Incorporation of new cell wall in differently shaped bacteria
Antibacterial Inhibitors of Cell Wall Synthesis
When the Gram stain was developed by Hans Christian Gram in 1884 the molecular basis of the stain was unknown. In fact very little was understood about bacteria in general. He just determined empirically that when bacterial smears were run through a four-step staining procedure using two different dyes, some cells retained the first dye and stained purple, while other only retained the second dye and stained pink. Years later it was discovered that the basis for this differential reaction relates to the cell wall as shown in .
Antibiotics; Inhibitors of Cell Wall Synthesis
The structure and synthesis of prokaryotic cell walls is unique and many compounds found in the bacterial cell wall are found nowhere else in nature. It is true that plants also make cell walls, but they are chemically and structurally different. There are two basic types of bacterial cell wall structures that have been studied in detail: gram-positive and gram-negative. These two classes of bacterial cells look very different following staining with the Gram stain and this has been a standard basis for starting to identify different bacterial species. Figures 2-36 and 2-37 show Gram stains of gram-positive and gram-negative bacteria, respectively.
Bacterial Cell Structure and Function
Oligosaccharins, which can result from normal development or pathogen attack, serve a variety of functions including: (a) stimulate ethylene synthesis; (b) induce phytoalexin (defense chemicals produced in response to a fungal/bacterial infection) synthesis; (c) induce chitinase and other enzymes; (d) increase cytoplasmic calcium levels and (d) cause an "oxidative burst". This burst produces hydrogen peroxide, superoxide and other active oxygen species that attack the pathogen directly or cause increased cross-links in the wall making the wall harder to penetrate.
Let's look at how this system works. Consider a pathogenic fungus like . In contact with the host plant the fungus releases enzymes such as pectinase that break down plant wall components into oligosaccharins. The oligosaccharins stimulate the oxidative burst and phytoalexin synthesis, both which will deter the advance of the fungus. In addition, the oligosaccharins stimulate chitinase and glucanase production in the plant. These are released and begin to digest the fungal wall. Fragments of fungal wall also act as oligosaccharins in the plant to further induce phytoalexin synthesis. Cool!