As discussed in my
previous blog post, proteorhodopsin (PR) is an integral membrane protein, which
may be used to ‘power’ marine bacteria when respiration is inhibited. This
allows them to switch from normal respiration and become light powered, using
the energy from the light to generate ATP. The previous study looked at was
Walter et al., 2006, who modified E.coli to
possess PR, to show how bacteria possessing it can survive in environments
where respiration is inhibited. Studies such as this demonstrate PR’s function
as proton pumps with energy-yielding potential, however the actual ecological
role of them and how they contribute to the success of the bacteria containing
them is still relatively unknown.
Furthering the work
done by Walter et al., (2006), a study was conducted by Gomez-Consamau et al., (2010). They aimed to uncover
the biological function of PR and how they contribute to the success of PR
containing marine bacteria. They used a strain of the widespread genus Vibrio, a strain known to contain PR.
The strain AND4 was isolated from ocean surface water. The whole-genome
sequence of AND4 was carried out and a phylogenetic tree of 16s RNA genes
constructed. Measures of AND4 PR absorption maximum and photolysis rates were
also taken (Gomez-Consamau et al.,
2010).
They investigated the
survival of the Vibrio bacteria when
incubated in light and dark conditions. They found that after 10 days of
incubation in each condition, numbers decreased in all cultures, but remained
2.5 times higher in light conditions. This shows that bacteria growing in light
conditions can respond more rapidly to improved growth conditions than those in
dark conditions (Gomez-Consamau et al.,
2010).
Therefore, this study
provides evidence linking the PR gene to its biological function in marine
bacterium, suggesting that it confers a fitness advantage, allowing marine
bacteria to endure periods of resource deprivation at the ocean’s surface
(Gomez-Consamau et al., 2010). Their
function as proton pumps has been covered in previous studies, however this
piece of research takes it step further in actually explaining the ecological
role of PR.
I believe a key aspect
of this study by Gomez-Consamau et al.,
is the fact that they generated a strain of Vibrio
that was deficient in PR. The PR gene was removed by an in frame deletion of
the near complete PR gene. This means that they were able to establish that the
PR gene is the direct conveyer of the light-enhanced survival during
starvation. This is of great importance as it shows that increased rates of
survival and the ability to actively respond to increased growth conditions are
as a direct consequence of having the energy harvesting potential of PR.
Gómez-Consarnau, L., Akram, N., Lindell, K.,
Pedersen, A., Neutze, R., Milton, D., González, J., Pinhassi, J.. (2010).
Proteorhodopsin Phototrophy Promotes Survival of Marine Bacteria during
Starvation. PLOS Biology Biol 8(4): e1000358. doi:10.1371/journal.pbio.1000358
Walter, J.M., Greenfield, D., Bustamante, C.,
Liphardt, J. . (2006). Light-powering Escherichia coli with proteorhodopsin. PNAS.
Vol. 104 pp.2408-2412.
Hi Sam,
ReplyDeleteInteresting post, when the Vibrio strain was incubated in light and dark conditions, was there any mention of the temperature fluctuations and did this have any effect on the strain at all? I wonder what the possible implications will be with regards to their abundance and ecophysiology due to the inevitable rise of mean global sea temperatures.
Thanks,
Dean
Hi Dean,
ReplyDeleteIndeed there was, they state that all experiments were carried out at 16 degrees (C). I'm assuming this must be around the temperature that the samples were collected from, makes the most sense! A very interesting thought on what implications the rising temperature may have on them. Containing the PR increases the fitness of the bacteria so I'm assuming that as the sea temperature rises they will maintain the ecological edge they possess, though this is only a guess!
Thanks for the interesting comments, Sam