title: Collapsing aged culture of the cyanobacterium Synechococcus elongatus produces compound(s) toxic to photosynthetic organisms.
abstract: Phytoplankton mortality allows effective nutrient cycling, and thus plays a pivotal role in driving biogeochemical cycles. A growing body of literature demonstrates the involvement of regulated death programs in the abrupt collapse of phytoplankton populations, and particularly implicates processes that exhibit characteristics of metazoan programmed cell death. Here, we report that the cell-free, extracellular fluid (conditioned medium) of a collapsing aged culture of the cyanobacterium Synechococcus elongatus is toxic to exponentially growing cells of this cyanobacterium, as well as to a large variety of photosynthetic organisms, but not to eubacteria. The toxic effect, which is light-dependent, involves oxidative stress, as suggested by damage alleviation by antioxidants, and the very high sensitivity of a catalase-mutant to the conditioned medium. At relatively high cell densities, S. elongatus cells survived the deleterious effect of conditioned medium in a process that required de novo protein synthesis. Application of conditioned medium from a collapsing culture caused severe pigment bleaching not only in S. elongatus cells, but also resulted in bleaching of pigments in a cell free extract. The latter observation indicates that the elicited damage is a direct effect that does not require an intact cell, and therefore, is mechanistically different from the metazoan-like programmed cell death described for phytoplankton. We suggest that S. elongatus in aged cultures are triggered to produce a toxic compound, and thus, this process may be envisaged as a novel regulated death program.
authors: The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
authors: Assaf
authors: A
authors: Cohen
authors: The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
authors: Eleonora
authors: E
authors: Sendersky
authors: Department of Chemistry, Tel-Aviv University, Israel.
authors: Shmuel
authors: S
authors: Carmeli
authors: The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
authors: Rakefet
authors: R
authors: Schwarz
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects; D001426:Bacterial Proteins / Q000378:metabolism*; D017077:Culture Media, Conditioned / Q000633:toxicity*; D010788:Photosynthesis; D010839:Phytoplankton / Q000187:drug effects; D046940:Synechococcus / Q000378:metabolism / Q000502:physiology*
chemical_list: D000975:Antioxidants; D001426:Bacterial Proteins; D017077:Culture Media, Conditioned