Buchbesprechungen

Ohne Zusammenfassung     

Dinoflagellate resting cysts as factors in phytoplankton ecology of the North Sea

The occurrence and distribution of dinoflagellate resting cysts were investigated at 11 locations in the south-eastern part of the North Sea. Twenty-six known cyst species and 7 unknown cyst types, which may act as seed population for planktonic dinoflagellate blooms, have been recorded for the first time in the area. The most common cysts in recent sediments were those ofScrippsiella trochoidea, Zygabikodinium lenticulatum, Peridinium dalei, Scrippsiella lachrymosa, Protoceratium reticulatum, Protoperidinium denticulatum, andP. conicum. At all stations,S. trochoidea dominated the cyst assemblages with a maximal abundance of 1303 living cysts/cm³ in the uppermost half centimetre. Cysts of the potentially toxic dinoflagellatesAlexandrium cf.excavatum andA. cf.tamarense were scarce. In the upper 2-cm layer of sediment, dinoflagellate cysts were found in concentrations of 1.8 up to 682 living cysts/cm³. Empty cysts constituted 22–56% of total cyst abundance. The comparative distribution of the cysts showed a general increase in abundance from inshore sites to the offshore area, whereby sandy stations exhibited the lowest cyst abundance and diversity. The wide distribution of living and empty cysts ofScrippsiella lachrymosa suggests that its motile form, which has not been officially recorded in the area until now, is a common plankton organism in German coastal waters. The relatively high abundance of cysts in recent sediments demonstrates the potential importance of benthic resting stages for the initiation of dinoflagellate blooms in the study area.     

Gymnodinium catenatum Graham (Dinophyceae)in Europe: a growing problem?

The microreticulate resting cyst of the potentially toxic, chain-forming,unarmoured neritic dinoflagellate Gymnodinium catenalum Graham1943. the planktonic stage of which is not known from NorthEuropean waters, is reported for the first time from recentGerman coastal sediments of the North Sea and Baltic Sea. Insandy mud sediments of the German Bight, a maximum of 8 5 livingcysts cm^–3 were found. In Kiel Bight sediments G.catenalumwas found in maximum concentrations of 17.0 living cysts cm^–3.In surface waters of the German Bight resuspended G catenatumcysts were observed at concentrations of up to 3.6 cysts l^–1.Successful germination experiments conducted with natural seawatershow that the occurrence of a vegetative form of G.catenatumin northern Europe is very likely. The present study highlightsthat cyst surveys provide an important tool for the evaluationof areas with potential toxicity problems, as they may indicatethe presence of hitherto overlooked species in the water column.     

Thymineless death is inhibited by CsrA in Escherichia coli lacking the SOS response

Thymineless death (TLD) is the rapid loss of colony-forming ability in bacterial, yeast and human cells starved for thymine, and is the mechanism of action of common chemotherapeutic drugs. In Escherichia coli, significant loss of viability during TLD requires the SOS replication-stress/DNA-damage response, specifically its role in inducing the inhibitor of cell division, SulA. An independent RecQ- and RecJ-dependent TLD pathway accounts for a similarly large additional component of TLD, and a third SOS- and RecQ/J-independent TLD pathway has also been observed. Although two groups have implicated the SOS-response in TLD, an SOS-deficient mutant strain from an earlier study was found to be sensitive to thymine deprivation. We performed whole-genome resequencing on that SOS-deficient strain and find that, compared with the SOS-proficient control strain, it contains five mutations in addition to the SOS-blocking lexA(Ind⁻) mutation. One of the additional mutations, csrA, confers TLD sensitivity specifically in SOS-defective strains. We find that CsrA, a carbon storage regulator, reduces TLD in SOS- or SulA-defective cells, and that the increased TLD that occurs in csrA⁻ SOS-defective cells is dependent on RecQ. We consider a hypothesis in which the modulation of nucleotide pools by CsrA might inhibit TLD specifically in SOS-deficient (SulA-deficient) cells.     

Kin-informative recognition cues in ants

Although social groups are characterized by cooperation, they are also often the scene of conflict. In non-clonal systems, the reproductive interests of group members will differ and individuals may benefit by exploiting the cooperative efforts of other group members. However, such selfish behaviour is thought to be rare in one of the classic examples of cooperation--social insect colonies--because the colony-level costs of individual selfishness select against cues that would allow workers to recognize their closest relatives. In accord with this, previous studies of wasps and ants have found little or no kin information in recognition cues. Here, we test the hypothesis that social insects do not have kin-informative recognition cues by investigating the recognition cues and relatedness of workers from four colonies of the ant Acromyrmex octospinosus. Contrary to the theoretical prediction, we show that the cuticular hydrocarbons of ant workers in all four colonies are informative enough to allow full-sisters to be distinguished from half-sisters with a high accuracy. These results contradict the hypothesis of non-heritable recognition cues and suggest that there is more potential for within-colony conflicts in genetically diverse societies than previously thought.     

The extracellular matrix protein MAGP-2 interacts with Jagged1 and induces its shedding from the cell surface

Elastic fibers are composed of the protein elastin and a network of 10-12-nm microfibrils, which are composed of several glycoproteins, including fibrillin-1, fibrillin-2, and MAGP1/2 (microfibril-associated glycoproteins-1 and -2). Although fibrillins and MAGPs covalently associate, we find that the DSL (Delta/Serrate/LAG2) protein Jagged1, an activating ligand for Notch receptor signaling, also interacts with MAGP-2 in both yeast two-hybrid and coimmunoprecipitation studies. Interaction between Jagged1 and MAGP-2 requires the epidermal growth factor-like repeats of Jagged1. MAGP-2 was found complexed with the Jagged1 extracellular domain shed from 293T cells and COS-7 cells coexpressing full-length Jagged1 and MAGP-2. MAGP-2 shedding of the Jagged1 extracellular domain was decreased by the metalloproteinase hydroxamate inhibitor BB3103 implicating proteolysis in its release. Although MAGP-2 also interacted with the other DSL ligands, Jagged2 and Delta1, they were not found associated with MAGP-2 in the conditioned media, identifying differential effects of MAGP-2 on DSL ligand shedding. The related microfibrillar protein MAGP-1 was also found to interact with DSL ligands but, unlike MAGP-2, was unable to facilitate the shedding of Jagged1. Our findings suggest that in addition to its role in microfibrils, MAGP-2 may also affect cellular differentiation through modulating the Notch signaling pathway either by binding to cell surface DSL ligands or by facilitating release and/or stabilization of a soluble extracellular form of Jagged1.     

Evaluation system for management measures of invasive alien species

The introduction and spread of invasive alien species is a serious threat to ecosystem structures, functions and services worldwide. At enormous cost and effort, attempts are being made to stop and reduce the ongoing appearance of alien species in ecosystems to protect the regional and native biodiversity. Still, management of invasive alien species in particular is often not successful. One reason is a lack of robust toolkits for the management of these species. Guidance on measures which are efficient and effective and which have no negative impact on the environment and human health is urgently needed for decision-making. As a result of an expert workshop, we present a set of three evaluation criteria: effectiveness, ecological impact, and impact on human health. These criteria allow an evaluation of management measures for the prevention, eradication, control and utilisation/disposal of invasive alien species for nature conservation purposes. We applied this evaluation system for 168 invasive and potentially invasive alien species of five taxonomic groups (fungi, non-vascular plants, vascular plants, invertebrates and vertebrates) involving 3619 different management measures. The evaluation of management measures and resulting recommendations for their application are a necessary basis for appropriate, ecologically necessary and professionally sound management. This new approach provides an essential framework for future decisions on management measures, for example in accordance with the provisions of the new Regulation (EU) No 1143/2014 of the European Parliament and of the Council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species.     

Characterization of Eag1 Channel Lateral Mobility in Rat Hippocampal Cultures by Single-Particle-Tracking with Quantum Dots

Voltage-gated ion channels are main players involved in fast synaptic events. However, only slow intracellular mechanisms have so far been described for controlling their localization as real-time visualization of endogenous voltage-gated channels at high temporal and spatial resolution has not been achieved yet. Using a specific extracellular antibody and quantum dots we reveal and characterize lateral mobility as a faster mechanism to dynamically control the number of endogenous ether-a-go-go (Eag)1 ion channels inside synapses. We visualize Eag1 entering and leaving synapses by lateral diffusion in the plasma membrane of rat hippocampal neurons. Mathematical analysis of their trajectories revealed how the motion of Eag1 gets restricted when the channels diffuse into the synapse, suggesting molecular interactions between Eag1 and synaptic components. In contrast, Eag1 channels switch to Brownian movement when they exit synapses and diffuse into extrasynaptic membranes. Furthermore, we demonstrate that the mobility of Eag1 channels is specifically regulated inside synapses by actin filaments, microtubules and electrical activity. In summary, using single-particle-tracking techniques with quantum dots nanocrystals, our study shows for the first time the lateral diffusion of an endogenous voltage-gated ion channel in neurons. The location-dependent constraints imposed by cytoskeletal elements together with the regulatory role of electrical activity strongly suggest a pivotal role for the mobility of voltage-gated ion channels in synaptic activity.