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Deep bacteria evolve without passing on genes?


But is that “evolution?”

From New Scientist:

Investigations over the last 30 years have revealed that life exists several kilometres below both the land surface and the seafloor. Or, perhaps more accurately, life endures: nutrient levels drop off so rapidly with depth that the microbes can barely function at all. In fact, the cells show so few signs of life that it wasn’t until 2011 that researchers confirmed that microbes in sediments below the seafloor are, indeed, living.

The results show – for the first time, Briggs thinks – that the bacterial genomes change with depth: the micro-organisms at 554 metres carry more mutations in genes that code for energy-related processes like cell division and biosynthesis of amino acids than are seen in their shallower counterparts.

So they changed more while doing less? Including less reproduction?

Here’s the summary of a talk given at the American Geophysical Union on the subject in December:

The ability of a microbe to persist in low-nutrient environments requires adaptive mechanisms to survive. These microorganisms must reduce metabolic energy and increase catabolic efficiency. For example, Escherichia coli surviving in low-nutrient extended stationary phase have mutations that confer a growth advantage in stationary phase (GASP) phenotype, thus allowing for persistence for years in low-nutrient environments. Based on the fact that subseafloor environments are characterized by energy flux decrease with time of burial we hypothesize that cells from older (deeper) sediment layers will have more altered genomes compared to sequenced surface relatives and that these differences reflect adaptations to a low-energy flux environment. To test this hypothesis, sediment samples were collected from the Andaman Sea from the depths of 21, 40 and 554 meters below seafloor, with the ages of 0.34, 0.66, and 8.76 million years, respectively. A single operational taxonomic unit within Firmicutes, based on full-length 16S rDNA, dominated these low diversity samples. This unique feature allowed for metagenomic sequencing using the Illumina HiSeq to identify nucleotide variations (NV) between the subsurface Firmicutes and the closest sequenced representative, Bacillus subtilis BEST7613. NVs were present at all depths in genes that code for proteins used in energy-dependent proteolysis, cell division, sporulation, and (similar to the GASP mutants) biosynthetic pathways for amino acids, nucleotides, and fatty acids. Conserved genes such as 16S rDNA did not contain NVs. More NVs were found in genes from deeper depths. These NV may be beneficial or harmful allowing them to survive for millions of years in the deep biosphere or may be latent deleterious gene alterations that are masked by the minimal-growth status of these deep microbes. Either way these results show that microbes present in the deep biosphere experience environmental forcing that alters the genome.

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"Escherichia coli surviving in low-nutrient extended stationary phase have mutations that confer a growth advantage in stationary phase (GASP) phenotype" How convenient. Mutations may be unguided and purposeless, but don't let any tell you they're inconvenient. ppolish

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