Benjamin E. Volcani

Silicon and siliceous structures in biological systems

Of course, from childhood to forever, we are always thought to love reading. It is not only reading the lesson book but also reading everything good is the choice of getting new inspirations. Religion, sciences, politics, social, literature, and fictions will enrich you for not only one aspect. Having more aspects to know and understand will lead you become someone more precious. Yea, becoming precious can be situated with the presentation of how your knowledge much.

Lipid components of diatoms

Abstract 1. 1. The total lipids of five species of marine diatoms and one fresh-water diatom were studied chromatographically and the major components identified. All species contained glycerides, sulfoquinovosyl diglyceride, digalactosyl diglyceride, monogalactosyl diglyceride, phosphatidyl glycerol, lecithin, and phosphatidyl inositol as major lipid components. Small to trace amounts of several unidentified sulfur-con-taining lipids, an unidentified glycolipid (sphingolipid?), phosphatidyl ethanolamine, phosphatidyl-N-methylethanolamine, phosphatidic acid, and diphosphatidyl glycerol were also present. In general, the lipid composition of the diatoms resembled that of green algae. 2. 2. Data on 32P-, 14C-, and 35S-incorporation into the diatom lipids are also included in this study. 3. 3. The major fatty acid constituents in the total lipids of the diatoms examined were palmitoleic, palmitic, eicosapentaenoic, and eicosatetraenoic acids ; small amounts of hexadecadienoic, hexadecatrienoic, octadecenoic, octadecadienoic, and octadecatrienoic acids were also present. The latter acid (linolenic acid), which is the major acid in algae and higher plants, was only a minor constituent of the diatom lipids.

Role of silicon in diatom metabolism. A silicon requirement for deoxyribonucleic acid synthesis in the diatom Cylindrotheca fusiformis Reimann and Lewin.

Silicon deprivation of young cells of C. fusiformis in light-dark synchronized cultures completely inhibited mitosis without affecting normal increase in volume. During the first 12 h of silicon starvation, all major cell constituents, including ribonucleic acid, increased by at least 75%; deoxyribonucleic acid (DNA), however, increased by only 10%. Reintroduction of silicic acid to 12 h silicon-starved cells resulted in immediate stimulation of net DNA synthesis followed by mitosis, cytokinesis, cell wall formation and cell separation in 85% of the population. The cells were sensitive to inhibition of DNA synthesis during the first half of their division cycle. Approx. 50% of the silicon required for cell wall formation was sufficient to reverse the inhibition. Low concentrations of germanium inhibited mitosis and cell wall formation, but not DNA synthesis; high concentrations inhibited overall growth.

Characterization of a silicon transporter gene family in Cylindrotheca fusiformis: sequences, expression analysis, and identification of homologs in other diatoms.

Abstract The transport of silicon is an integral part of the synthesis of the silicified cell wall of diatoms, yet knowledge of the number, features, and regulation of silicon transporters is lacking. We report the isolation and sequence determination of five silicon transporter (SIT) genes from Cylindrotheca fusiformis, and examine their expression patterns during cell wall synthesis. The encoded SIT amino acid sequences are highly conserved in their putative transmembrane domains. Nine conserved cysteines in this domain may account for the sensitivity of silicon uptake to sulfhydryl blocking agents. A less conserved C-terminal domain is predicted to form coiled-coil structures, suggesting that the SITs interact with other proteins. We show that SIT gene expression is induced just prior to, and during, cell wall synthesis. The genes are expressed at very different levels, and SIT1 is expressed in a different pattern from SIT 2–5. Hybridization experiments show that multiple SIT gene copies are present in all diatom species tested. From the data we infer that individual transporters play specific roles in silicon uptake, and propose that the cell regulates uptake by controlling the amount or location of each. The identification of all SIT genes in C. fusiformis will enhance our understanding of the mechanism and control of silicon transport in diatoms.

STUDIES ON THE BIOCHEMISTRY AND FINE STRUCTURE OF SILICA SHELL FORMATION IN DIATOMS. II. THE STRUCTURE OF THE CELL WALL OF NAVICULA PELLICULOSA (BRÉB.) HILSE

The cell wall of the freshwater diatom Navicula pelliculosa (Bréb.) Hilse is composed of the silica shell and an organic skin which surrounds it. Isolated skins can be prepared by first removing the contents of the cell by mechanical shaking, followed by a posttreatment of these isolated cell walls with HF vapor to remove the silica shell. T h e skins can also be seen in sections, particularly well after the silica shell has been removed B y H. F; vapor.

THE POLYMORPHIC DIATOM PHAEODACTYLUM TRICORNUTUM: ULTRASTRUCTURE OF ITS MORPHOTYPES1,2

The ultrastructure of the oval, fusiform and triradiate morphotypes of Phaeodactylum tricornutum Bohlin is described. The organization and structure of the cytoplasmic organelles is similar in all three morphotypes, except that the vacuoles occupy the extra volume created by the arms of the fusiform and triradiate cells. The frustule in fusiform and triradiate cells is organic; in the oval type it may be organic or one of the valves may have a silica frustule surrounded by an organic wall. In all cells, the organic cell wall has up to 10 silica bands (13 nm wide) embedded in its surface in the girdle region, lacks girdle bands, and has an outer corrugated cell wall layer, except in the girdle region. Cell division, organic wall formation and silica deposition are described in detail. Four types of oval cells are also described. The relation to other diatoms is discussed.

Bacillus marismortui sp. nov., a new moderately halophilic species from the Dead Sea

A group of 91 moderately halophilic, Gram-positive, rod-shaped strains were isolated from enrichments prepared from Dead Sea water samples collected 57 years ago. These strains were examined for 117 morphological, physiological, biochemical, nutritional and antibiotic susceptibility characteristics. All strains formed endospores and were motile, strictly aerobic and positive for catalase and oxidase. They grew in media containing 5-25% (w/v) total salts, showing optimal growth at 10% (w/v). Eighteen strains were chosen as representative isolates and were studied in more detail. All these strains had mesodiaminopimelic acid in the cell wall and a DNA G + C content of 39.0-42.8 mol%; they constitute a group with levels of DNA-DNA similarity of 70-100%. The sequences of the 16S rRNA genes of three representative strains (strains 123T, 557 and 832) were almost identical (99.9%), and placed the strains in the low G + C content Gram-positive bacteria. On the basis of their features, these isolates should be regarded as members of a new species of the genus Bacillus, for which the name Bacillus marismortui sp. nov. is proposed. The type strain is strain 123T (= DSM 12325T = ATCC 700626T = CIP 105609T = CECT 5066T).

Studies on the biochemistry and fine structure of silicia shell formation in diatoms VII. Sequential cell wall development in the pennateNavicula pelliculosa

SummaryThe development of the wall of synchronized culture ofN. pelliculosa is described. The first step, modification of the 3-2 configuration of the girdle bands of the wall during interphase, occurs immediately before mitotic division by the addition of a third girdl band to the hypotheca. Following cytokenesis, the new valve is initiated when a primary central band is formed within a silica deposition vesicle. This band extends the length of the cell and contains a central nodule. Secondary arms extend from the central nodule, join with extensions of the primary central band, and constitute the raphe rib. Mounds or knolls are formed on the central nodule and disappear as the valve matures. Transapical ribs appear on both the primary central band and secondary arms, and cross extensions join to form the sieve plate areas. The wall appears to be released by a joining of the inner silicalemma and the plasmalemma. An organic coat covers the newly released wall. Two girdle bands are formed and released sequentially.

3,4-Dihydroxyproline: A New Amino Acid in Diatom Cell Walls

An analog of proline, 2, 3-cis-3, 4-trans-3, 4-dihydroxy-L-proline, was found in the cell walls of the eight species of diatoms studied and was isolated from the proteinaceous material of the wall of Navicula pelliculosa. The properties of this substance are described; its structure was confirmed by nuclear magnetic resonance spectros-copy.

Germanium incorporation into the silica of diatom cell walls

Summary1.The diatoms, Nitzschia alba, Navicula pelliculosa, Cylindrotheca fusiformis, and Cyclotella nana, took up radioisotopically labelled germanic acid, 68Ge(OH)4, from their growth media and incorporated up to 80% of it into the silica of their cell walls. Silicification appeared to be required for germanium incorporation.2.The uptake and incorporation of germanic acid was dependent upon the relative concentrations of Ge(OH)4 and Si(OH)4, i.e., the [Ge]/[Si].3.At [Ge]/[Si] of 0.01, no inhibition of growth or of silicic acid uptake by N. alba was observed. The cell morphology was also normal. 60 to 80% of the 68Ge(OH)4 taken up was incorporated.4.At [Ge]/[Si] of 0.1, silicic acid uptake and growth of N. alba were inhibited by about 95%. Concomitantly, striking morphological aberrations occurred. 10 to 20% of the 68Ge(OH)4 taken up was incorporated.5.The possible use of 68Ge(OH)4 for the study of silicon metabolism is discussed.