Universiteit Leiden

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This Week’s Discoveries | 19 December 2017

  • Norbert Peeters
dinsdag 19 december 2017
Niels Bohrweg 2
2333 CA Leiden
De Sitterzaal

First Lecture

Stress-induced release of cell wall-deficient cells in filamentous actinomycetes

Karina Ramijan Carmiol (IBL)

Karina is a PhD student in the Microbial Biotechnology & Health cluster of IBL. Her supervisors are Dennis Claessen and Gilles van Wezel. The Claessen lab addresses fundamental questions related to multicellular growth and development in filamentous bacteria called streptomycetes. By making use of genetic, biochemical, cell-biological, and various next-generation sequencing technologies we use a multidisciplinary approach to understand and control the physiology of these bacteria.

The cell wall is a shape-defining and protective structure that envelops virtually all bacteria. Nonetheless, all free-living bacteria are challenged by environmental stresses, and their survival depends on their ability to sense and respond to these changes. We here show that hyperosmotic stress has a dramatic effect on the morphology and growth dynamics of the filamentous actinomycete Kitasatosporaviridifaciens. Unexpectedly, under these conditions hyphae extrude cells lacking a cell wall. These cell wall-deficient (CWD) cells reinitiate peptidoglycan synthesis and revert to the mycelial mode-of-growth. Sporadically, we detected that CWD cells gained the ability to proliferate in the wall-deficient state as so-called L-forms, which coincided with the accumulation of mutations. For decades, such L-forms have been generated in laboratories under highly specialized conditions, invariably aimed at interrupting cell wall synthesis. Our work thus represents the first example of generation and proliferation of CWD cells as an adaptation to environmental stress. Altogether, our work shows the natural ability of K. viridifaciens to switch between the cell wall-deficient state and the canonical mycelial mode of growth.

Second Lecture

What’s in a name? The philosophical roots of phylogeny

Norbert Peeters studied archaeology and philosophy at Leiden University. Together with former professor Th.C.W. Oudemans he wrote Plantaardig – Vegetatieve filosofie (2014). In 2016 he published his own debut book: Botanische revolutie: de plantenleer van Charles Darwin. His research focuses on a number of topics at the interface between philosophy, history of botany and plant sciences. Currently he is editing an volume on Victorian female naturalists that corresponded with Darwin.

On Friday the 13th of October, the Hortus botanicus Leiden opened its renewed systematic garden. This is a strange type of garden. Ornamental, herb and vegetable gardens serve a clear purpose: they are a treat for the eye and stomach. The system garden satisfies another human need, the desire to bring order to chaos. Taxonomy, a branch of biology that focuses on organizing and describing organisms, has turned the ordering of nature into an art form. The taxonomist sees it as his task to reflect the natural order in his classification. But what does it mean when we assign a species name to a group of organisms? Or, what’s in a name?

This Week's Discoveries

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