Recovery of Soil Ammonia Oxidation After Long-Term Zinc Exposure Is Not Related to the Richness of the Bacterial Nitrifying Community

A soil sterilization–reinoculation approach was used to manipulate soil microbial diversity and to assess the effect of the diversity of the ammonia-oxidizing bacteria (AOB) on the recovery of the nitrifying community to metal stress (zinc). Gamma-irradiated soil was inoculated with 13 different combinations of up to 22 different soils collected worldwide to create varying degrees of AOB diversity. Two months after inoculation, AOB amoA DGGE based diversity (weighted richness) varied more than 10-fold among the 13 treatments, the largest value observed where the number of inocula had been largest. Subsequently, the 13 treatments were either or not amended with ZnCl₂. Initially, Zn amendment completely inhibited nitrification. After 6 months of Zn exposure, recovery of the potential nitrification activity in the Zn amended soils ranged from <10 % to >100 % of the potential nitrification activity in the corresponding non-amended soils. This recovery was neither related to DGGE-based indices of AOB diversity nor to the AOB abundance assessed 2 months after inoculation (p?>?0.05). However, recovery was significantly related (r?=?0.75) to the potential nitrification rate before Zn amendment and only weakly to the number of soil inocula used in the treatments (r?=?0.46). The lack of clear effects of AOB diversity on recovery may be related to an inherently sufficient diversity and functional redundancy of AOB communities in soil. Our data indicate that potential microbial activity can be a significant factor in recovery.     

Properties of Oligomeric Forms of Phosphofructokinase from Chlorella kessleri Grown under Different Light Conditions

Fast protein liquid chromatography on Superose 6 of crude extracts from Chlorella kessleri, Fott et Novákóva, grown autotrophically in blue or in red light yields three different oligomeric forms of phosphofructokinase (PFK, EC 2.7.1.11). Their substrate affinities and responses to homotropic and heterotropic effectors are different. In vitro, the degree of oligomerization of the enzyme can be influenced by specific intermediates or cofactors. Its substrate, MgATP (10 mM/5 mM), and the negative effector, phosphoenolpyruvate (5 mM), both lead to some dissociation, while the second substrate, fructose-6-phosphate (5 mM), and the positive effector, inorganic phosphate (50 mM), have no effect. It is discussed whether formation or dissociation of oligomeric PFK forms in vivo result from alterations in the levels or in the intracellular distribution of effector molecules and whether such processes are involved in the different regulation of cell metabolism in blue or in red light.     

Murein Synthesis and Identification of Cell Wall Precursors of Temperature-Sensitive Lysis Mutants of Escherichia coli

A group of temperature-sensitive lysis mutants of Escherichia coli K-12 was studied. Mutants impaired in the synthesis of uridine diphosphate-N-acetylmuramyl (UDP-MurNAc)-pentapeptide or in the synthesis of murein amino acids were found. Their rate of murein synthesis at the restrictive temperature was decreased. A large number of mutants did not differ from the parent strain with respect to the rate of murein synthesis and the precursor pattern. The behavior of these mutants is discussed. It was impossible to accumulate UDP-MurNAc-pentapeptide in E. coli by the antibiotics penicillin and vancomycin. The hypothesis is put forward that the amount of this murein precursor is regulated by feedback inhibition.     

Light-stimulated respiration in the green algaDunaliella tertiolecta: Involvement of the ultraviolet/blue-light photoreceptor(s) and phytochrome?

Starch breakdown and respiratory O₂ uptake in the green algaDunaliella tertiolecta (Butcher) are stimulated not only by blue, but also by red light. In the present study, attempts are described to identify the photoreceptor(s) involved. Fluence rate-response curves with different slopes in the ultraviolet (UV)/blue and in the red spectral region as well as differences in the kinetics and in the unfluence of dark pre-incubation on the stimulation of respiratory O₂ uptake by blue and red light strongly indicate the action of two photoreceptors. Since the effect of red light shows some far-red reversibility, and since simultaneous irradiation with red and far-red light decreases the effectiveness of red light, the involvement of phytochrome — in addition to the UV/blue photoreceptor(s) — is suggested in the light-stimulated respiration inDunaliella.Abbreviation UV ultraviolet     

Über Aktivitätssteigerungen der Pyruvatkinase durch Blaulicht oder Glucose bei einer chlorophyllfreien Chlorella-Mutante

Summary Crude extracts of dark-kept resting cells of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris Beijerinck (211-11h/20) were found to convert 14.44±0.77 nmol PEP per min and mg protein into pyruvate by the action of pyruvate kinase (=PK; EC 2.7.1.40). When such cells were exposed to blue light (<550 nm, 300 W cm^-2) for 3 hrs the PK-activity/protein of their crude extracts rose to 21.47±1.30, i.e., it was enhanced by 43%. Poisoning with 10^-3 mol cycloheximide or with 150 g actinomycin D/ml prevented the effect of blue light by 80–90% (Table 1). This result points to an induction of enzyme synthesis in blue light. Addition of 1% glucose in the dark resulted in an increase in PK-activity, too. Three hrs after application of glucose the PK-activity was 28.05±1.88 nmol/min and mg protein, which was 94% greater than in the control. The effect of glucose was also largely preventable by cycloheximide (10^-3 mol) or by actinomycin D (150 g/ml) (Table 2). These results lead to the conclusion that blue light may induce the synthesis of PK by supplying free sugars at the site of enzyme synthesis. The assumption is supported by the observation that in hot water extracts of blue illuminated cells in which glucose oxidation had been poisoned by. 10^-2 mol monoiodoacetic acid there was 60% more glucose, glucose-6-phosphate, fructose-6-phosphate and sucrose detectable than in extracts of equally poisoned algae from darkness (Table 3). It is suggested that blue light activates a system for the transport of sugar out of the chloroplast, which results in the induction of respiratory enzyme synthesis and thus in enhanced respiration.

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Abkürzungen PK Pyruvatkinase (EC 2.7.1.40) - PEP Phosphoenolpyruvat - LDH Lactatdehydrogenase     

Regulation of Carbohydrate Breakdown of Chlorella Mutant No. 20, Studied by 31P NMR Spectroscopy and Enzymatic Analysis: 1. Regulation under Blue Light Conditions

The regulation of carbohydrate degradation, especially of itsglycolytic part, is studied in darkness and under blue lightconditions in the chlorophyll-free Chlorella mutant no. 20.The mass action ratios of glycolytic reactions are calculatedfrom the concentrations of the respective intermediates, measuredvia enzymatic analysis and ³¹P NMR spectroscopy. Comparisonwith the equilibrium constants indicates that the reactionscatalyzed by hexokinase, phosphofructokinase, and pyruvate kinaseare able to control the glycolytic pathway. Blue light illumination leads to rapid changes in the levelof various metabolites. The decrease in PEP proves the regulatoryrole of pyruvate kinase in vivo, a finding supported by thecrossover plot as well as by the move of the mass action ratiotowards equilibrium. Also, the starch degrading enzymes phosphorylaseand possibly amylase, but not phosphofructokinase, seem to beinvolved in the regulation of carbohydrate breakdown in bluelight. The kinetics of the different blue light responses clearly indicatethat not the increase in respiratory O₂ uptake, but an appropriatechange in the concentration of effectors of the regulatory enzymespyruvate kinase, phosphorylase, and maybe amylase is a primaryblue light effect in the Chlorella mutant. The involvement ofa proton pump seems to be ruled out by the constant intracellularpH measured by in vivo ³¹P NMR spectroscopy. (Received October 5, 1987; Accepted January 7, 1988)     

Gravitational biology within the German Space Program: goals, achievements, and perspectives

Summary. Gravity plays an important role for the evolution, orientation and development of organisms. Most of us, however, tend to overlook its importance because – due to its constant presence from the beginning of evolution some 4 billion years ago – this environmental parameter is almost hardwired into our interpretation of reality. This negligence of gravity is the more surprising as we all have our strong fights with this factor, especially during the very early and again during the late phases of our lives. On the other hand, scientists have been fascinated to observe the effects of gravity especially on plants and microorganisms for more than a hundred years, since Darwin and Sachs demonstrated the role of the root cap for downward growing plants. Different experimental approaches are nowadays available in order to change the influence of gravity and to study the corresponding influences on the physiology of biological systems. With the advent of spaceflight, a long-term nearly nullification of gravity is possible. Utilisation of this so-called “microgravity” condition for research in life sciences thus became an important asset in the space programs of various space agencies around the world. The German Space Life Sciences Program is managed – like all other space programs and activities in Germany – by the German Aerospace Center (DLR) in its role as space agency for Germany. Within the current space program, approved by the German government in May 2001, the overall goal for its life sciences part was defined as to gain scientific knowledge and to disclose new application potential by research under space conditions, especially by utilising the microgravity environment of the International Space Station. Three main scientific fields have been identified in collaboration with the scientific community: integrative human physiology, biotechnological applications of the microgravity environment, and fundamental biology of gravity and radiation responses (i.e., gravitational and radiation biology). In the present contribution, specific goals as well as achievements and perspectives of research in gravitational biology are given. In addition, some information is provided on spaceflight opportunities available. Correspondence and reprints: German Aerospace Center (DLR), Space Agency, P.O. Box 300364, 53183 Bonn, Federal Republic of Germany.     

Phosphate Compounds of Scenedesmus C-2A' in Darkness or Blue Light as Measured by 31P NMR

Phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra ofintact cells of Scenedesmus mutant C-2A' and of their perchloricacid extracts are presented. Sugarphosphates, including glucose-6-phosphateand fructose-1,6-bisphosphate, orthophosphate, nucleotide di-and triphosphates, NAD(P), UDPG and—in the case of intactcells—also polyphosphates were identified. Blue light,which is known to stimulate the carbohydrate breakdown of greenalgae, leads to a transient drop in P_i, a pronounced decreasein the ATP/ADP ratio, and an increase in sugarphosphates, givingrise to the idea that the enhancement of phosphorolytic starchbreakdown is a primary response to blue light. Addition of glucoseto Scenedesmus mutant cells leads to comparable changes (besidesan additionally enhanced glucose-6-phosphate level), which thussupport the view that blue light stimulates dark-type respiration.Altogether the results demonstrate the applicability of ³¹PNMR spectroscopy to the study of the metabolism of green algae. (Received December 7, 1984; Accepted February 12, 1985)