Morphology Ultrastructure and Surface Proteins

Legionella pneumophila displays a typical Gram-negative envelope in which the inner membrane and outer membrane can be readily distinguished in thin sections by electron microscopy (see Figure 7.1a). In some thin sections of L. pneumophila, outer membrane blebs are observed, a feature typical of most Gram-negative bacteria. In contrast, the cyst form contains a thick cell wall; laminations of intracytoplasmic membranes, and a cytoplasm occupied with inclusions of PHBA (see Figure 7.1b,c,d). While biochemical studies have been done on the composition of cell wall components from vegetative forms, little

Legionella Pneumophila Cytoplasm

Figure 7.1. Morphological features of vegetative and cyst forms of L. pneumophila. Ultrathin sections of vegetative L. pneumophila (A) and cyst forms (B, C, and D). The vegetative bacteria have a thing outer membrane and defined inner membrane. The cytoplasm generally contains no inclusion bodies. in contrast, cyst forms have a thickened cell wall and laminations of intracytoplasmic membranes. The cytoplasm begins to accumulate inclusions that contain PHBA (poly-ß-hydroxybutyrate).

Figure 7.1. Morphological features of vegetative and cyst forms of L. pneumophila. Ultrathin sections of vegetative L. pneumophila (A) and cyst forms (B, C, and D). The vegetative bacteria have a thing outer membrane and defined inner membrane. The cytoplasm generally contains no inclusion bodies. in contrast, cyst forms have a thickened cell wall and laminations of intracytoplasmic membranes. The cytoplasm begins to accumulate inclusions that contain PHBA (poly-ß-hydroxybutyrate).

information exists on the biochemical composition of the cyst forms (Faulkner and Garduño, 2002). The thickened cell wall and loss of typical Gram-negative cell wall architecture resembles cyst forms of other bacterial species such as Azotobacter and Rhotobacter. Developmental forms are discussed in more detail in Chapter 4.

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