Catalytic linkage between caspase activity and proteostasis in Archaea

To Die or Not to Die—Regulated Cell Death and Survival in Cyanobacteria

Regulated cell death (RCD) is central to the development, integrity, and functionality of multicellular organisms. In the last decade, evidence has accumulated that RCD is a universal phenomenon in all life domains. Cyanobacteria are of specific interest due to their importance in aquatic and terrestrial habitats and their role as primary producers in global nutrient cycling. Current knowledge on cyanobacterial RCD is based mainly on biochemical and morphological observations, often by methods directly transferred from vertebrate research and with limited understanding of the molecular genetic basis. However, the metabolism of different cyanobacteria groups relies on photosynthesis and nitrogen fixation, whereas mitochondria are the central executioner of cell death in vertebrates. Moreover, cyanobacteria chosen as biological models in RCD studies are mainly colonial or filamentous multicellular organisms. On the other hand, unicellular cyanobacteria have regulated programs of cellular survival (RCS) such as chlorosis and post-chlorosis resuscitation. The co-existence of different genetically regulated programs in cyanobacterial populations may have been a top engine in life diversification. Development of cyanobacteria-specific methods for identification and characterization of RCD and wider use of single-cell analysis combined with intelligent image-based cell sorting and metagenomics would shed more light on the underlying molecular mechanisms and help us to address the complex colonial interactions during these events. In this review, we focus on the functional implications of RCD in cyanobacterial communities.

Dynamics of cell death across growth stages and the diel cycle in the dinoflagellate Karenia brevis

Recent evidence suggests that programmed cell death (PCD) can play a role in stress-induced decline and termination of harmful algal blooms. However, components of the PCD cascade, i.e. reactive oxygen species (ROS) and caspase-like activity, have also been observed in the absence of exogenous stress, where their activities and functions remain unclear. Here, we characterized the variability of prevalence of cell death, ROS, and caspase-like activity at different growth phases and diel cycles in cultures of dinoflagellate Karenia brevis. Results show that ROS percentages increased with culture age and fluctuated in a phasing diel pattern, while caspase-like activity was observed throughout growth. In actively growing K. brevis cells, PCD components may be involved in key metabolic processes, while in stationary phase they may relate to stress acclimation. The circadian diel pattern of ROS may be explained by the balance between the metabolic generation of ROS and circadian rhythmicity of antioxidant enzymes. Overall, this work highlights not only the involvement of PCD components in the growth of marine phytoplankton, but the importance of understanding mechanisms controlling their accumulation, which would help to better interpret their presence in the field.