Bacterial Endospores

Abstract

Species of the genera Bacillus and Clostridium form dormant, resistant cells are known as endospores in response to stressful conditions. Endospores form inside of a mother cell, or sporangia, via a modified, asymmetrical cell division pathway followed by a variety of spore‐specific modifications to cell structure and content. Once the spore is formed, it is metabolically dormant and highly resistant to various insults such as heat, noxious chemicals, desiccation and UV irradiation. Several significant pathogens are spore formers, which makes disease prevention via food and environment sterilisation challenging. The resistance properties of spores are derived from chemical and physical alterations such as dehydration and mineralisation of the cytoplasm, protective alteration of DNA structure by specialised proteins and formation of impermeable proteinaceous spore coats. Dormancy is ended when the spore enters an environment where spore germination is favourable.

Key Concepts

  • Bacterial endospores can survive for decades and are highly resistant to numerous environmental insults.
  • The resistance properties of bacterial endospores contribute to their roles in food spoilage and in human and animal pathogenesis.
  • Bacterial endospores are cells with specialised modifications to their structure and contents.
  • Bacterial endospores are produced via a simple developmental process involving cooperative and regulated gene expression of two cells.
  • Heat resistance of bacterial endospores is determined by several factors, the most important being the relative dehydration of the spore core.
  • Bacterial endospores possess a unique mode of resistance to UV irradiation involving specialised DNA‐binding proteins.

Keywords: differentiation; disinfection; dormancy; endospore; germination; heat resistance; resistance; spore; spore‐forming bacteria; sterilisation

Figure 1. Phase‐contrast light microscope images of unstained cells of Bacillus megaterium: (a) Actively multiplying vegetative cells; (b) Sporangia containing phase‐dark forespores; (c) Sporangia containing phase‐bright immature spores; (d) Free mature spores after sporangia lysis.
Figure 2. Electron microscopic image of a metal‐stained transverse section of a mature B. megaterium spore. The spore contains a central core with a faintly visible inner spore membrane (IM) surrounding a cytoplasm that includes light‐staining DNA regions (NP) and ribosome granules (CP). Surrounding the core is a thin, darkly stained germ cell wall and a contiguous unstained cortex (CX‐GCW). Surrounding the cortex is a lightly stained inner coat, an intermittently visible outer membrane and a thin outer coat (C‐OM). Enveloping all is a loosely fitting exosporium (EX). Bar, 200 nm.
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Flores, Matthew J, and Popham, David L(Feb 2020) Bacterial Endospores. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000300.pub3]