INTRACYTOPLASMIC MEMBRANE STRUCTURES IN BACTERIA

Intracytoplasmic membrane structures (ICM) are regular in domain Bacte ria. Phenetically, ICM associate themselves with the gram-negative typ e cell envelope and with energy metabolism of photo-, litho-, or methy lotrophic type. Morphologically, ICM are represented by monotonous arr ays of interconnected vesicular, tubular, or disc-shaped elements, as well as by membrane duplexes of complex geometry termed the lamellar s ystem. ICM are permanently, though to a variable extent, anastomosing with the cytoplasmic membrane (CM). Variant modes of ICM biogenesis ar e regulated (post)transcriptionally, and proceed autonomously or in as sociation with the CM. ICM are specialized for the generation of metab olic energy and, to a minor degree, for biosyntheses; interactions of ICM with the genetic material, ribosomes, and functional inclusions ar e also indicated. The properties of ICM in special cell types are dete rmined by the genomic and metabolic statuses of particular differentia ted cells or endocytobionts. ICM are typical of ancestral phenotypes; in the phylogeny of bacteria, they tend to be discarded and, in some i nstances, secondarily acquired. The distinctions in ICM organization b etween bacteria and nucleate organisms, as well as the global routes o f ICM evolution, are commented.