Antagonistic bacteria disrupt calcium homeostasis and immobilize algal cells

Prasad Aiyar,David Carrasco Flores,Daniel Schaeme,Severin Sasso,María García-Altares,Hannes Dathe,Maria Mittag,Christian Hertweck

doi:10.1038/s41467-017-01547-8

Prasad Aiyar, David Carrasco Flores + Show 6 more

Open Access

https://doi.org/10.1038/s41467-017-01547-8

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Abstract

Photosynthetic unicellular organisms, known as microalgae, are key contributors to carbon fixation on Earth. Their biotic interactions with other microbes shape aquatic microbial communities and influence the global photosynthetic capacity. So far, limited information is available on molecular factors that govern these interactions. We show that the bacterium Pseudomonas protegens strongly inhibits the growth and alters the morphology of the biflagellated green alga Chlamydomonas reinhardtii. This antagonistic effect is decreased in a bacterial mutant lacking orfamides, demonstrating that these secreted cyclic lipopeptides play an important role in the algal–bacterial interaction. Using an aequorin Ca2+-reporter assay, we show that orfamide A triggers an increase in cytosolic Ca2+ in C. reinhardtii and causes deflagellation of algal cells. These effects of orfamide A, which are specific to the algal class of Chlorophyceae and appear to target a Ca2+ channel in the plasma membrane, represent a novel biological activity for cyclic lipopeptides.

Highlights

Photosynthetic unicellular organisms, known as microalgae, are key contributors to carbon fixation on Earth
By means of high-resolution mass spectrometry and a tailor-made reporter system, we found that P. protegens employs chemical mediators, including cyclic lipopeptides to deflagellate the C. reinhardtii cells and alter cytosolic Ca2+ levels
To investigate whether heterotrophic bacteria sharing the same habitat as C. reinhardtii affect algal growth, we selected Flavobacterium johnsoniae, Xanthomonas campestris pv. campestris, and P. protegens

Summary

Introduction

Photosynthetic unicellular organisms, known as microalgae, are key contributors to carbon fixation on Earth Their biotic interactions with other microbes shape aquatic microbial communities and influence the global photosynthetic capacity. We show that the bacterium Pseudomonas protegens strongly inhibits the growth and alters the morphology of the biflagellated green alga Chlamydomonas reinhardtii This antagonistic effect is decreased in a bacterial mutant lacking orfamides, demonstrating that these secreted cyclic lipopeptides play an important role in the algal–bacterial interaction. Apart from higher plants, prokaryotic and eukaryotic microalgae in aquatic environments are responsible for approximately 50% of all carbon fixation annually[1] These photosynthetic microorganisms are at the base of aquatic food webs, playing a key role in diverse ecosystems. An increasing number of studies were reported on a Flavobacterium johnsoniae UW 101

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