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D Kaiser

Publications and source records attributed to D Kaiser.

At least 91 records · Page 5Linked to original sources
PubMed1994

Influence of increased dissolved oxygen concentration on the formation of secondary metabolites by manumycin-producing Streptomyces parvulus.

The influence of increased dissolved O2 concentrations (DOC) on cell growth and production of the secondary metabolite manumycin by a strain of Streptomyces parvulus (Tü 64) was investigated in a stirred tank fermentor. DOC is given as the O2 partial pressure (po2) in the gas phase in an equilibrium state with the liquid phase. Growth of S. parvulus was not influenced up to DOC equivalent to po2 = 1260 mbar. At po2 = 2205 mbar the maximum biomass concentration was lowered by 40%. Production of manumycin was markedly influenced by DOC and reached the maximal concentration at po2 = 315 mbar. At increased DOC three new metabolites were observed. Two of them, 64p-A and 64p-B, were identified as carboxamides, which represent the branched side chain of the manumycin molecule and a derivative with a shorter chain length. The third metabolite, 64p-C, was a manumycin derivative containing an aromatic ring system. Feeding of glycerol during the production phase increased the total yield and showed a similar effect of DOC. Since DOC has significant regulation effects on product formation and selectivity, it should be used as a major parameter in development strategies of aerobic microbial processes.

Anti-Bacterial Agents↗
PubMed1994

The dsg gene of Myxococcus xanthus encodes a protein similar to translation initiation factor IF3.

The dsg mutants of Myxococcus xanthus are defective in fruiting body development and sporulation, yet they grow normally. The deduced amino acid sequence of the dsg gene product is 50 and 51% identical to the amino acid sequence of translation initiation factor IF3 of both Escherichia coli and Bacillus stearothermophilus, respectively. However, the Dsg protein has a carboxy-terminal extension of 66 amino acids, which are absent from its E. coli and B. stearothermophilus homologs. The Shine-Dalgarno sequence GGAGG and 5 bases further upstream are identical in M. xanthus and several enteric bacteria, despite the wide phylogenetic gap between these species. The infC gene, which encodes IF3 in enteric bacteria, starts with the atypical translation initiation codon AUU, which is known to be important for regulating the cellular level of IF3 in E. coli. Translation of the Dsg protein overexpressed from the M. xanthus dsg gene in E. coli cells initiates at an AUC codon, an atypical initiation codon in the AUU class. The dsg mutants DK429 and DK439 carry the same missense mutation that changes Gly-134 to Glu in a region of amino acid identity.

Amino Acid Sequence↗
PubMed1994

The Myxococcus xanthus dsg gene product performs functions of translation initiation factor IF3 in vivo.

The amino acid sequence of the Dsg protein is 50% identical to that of translation initiation factor IF3 of Escherichia coli, the product of its infC gene. Anti-E. coli IF3 antibodies cross-react with the Dsg protein. Tn5 insertion mutations in dsg are lethal. When ample nutrients are available, however, certain dsg point mutant strains grow at the same rate as wild-type cells. Under the starvation conditions that induce fruiting body development, these dsg mutants begin to aggregate but fail to develop further. The level of Dsg antigen, as a fraction of total cell protein, does not change detectably during growth and development, as expected for a factor essential for protein synthesis. The amount of IF3 protein in E. coli is known to be autoregulated at the translational level. This autoregulation is lost in an E. coli infC362 missense mutant. The dsg+ gene from Myxococcus xanthus restores normal autoregulation to the infC362 mutant strain. Dsg is distinguished from IF3 of E. coli, other enteric bacteria, and Bacillus stearothermophilus by having a C-terminal tail of 66 amino acids. Partial and complete deletion of this tail showed that it is needed for certain vegetative and developmental functions but not for viability.

Amino Acid Sequence↗
PubMed1993

Beta-galactosidase activity in single differentiating bacterial cells.

Myxococcus xanthus strains containing transcriptional fusions to lacZ were analyzed and fractionated by differences in their levels of beta-galactosidase expression. The fluorogenic substrate for beta-galactosidase, fluorescein di-beta-galactopyranoside, was introduced into M. xanthus cells during a rapid decrease in osmolarity of the medium followed by a return to isoosmolarity. Fluorescein, the product of hydrolysis, was retained within the cells and their viability was preserved. Fluorescence increased linearly with time and was proportional to beta-galactosidase activity. beta-Galactosidase expression in most fusion strains, though beginning at different phases of growth or development, was distributed unimodally amongst cells. However, fusion strain Tn5 lac omega 4473 was shown to be heterogeneous at 9 hr of development. It was possible to separate physically cells that expressed beta-galactosidase at a high level from other, still viable, cells with no expression. The approach described here could be adapted to study differentiation in plants and animals as well, where transcriptional fusions and fluorogenic substrates for enzyme probes of gene expression also can be used.

DNA Transposable Elements↗
PubMed1993

Two cell-density domains within the Myxococcus xanthus fruiting body.

Myxococcus xanthus, one of the simplest of multicellular organisms, develops into an organized, multicellular aggregate, called a fruiting body. Examination of the internal structure of the nascent fruiting body showed it to consist of a hemispherical outer domain of densely packed and ordered cells. Inside this dense shell is an inner domain of less ordered cells at 3-fold lower cell density. Single cells move in a bidirectional stream in the outer domain, orbiting the fruiting body throughout development, whereas in the inner domain, cell movement ceases as the fruiting body matures. The fruiting body thus consists of two domains, distinguished from each other by differential cell density, cell arrangements, and cell movements.

Cell Movement↗
PubMed1993

["Single-shot" antibiotic prophylaxis in thoracic surgery; reduction of the postoperative infection rate].

A prospective, controlled and randomised trial was started to detect the effectivity of a "single-shot" antibiotic prophylaxis in thoracic surgery using cefuroxime. Therefore 200 unselected patients, consecutively scheduled for major thoracic surgery except endoscopic procedures or mediastinoscopy were enrolled in this study and randomized into either the control group (no antibiotics perioperatively; n = 100) or the prophylaxis group (one dose of 1.5 g cefuroxime i.v. at induction of anaesthesia; n = 100). Clinical signs correlated with infection, radiological findings and the results of repeated microbiological examinations were recorded and a comparative statistical analysis was done. Compared to controls the prophylaxis group had fewer (not significant) infections of the wound, the pleural cavity and the urinary tract and fewer patients of this group showed "pronounced infiltration" in daily taken chest roentgenograms (significant), clinical signs for pneumonia and pathologic sputum findings, or new bacterial colonisation of sputum specimens on the first postoperative day, whereas bacteria, isolated from tracheal aspirates, immediately taken after intubation disappeared more often. Specimens of pleural fluid taken postoperatively were less often positive for bacteria. Fewer patients were treated with antibiotics in the postoperative course and the courses were shorter in the prophylaxis group compared to controls. Considering the risk factor "positive microbiological culture" in preoperative tracheal aspirates, patients of the prophylaxis group showed much more seldom new radiological "infiltration" (statistically highly significant) and, in addition, had lower white blood cell counts (significant) and lower mean maximal body temperatures. The results of our trial confirm the preventive effect of "single-shot" antibiotic prophylaxis in thoracic surgery against infections.

Bacterial Infections↗
PubMed1993

Video-assisted thoracoscopic surgery--indications, results, complications, and contraindications.

In recent times minimally invasive surgery has secured a firm place among the therapeutic options in thoracic surgery. The experience and results gained from video-assisted surgery on 109 patients between January 1, 1992 and July 31, 1993 are critically discussed. The procedure could be completed thoracoscopically on 94 of them. A change of method was necessary nine times for technical reasons and six times for oncological reasons (two times due to metastasis, four times due to bronchial carcinoma). A total of 154 individual operations were conducted. Sixty-three patients with recurrent spontaneous pneumothorax were successfully treated. The relapse rate was 1.5%. With the exception of three rethoracotomies (one due to postoperative hemorrhaging and two to persistent fistula) no significant complications occurred. Further indications included capsulated pleural empyema (n = 1), persistent hematothorax (n = 2), pleurectomy for malignant pleural effusion (n = 2), pleural tumors (n = 3), pulmonary parenchyma (n = 2), interstitial lung diseases (n = 3), bullous emphysema (n = 2), peripheral lung nodules (n = 18), mediastinal tumors (n = 8), and sympathectomy (n = 2). The advantages of video-assisted thoracoscopic surgery for patients include cosmetic considerations, low pain, earlier postoperative mobilization, and for some indications, a shorter operation period. The significant disadvantages for the surgeon are the loss of binocular vision as well as the impossibility of intraoperative palpation.

Bronchial Neoplasms↗
PubMed1993

Spatial restriction of cellular differentiation.

Myxococcus xanthus cells differentiate into myxospores within a fruiting body, an aggregate of approximately 10(5) cells. Previous work had discerned an inner and outer domain within the fruiting body differentiated by cell density and cell alignment. To test whether the two domains might play different roles in spore differentiation, developmentally regulated gene fusions were screened for expression restricted to one domain or the other. Transcriptional lacZ fusions to 80 developmentally regulated genes were examined and eight fusions were found that restricted expression to the inner domain, while one fusion, omega 7621, showed initial expression in the outer domain. Initial omega 7621 expression coincided with patches of spore precursors evident in bright-field microscopy. Later in development, both omega 7621 expression and the patches expanded inward, eventually filling both the inner and outer domains. Previous work had also shown that high cell density and cell alignment are required for transmission of the C-signal, which is needed to initiate spore differentiation. Evidence is presented for a novel morphogenetic mechanism in which C-signaling in the outer (high density) domain initiates spore differentiation. It is proposed that spore precursors are passively transported from the outer to the inner domain by the movements of undifferentiated rod cells. Reconstruction experiments showed that developing rod cells move with sufficient force to displace spores. Spore precursors thus accumulate in the inner domain where they express spore-specific genes at high levels and account for inner domain specific expression.

Biological Transport↗
PubMed1993

devRS, an autoregulated and essential genetic locus for fruiting body development in Myxococcus xanthus.

Two Tn5 lac insertions into the Myxococcus genome at sites omega 4414 and omega 4473, which are separated by 550 nucleotides, inactivate fruiting body development. Sporulation is decreased 100- to 10,000-fold. At least two genes, devR and devS, are transcribed in this region, probably as an operon. Expression of devR begins by 6 h after starvation has initiated development. On the basis of their nucleotide sequences, devR and devS are expected to encode proteins of 302 and 214 amino acids, respectively. Dev+ function can be restored by a segment of 7.8 kb cloned from the devRS region of wild-type cells. Two experiments show that devR expression is under strong negative autoregulation. beta-Galactosidase is expressed at a higher level from a transcriptional devR::lacZ fusion when the fused operon is in a dev strain than when it is in the dev/dev+ genetic background of a partial diploid. There is more mRNA accumulation from the devRS region in the dev strain than in a rescued dev/dev+ tandem duplication strain. Sporulation rescue is correlated with some degree of negative autoregulation, even though sporulation is not inversely proportional to beta-galactosidase expression from omega 4414. A second level of regulation is suggested by complementation of dev by dev+ in duplication strains. The expression of devRS, measured by sporulation levels, differs 1,000-fold when devRS+ is moved from a distance of 20 kb to 3 Mb from the mutant devRS locus. Expression of devR is also dependent on the cell density at which development is initiated, a third level of regulation. Multiple levels of regulation suggest that devRS is a switch required to activate completion of aggregation and sporulation.

Amino Acid Sequence↗