• CUBE - Computational Systems Biology

  • DOME - Microbial Ecology

  • TER - Terrestrial Ecosystem Research


Latest publications

Chemosynthetic symbionts of marine invertebrate animals are capable of nitrogen fixation

Chemosynthetic symbioses are partnerships between invertebrate animals and chemosynthetic bacteria. The latter are the primary producers, providing most of the organic carbon needed for the animal host's nutrition. We sequenced genomes of the chemosynthetic symbionts from the lucinid bivalve Loripes lucinalis and the stilbonematid nematode Laxus oneistus. The symbionts of both host species encoded nitrogen fixation genes. This is remarkable as no marine chemosynthetic symbiont was previously known to be capable of nitrogen fixation. We detected nitrogenase expression by the symbionts of lucinid clams at the transcriptomic and proteomic level. Mean stable nitrogen isotope values of Loripes lucinalis were within the range expected for fixed atmospheric nitrogen, further suggesting active nitrogen fixation by the symbionts. The ability to fix nitrogen may be widespread among chemosynthetic symbioses in oligotrophic habitats, where nitrogen availability often limits primary productivity.

Petersen JM, Kemper A, Gruber-Vodicka H, Cardini U, van der Geest M, Kleiner M, Bulgheresi S, Mussmann M, Herbold C, Seah BKB, Chakkiath PA, Liu D, Belitz A, Weber M
2016 - Nature Microbiology, in press

Nitrogen isotope fractionation during N uptake via arbuscular mycorrhizal and ectomycorrhizal fungi into grey alder

Arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi affect plant nitrogen (N) dynamics. Plant
N isotope patterns have been used to characterise the contribution of ECM fungi to plant N uptake. By
quantifying and comparing the effects of an AM and an ECM fungus on growth, N uptake and isotopic
composition of one host plant grown at different relative N supply levels, the aim of this study was to
improve the mechanistic understanding of natural 15N abundance patterns in mycorrhizal plants and
their underlying causes.
Grey alders were inoculated with one ECM fungus or one AM fungus or left non-mycorrhizal. Plants
were grown under semi-hydroponic conditions and were supplied with three rates of relative N supply
ranging from deficient to luxurious.
Neither mycorrhizal fungus increased plant growth or N uptake. AM root colonisation had no effect
on whole plant 15N and decreased foliar 15N only under N deficiency. The roots of these plants were
15N-enriched. ECM root colonisation consistently decreased foliar and whole plant 15N.
It is concluded, that both mycorrhizal fungi contributed to plant N uptake into the shoot. Nitrogen
isotope fractionation during N assimilation and transformations in fungal mycelia is suggested to have
resulted in plants receiving 15N-depleted N via the mycorrhizal uptake pathways. Negative mycorrhizal
growth effects are explained by symbiotic resource trade on carbon and N and decreased direct plant N
© 2016 Elsevier GmbH. All rights reserved.

Schweiger P
2016 - Journal of Plant Physiology, 205: 84-92

Convergent patterns in the evolution of mealybug symbioses involving different intrabacterial symbionts

Mealybugs (Insecta: Hemiptera: Pseudococcidae) maintain obligatory relationships with bacterial symbionts, which provide essential nutrients to their insect hosts. Most pseudococcinae mealybugs harbor a unique symbiosis setup with enlarged betaproteobacterial symbionts (‘Candidatus Tremblaya princeps’) which themselves contain gammaproteobacterial symbionts. Here we investigated the symbiosis of the manna mealybug, Trabutina mannipara, using a metagenomic approach. Phylogenetic analyses revealed that the intrabacterial symbiont of T. mannipara represents a novel lineage within the Gammaproteobacteria, for which we propose the tentative name ‘Candidatus Trabutinella endobia’. Combining our results with previous data available for the nested symbiosis of the citrus mealybug, Planococcus citri, we show that synthesis of essential amino acids and vitamins, and translation related functions partition between the symbiotic partners in a highly similar manner in the two systems, despite the distinct evolutionary origin of the intrabacterial symbionts. Bacterial genes found in both mealybug genomes and complementing missing functions in both symbioses were likely integrated in ancestral mealybugs before T. mannipara and P. citri diversified. The high level of correspondence between two mealybug systems and their highly intertwined metabolic pathways are unprecedented. Our work contributes to a better understanding of the only known intracellular symbiosis between two bacteria and suggests that the evolution of this unique symbiosis included the replacement of intrabacterial symbionts in ancestral mealybugs.

Szabó G, Schulz F, Toenshoff ER, Volland JM, Finkel OM, Belkin S, Horn M
2016 - ISME J, in press