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The Gain and Loss of Genes at Hydrothermal Vents

Status Report From: NASA Astrobiology
Posted: Wednesday, May 6, 2020

Scientists supported in part by the NASA Astrobiology program have evaluated how natural selection affects the gene content of microbial populations around hydrothermal vents at the ocean floor. The genomes of microbes on Earth can be highly variable, with the loss and gain of genes greatly affecting the evolution of microbial populations. Horizontal gene transfer, or lateral gene transfer, is an important process when it comes to microorganisms gaining genes.

Horizontal gene transfer occurs when genetic material is transferred from one organism to another without reproduction (e.g. without a parent passing genes on to offspring). There are three known ways for this process to occur: transformation, transduction, and conjugation. Transformation happens when short fragments of DNA are taken up by bacteria that are naturally able to incorporate them into their genome. Transduction is the transfer of DNA from one microbe to another by bacteriophages (viruses that attack bacteria). Conjugation is when DNA is transferred by cell-to-cell contact through a hair-like structure known as a pilus.

The research team examined a total of twenty-two metagenome-assembled genomes (MAGs). Thirteen MAGs were recovered from the Axial Seamount in the northeastern Pacific Ocean, and nine MAGs came from the Mid-Cayman Rise in the Caribbean Sea. While the samples were collected from different locations, all of the microorganisms examined were ubiquitous vent Epsilonbacteraeota of the genus Sulfurovum.

The results show how selective pressures from the environments have shaped the structure of the genomes in each population. Genes involved in basic cellular function (referred to as ‘housekeeping’ genes) were the same across both sites. However, genes that are necessary for functions specific to the environment were different. This includes genes involved in phosphate regulation, which were found mostly in genomes from the low-phosphate environment of the Mid-Cayman rise. Overall, the results of the research indicate that selective pressures are a significant driver for the gain and loss of genes in microbes at hydrothermal vents, where nutrient limitation is an important factor driving microbial evolution.

The study, “Selection Is a Significant Driver of Gene Gain and Loss in the Pangenome of the Bacterial Genus Sulfurovum in Geographically Distinct Deep-Sea Hydrothermal Vents,” was published in the journal mSystems. The work was supported by the Astrobiology Science and Technology for Exploring Planets (ASTEP) element of the NASA Astrobiology Program and through the Exobiology Program. Additional support came from the NASA Astrobiology Postdoctoral Program.

This newly-revealed science is also a critical part of NASA’s work to understand the Universe, advance human exploration, and inspire the next generation. As NASA’s Artemis program moves forward with human exploration of the Moon, the search for life on other worlds remains a top priority for the agency.

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