Nitrate/oxygen co‐sensing by an NreA/NreB sensor complex of Staphylococcus carnosus

In Staphylococci maximal induction of nitrate reductase (narGHJI genes) requires anaerobic conditions, the presence of nitrate, and the NreABC regulatory system. Aerobic regulation is effected by the NreB/NreC two‐component system. The role of the nitrate receptor NreA in nitrate induction and its relation to aerobic regulation was analysed in Staphylococcus carnosus. Nitrate induction of a narG‐lip reporter gene required presence of NreB/NreC. When nreA was deleted, nitrate was no longer required for maximal induction, suggesting that NreA is a nitrate regulated inhibitor of NreB/NreC. In vitro, NreA and mutant NreA(Y95A) decreased NreB phosphorylation in part or completely, which was due to the inhibition of the autophosphorylating activity rather than an increase of phosphatase activity. Inhibition of phosphorylation was relieved completely when the nitrate‐bound NreA was used instead of the nitrate‐free form. In the bacterial two‐hybrid BACTH system and HPINE interaction assays, NreA interacted with NreB, but not with NreC, and the interaction was diminished by nitrate. In summary, NreA interacts with NreB and controls its phosphorylation level in a nitrate dependent manner. In this way nitrate and NreA modulate the function of the oxygen sensor NreB, resulting in nitrate/oxygen co‐sensing by an NreA/NreB sensor unit as part of the NreABC‐system.     

Large-Scaled Metabolic Profiling of Human Dermal Fibroblasts Derived from Pseudoxanthoma Elasticum Patients and Healthy Controls

Mutations in the ABC transporter ABCC6 were recently identified as cause of Pseudoxanthoma elasticum (PXE), a rare genetic disorder characterized by progressive mineralization of elastic fibers. We used an untargeted metabolic approach to identify biochemical differences between human dermal fibroblasts from healthy controls and PXE patients in an attempt to find a link between ABCC6 deficiency, cellular metabolic alterations and disease pathogenesis. 358 compounds were identified by mass spectrometry covering lipids, amino acids, peptides, carbohydrates, nucleotides, vitamins and cofactors, xenobiotics and energy metabolites. We found substantial differences in glycerophospholipid composition, leucine dipeptides, and polypeptides as well as alterations in pantothenate and guanine metabolism to be significantly associated with PXE pathogenesis. These findings can be linked to extracellular matrix remodeling and increased oxidative stress, which reflect characteristic hallmarks of PXE. Our study could facilitate a better understanding of biochemical pathways involved in soft tissue mineralization.     

Prefrontal neural activity when feedback is not relevant to adjust performance

It has been shown that the rostral cingulate zone (RCZ) in humans uses both positive and negative feedback to evaluate performance and to flexibly adjust behaviour. Less is known on how the feedback types are processed by the RCZ and other prefrontal brain areas, when feedback can only be used to evaluate performance, but cannot be used to adjust behaviour. The present fMRI study aimed at investigating feedback that can only be used to evaluate performance in a word-learning paradigm. One group of volunteers (N = 17) received informative, performance-dependent positive or negative feedback after each trial. Since new words had to be learnt in each trial, the feedback could not be used for task-specific adaptations. The other group (N = 17) always received non-informative feedback, providing neither information about performance nor about possible task-specific adaptations. Effects of the informational value of feedback were assessed between-subjects, comparing trials with positive and negative informative feedback to non-informative feedback. Effects of feedback valence were assessed by comparing neural activity to positive and negative feedback within the informative-feedback group. Our results show that several prefrontal regions, including the pre-SMA, the inferior frontal cortex and the insula were sensitive to both, the informational value and the valence aspect of the feedback with stronger activations to informative as compared to non-informative feedback and to informative negative compared to informative positive feedback. The only exception was RCZ which was sensitive to the informational value of the feedback, but not to feedback valence. The findings indicate that outcome information per se is sufficient to activate prefrontal brain regions, with the RCZ being the only prefrontal brain region which is equally sensitive to positive and negative feedback.     

Locomotory activity and exploration behaviour of juvenile European lobsters (Homarus gammarus) in the laboratory

The behaviour of juvenile European lobsters (Homarus gammarus) in the wild is little understood. A laboratory system was designed with a maze-like environment as an alternative to the large technological expenditure of a field study. It provided an apparently endless runway with uniform thigmotactical cues. Juvenile lobsters having a total length of 68 to 115 mm were studied. The lobsters showed an extensive nocturnal locomotory activity. They established home shelters in which they spent the day and covered distances of 1200 to 1600 m during the night. On average, the lobsters performed 136 excursions from their shelters, of which 10% led only to the immediate surroundings of the shelters. Of all the excursions 90% were shorter than 16 m. In some exceptional cases distances of several hundred meters were covered in the maze between shelter visits. Excursions of less than 16 m lasted on average less than 5 min. The frequencies of shelter visits during the dark phase were highest in small lobsters (300 visits) and lowest in larger lobsters (50 visits). The time spent within shelters decreased from 10% to less than 2% with lobster size. A distinct change in behaviour was obvious at a body length of 75 to 80 mm. Smaller lobsters behaved defensively and relied on shelter protection. Larger lobsters were less dependent on shelter protection and thus were able to explore and utilize their environment more intensively.     

Perfectly misleading distances from ternary characters

D. Huson and M. Steel showed that for any two binary phylogenetic trees on the same set of n taxa, there exists a sequence of multistate characters that is homoplasy-free only on the first tree but perfectly additive only on the second one. The original construction of such a sequence required n - 1 character states and it remained an open question whether a sequence using fewer character states can always be found. In the present note we will answer this question by showing that three character states suffice to construct such misleading sequences--even if we insist that they conform to an ultrametric (i.e., fit a molecular clock).     

Release from prey preservation behavior via prey switch allowed diversification of cuticular hydrocarbon profiles in digger wasps

The cuticle of insects is covered by a layer of hydrocarbons (CHC), whose original function is the protection from desiccation and pathogens. However, in most insects CHC profiles are species specific. While this variability among species was largely linked to communication and recognition functions, additional selective forces may shape insect CHC profiles. Here, we show that in Philanthinae digger wasps (Crabronidae) the CHC profile coevolved with a peculiar brood‐care strategy. In particular, we found that the behavior to embalm prey stored in the nest with hydrocarbons is adaptive to protect larval food from fungi in those species hunting for Hymenoptera. The prey embalming secretion is identical in composition to the alkene‐dominated CHC profile in these species, suggesting that their profile is adaptively conserved for this purpose. In contrast, prey embalming is not required in those species that switched to Coleoptera as prey. Released from this chemical brood‐care strategy, Coleoptera‐hunting species considerably diversified their CHC profiles. Differential needs to successfully protect prey types used as larval food have thus driven the diversification of CHCs profiles of female Philanthinae wasps. To the best of our knowledge, this is the first evidence of a direct link between selection pressure for food preservation and CHC diversity.     

Thermococcus waiotapuensis sp. nov., an extremely thermophilic archaeon isolated from a freshwater hot spring

An extremely thermophilic, sulfur-dependent archaeon, strain WT1, was isolated from a freshwater hot spring in the Lake Taupo area of North Island, New Zealand. The cells are flagellated, strictly anaerobic cocci that grow optimally at 85 °C and 5.4 g NaCl l^–1. The strain grows heterotrophically on complex proteinaceous substrates or on appropriate salts plus amino acid mixtures and is also able to utilize maltose, starch, and pyruvate. Elemental sulfur could be replaced by cystine or thioglycollate. The range of temperatures allowing growth is from 60 to 90 °C; the pH supporting growth ranges from 5 to 8 (optimum, pH 7). Strain WT1 grew in a defined medium containing amino acids as the sole carbon and energy sources. The required amino acids were: Arg, His, Ile, Leu, Phe, Ser, Thr, Trp, Tyr, and Val. Strain WT1 showed sensitivity to rifampicin. DNA G+C content was 50.4 mol%. Phylogenetic analysis of the sequence encoding the 16S rRNA gene indicated that this isolate is a member of the Thermococcales. DNA/DNA hybridization studies revealed no similarity to several species of Thermococcus and Pyrococcus, with the exception of Thermococcus zilligii. Based on the reported results, we propose strain WT1 as a new species to be named Thermococcus waiotapuensis sp. nov. Received: 5 January 1999 / Accepted: 19 May 1999