Phyla with no cultivated species

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The extreme case of a phylum with few known cultivated species is, of course, a phylum with no known cultivated members. There are many of these; some are large groups that are commonly seen in microbial surveys (e.g. OP10, TM7), but most are small groups, and many are only one or a few sequences that are not specifically related to any bacterial phylum. Some of these will be found to be deep branches in known phyla once additional related sequences are obtained. Most, however, probably represent the hidden bulk of bacterial diversity.

Example phylum : OP11

OP11 tree

This is a large group containing bout 100 unique sequences (only 43 are nearly full-length) from a very wide range of environments - but there are no known cultivated species in this group, so nothing is know anything about their phenotype. This phylum is particularly interesting because of its high evolutionary rate, reflected in its long branch length; this is an unusually 'advanced' group of Bacteria. Despite years of attempts to cultivate something, anything, from this group, so far none are in culture.

Like most of these phyla, OP11 gets its name from a sequence designation of the original sequence identified in this group. OP11 was sequence number 11 from a collection of cloned bacterial ssu-rRNA sequences from Obsidian Pool (OP).

Jim's Black Pool
Obsidian Pool, Yellowstone National Park : James W. Brown

Example phylum : SR1


A large number of environmental ssu-rRNA sequences do not fall into any of the recognized bacterial Phyla; conceptually, each group of these is a cryptic phylum. Even if you demand that at least 2 related, non-identical, nearly full-length sequences be identified before describing them as a new phylum, there are several hundred such cryptic Phyla. The phylum “SR1” is an example, composed of only 2 nearly full-length and 23 shorter sequences. (SR is from Sulfur River)