Nav: Home

Surprising role of bacterial genes in evolution

October 11, 2016

Stanford, CA--We generally think of inheritance as the genetic transfer from parent to offspring and that evolution moves toward greater complexity. But there are other ways that genes are transferred between organisms.

Sometimes a "host" organism can obtain genes from another organism that resides within its own cell (called an endosymbiont) through a process known as endosymbiotic gene transfer. At other times, an organism can obtain genes from a creature that lives in the surrounding environment, or from something that it eats, which is called horizontal gene transfer.

Furthermore, some levels of gene transfer can result in extensive loss of genes and genome reduction, especially for organisms that live as endosymbionts. For the first time, researchers have demonstrated that horizontal gene transfer may play a dominant role in compensating for genome reduction in an endosymbiont, and that this may be a key feature in the evolutionary transformation of an endosymbiont into an organelle (a longstanding organ inside a cell that often has specialized functions).

The research, published in the October 10 on-line edition of the Proceedings of the National Academy of Sciences, was conducted as a collaboration between scientists at Carnegie's Department of Plant Biology*, Rutgers University and Heinrich-Heine-Universität in Düsseldorf.

Specialized organelles called chloroplasts, which occur in plants and algae, are critical for performing the process of photosynthesis, and thus manufacturing sugars, starch and oils. These organelles originated more than 1 billion years ago when a photosynthetic bacterium, called a cyanobacterium, was engulfed by a host organism called a protist. There was a subsequent massive loss of genes from the genome of the cyanobacterium. Some of the lost cyanobacterial genes were transferred to the nucleus of the host cell through endosymbiotic gene transfer, while others were completely lost. This genome reduction was accompanied by the loss of many endosymbiont genes critical for the chain of enzymatic reactions involved in the biosynthesis of various essential compounds. How the host compensated for this gene reduction was only partially known.

Surprising results that shed light on the evolution of organelles from endosymbionts were obtained using the green, single-celled organism Paulinella chromatophora. Carnegie co-author Arthur Grossman explained: "We have recently proposed that the loss of genes from the photosynthetic organelle of P. chromatophora, which is called a chromatophore (originally an endosymbiotic cyanobacterium that was engulfed by a Paulinella species 60-200 million years ago), was in many cases compensated for by genes coming from neighboring bacteria in the environment. These new genes were integrated into the host nucleus and the proteins made from these genes were routed into chromatophores, where they compensate for the loss of genes."

Lead author Eva Nowack remarked: "Of the at least 229 genes in the P. chromatophora nucleus that were acquired from various bacteria, only about 25% are of cyanobacterial origin and may have originated from endosymbiotic gene transfer. Excitingly, many of the remainder were acquired through horizontal gene transfer, representing genes from a variety of bacteria. Many of these bacteria-derived genes produce proteins that fill in gaps in chromatophore localized biosynthetic pathways. The original genes that filled the gaps were lost as a consequence of chromatophore genome reduction. This result suggests a dominant role for horizontal gene transfer in compensating for endosymbiont genome reduction."

Furthermore, researchers found that a sister (ancestral) organism to P. chromatophora does not have a chromatophore and feeds on a variety of different bacteria, much like the way that white blood cells consume invading bacteria. In this new work, it is hypothesized that this method of feeding, called phagotrophy, may allow for the acquisition of different bacterial genes through horizontal gene transfer. In this way, the process of feeding facilitated bacterial gene selection as the cyanobacterial endosymbiont became a permanent resident within the phagotrophic host during early stages of chromatophore evolution.
* Authors on the paper are Eva C.M. Nowack, Dana C. Price, Debashish Bhattacharya, Anna Singer, Michael Melkonian, and Arthur R. Grossman This study was supported by National Science Foundation grant MCB-10370 (to A.R.G.), EF 08-27023 and OCE 11-29203 (to D.B.), and Deutsche Forschungsgemeinschaft Grant NO 1090/1-1 (to E.C.M.N.)

The Carnegie Institution for Science is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

Related Bacteria Articles:

Conducting shell for bacteria
Under anaerobic conditions, certain bacteria can produce electricity. This behavior can be exploited in microbial fuel cells, with a special focus on wastewater treatment schemes.
Controlling bacteria's necessary evil
Until now, scientists have only had a murky understanding of how these relationships arise.
Bacteria take a deadly risk to survive
Bacteria need mutations -- changes in their DNA code -- to survive under difficult circumstances.
How bacteria hunt other bacteria
A bacterial species that hunts other bacteria has attracted interest as a potential antibiotic, but exactly how this predator tracks down its prey has not been clear.
Chlamydia: How bacteria take over control
To survive in human cells, chlamydiae have a lot of tricks in store.
Stress may protect -- at least in bacteria
Antibiotics harm bacteria and stress them. Trimethoprim, an antibiotic, inhibits the growth of the bacterium Escherichia coli and induces a stress response.
'Pulling' bacteria out of blood
Magnets instead of antibiotics could provide a possible new treatment method for blood infection.
New findings detail how beneficial bacteria in the nose suppress pathogenic bacteria
Staphylococcus aureus is a common colonizer of the human body.
Understanding your bacteria
New insight into bacterial cell division could lead to advancements in the fight against harmful bacteria.
Bacteria are individualists
Cells respond differently to lack of nutrients.

Related Bacteria Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#513 Dinosaur Tails
This week: dinosaurs! We're discussing dinosaur tails, bipedalism, paleontology public outreach, dinosaur MOOCs, and other neat dinosaur related things with Dr. Scott Persons from the University of Alberta, who is also the author of the book "Dinosaurs of the Alberta Badlands".