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181.
Candida bombicola ATCC 22214 produces the glycolipid sophoroselipid when cultivated on a medium with glucose as the sole carbon source. Under
phosphate-limiting conditions the product yield rises from 0.033 to 0.143 and the specific product formation rate rises from
0.004 h-1 to 0.007 h-1. Enhanced sophoroselipid synthesis is initiated by the decline of the specific activities of NAD- and NADP-dependent isocitrate
dehydrogenase (EC 1.1.1.41 and 1.1.1.42) to 2% and 0% of the initial activities respectively. Constantly high specific activity
of citrate synthase (EC 4.1.3.7) causes an accumulation of isocitrate and citrate in the mitochondria. Both acids are transported
into the cytosol where citrate is cleaved by ATP: citrate lyase (EC 4.1.3.8) giving rise to acetyl-CoA, the precursor of fatty
acid synthesis. The ATP: citrate lyase is unaffected by different energy charges; the apparent K
m values for coenzyme A, ATP and citrate are 23 μM, 250 μM and 256 μM respectively. NADPH for fatty acid synthesis might be
generated by further metabolism of oxaloacetate, the other product of the citrate-cleaving reaction, by oxidation of the isocitrate
by the cytosolic NADP-dependent isocitrate dehydrogenase or via the hexose monophosphate shunt. A possible explanation for
sophoroselipid formation during exponential growth is given.
Received: 7 November 1995/Received revision: 19 March 1996/Accepted: 25 March 1996 相似文献
182.
P. Kämpfer R. Erhart C. Beimfohr J. Böhringer M. Wagner R. Amann 《Microbial ecology》1996,32(2):101-121
The structures of bacterial communities were studied in activated sludge samples obtained from the aerobic and anaerobic zones of a wastewater treatment plant showing enhanced phosphorous removal. Samples were analyzed by in situ hybridization with oligonucleotide probes complementary to selected regions of the 16S and 23S ribosomal RNA (rRNA) characteristic for defined phylogenetic entities (genera and larger groups). The microbial community structures revealed by molecular techniques were compared with the compositions of culturable bacterial communities, obtained from the characterization of 255 isolates from tryptone-soy (TS) agar and R2A agar. These isolates were characterized by 89 physiological tests and their cellular fatty acid patterns, and identified. Culture-dependent techniques indicated the following distribution: different Aeromonas spp. (2.7–8.3% on R2A agar; 45.0–63.7% on TS agar), Acinetobacter spp. (5.4–9.0% on R2A agar; 5.0–9.1% on TS agar), Pseudomonas spp. (up to 10% on R2A agar) and Shewanella putrefaciens (up to 3.0% on R2A agar), all members of the gamma subclass of Proteobacteria, were isolated most frequently. The relatively rare isolates of the beta subclass were identified as Acidovorax spp., Alcaligenes spp., and Comamonas spp., The Gram-positive bacteria (high DNA G+C) were assigned mainly to Arthrobacter spp., Microbacterium spp., and Mycobacterium phlei. In order to assess the in situ abundance of the most frequently isolated genus, Aeromonas, two rRNA-targeted oligonucleotide probes were developed. The two gamma proteobacterial genera Aeromonas and Acinetobacter constituted less than 5% of all bacteria. In situ, Proteobacteria belonging to the beta subclass and high G+C Gram-positive bacteria were dominant. From filamentous bacteria, Sphaerotilus spp. and Leptothrix spp. could be detected occasionally. In addition, one sample contained a high proportion of the morphologically distinct filaments of Microthrix parvicella.As for the genus Acinetobacter, the relative abundance of the most frequently gamma-proteobacterial genus Aeromonas was overestimated by the intrinsic selectivity of cultivation. Cultivation on nutrient-rich medium (TS-agar) especially supported an enhanced isolation of bacteria belonging to these two genera.
Correspondence to: P. Kämpfer. 相似文献
183.
184.
In the short day plant Chenopodium rubrum and the long day plant Nicotiana tabacum cv. Havana 425, adenylate kinase (EC 2.7.4.3) occurs as a family of isoforms, with at least two members localized in the chloroplast representing the main isoforms. In this work, isoforms were separated by anion exchange chromatography and relative isoform activities were compared between vegetative plants and plants induced to flowering. In both species examined, a light regime leading to floral induction resulted in a significant decrease in the activity of one chloroplast isoform. This decrease modified considerably the relative distribution of isoform activities, especially that between the two chloroplast activities. 相似文献
185.
186.
U Dammer M Hegner D Anselmetti P Wagner M Dreier W Huber H J Güntherodt 《Biophysical journal》1996,70(5):2437-2441
Molecular recognition between biotinylated bovine serum albumin and polyclonal, biotin-directed IG antibodies has been measured directly under various buffer conditions using an atomic force microscope (AFM). It was found that even highly structured molecules such as IgG antibodies preserve their specific affinity to their antigens when probed with an AFM in the force mode. We could measure the rupture force between individual antibody-antigen complexes. The potential and limitations of this new approach for the measurement of individual antigen/antibody interactions and some possible applications are discussed. 相似文献
187.
188.
HAU3是寄主范围很广的放线菌噬菌体。Southern杂交实验表明,HAU3可以整合到吸水链霉菌应城变种10-22和变铅青链霉菌66的突变体ZX1的染色体中,形成溶原,其溶原菌自发释放HAU3,不受热激和紫外线照射的诱导。通过比较HAU3衍生噬粒pIJ8300的DNA酶切片段在加热前、后电泳带谱的区别,将HAU3的cos位点在pIJ8300的图谱上得到了定位。还利用Southern杂交的方法定位了HAU3与宿主形成溶原时附着位点(attP),并利用脉冲电泳技术定位了在变铅青链霉菌ZX7和吸水链霉菌应城变种10-22中形成溶原的附着位点(attB)。这些信息均有利于以HAU3为基础的载体的发展和优化。 相似文献
189.
A. Quesada-Chanto A. S.-Afschar F. Wagner 《Applied microbiology and biotechnology》1994,41(4):378-383
With a cell concentration of 125 g dry biomass 1–1 and a dilution rate of 0.1 h–1,Propionibacterium acidipropionici produces 30 g propionic acid 1–1 from sugar with a productivity of 3 g 1–1 h–1. The yield of propionic acid is approx. 0.36–0.45 g propionic acid g–1 sucrose and is independent of the dilution rate and cell concentration. Acetic acid is an unwanted by-product in the production of propionic acid. The concentration of acetic acid only increases slightly when the cell concentration is increased. A two-stage fermentation process was developed for the conversion of sugar or molasses of various types to propionic acid and vitamin B12. By fermentation of blackstrap molasses (from sugar beet and sugar cane) in the first fermentation stage 17.7 g propionic acid 1–1 with a yield of 0.5 g propionic acid g–1 carbohydrate was produced with a dilution rate of 0.25 h–1. In the second stage 49 mg vitamin B12 1–1 was produced at a dilution rate of 0.03 h–1. 相似文献