For the growth of a cell culture, one inoculates not with one cell but with a quorum of cells. This most often a requirement, not just a convenience, and most of us take this for granted without question. Here this observation is re-examined to understand why a quorum may be required to grow cells. The importance of quorums may be widespread in the aspects of microbiology they affect. It is very likely that quorums are connected with and have a large impact on the determination of Minimal Inhibitory Concentrations. It is also possible that low cell density may adversely affect cell survival, however, this is an area where even less is known. The need for a quorum might affect other aspects of microbial cell culture, cell isolation and cell preservation. Effects also extend to mammalian cell culture. Here I seek to review studies that have been documented and speculate on how the information might be utilized in the future.

Apoptosis is an active form of programmed cell death (PCD) that plays critical roles in the development, differentiation and resistance to pathogens in multicellular organisms. Ribosome inactivating proteins (RIPs) are able to induce apoptotic cell death in mammalian cells. In this study, using yeast as a model system, we showed that yeast cells expressing pokeweed antiviral protein (PAP), a single-chain ribosome-inactivating protein, exhibit apoptotic-like features, such as nuclear fragmentation and ROS production. We studied the interaction between PAP and AtBI-1 (Arabidopsis thaliana Bax Inhibitor-1), a plant anti-apoptotic protein, which inhibits Bax induced cell death. Cells expressing PAP and AtBI-1 were able to survive on galactose media compared to PAP alone, indicating a reduction in the cytotoxicity of PAP in yeast. However, PAP was able to depurinate the ribosomes and to inhibit total translation in the presence of AtBI-1. A C-terminally deleted AtBI-1 was able to reduce the cytotoxicity of PAP. Since anti-apoptotic proteins form heterodimers to inhibit the biological activity of their partners, we used a co-immunoprecipitation assay to examine the binding of AtBI-1 to PAP. Both full length and C-terminal deleted AtBI-1 were capable of binding to PAP. These findings indicate that PAP induces cell death in yeast and AtBI-1 inhibits cell death induced by PAP without affecting ribosome depurination and translation inhibition.

The antimalarial drug chloroquine (CQ) has been sidelined in the fight against falciparum malaria due to wide-spread CQ resistance. Replacement drugs like sulfadoxine, pyrimethamine and mefloquine have also since been surpassed with the evolution of multi-drug resistant parasites. Even the currently recommended artemisinin-based combination therapies show signs of compromise due to the recent spread of artemisinin delayed-clearance parasites. Though there have been promising breakthroughs in the pursuit of new effective antimalarials, the development and strategic deployment of such novel chemical entities takes time. We therefore argue that there is a crucial need to re-examine the usefulness of ‘outdated’ drugs like chloroquine, and explore if they might be effective alternative therapies in the interim. We suggest that a novel parasite cell death (pCD) pathway may be exploited through the reformulation of CQ to address this need.

Much progress has been made in identifying the components of the divisome, the assembly of proteins that undertakes the vital process of cell division in bacteria. However, how the highly interdependent processes on either side of the membrane are coordinated during division is a major unresolved question. How is the degradation and synthesis of the cell wall on the outside of the cell coordinated with cytokinesis and membrane fission, which are driven from the inside of the cell by the tubulin homologue FtsZ? A possible key mediator of such coordination is the membrane protein EzrA, as it interacts both with FtsZ and the penicillin binding proteins (PBPs) that synthesize peptidoglycan. Cleverley et al. [Nature Communications (2014) 5, 5421] have recently solved the crystal structure of the cytoplasmic domain of B. subtilis EzrA, which points to an important scaffolding role for EzrA in the divisome. The structure resembles the eukaryotic, cytoskeletal spectrin proteins, which link actin filaments in the cytoskeleton and also connect the actin cytoskeleton to membrane-bound integrin proteins.