Bacteria, phylogenetic tree

Fig. 1. (a) Schematic representation of the three types of anoxygenic ([1] and [2]) and oxygenic ([3]) photosynthesis found in plants and bacteria, (b) Phylogenetic tree based on 16S-rRNA sequence comparisons featuring only photo synthetic phyla. 

Some authors concentrate mainly on phylogenetic aspects based on sequence data. The amino acid sequences of a considerable number of well-studied transporters from many bacteria are published, and an immense set of primary sequence data will become available within the next few years (primarily from numerous genome projects). Phylogenetic trees of transport proteins are... 

Cultivated marine bacteria are scattered throughout the phylogenetic tree of the domain Bacteria. However, at lower phylogenetic levels, clusters of marine bacteria have been found which are distinct from those of terrestrial origin. One example is the so-called a3-subgroup of the a-Proteobacteria subclass of the division Proteobacteria, the Roseobacter clade [20]. A marine group of Actinobacteria [21] has been described, which has, to date, however not been cultivated. 

So much gene transfer between organisms has occurred that it is difficult to establish the earliest parts of a phylogenetic tree of the type shown in Fig. 1-5. Another factor that confuses our study of bacteria is that less than 1% of all living microorganisms have been grown in pure cultures.355 356... 

Despite their antiquity (perhaps 2.5 billion years old), the resurrected ancestral elongation factors are inferred for bacteria that lived long after the origin of life. Nevertheless, the notion that early life lived at high temperatures, in water, and at nearly neutral pH is consistent with available data. For example, a recent reconstruction of the phylogenetic tree of life based on 31 common gene families supports the notion that the last common ancestor lived at high temperatures.65... 

In 1866, Ernst Haeckel proposed a phylogenetic tree where the first forms of life were cells without a nucleus (which he called Monera), which later generated nucleated cells (Protista), which in turn gave rise to all multicellular organisms. Already in 1883, Schimper proposed that chloroplasts had once been free-living bacteria that happened to be incorporated, by a kind of symbiosis, into some eukaryotes, and from 1905 to 1930 this hypothesis was not only reproposed but also extended to mitochondria by Mereschowsky, by Portier and by Wallin. 

On the basis of the 16S/18S rRNA sequence comparisons, the hyperthermophilic bacteria (optimal growth temperature higher than 80°C) are located nearer to origins of life in the phylogenetic tree (Stetter, 1994). Therefore, many researchers think that life might have originated at temperatures as high as 100°C, before the surface of the Earth had cooled to around 30° K)°C. 

Only a short time after life came into being, the phylogenetic tree branched into two distinctive lines (Fig. 1). The one led to bacteria and the other, millions of years later, divided into archaea and eukarya. Bacteria and archaea are prokaryotic, eukarya are eukaryotic organisms. 

The phylogenetic tree of bacteria (Fig. 2) consists of twelve distinct groups (phyla) of which that of the purple bacteria is the largest. Although most are phototrophic, chemoorganotrophic and chemolithotrophic forms exist as well. It is likely that the ancestor of the purple bacteria was phototrophic although... 

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