<Emphasis Type="Italic">Chlorobaculum tepidum</Emphasis> regulates chlorosome structure and function in response to temperature and electron donor availability

Green sulfur bacteria (GSB) rely on the chlorosome, a light-harvesting apparatus comprised almost entirely of self-organizing arrays of bacteriochlorophyll (BChl) molecules, to harvest light energy and pass it to the reaction center. In Chlorobaculum tepidum, over 97% of the total BChl is made up of a mixture of four BChl c homologs in the chlorosome that differ in the number and identity of alkyl side chains attached to the chlorin ring. C. tepidum has been reported to vary the distribution of BChl c homologs with growth light intensity, with the highest degree of BChl c alkylation observed under low-light conditions. Here, we provide evidence that this functional response at the level of the chlorosome can be induced not only by light intensity, but also by temperature and a mutation that prevents phototrophic thiosulfate oxidation. Furthermore, we show that in conjunction with these functional adjustments, the fraction of cellular volume occupied by chlorosomes was altered in response to environmental conditions that perturb the balance between energy absorbed by the light-harvesting apparatus and energy utilized by downstream metabolic reactions.     

Isolation of the murI gene from Brevibacterium lactofermentum ATCC 13869 encoding d-glutamate racemase

The murI gene encoding D-glutamate racemase plays an important role in the biosynthesis of D-glutamic acid, an essential component of cell wall peptidoglycan of almost all eubacteria. A DNA fragment that could rescue the auxotrophy of D-glutamic acid in the Escherichia coli murI mutant strain WM335 was isolated from Brevibacterium lactofermentum ATCC 13869 belonging to the coryneform bacteria. DNA sequencing reveals that it encodes a protein of 284 amino acid residues, which shows a high level of homology with D-glutamate racemases from several other bacteria.     

Schistosoma mansoni: Phospholipid nature of the “agglutinin”

The haemagglutinating activity of the membrane-associated Schistosoma mansoni “agglutinin” is mainly due to acidic phospholipids, particularly phosphatidylinositol and phosphatidylserine. The role of these phospholipids in possible lipid-protein interactions in the host-parasite relationship is discussed.     

Expression of CspA and GST by an Antarctic psychrophilic bacterium Colwellia sp. NJ341 at near-freezing temperature

Summary A psychrotrophic bacterium Colwellia sp. NJ341 from Antarctic sea ice could grow at −5 and 22 °C, and the extent of cellular protein content and growth were greater at low temperatures (0–10 °C) than at higher temperatures. SDS-PAGE analysis demonstrated the presence of a 7 kDa cold-shock protein. The further result of two-dimensional electrophoresis (2-DE) showed that two proteins a and c were newly synthesized at near-freezing temperatures. With matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) analysis, proteins a and c were identified as glutathione S-transferase (GST) and cold-shock protein A (CspA), respectively, which were involved in cold-adaptation at near-freezing temperature in an Antarctic psychrophilic bacterium Colwellia sp. NJ341.     

A Na+/H+ antiporter gene of the moderately halophilic bacterium Halobacillus dabanensis D-8T: cloning and molecular characterization

A gene encoding a Na(+)/H(+) antiporter was cloned from a chromosomal DNA of Halobacillus dabanensis strain D-8(T) by functional complementation. Its presence enabled the antiporter-deficient Escherichia coli strain KNabc to survive in the presence of 0.2 M NaCl or 5 mM LiCl. The gene was sequenced and designated as nhaH. The deduced amino-acid sequence of NhaH consists of 403 residues with a calculated molecular mass of 43,481 Da, which was 54% identical and 76% similar to the NhaG Na(+)/H(+) antiporter of Bacillus subtilis. The hydropathy profile was characteristic of a membrane protein with 12 putative transmembrane domains. Everted membrane vesicles prepared from E. coli cells carrying nhaH exhibited Na(+)/H(+) as well as Li(+)/H(+) antiporter activity, which was pH-dependent with highest activities at pH 8.5-9.0 and at pH 8.5, respectively. Moreover, nhaH confers upon E. coli KNabc cells the ability to grow under alkaline conditions.     

耐热蛋白质延长因子(EF-Tu)的分子和功能的性质(英文)

本文用亲和层析法从Calderobacteriumhydrogenophilum(极端耐热细菌)中分离得到纯的耐热蛋白质延长因子。测得其相对的分子量为51000。该蛋白质对热极其稳定,从膜过滤分析法测定EF-Tu 的活性可知,在80℃加热5 min后,原活性仅仅失去50%。Ouchterlony双向免疫扩散的结果表明,该蛋白延长因子与E.coli 延长因子有着抗原的相似性。而且该因子只含一个半胱氨酸残基,其位置在半胱氨酸81,即肽段T_(13)。Southern 杂交试验的结果显示出C.hydrogenophilum 的染色体DNA 中可能有两个基因编码同一蛋白。     

Quantitative real-time PCR using TaqMan and SYBR Green for Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, tetQ gene and total bacteria

Accurate quantification of bacterial species in dental plaque is needed for microbiological diagnosis of periodontal diseases. The present study was designed to assess the sensitivity, specificity and quantitativity of the real-time PCR using the GeneAmp Sequence Detection System with two fluorescence chemistries. TaqMan probe with reporter and quencher dye, and SYBR Green dye were used for sources of the fluorescence. Primers and probes were designed for Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia and total bacteria based on the nucleotide sequences of the respective 16S ribosomal RNA genes. Since spread of antibiotic resistance genes is one of the crucial problems in periodontal therapy, quantitative detection of tetQ gene, which confers resistance to tetracycline, was included in the examination. The detection of P. gingivalis, P. intermedia and A. actinomycetemcomitans was linear over a range of 10-10(7) cells (10-10(7) copies for tetQ gene), while the quantitative range for total bacteria was 10(2)-10(7) cells. Species-specific amplifications were observed for the three periodontal bacteria, and there was no significant difference between the TaqMan and SYBR Green chemistry in their specificity, quantitativity and sensitivity. The SYBR Green assay, which was simpler than TaqMan assay in its manipulations, was applied to the clinical plaque samples. The plaque samples were obtained from eight patients (eight periodontal pockets) before and 1 week after the local drug delivery of minocycline. Although the number of P. gingivalis, P. intermedia and A. actinomycetemcomitans markedly decreased after the antibiotic therapy in most cases, higher copy numbers of the tetQ gene were detectable. The real-time PCR demonstrated sufficient sensitivity, specificity and quantitativity to be a powerful tool for microbiological examination in periodontal disease, and the quantitative monitoring of antibiotic resistance gene accompanied with the antibiotic therapy should be included in the examination.     

Effects of Temperature and Dietary Lipids on Phospholipid Fatty Acids and Membrane Fluidity in Steinernema carpocapsae

The phospholipid composition of Steinernema carpocapsae was studied in relation to diet and culture temperature. When reared at 18 and 27.5 C on Galleria mellonella or on an artificial diet supplemented with lard, linseed oil, or fish oil as lipid sources, nematode phospholipids contained an abundance of 20-carbon polyunsaturated fatty acids, with eicosapentaenoic acid (20:5(n - 3)) predominant, regardless of the fatty acid composition of the diet. Because the level of linolenic acid (18:3(n - 3)) in nematode phospholipids was very low and because eicosapentaenoic acid was present even when its precursor (linolenic acid) was undetectable in the diet, S. carpocapsae likely produces n - 3 polyunsaturated fatty acids by de novo biosynthesis, a pathway seldom reported in eukaryotic animals. Reduction of growth temperature from 25 to 18 C increased the proportion of 20:5(n - 3) but not other polyunsaturated fatty acids. A fluorescence polarization technique revealed that vesicles produced from phospholipids of nematodes reared at 18 C were less ordered than those from nematodes reared at 27.5 C, especially in the outermost region of the bilayer. Dietary fish oil increased fluidity in the outermost region but increased rigidity in deeper regions. Therefore, S. carpocapsae appears to modify its membrane physical state in response to temperature, and eicosapentaenoic acid may be involved in this response. The results also indicate that nematode membrane physical state can be modified dietarily, possibly to the benefit of host-finding or survival of S. carpocapsae at low temperatures.     

Characterization of an organic-solvent-tolerant Brevibacillus agri strain 13 able to stabilize solvent/water emulsion

Brevibacillus agri strain 13 was isolated and characterized as a Gram-positive organic-solvent-tolerant bacterium able to grow at 45 °C. It can tolerate high concentrations (5% and 20%, v/v) of various organic solvents with a broad range of log P _ow when the organic solvent was provided as a nonaqueous layer. Although it can tolerate a number of aromatic solvents, it cannot utilize them as a sole carbon source. The surface characteristics of cells exposed to organic solvent were investigated using the bacterial adhesion to hydrocarbon test, a contact angle measurement, ζ potential determination, and fluorescence microscopy analysis and compared with that of nonexposed cells. The results showed that although it has a hydrophilic cell surface, it has a unique indigenous cell surface characteristic in which the cells can stabilize solvent-in-water emulsion by adhering to the solvent–water interface of the solvent droplets. The tolerance and predilection of B. agri strain 13 toward organic solvents may suggest its potential application as a whole-cell biocatalyst for the biotransformation process of water-immiscible substrate(s).