Characterization of a plant-like protochlorophyllide a divinyl reductase in green sulfur bacteria

The green sulfur bacterium Chlorobium tepidum synthesizes three types of (bacterio)chlorophyll ((B)Chl): BChl a(P), Chl a(PD), and BChl c(F). During the synthesis of all three molecules, a C-8 vinyl substituent is reduced to an ethyl group, and in the case of BChl c(F), the C-8(2) carbon of this ethyl group is subsequently methylated once or twice by the radical S-adenosylmethionine enzyme BchQ. The C. tepidum genome contains homologs of two genes, bchJ (CT2014) and CT1063, that are highly homologous to genes, bchJ and AT5G18660, and that have been reported to encode C-8 vinyl reductases in Rhodobacter capsulatus and Arabidopsis thaliana, respectively. To determine which gene product actually encodes a C-8 vinyl reductase activity, the bchJ and CT1063 genes were insertionally inactivated in C. tepidum. All three Chls synthesized by the CT1063 mutant of C. tepidum have a C-8 vinyl group. Using NADPH but not NADH as reductant, recombinant BciA reduces the C-8 vinyl group of 3,8-divinyl-protochlorophyllide in vitro. These data demonstrate that CT1063, renamed bciA, encodes a C-8 divinyl reductase in C. tepidum. The bchJ mutant produces detectable amounts of Chl a(PD), BChl a(P), and BChl c(F), all of which have reduced C-8 substituents, but the mutant cells secrete large amounts of 3,8-divinyl-protochlorophyllide a into the growth medium and have a greatly reduced BChl c(F) content. The results suggest that BchJ may play an important role in substrate channeling and/or regulation of Chl biosynthesis but show that it is not a vinyl reductase. Because only some Chl-synthesizing organisms possess homologs of bciA, at least two types of C-8 vinyl reductases must occur.     

Identification of a gene essential for the first committed step in the biosynthesis of bacteriochlorophyll c

Bacteriochlorophylls (BChls) c, d, and e are the major chlorophylls in chlorosomes, which are the largest and one of the most efficient antennae produced by chlorophototrophic organisms. In the biosynthesis of these three BChls, a C-13(2)-methylcarboxyl group found in all other chlorophylls (Chls) must be removed. This reaction is postulated to be the first committed step in the synthesis of these BChls. Analyses of gene neighborhoods of (B)Chl biosynthesis genes and distribution patterns in organisms producing chlorosomes helped to identify a gene (bciC) that appeared to be a good candidate to produce the enzyme involved in this biochemical reaction. To confirm that this was the case, a deletion mutant of an open reading frame orthologous to bciC, CT1077, was constructed in Chlorobaculum tepidum, a genetically tractible green sulfur bacterium. The CT1077 deletion mutant was unable to synthesize BChl c but still synthesized BChl a and Chl a. The deletion mutant accumulated large amounts of various (bacterio)pheophorbides, all of which still had C-13(2)-methylcarboxyl groups. A C. tepidum strain in which CT1077 was replaced by an orthologous gene, Cabther_B0081 [corrected] from "Candidatus Chloracidobacterium thermophilum" was constructed. Although the product of Cabther_B0081 [corrected] was only 28% identical to the product of CT1077, this strain synthesized BChl c, BChl a, and Chl a in amounts similar to wild-type C. tepidum cells. To indicate their roles in the first committed step of BChl c, d, and e biosynthesis, open reading frames CT1077 and Cabther_B0081 [corrected] have been redesignated bciC. The potential mechanism by which BciC removes the C-13(2)-methylcarboxyl moiety of chlorophyllide a is discussed.     

Chlorophyll content and fluorescence responses cannot be used to gauge reliably phytoplankton biomass, nutrient status or growth rate

To consider the relationship between chlorophyll a (Chl a) content and phytoplankton growth and nutrient status, four phytoplankton species were grown in nitrogen (N)-limited [and, for one species, phosphorus (P)-limited] culture and measurements were made of CNP biomass, in vivo and in vitro Chl a content, the ratio of variable to maximum fluorescence (FV/FM) and the performance index for photosynthesis, PIABS (a derivative of the O-J-I-P analysis of photosystem II functionality). Interspecies differences plus the development of intraspecies differences during nutrient stress produced c. 10-fold variations in Chl : C. Estimates of C from in vivo Chl content were better than those from extracted Chl content, as the decline in Chl : C during nutrient stress was offset in part by increased Chl fluorescence. FV/FM was not a robust indicator of nutrient status or relative growth rate. Responses of FV/FM in cells re-fed the limiting nutrient showed no consistent pattern with which to gauge nutrient status. PIABS showed some promise as an indicator of nutrient status and relative growth rate. Chl a content and fluorescence parameters do not deserve the unquestioned status they usually enjoy as indicators of biomass and physiological status.     

Electron transfer in reaction center core complexes from the green sulfur bacteria Prosthecochloris aestuarii and Chlorobium tepidum

Electron transfer in reaction center core (RCC) complexes from the green sulfur bacteria Prosthecochloris aestuarii and Chlorobium tepidum was studied by measuring flash-induced absorbance changes. The first preparation contained approximately three iron-sulfur centers, indicating that the three putative electron acceptors F(X), F(A), and F(B) were present; the Chl. tepidum complex contained on the average only one. In the RCC complex of Ptc. aestuarii at 277 K essentially all of the oxidized primary donor (P840(+)) created by a flash was rereduced in several seconds by N-methylphenazonium methosulfate. In RCC complexes of Chl. tepidum two decay components, one of 0.7 ms and a smaller one of about 2 s, with identical absorbance difference spectra were observed. The fast component might be due to a back reaction of P840(+) with a reduced electron acceptor, in agreement with the notion that the terminal electron acceptors, F(A) and F(B), were lost in most of the Chl. tepidum complexes. In both complexes the terminal electron acceptor (F(A) or F(B)) could be reduced by dithionite, yielding a back reaction of 170 ms with P840(+). At 10 K in the RCC complexes of both species P840(+) was rereduced in 40 ms, presumably by a back reaction with F(X)(-). In addition, a 350 micros component occurred that can be ascribed to decay of the triplet of P840, formed in part of the complexes. For P840(+) rereduction a pronounced temperature dependence was observed, indicating that electron transfer is blocked after F(X) at temperatures below 200 K.     

CO2 and vitamin B12 interactions determine bioactive trace metal requirements of a subarctic Pacific diatom

Phytoplankton growth can be limited by numerous inorganic nutrients and organic growth factors. Using the subarctic diatom Attheya sp. in culture studies, we examined how the availability of vitamin B₁₂ and carbon dioxide partial pressure (pCO₂) influences growth rate, primary productivity, cellular iron (Fe), cobalt (Co), zinc (Zn) and cadmium (Cd) quotas, and the net use efficiencies (NUEs) of these bioactive trace metals (mol C fixed per mol cellular trace metal per day). Under B₁₂-replete conditions, cells grown at high pCO₂ had lower Fe, Zn and Cd quotas, and used those trace metals more efficiently in comparison with cells grown at low pCO₂. At high pCO₂, B₁₂-limited cells had ∼50% lower specific growth and carbon fixation rates, and used Fe ∼15-fold less efficiently, and Zn and Cd ∼3-fold less efficiently, in comparison with B₁₂-replete cells. The observed higher Fe, Zn and Cd NUE under high pCO₂/B₁₂-replete conditions are consistent with predicted downregulation of carbon-concentrating mechanisms. Co quotas of B₁₂-replete cells were ∼5- to 14-fold higher in comparison with B₁₂-limited cells, suggesting that >80% of cellular Co of B₁₂-limited cells was likely from B₁₂. Our results demonstrate that CO₂ and vitamin B₁₂ interactively influence growth, carbon fixation, trace metal requirements and trace metal NUE of this diatom. This suggests the need to consider complex feedback interactions between multiple environmental factors for this biogeochemically critical group of phytoplankton in the last glacial maximum as well as the current and future changing ocean.     

Production of Propionibacterium shermanii biomass and vitamin B12 on spent media

AIMS: The propionibacteria are commercially important due to their use in the cheese industry, and there is a growing interest for their probiotic effects. Stimulatory effects of lactic acid bacteria (LAB) on propionic acid bacteria have been observed. This study was designed to examine the possibility of using spent media previously used to grow LAB for the production of biomass and metabolites of Propionibacterium freudenreichii subsp. shermanii. METHODS AND RESULTS: Seventeen MRS and vegetable juice media were prefermented by various LAB and evaluated for their ability to subsequently support the growth of Propionibacterium, using automated spectrophotometry (AS). Growth of Propionibacterium in spent media was strongly affected by the LAB strain used to produce the spent medium. The native MRS medium (not prefermented) yielded the highest optical density values followed by prefermented media by Lactobacillus acidophilus, Bifidobacterium longum and Lactococcus lactis. Prefermented cabbage juice enabled good growth of Propionibacterium. For the production of organic acids and vitamin B12, cells of Propionibacterium were concentrated and immobilized in alginate beads in the aim of accelerating the bioconversions. More propionic acid was obtained in spent media than in native MRS. The concentration of vitamin B12 was higher in media fermented with free cells than those with immobilized cultures; with the free cells, its concentration varied from 900 to 1800 ng ml(-1) of media. CONCLUSIONS: It was demonstrated that spent media could be recycled for the production of Propionibacterium and metabolites, depending on the LAB strain that was previously grown. Media remediation is needed to improve the production of vitamin B12, especially with immobilized cells. SIGNIFICANCE AND IMPACT OF THE STUDY: This study presents an option for recycling of spent media generated by producers of LAB or producers of fermented vegetables. The propionic fermentation may result in three commercial products: biomass, vitamin B12 or organic acids, which may be used as starters, supplements or food preservatives. It is an attractive process from economical and environmental standpoints.     

Chlorobium Tepidum: Insights into the Structure,Physiology, and Metabolism of a Green Sulfur Bacterium Derived from the Complete Genome Sequence

Green sulfur bacteria are obligate, anaerobic photolithoautotrophs that synthesize unique bacteriochlorophylls (BChls) and a unique light-harvesting antenna structure, the chlorosome. One organism, Chlorobium tepidum, has emerged as a model for this group of bacteria primarily due to its relative ease of cultivation and natural transformability. This review focuses on insights into the physiology and biochemistry of the green sulfur bacteria that have been derived from the recently completed analysis of the 2.15-Mb genome of Chl. tepidum. About 40 mutants of Chl. tepidum have been generated within the last 3 years, most of which have been made based on analyses of the genome. This has allowed a nearly complete elucidation of the biosynthetic pathways for the carotenoids and BChls in Chl. tepidum, which include several novel enzymes specific for BChl c biosynthesis. Facilitating these analyses, both BChl c and carotenoid biosynthesis can be completely eliminated in Chl. tepidum. Based particularly on analyses of mutants lacking chlorosome proteins and BChl c, progress has also been made in understanding the structure and biogenesis of chlorosomes. In silico analyses of the presence and absence of genes encoding components involved in electron transfer reactions and carbon assimilation have additionally revealed some of the potential physiological capabilities, limitations, and peculiarities of Chl. tepidum. Surprisingly, some structural components and biosynthetic pathways associated with photosynthesis and energy metabolism in Chl. tepidum are more similar to those in cyanobacteria and plants than to those in other groups of photosynthetic bacteria.     

Carbon isotope fractionation by thermophilic phototrophic sulfur bacteria: evidence for autotrophic growth in natural populations

Purple phototrophic bacteria of the genus Chromatium can grow as either photoautotrophs or photoheterotrophs. To determine the growth mode of the thermophilic Chromatium species, Chromatium tepidum, under in situ conditions, we have examined the carbon isotope fractionation patterns in laboratory cultures of this organism and in mats of C. tepidum which develop in sulfide thermal springs in Yellowstone National Park. Isotopic analysis (13C/12C) of total carbon, carotenoid pigments, and bacteriochlorophyll from photoautotrophically grown cultures of C. tepidum yielded 13C fractionation factors near -20%. Cells of C. tepidum grown on excess acetate, wherein synthesis of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase ribulose bisphosphate carboxylase) was greatly repressed, were isotopically heavier, fractionation factors of ca. -7% being observed. Fractionation factors determined by isotopic analyses of cells and pigment fractions of natural populations of C. tepidum growing in three different sulfide thermal springs in Yellowstone National Park were approximately -20%, indicating that this purple sulfur bacterium grows as a photoautotroph in nature.     

Bacteriochlorophyllide c C-8(2) and C-12(1) methyltransferases are essential for adaptation to low light in Chlorobaculum tepidum

Bacteriochlorophyll (BChl) c is the major photosynthetic pigment in the green sulfur bacterium Chlorobaculum tepidum, in which it forms protein-independent aggregates that function in light harvesting. BChls c, d, and e are found only in chlorosome-producing bacteria and are unique among chlorophylls because of methylations that occur at the C-8(2) and C-12(1) carbons. Two genes required for these methylation reactions were identified and designated bchQ (CT1777) and bchR (CT1320). BchQ and BchR are members of the radical S-adenosylmethionine (SAM) protein superfamily; each has sequence motifs to ligate a [4Fe-4S] cluster, and we propose that they catalyze the methyl group transfers. bchQ, bchR, and bchQ bchR mutants of C. tepidum were constructed and characterized. The bchQ mutant produced BChl c that was not methylated at C-8(2), the bchR mutant produced BChl c that was not methylated at C-12(1), and the double mutant produced [8-ethyl, 12-methyl]-BChl c that lacked methylation at both the C-8(2) and C-12(1) positions. Compared to the wild type, the Qy absorption bands for BChl c in the mutant cells were narrower and blue shifted to various extents. All three mutants grew slower and had a lower cellular BChl c content than the wild type, an effect that was especially pronounced at low light intensities. These observations show that the C-8(2) and C-12(1) methylations of BChl c play important roles in the adaptation of C. tepidum to low light intensity. The data additionally suggest that these methylations also directly or indirectly affect the regulation of the BChl c biosynthetic pathway.     

Carbon isotope fractionation by thermophilic phototrophic sulfur bacteria: evidence for autotrophic growth in natural populations.

Purple phototrophic bacteria of the genus Chromatium can grow as either photoautotrophs or photoheterotrophs. To determine the growth mode of the thermophilic Chromatium species, Chromatium tepidum, under in situ conditions, we have examined the carbon isotope fractionation patterns in laboratory cultures of this organism and in mats of C. tepidum which develop in sulfide thermal springs in Yellowstone National Park. Isotopic analysis (13C/12C) of total carbon, carotenoid pigments, and bacteriochlorophyll from photoautotrophically grown cultures of C. tepidum yielded 13C fractionation factors near -20%. Cells of C. tepidum grown on excess acetate, wherein synthesis of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase ribulose bisphosphate carboxylase) was greatly repressed, were isotopically heavier, fractionation factors of ca. -7% being observed. Fractionation factors determined by isotopic analyses of cells and pigment fractions of natural populations of C. tepidum growing in three different sulfide thermal springs in Yellowstone National Park were approximately -20%, indicating that this purple sulfur bacterium grows as a photoautotroph in nature.     

Influence of growth condition on the concentration of potassium in Bacillus subtilis var. niger and its possible relationship to cellular ribonucleic acid, teichoic acid and teichuronic acid

1. Mg(2+)-limited Bacillus subtilis var. niger, growing in a chemostat in a simple salts medium, contained considerably more potassium and phosphorus than Mg(2+)-limited Aerobacter aerogenes growing in a similar medium at corresponding dilution rates. 2. Growth of the bacillus in a K(+)-limited environment did not lower the cellular potassium and phosphorus contents, the molar proportions of cell-bound magnesium, potassium, RNA (as nucleotide) and phosphorus being approximately constant at 1:13:5:13 (compared with 1:4:5:8 in Mg(2+)-limited or K(+)-limited A. aerogenes). 3. Growth of B. subtilis in a phosphate-limited environment caused the cellular phosphorus content to be lowered to a value similar to that of Mg(2+)-limited A. aerogenes, but the potassium content was not correspondingly lowered; the molar potassium:magnesium ratio varied from 14 to 17 with changes in dilution rate from 0.4 to 0.1hr.(-1). 4. Whereas over 70% of the cell-bound phosphorus of Mg(2+)-limited or K(+)-limited A. aerogenes was contained in the nucleic acids, these polymers accounted for less than 50% of the phosphorus present in similarly limited B. subtilis; much phosphorus was present in the walls of the bacilli, bound in a teichoic acid-type compound composed of glycerol phosphate and glucose (but no alanine). 5. Phosphate-limited B. subtilis cell walls (from organisms grown at a dilution rate of 0.2hr.(-1)) contained little phosphorus and no detectable amounts of teichoic acid, but 40% of the cell-wall dry weight could be accounted for by a teichuronic acid-type compound; this contained a glucuronic acid and galactosamine, neither of which could be detected in the walls of Mg(2+)-limited B. subtilis grown at a corresponding rate. 6. It is suggested that the high concentration of potassium in growing B. subtilis (compared with A. aerogenes) results from the presence of large amounts of anionic polymer (teichoic acid or teichuronic acid) in the bacillus cell walls.     

Accumulation of chlorophyllous pigments esterified with the geranylgeranyl group and photosynthetic competence in the CT2256-deleted mutant of the green sulfur bacterium Chlorobium tepidum

Green sulfur bacteria contain chlorophyllous pigments, chlorophyll (Chl) aPD and bacteriochlorophyll (BChl) aP, esterified with Delta2,6-phytadienol and phytol, respectively, which would be produced by reduction of the geranylgeranyl group at the C-17 propionate residue. In the genome of Chlorobium tepidum, two paralogous genes presumably encoding geranylgeranyl reductase, CT1232 and CT2256, are found. The deletion mutants of the CT1232 and CT2256 genes were constructed using an insertional inactivation method in order to clarify the biosynthetic process of the Delta2,6-phytadienyl and phytyl groups in green sulfur bacteria. The compositions of chlorophyllous pigments in the two mutants were determined by LC-MS analysis. The CT2256-deleted mutant accumulated Chl aGG and BChl aGG esterified with geranylgeraniol, indicating that CT2256 was involved in the production of both Delta2,6-phytadienyl and phytyl groups. The relatively high fluorescence emission from chlorosomes in the mutant also suggested some hindrance of the energy transfer from chlorosomes to the reaction center complex. However, the CT1232-deleted mutant almost showed no apparent phenotype compared to the wild type. Furthermore, the purple bacterium Rhodobacter capsulatus mutant defective in the bchP gene was partially complemented with the CT2256 gene; BChl aP was synthesized in the mutant in addition to accumulating other intermediates.     

Nitrogen fixation by the thermophilic green sulfur bacterium Chlorobium tepidum.

The thermophilic green sulfur bacterium Chlorobium tepidum grew with N2, NH4+, or glutamine as the sole nitrogen source under phototrophic (anaerobic-light) conditions. Growth on N2 required increased buffering capacity to stabilize uncharacterized pH changes that occurred during diazotrophic growth. Increased sulfide levels were stimulatory for growth on N2. Levels of nitrogenase activity (acetylene reduction) in N2-grown C. tepidum cells were very high, among the highest ever reported for anoxygenic phototrophic bacteria. Maximal acetylene reduction rates in C. tepidum cells were observed at 48 to 50 degrees C, which is about 15 degrees C higher than the optimum temperature for nitrogenase activity in mesophilic chlorobia, and nitrogenase activity in C. tepidum responded to addition of ammonia by a "switch-off/switch-on" mechanism like that in phototrophic purple bacteria. C. tepidum cells assimilated ammonia mainly via the glutamine synthetase-glutamate synthase pathway, elevated levels of both of these enzymes being present in cells grown on N2. These results show that N2 fixation can occur in green sulfur bacteria up to at least 60 degrees C and that regulatory mechanisms important in control of nitrogenase activity in mesophilic anoxygenic phototrophs also appear to regulate thermally active forms of the enzyme.     

Dependence of vitamin B12 levels on the growth rate of cells cultured in vitro

Vitamin B12 content has been determined in different kinds of cells grown in vitro and in the culture media. The results indicate a dependence of the vitamin levels on the growth rate and growth characteristics.     

Internal structure of chlorosomes from brown-colored chlorobium species and the role of carotenoids in their assembly

Chlorosomes are the main light harvesting complexes of green photosynthetic bacteria. Recently, a lamellar model was proposed for the arrangement of pigment aggregates in Chlorobium tepidum chlorosomes, which contain bacteriochlorophyll (BChl) c as the main pigment. Here we demonstrate that the lamellar organization is also found in chlorosomes from two brown-colored species (Chl. phaeovibrioides and Chl. phaeobacteroides) containing BChl e as the main pigment. This suggests that the lamellar model is universal among green sulfur bacteria. In contrast to green-colored Chl. tepidum, chlorosomes from the brown-colored species often contain domains of lamellar aggregates that may help them to survive in extremely low light conditions. We suggest that carotenoids are localized between the lamellar planes and drive lamellar assembly by augmenting hydrophobic interactions. A model for chlorosome assembly, which accounts for the role of carotenoids and secondary BChl homologs, is presented.     

The role of vitamin B12 in the metabolism of Euglena gracilis var. bacillaris

1. The concentrations of RNA, DNA and protein are decreased in cells of Euglena gracilis var. bacillaris grown on suboptimum concentrations of vitamin B(12). 2. The addition of vitamin B(12) to deficient cells stimulates the incorporation of [(14)C]formate into the above cell components as well as into thymine of DNA and serine and methionine of protein. 3. In a cell-free system from vitamin B(12)-deficient cells, the incorporation of labelled formate into thymidylate is decreased to a greater extent with uridine than with deoxyuridine as the substrate. 4. The addition of unlabelled glutamate dilutes the radioactivity incorporated into thymine from labelled formate. 5. These results are interpreted to mean that, in DNA synthesis, vitamin B(12) has a greater role in the reduction of ribotides to deoxyribotides than in the reduction of formate to thymine methyl and that the vitamin B(12)-dependent conversion of glutamate into beta-methylaspartate also contributes to thymine synthesis.     

Lipotropes alter casein gene expression in bovine mammary acinar culture

Lipotropes (methyl group containing nutrients, including methionine and choline, folic acid, and vitamin B(12)) are essential for cell proliferation and differentiation of mammary tissues. Lipotropes interact in the supply and regulation of intracellular methyl group pools, thereby affecting synthesis and methylation of DNA. To determine the effect of lipotropes on milk protein gene expression, acini isolated from mammary tissues of lactating cows were cultured in one of three treatment media: (1) control, (2) lipotrope deficient, and (3) lipotrope supplemented. beta-Casein mRNA was determined by Northern blotting, and milk protein secretion was measured by a pulse-chase method. The level of beta-casein mRNA was lower in cells grown in lipotrope-deficient medium than in cells grown in the lipotrope-supplemented and control media. Acinar cells cultured in lipotrope-deficient medium also had approximately threefold less milk protein secretion than that of cells in either control or lipotrope-supplemented media. Protein secretion did not differ in the control and lipotrope-supplemented groups. The present study indicates that lipotrope deficiency suppresses total protein secretion and beta-casein gene expression in bovine mammary alveolar epithelial cells in culture.     

Biosynthesis of unnatural bacteriochlorophyll c derivatives esterified with α,ω-diols in the green sulfur photosynthetic bacterium Chlorobaculum tepidum

Unnatural bacteriochlorophyll (BChl) c derivatives possessing a hydroxy group at the terminus of a hydrocarbon chain at the 17-propionate were biosynthesized in the green sulfur photosynthetic bacterium Chlorobaculum tepidum. Addition of exogenous 1,8-octanediol, 1,12-dodecanediol, and 1,16-hexadecanediol in acetone to liquid cultures resulted in accumulation of BChl c monoesterified with the corresponding diols. The relative ratios of the novel BChl c derivatives esterified with 1,8-, 1,12-, and 1,16-diols to totally producing BChl c were 8.2, 50.2, and 57.6% in the cells grown with additive α,ω-diols at concentrations of 1.5, 0.06, and 0.06 mM, respectively, at the final concentration. The homologue composition of BChl c derivatives esterified with these α,ω-diols was similar to that of original, coexisting BChl c esterified with farnesol (BChl c(F)), suggesting that esterification of α,ω-diols occurred at the last step of the BChl c biosynthetic pathway by BChl c synthase, BchK, in the same manner as in BChl c(F). Chlorosomes, which were isolated from cells grown in the presence of exogenous α,ω-diols, contained a ratio and a composition of BChl c derivatives esterified with the diols similar to those in the whole cells, indicating that these BChl c derivatives were actually present in chlorosomes. Q(y) absorption bands of C. tepidum cells containing the novel BChl c derivatives were shifted to a shorter wavelength, although their bandwidths were analogous to those of cells obtained by normal cultivation. Circular dichroism spectra of cells that had BChl c derivatives esterified with α,ω-diols exhibited S-shaped signals in the Q(y) region, whose polarities were the reverse of those of cells grown in the normal medium and by supplementation with neat acetone as a control experiment. These spectral features of C. tepidum possessing BChl c derivatives esterified with α,ω-diols imply that the novel BChl c derivatives possessing a hydroxy group at the terminus of a hydrocarbon chain affect their self-assembly in chlorosomes.     

维生素B12的生物合成、发酵生产与应用

维生素B12(VB12)是一种重要的动物和人类营养因子, 广泛应用于饲料、食品和医药卫生领域。中国已成为全球VB12的主要产地, 2007年产量为27 t, 占全球总产量的77%。VB12是目前已发现的最大、最复杂的维生素分子, 化学合成极其困难, 所有VB12产品均采用生物发酵制备其主体结构。VB12主要由古生菌和一些真细菌通过有氧或厌氧两种途径合成, 工业上主要采用费式丙酸菌(Propionibacterium freudenrechii）和脱氮假单胞菌(Pseudomonas denitrificans)进行发酵生产。综述了VB12的基本性质, 生物合成途径, 以及发酵生产工艺, 并对VB12的应用与市场前景作了分析。     

Effects of temperature,irradiance, and daylength on the marine diatom leptocylindrus danicus cleve. I. Photosynthesis and cellular composition

Rates of ¹⁴C uptake and cellular composition of C, N, and Chl a in the marine diatom Leptocylindrus danicus Cleve were measured in axenic batch culture under 49 combinations of temperature (5, 10, 15, 20 °C), daylength (15: 9, 12: 12, 9: 15 LD), and irradiance (at least four irradiances per daylength). ¹⁴C uptake exhibited a temperature-dependent daylength effect. Similar P-I curves characterized cells grown under 15: 9 and 12: 12 LD; P_max values were 17.2, 11.2, 4.3, and 1.8 pg C. pg Chl a^?1. h^?1 at 20, 15, 10, and 5°C, respectively. Under 9:15 LD at 20 and 15°C, the lightsaturated photosynthetic rate was ≈50% that in cells grown under longer daylengths. ¹⁴C uptake was independent of daylength at 10 and 5°C. The initial slope, a, of cells grown under long daylengths increased by five-fold between 5 and 20 °C. α values of cells grown under 9: 15 LD at 15 and 20 °C were depressed relative to longer daylengths. Chl a was inversely related to irradiance, and increased with temperature from 10 to 20 °C, whereas cell carbon and nitrogen showed a similar temperature dependence but was not influenced by irradiance or daylength. The C : N ratio and cell volume were independent of temperature, irradiance, and daylength. Both the C : Chl a and N : Chl a ratios increased with irradiance by greater amounts at lower temperatures.