginal mantle. This ratio remains constant in specimens of all sizes (i.e. an ontogenetic trend in the ratio is absent at p≤ 0.05). Organic acids are not detectable within the mantle (HPLC techniques) even after simulated anoxia (N₂ bubbling during mantle incubation). Glucose metabolism in vitro declines in both the marginal and ‘posterior’ mantles during anoxia and the metabolic ratio between marginal/‘posterior’ mantles becomes 1/1. We found no difference (at p≤ 0.05) in mean metabolic activity or in sue-related metabolic trends among populations from depths ranging between mean sea level and 70 m. However, the activity within the ‘posterior’ mantle was more variable in specimens from 70 m than in those from shallower habitats (10 m - mean sea level). The size of the specimens analyzed was most variable in the groups obtained from the shallowest habitats and least variable at 70 m depth. Our results may help define the energetics of fossil as well as living brachiopod shell growth. Brachiopod shell growth is known to be very slow relative to that of bivalves and our results indicate that this is a result of the animals' slow metabolism. The inflation of the valves in T. transversa is, in part, a function of the high ratio of intermediary metabolism in the marginal vs‘posterior’ mantle (i.e. parallels the relative growth rates at the shell margin vs‘posterior’ areas). We found that the bivalve, Chlamys hastata, which is commonly associated with T. transversa, has a lower ratio of metabolic activities in the ventral/dorsal mantle areas than the brachiopod has in the anterior/posterior. The difference produces a flatter shell in the bivalve in accord with allometric principles. The higher metabolic rate in the marginal vs‘posterior’ brachiopod mantle and its more pronounced decline with anaerobiosis is reflected in the greater definition of growth increments in the outer shell layer. Our results do not support recent generalizations that correlate shell thickness of a wide variety of invertebrates inversely with metabolic rate. Growth rate as determined from width of shell growth increments is a better index of metabolic rate. Although the genetic basis of glucose metabolism is unknown, the observed metabolic variability is consistent with suggestions that populations of marine organisms living in stable offshore environments are genetically more variable but morphologically more uniform than populations from shallow water. Furthermore, our results support suggestions that bivalved molluscs and brachiopods are very different metabolically, but the data are neutral with respect to theories of competitive exclusion of the two taxa throughout geologic history.     

PHOTOSYNTHETIC CHARACTERISTICS OF THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) EXPOSED TO ELEVATED CONCENTRATIONS OF DISSOLVED INORGANIC CARBON1

Light-saturated photosynthesis (P_max) of Emiliania huxleyi (Lohmann) Hay et Mohler is known to be carbonlimited at natural concentrations of dissolved inorganic carbon (DIC). In the present study, light-limited and light-saturated photosynthetic rates of E. huxleyi were studied at three concentrations of DIC (2.4, 7.4, and 12.4 mM) for high-calcite (C_in/C_tot=0.48) and low-calcite (C_in/C_tot=0.08) cells of the same strain. The photosynthetic efficiency (α) and the maximum quantum yield (θ_max)A increased by more than a factor of 2 from the lowest to the highest DIC level. P_max a, and θ_max were always higher for the high-calcite than for the low-calcite cells at identical DIC levels. This may indicate that the calcifcation process acts as an extra supplier of CO₂ for photosynthesis making the CO₂ shortage at natural DIC levels a little smaller for high-calcite than for low-calcite E. huxleyi. A dependency of θ_max on DIC has not previously been shown for marine phytoplankton. θ_max is a key parameter in recent biooptical models of phytoplankton productivity, and the results from the present study are therefore important for modeling the productivity of E. huxleyi.     

CALCIFICATION IN THE GREEN ALGA HALIMEDA. I. AN ULTRASTRUCTURE STUDY OF THALLUS DEVELOPMENT1

The ultrastructure of 4 species of the calcareous, siphonaceous alga Halimeda (H. cylindracea Decaisne, H. discoidea Decaisne, H. macroloba Decaisne and H. tuna (Ellis & Solander) Lamour) has been studied, and the observed changes during growth and development are related to changes in the degree of calcification. A distinct gradient in the types and quantities of cell organelles exists in a growing apical filament. As these filaments grow, branch, and eventually develop into a mature segment, changes in the organization of organelles such as mitochondria and chloroplasts are observed. Calcification begins when the chloroplasts reach structural maturity and when the peripheral utricles adhere (fuse). This adhesion of the peripheral utricles isolates the intercellular space (ICS) in which calcification occurs from the external seawater. Calcification begins in the outermost (pilose) cell wall layer of the walls facing into the ICS. The cell walls at the thallus exterior undergo extensive changes after utricular fusion; the pilose layer is lost, the cuticles of adjacent utricles fuse forming a ridge at their junction, and multiple cuticles are formed. The aragonite (CaCO₃) crystals which are initially precipitated within the pilose wall layer, rapidly increase in size and number, eventually filling much of the ICS. Only the initial nucleation of aragonite is associated with the pilose wall layer, the later precipitation of aragonite is totally independent of the pilose layer. In older segments secondary deposition of CaCO₃ also occurs around existing aragonite needles.     

CARBONIC ANHYDRASE AND CARBON FIXATION IN COCCOLITHOPHORIDS1

Rates of carbon fixation in coccolithophorids in culture, unlike many other algae, are carbon limited at ambient levels of dissolved inorganic carbon (DIC). Apparently, plants often rely on activity of carbonic anhydrase (CA) to raise the level of CO₂ in cells and achieve carbon saturation. However, CA activities in the coccolithophorids, Coccolithus (= Emiliania) huxleyi Lohmann and Hymenomonas (=Cricosphaera) carterae Braarud, were either not detectable or very low compared to activities in other systems, including other algae, higher plants, and representative animals. Furthermore, additions of CA to medium with 2 mM DIC at pH 8.1 resulted in nearly 30% enhancement of photosynthesis, but not coccolith formation. Although carbon fixation in coccolithophorids can be suppressed by the CA inhibitor acetazolamide, studies of CaCO₃ nucleation revealed a non-specific effect of the inhibitor. Using a 30 min assay based on pH decreases accompanying loss of dissolved. CO₃^2-, inhibition of crystal formation in the absence of CA at 1 mM acetazolamide was demonstrated for decalcified crab carapace, a tissue with which normal CaCo₃ deposition in vitro has been shown. The results suggest only a minor role for CA in coccolithophorids.     

CALCIFICATION BY COCCOLITHOPHORIDS: EFFECTS OF pH AND Sr1

Cells of Coccolithus huxleyi which fail to deposit CaCO₃ and form coccoliths often occur as unwanted components in cultures used for studies of calcification. Non-calcified cells generally cannot be made to recalcify, but they can be removed from cultures by treatment at elevated pH or by a method based on faster sinking of calcified cells. Lowering the concentrations of nitrate, phosphate, or trace metals in the medium did not restore calcifying ability of non-calcified cells. However, addition of strontium did promote recalcification of decalcified Cricosphaera carterae grown under calcium limitation. Strontium seemed to promote coccolith attachment to cells rather than to affect calcium uptake or coccolith formation itself.     

钙化胎盘中纳米细菌的分离培养与鉴定

目的分离、培养与鉴定钙化胎盘中的纳米细菌,为进一步探讨纳米细菌致胎盘钙化的机制奠定基础。方法剖腹产手术收集25份钙化胎盘组织标本,通过脱矿、过滤、离心处理,用细胞培养的方法进行纳米细菌培养,观察其生长情况。运用透射电镜、扫描电镜观察培养物形态。结果 (1)培养3~4周后,对钙化组织培养标本进行观察,发现部分培养管底部出现紧贴管壁生长的白色沉淀物。(2)扫描电镜见纳米细菌为大颗粒成簇分布。(3)透射电镜可见纳米细菌为针状物的聚集体,大小不一。结论首次从钙化胎盘组织中分离培养鉴定出纳米细菌,表明其感染与胎盘钙化有关,需进一步研究其矿化机制以及所致钙化对后代的影响。     

High density micromass cultures of embryonic limb bud mesenchymal cells: An in vitro model of endochondral skeletal development

Summary To study the mechanisms regulating endochondral skeletal development, we examined the characteristics of long-term, high density micromass cultures of embryonic chicken limb bud mesenchymal cells. By culture Day 3, these cells underwent distinct chondrogenesis, evidenced by cellular condensation to form large nodules exhibiting cartilage-like morphology and extracellular matrix. By Day 14, extensive cellular hypertrophy was seen in the core of the nodules, accompanied by increased alkaline phosphatase activity, and the limitation of cellular proliferation to the periphery of the nodules and to internodular areas. By Day 14, matrix calcification was detected by alizarin red staining, and calcium incorporation increased as a function of culture time up to 2 to 3 wk and then decreased. X-ray probe elemental analysis detected the presence of hydroxyapatite. Analogous to growth cartilage developing in vivo, these cultures also exhibited time-dependent apoptosis, on the basis of DNA fragmentation detected in situ by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL), ultrastructural nuclear morphology, and the appearance of internucleosomal DNA degradation. These findings showed that cellular differentiation, maturation, hypertrophy, calcification, and apoptosis occurred sequentially in the embryonic limb mesenchyme micromass cultures and indicate their utility as a convenient in vitro model to investigate the regulatory mechanisms of endochondral ossification.     

Ocean acidification bends the mermaid's wineglass

Ocean acidification lowers the saturation state of calcium carbonate, decreasing net calcification and compromising the skeletons of organisms such as corals, molluscs and algae. These calcified structures can protect organisms from predation and improve access to light, nutrients and dispersive currents. While some species (such as urchins, corals and mussels) survive with decreased calcification, they can suffer from inferior mechanical performance. Here, we used cantilever beam theory to test the hypothesis that decreased calcification would impair the mechanical performance of the green alga Acetabularia acetabulum along a CO₂ gradient created by volcanic seeps off Vulcano, Italy. Calcification and mechanical properties declined as calcium carbonate saturation fell; algae at 2283 µatm CO₂ were 32% less calcified, 40% less stiff and 40% droopier. Moreover, calcification was not a linear proxy for mechanical performance; stem stiffness decreased exponentially with reduced calcification. Although calcifying organisms can tolerate high CO₂ conditions, even subtle changes in calcification can cause dramatic changes in skeletal performance, which may in turn affect key biotic and abiotic interactions.     

Paradise lost: End‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

Despite recent efforts to curtail greenhouse gas emissions, current global emission trajectories are still following the business‐as‐usual representative concentration pathway (RCP) 8.5 emission pathway. The resulting ocean warming and acidification have transformative impacts on coral reef ecosystems, detrimentally affecting coral physiology and health, and these impacts are predicted to worsen in the near future. In this study, we kept fragments of the symbiotic corals Acropora intermedia (thermally sensitive) and Porites lobata (thermally tolerant) for 7 weeks under an orthogonal design of predicted end‐of‐century RCP8.5 conditions for temperature and pCO₂ (3.5°C and 570 ppm above present‐day, respectively) to unravel how temperature and acidification, individually or interactively, influence metabolic and physiological performance. Our results pinpoint thermal stress as the dominant driver of deteriorating health in both species because of its propensity to destabilize coral–dinoflagellate symbiosis (bleaching). Acidification had no influence on metabolism but had a significant negative effect on skeleton growth, particularly when photosynthesis was absent such as in bleached corals or under dark conditions. Total loss of photosynthesis after bleaching caused an exhaustion of protein and lipid stores and collapse of calcification that ultimately led to A. intermedia mortality. Despite complete loss of symbionts from its tissue, P. lobata maintained small amounts of photosynthesis and experienced a weaker decline in lipid and protein reserves that presumably contributed to higher survival of this species. Our results indicate that ocean warming and acidification under business‐as‐usual CO₂ emission scenarios will likely extirpate thermally sensitive coral species before the end of the century, while slowing the recovery of more thermally tolerant species from increasingly severe mass coral bleaching and mortality. This could ultimately lead to the gradual disappearance of tropical coral reefs globally, and a shift on surviving reefs to only the most resilient coral species.