Determination of substrate utilization patterns of soil microbial communities: An approach to assess population changes after hydrocarbon pollution

Abstract: Changes in hydrocarbon content in soils resulted in characteristic shifts of the substrate utilization patterns as tested with the Biolog system. The altered patterns of substrate utilization corresponded to similar changes in abundance of hydrocarbon-utilizing bacteria and the occurrence of specific bacterial groups in the soils. Substrate utilization patterns as recorded with the Biolog system are suitable for rapidly assessing dynamics of autochthonous soil communities and evaluating their biodegradative potential.     

Transformation of difluorinated phenols by Penicillium frequentans Bi 7/2

The Penicillium frequentans strain Bi 7/2, using phenol as a sole source of carbon and energy,transformed the fluorinated phenols 2,3-, 2,4-, 2,5-and 3,4-difluorophenol rapidly. After growth on phenol, resting mycelia of the fungus converted the difluorophenols completely at an initial concentration of 0.5 mM within 6 hours. The corresponding difluorinated catechols were found to be intermediates of all difluorophenols investigated. A relatively unspecific phenol hydroxylase catalyzed this hydroxylation step and showed activities towards all difluorophenols tested. One difluorocatechol was formed from each difluorophenol substituted with fluorine in the ortho-position, whereas two catechols were formed from 3,4-difluorophenol, due to its two vacant ortho-positions. A partial defluorination (50-77%) was observed in all cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Perturbation analysis of a two-locus model with directional selection and recombination

A population genetic two-locus model with additive, directional selection and recombination is considered. It is assumed that recombination is weaker than selection; i.e., the recombination parameter r is smaller than the selection coefficients. This assumption is appropriate for describing the effects of two-locus selection at the molecular level. The model is formulated in terms of ordinary differential equations (ODES) for the gamete frequencies x = (x ₁, x ₂, x ₃, x ₄), defined on the simplex S ₄. The ODEs are analyzed using first a regular pertubation technique. However, this approach yields satisfactory results only if r is very small relative to the selection coefficients and if the initial values x(0) are in the interior part of S ₄. To cope with this problem, a novel two-scale perturbation method is proposed which rests on the theory of averaging of vectorfields. It is demonstrated that the zeroth-order solution of this two-scale approach approximates the numerical solution of the model well, even if recombination rate is on the order of the selection coefficients.     

Deletion mutagenesis of Tn10 Tet repressor — localization of regions important for dimerization and inducibility in vivo

The gene for the Tn 10 Tet repressor (TetR) was subjected to deletion mutagenesis. Screening for a transdominant operator-binding negative phenotype yielded 10 mutants with internal deletions. Three deletions extend from residue D5 to residues L41, W75, or Q76, respectively, and two contain deletions of the α-helix-turn-α-helix DNA-binding motif. Five deletions range from residue K84 to residues between R87 and K98. Since residues from the N-terminus up to position 98 are not necessary for dimerization, this must take place in the C-terminal half of the protein. Ability to dimerize was probed by introducing ochre non-sense codons (oc) at residues G138, H151, E159, l174, or K202. Koc202 shows wild-type in vivo operator-binding and inducibility by tetracycline indicating that the six C-terminal residues of TetR are not important for activity. Mutants with longer C-terminal truncations are inactive and not transdominant. They show reduced steady-state protein levels and are probably impaired in folding and degraded in vivo . Two mutants (Δ151–166, Δ164–166) with deletions in a region variable in primary structure and length among Tet repressers from different resistance determinants bind tet operator efficiently, but are not inducibie by tetracycline. This result indicates that these residues are not important for dimer formation in the operator-binding form.     

Intrinsic factor secretion from isolated human gastric mucosal cells

Human gastric mucosal cells were isolated from the resected fundic mucosa of peptic ulcer patients. The intracellular content and secretion of intrinsic factor were estimated by binding to cyano[⁵⁷Co]cobalamin. The content was maximal in the enriched parietal cell fraction which also displayed the highest H⁺ production as measured by amino[¹⁴C]pyrine uptake. Secretagogues evoked full response after 15 min of incubation: pentagastrin (181% of basal secretion), carbachol (208%), histamine (250%) and dibutyryl cyclic adenosine monophosphate (304%). The phosphodiesterase inhibitor isobutylmethylxanthine was slightly more effective even than dibutyryl cAMP. The response to histamine was abolished by ranitidine, indicating activation of adenylate cyclase via histamine H₂ receptors, but remained unaffected by atropine, which in turn blocked the carbachol effect, whereas ranitidine was ineffective. The mean formation rate was 8.4 fmol intrinsic factor/10⁶ cells per h under basal conditions and 14.3 fmol in response to histamine.     

Responsiveness of mesolimbic, mesocortical, septal and hippocampal cholecystokinin and substance P neuronal systems to stress, in the male rat

The effects of acute and subchronic stress upon discrete cholecystokinin (CCK) and Substance P (SP) neuronal systems have been studied. Adult male rats were exposed to foot-shock stress for periods of 2, 4, 10, 30 or 60 min, immediately following which they were decapitated; brains were rapidly removed and frozen, and subsequently microdissected and extracted. CCK and SP were determined by RIA. In the olfactory tubercule, stress had no effect upon CCK content, but induced a rapid depletion of SP. In the prefrontal cortex, increased CCK concentrations were found following 30 min of stress exposure. In the medial septum, foot-shock led to a rapid increase in CCK content, and to a similar but delayed change in SP levels. A rapid rise in CCK concentrations was also seen in the lateral septum, but no stress effect whatsoever upon SP occurred in this structure. In the dentate gyrus, CCK exhibited a biphasic responsiveness to stress, while SP levels were increased only at the later time intervals. These data demonstrate that discrete CCK and SP neuronal systems are responsive to stress, and thereby support a functional role for these peptides in the processing of neural and hormonal signals by the CNS.