From observations to paradigms; the importance of theories and models. An interview with Hans Meinhardt by Richard Gordon and Lev Beloussov

Hans Meinhardt received his PhD in physics from the University of Cologne at 1966. For a postdoctoral fellowship, he went to the European High Energy Laboratory CERN in Geneva where he joined a group working on the leptonic decay of the Xi-minus particle. One of his duties was to perform computer simulations to optimize the complex experimental setup -- a skill which turned out to be helpful later on. In 1969 he switched to biology and joined the department of Alfred Gierer at the Max Planck Institute for Developmental Biology (formerly Virus Research) in Tubingen. His interest was focused on mechanisms of biological pattern formation. Using computer simulations as a tool, he developed models for essential steps in development. Most fascinating for him was the possibility to recapitulate and to reconstructusing the computer the genesis of structures where no structures were before and to see how these emerging structures become subsequently further refined. In addition to the interaction with Alfred Gierer and his group working on hydra development, the Max-Planck Institute as a whole provided a very stimulating environment. In the seventies, the work of Klaus Sander on gradients in early insect development was highly influential. Collaboration with Martin Klinger in the eighties revealed that the pigmentation patterns on tropical sea shells are convenient to study highly dynamic patterning processes. The variability and the asthetic beauty of these patterns turned out to result from the chaotic nature of the underlying reactions. Mechanisms deduced from shell patterns became a key to understand other developing systems such as orientation of chemotactic cells or phyllotaxis. Officially Hans Meinhardt retired at the end of 2003. At present he works on refinements and extensions of models which account for the different modes of embryonic axis formation in different phyla from an evolutionary point of view.     

Lysine and threonine biosynthesis in sorghum seeds: characterisation of aspartate kinase and homoserine dehydrogenase isoenzymes

Aspartate kinase (AK, EC 2.7.2.4) and homoserine dehydrogenase (HSDH, EC 1.1.1.3) have been partially purified and characterised from immature sorghum seeds. Two peaks of AK activity were eluted by anion‐exchange chromatography [diethylaminoethyl (DEAE)‐Sephacel] with 183 and 262 mM KCl, and both activities were inhibited by lysine. Similarly, two peaks of HSDH activity were eluted with 145 and 183 mM KCl; the enzyme activity in the first peak in elution order was shown to be resistant to threonine inhibition, whereas the second was sensitive to threonine inhibition. However, following gel filtration chromatography (Sephacryl S‐200), one peak of AK activity co‐eluted with HSDH and both activities were sensitive to threonine inhibition, suggesting the presence of a bifunctional threonine‐sensitive AK–HSDH isoenzyme with a molecular mass estimated as 167 kDa. The activities of AK and HSDH were studied in the presence of lysine, threonine, methionine, valine, calcium, ethylene glycol bis(2‐aminoethylether)‐N,N,N′N′‐tetraacetic acid, calmodulin, S‐adenosylmethionine (SAM), S‐2‐aminoethyl‐l ‐cysteine (AEC) and increasing concentrations of KCl. AK was shown to be inhibited by threonine and lysine, confirming the existence of two isoenzymes, one sensitive to threonine and the other sensitive to lysine, the latter being predominant in sorghum seeds. Methionine, SAM plus lysine and AEC also inhibited AK activity; however, increasing KCl concentrations and calcium did not produce any significant effect on AK activity, indicating that calcium does not play a role in AK regulation in sorghum seeds. HSDH also exhibited some inhibition by threonine, but the majority of the activity was not inhibited, thus indicating the existence of a threonine‐sensitive isoenzyme and a second predominant threonine‐insensitive isoenzyme. Valine and SAM plus threonine also inhibited HSDH; however, increasing concentrations of KCl and calcium had no inhibitory effect.     

Isolation and Molecular Characterization of Chitinase-Deficient Bacillus licheniformis Strains Capable of Deproteinization of Shrimp Shell Waste To Obtain Highly Viscous Chitin

Proteolytic but chitinase-deficient microbial cultures were isolated from shrimp shell waste and characterized. The most efficient isolate was found to be a mixed culture consisting of two Bacillus licheniformis strains, which were first determined microscopically and physiologically. Molecular characterization was carried out by sequencing the 16S rRNA gene of both strains. According to the residual protein and ash content, the chitin obtained by fermentation of such a mixed culture was found to be comparable to a commercially available, chemically processed product. However, the strikingly high viscosity (80 versus 10 mPa of the commercially available sample) indicates its superior quality. The two strains differed in colony morphology and in their secretion capabilities for degradative extracellular enzymes. Sequencing of the loci encoding amylase, cellulase, chitinases, and proteases, as well as the degS/degU operon, which is instrumental in the regulation of degradative enzymes, and the pga operon, which is responsible for polyglutamic acid production, revealed no differences. However, a frameshift mutation in chiA, encoding a chitinase, was validated for both strains, providing an explanation for the ascertained absence of chitinolytic activities and the concomitant possibility of producing highly viscous chitin in a fermentational deproteinization process.     

Models for organizer and notochord formation

In the development of higher organisms, small groups of cells can play an important role by directing the fate of the surrounding cells. Models are discussed that account for the generation of such organizing regions. The generation of local high concentrations of signalling substances was proposed to depend on local self-enhancement combined with a long-range inhibition. The model accounts for pattern regulation, for instance, for the formation of multiple embryos after fragmentation of the early blastodisc in chickens or for head regeneration in the fresh water polyp Hydra. The model has found support from more recently discovered interactions involved in organizer formation. The mutual down-regulation of noggin/chordin and BMP-4 is proposed to function as an indirect self-enhancement, establishing in this way an essential prerequisite for primary pattern formation. Self-enhancement and long-range inhibition is also crucial for the generation of substructures such as bristles or tracheae. A poisoning of an organizing region by a second antagonistic reaction of a short range but a long time constant can lead to its displacement. Long extended structures can be formed as a trace behind the moving organizer. The notochord and the tracheae of insects are discussed as examples.     

Genetic analysis of the Bacillus licheniformis degSU operon and the impact of regulatory mutations on protease production

Disruption experiments targeted at the Bacillus licheniformis degSU operon and GFP-reporter analysis provided evidence for promoter activity immediately upstream of degU. pMutin mediated concomitant introduction of the degU32 allele--known to cause hypersecretion in Bacillus subtilis-- resulted in a marked increase in protease activity. Application of 5-fluorouracil based counterselection through establishment of a phosphoribosyltransferase deficient Δupp strain eventually facilitated the marker-free introduction of degU32 leading to further protease enhancement achieving levels as for hypersecreting wild strains in which degU was overexpressed. Surprisingly, deletion of rapG--known to interfere with DegU DNA-binding in B. subtilis--did not enhance protease production neither in the wild type nor in the degU32 strain. The combination of degU32 and Δupp counterselection in the type strain is not only equally effective as in hypersecreting wild strains with respect to protease production but furthermore facilitates genetic strain improvement aiming at biological containment and effectiveness of biotechnological processes.     

The mitochondrial genome of Moniliophthora roreri, the frosty pod rot pathogen of cacao

In this study, we report the sequence of the mitochondrial (mt) genome of the Basidiomycete fungus Moniliophthora roreri, which is the etiologic agent of frosty pod rot of cacao (Theobroma cacao L.). We also compare it to the mtDNA from the closely-related species Moniliophthora perniciosa, which causes witches' broom disease of cacao. The 94 Kb mtDNA genome of M. roreri has a circular topology and codes for the typical 14 mt genes involved in oxidative phosphorylation. It also codes for both rRNA genes, a ribosomal protein subunit, 13 intronic open reading frames (ORFs), and a full complement of 27 tRNA genes. The conserved genes of M. roreri mtDNA are completely syntenic with homologous genes of the 109 Kb mtDNA of M. perniciosa. As in M. perniciosa, M. roreri mtDNA contains a high number of hypothetical ORFs (28), a remarkable feature that make Moniliophthoras the largest reservoir of hypothetical ORFs among sequenced fungal mtDNA. Additionally, the mt genome of M. roreri has three free invertron-like linear mt plasmids, one of which is very similar to that previously described as integrated into the main M. perniciosa mtDNA molecule. Moniliophthora roreri mtDNA also has a region of suspected plasmid origin containing 15 hypothetical ORFs distributed in both strands. One of these ORFs is similar to an ORF in the mtDNA gene encoding DNA polymerase in Pleurotus ostreatus. The comparison to M. perniciosa showed that the 15 Kb difference in mtDNA sizes is mainly attributed to a lower abundance of repetitive regions in M. roreri (5.8 Kb vs 20.7 Kb). The most notable differences between M. roreri and M. perniciosa mtDNA are attributed to repeats and regions of plasmid origin. These elements might have contributed to the rapid evolution of mtDNA. Since M. roreri is the second species of the genus Moniliophthora whose mtDNA genome has been sequenced, the data presented here contribute valuable information for understanding the evolution of fungal mt genomes among closely-related species.     

Adaptive changes of rat liver cells induced by repeated intraperitoneal injections of d-galactosamine. III-Light- and electron-microscopic investigations of hepatocellular cytoplasmic changes.

In rats hepatocellular cytoplasmic changes after daily repeated D-galactosamine (GalN) intoxication--i.e. subacute GalN intoxication--were studied by light and electron microscopy. The number of GalN injections--and thus the days of survival--was between one and 30. The rats were killed six hours after the last GalN injection. Less degenerative changes were found after repeated GalN injections. An increased formation of atypical dense bodies (ADB), a temporary pronounced lipid accumulation and changes of the rough and smooth endoplasmic reticulum were prominent features of subacute GalN intoxication. The implications with respect to a modified GalN action in subacute GalN intoxication are discussed with special reference to biochemical data obtained in the same experimental model (Schuchhardt et al., 1977).     

Gut microbiota composition is associated with environmental landscape in honey bees

There is growing recognition that the gut microbial community regulates a wide variety of important functions in its animal hosts, including host health. However, the complex interactions between gut microbes and environment are still unclear. Honey bees are ecologically and economically important pollinators that host a core gut microbial community that is thought to be constant across populations. Here, we examined whether the composition of the gut microbial community of honey bees is affected by the environmental landscape the bees are exposed to. We placed honey bee colonies reared under identical conditions in two main landscape types for 6 weeks: either oilseed rape farmland or agricultural farmland distant to fields of flowering oilseed rape. The gut bacterial communities of adult bees from the colonies were then characterized and compared based on amplicon sequencing of the 16S rRNA gene. While previous studies have delineated a characteristic core set of bacteria inhabiting the honey bee gut, our results suggest that the broad environment that bees are exposed to has some influence on the relative abundance of some members of that microbial community. This includes known dominant taxa thought to have functions in nutrition and health. Our results provide evidence for an influence of landscape exposure on honey bee microbial community and highlight the potential effect of exposure to different environmental parameters, such as forage type and neonicotinoid pesticides, on key honey bee gut bacteria. This work emphasizes the complexity of the relationship between the host, its gut bacteria, and the environment and identifies target microbial taxa for functional analyses.