Molecular Control of Bacterial Death and Lysis
Kelly C. Rice and Kenneth W. Bayles



SUMMARY
INTRODUCTION
THE CELL WALL AND INTRINSIC CONTROL OF LYSIS
Peptidoglycan
Murein Hydrolases
Teichoic Acids
REGULATED DEATH AND LYSIS
Bacteriophage Holins
The Cid/Lrg Regulatory System
The cid and lrg operons.
The CidR and LytSR regulators.
Similarities between the Cid/Lrg regulatory system and apoptosis.
Bacterial Caspases
Fratricide
Cannibalism
Toxin-Antitoxin Systems
MazEF.
RelBE.
HipBA.
Role(s) of TA systems in bacterial physiology.
CONCLUSIONS
ACKNOWLEDGMENTS
REFERENCES




Although the phenomenon of bacterial cell death and lysis has been studied for over 100 years, the contribution of these important processes to bacterial physiology and development has only recently been recognized. Contemporary study of cell death and lysis in a number of different bacteria has revealed that these processes, once thought of as being passive and unregulated, are actually governed by highly complex regulatory systems. An emerging paradigm in this field suggests that, analogous to programmed cell death in eukaryotes, regulated cell death and lysis in bacteria play an important role in both developmental processes, such as competence and biofilm development, and the elimination of damaged cells, such as those irreversibly injured by environmental or antibiotic stress. Further study in this exciting field of bacterial research may provide new insight into the potential evolutionary link between control of cell death in bacteria and programmed cell death (apoptosis) in eukaryotes.

Based on the examples highlighted in this review, it is obvious that the traditional view of bacterial cell death and lysis as a passive and insipid process is being rapidly replaced by a vision of cell death and lysis as a complex, highly regulated, and important component of bacterial physiology. This concept is mirrored by our ever-evolving view and study of bacteria from selfish, single-celled organisms to complex multicellular communities of cells that display sophisticated social behaviors and developmental processes. Because we have been slow to appreciate the multicellular nature of bacterial communities, our understanding of the importance and control of cell death and apoptosis in the more "highly evolved" eukaryotic organisms is much more advanced compared to the study of the relatively "simple" prokaryotes. Perhaps current and future studies of bacterial cell death and lysis can glean additional clues from the well-studied and defined mechanisms of eukaryotic apoptosis in developmental processes, cellular defense, and cancer. Although we are a long way from completely understanding the complex regulatory signals and pathways that dictate whether individual bacterial cells live or die, further study in this exciting field of research is bound to yield insights into these processes. Furthermore, these studies should also provide new insight into the potential evolutionary link between control of cell death in bacteria and PCD in eukaryotes.

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