Physiological And Biochemical Aspects Of The Valve Snap And Valve Closure Responses In The Giant Scallop Placopecten-Magellanicus .1. Physiology

1. Catabolic processes of the phasic and catch parts of the adductor muscle ofPlacopecten magellanicus have been studied in relation to valve snap and valve closure responses. It is concluded that the snap response is powered by both parts of the adductor muscle and the valve closure response is powered exclusively by the catch part. 2. Both parts of the adductor muscle show a high glycolytic potential, reflected by high levels of glycolytic enzymes (Table 1) and high glycogen levels (Table 2). Lactate dehydrogenase could not be detected. In contrast, octopine dehydrogenase shows high activities in both parts of the adductor muscle. It is therefore concluded that a main anaerobic pathway in both tissues is the breakdown of glycogen to octopine. In the catch part, however, a considerable amount of the pyruvate formed from glycogen may also be converted into alanine (see below). The glycolytic flux in the catch part is much higher during the snap response than during valve closure. 3. The absence of phosphoenolpyruvate carboxykinase in the adductor muscle ofP. magellanicus and the observed changes in aspartate, alanine and succinate demonstrate that the energy metabolism in the catch part during valve closure shows great similarities to that which occurs only in the initial stage of anaerobiosis in the catch adductor muscle of the sea musselMytilus edulis L. 4. Arginine kinase activity and arginine phosphate content of the phasic part are much higher than those of the catch part (Tables 1 and 3). This may explain why in the phasic part during the snap response most ATP equivalents are derived from arginine phosphate, and in the catch part during both valve responses most are derived from glycolysis (Table 6). Despite the limited contribution of glycolysis in the phasic part during the snap response, the glycolytic flux increases by a factor of at least 75. 5. Evidence is obtained that octopine is neither transported from one part of the adductor muscle to the other, nor from the adductor muscle to other tissues.

Physiological And Biochemical Aspects Of The Valve Snap And Valve Closure Responses In The Giant Scallop Placopecten-Magellanicus .2. Biochemistry

1. Catabolic processes of the phasic and catch parts of the adductor muscle ofPlacopecten magellanicus have been studied in relation to valve snap and valve closure responses. It is concluded that the snap response is powered by both parts of the adductor muscle and the valve closure response is powered exclusively by the catch part. 2. Both parts of the adductor muscle show a high glycolytic potential, reflected by high levels of glycolytic enzymes (Table 1) and high glycogen levels (Table 2). Lactate dehydrogenase could not be detected. In contrast, octopine dehydrogenase shows high activities in both parts of the adductor muscle. It is therefore concluded that a main anaerobic pathway in both tissues is the breakdown of glycogen to octopine. In the catch part, however, a considerable amount of the pyruvate formed from glycogen may also be converted into alanine (see below). The glycolytic flux in the catch part is much higher during the snap response than during valve closure. 3. The absence of phosphoenolpyruvate carboxykinase in the adductor muscle ofP. magellanicus and the observed changes in aspartate, alanine and succinate demonstrate that the energy metabolism in the catch part during valve closure shows great similarities to that which occurs only in the initial stage of anaerobiosis in the catch adductor muscle of the sea musselMytilus edulis L. 4. Arginine kinase activity and arginine phosphate content of the phasic part are much higher than those of the catch part (Tables 1 and 3). This may explain why in the phasic part during the snap response most ATP equivalents are derived from arginine phosphate, and in the catch part during both valve responses most are derived from glycolysis (Table 6). Despite the limited contribution of glycolysis in the phasic part during the snap response, the glycolytic flux increases by a factor of at least 75. 5. Evidence is obtained that octopine is neither transported from one part of the adductor muscle to the other, nor from the adductor muscle to other tissues.

Discovery of a SAR11 growth requirement for thiamin’s pyrimidine precursor and its distribution in the Sargasso Sea

Vitamin traffic, the production of organic growth factors by some microbial community members and their use by other taxa, is being scrutinized as a potential explanation for the variation and highly connected behavior observed in ocean plankton by community network analysis. Thiamin (vitamin B1), a cofactor in many essential biochemical reactions that modify carbon-carbon bonds of organic compounds, is distributed in complex patterns at subpicomolar concentrations in the marine surface layer (0-300 m). Sequenced genomes from organisms belonging to the abundant and ubiquitous SAR11 clade of marine chemoheterotrophic bacteria contain genes coding for a complete thiamin biosynthetic pathway, except for thiC, encoding the 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) synthase, which is required for de novo synthesis of thiamin's pyrimidine moiety. Here we demonstrate that the SAR11 isolate 'Candidatus Pelagibacter ubique', strain HTCC1062, is auxotrophic for the thiamin precursor HMP, and cannot use exogenous thiamin for growth. In culture, strain HTCC1062 required 0.7 zeptomoles per cell (ca. 400 HMP molecules per cell). Measurements of dissolved HMP in the Sargasso Sea surface layer showed that HMP ranged from undetectable (detection limit: 2.4 pM) to 35.7 pM, with maximum concentrations coincident with the deep chlorophyll maximum. In culture, some marine cyanobacteria, microalgae and bacteria exuded HMP, and in the Western Sargasso Sea, HMP profiles changed between the morning and evening, suggesting a dynamic biological flux from producers to consumers.

Fundamental shift in vitamin B12 eco-physiology of a model alga demonstrated by experimental evolution.

A widespread and complex distribution of vitamin requirements exists over the entire tree of life, with many species having evolved vitamin dependence, both within and between different lineages. Vitamin availability has been proposed to drive selection for vitamin dependence, in a process that links an organism's metabolism to the environment, but this has never been demonstrated directly. Moreover, understanding the physiological processes and evolutionary dynamics that influence metabolic demand for these important micronutrients has significant implications in terms of nutrient acquisition and, in microbial organisms, can affect community composition and metabolic exchange between coexisting species. Here we investigate the origins of vitamin dependence, using an experimental evolution approach with the vitamin B(12)-independent model green alga Chlamydomonas reinhardtii. In fewer than 500 generations of growth in the presence of vitamin B(12), we observe the evolution of a B(12)-dependent clone that rapidly displaces its ancestor. Genetic characterization of this line reveals a type-II Gulliver-related transposable element integrated into the B(12)-independent methionine synthase gene (METE), knocking out gene function and fundamentally altering the physiology of the alga.