Modifying one cell factor alters many others

November 15, 2013
Scanning electron microscopy images showing the difference in size between normal (left) and sigE-overexpressing Synechocystis cells (right). Credit: T. Osanai et al. and John Wiley & Sons Ltd

Using a widely studied species of cyanobacterium, researchers from the RIKEN Center for Sustainable Resource Sciences have shown how difficult it is to alter the metabolism of a unicellular organism with the aim of producing a particular product without affecting other aspects of its functioning1.

Takashi Osanai and his team genetically engineered a strain of Synechocystis to stimulate the breakdown of sugar and the production of biopolymers. Although the modification enhanced biopolymer production as intended, they found that the change also affected the size and shape of the cell, as well as photosynthesis, respiration and other aspects of its metabolism.

The Osanai and his team engineered in Synechocystis involved overexpression of the sigE gene, which encodes a protein that regulates RNA synthesis known as a sigma factor. Under transmission electron and scanning probe microscopy, they found that the cell size of the engineered strain was larger than normal (Fig. 1) and there was evidence that the cell division process had been affected by the modification. Photosynthetic activity also tended to be higher when nitrogen was depleted but lower when nitrogen levels were normal and under high light conditions. Furthermore, increased at low oxygen levels. Several regulatory proteins were also seen to change with the elevated levels of the sigma factor protein.

According to the researchers, the results suggest a close relationship between , photosynthesis, cell form and hydrogen production. Despite all these differences, however, the modified strain remained just as viable as the normal strain over a range of nitrogen levels.

Apart from demonstrating the challenge in isolating cell factor-related alterations, the work also highlights the potential of cyanobacteria for the production of hydrogen for plastics and renewable energy applications. "We succeeded in increasing the production of hydrogen using the modified cyanobacteria," Osanai says. "The hydrogen was produced using light energy and the cells were cultured with carbon dioxide as a carbon source. Thus, we could possibly use our cyanobacterial strain to produce renewable energy that could replace fossil fuels and even nuclear power."

At present, the amount of hydrogen produced by this modified cyanobacterium is quite low, but Osanai is focused on exploiting the opportunity. "We will now try to increase productivity by additional genetic engineering," he says. "We will also try to increase the synthesis of bioplastics. A deeper understanding of the mechanism of the relationship between all the factors we have uncovered will be important."

Explore further: Sustained hydrogen production from cyanobacteria in the presence of oxygen

More information: Osanai, T., Kuwahara, A., Iijima, H., Toyooka, K., Sato, M., Tanaka, K., Ikeuchi, M., Saito, K. and Hirai, M. Y. (2013), Pleiotropic effect of sigE over-expression on cell morphology, photosynthesis and hydrogen production in Synechocystis sp. PCC 6803. The Plant Journal, 76: 456–465. doi: 10.1111/tpj.12310

Related Stories

Increasing efficiency of hydrogen production from green algae

April 15, 2013

New research results from Uppsala University, Sweden, instill hope of efficient hydrogen production with green algae being possible in the future, despite the prevailing scepticism based on previous research. The study, which ...

Engineered microbes grow in the dark

May 20, 2013

Scientists at the University of California, Davis have engineered a strain of photosynthetic cyanobacteria to grow without the need for light. They report their findings today at the 113th General Meeting of the American ...

Bacteria use hydrogen, carbon dioxide to produce electricity

May 20, 2013

Researchers have engineered a strain of electricity-producing bacteria that can grow using hydrogen gas as its sole electron donor and carbon dioxide as its sole source of carbon. Researchers at the University of Massachusetts, ...

Metabolically engineered E. coli producing phenol

October 8, 2013

Many chemicals we use in everyday life are derived from fossil resources. Due to the increasing concerns on the use of fossil resources, there has been much interest in producing chemicals from renewable resources through ...

Recommended for you

The universe's most miraculous molecule

October 9, 2015

It's the second most abundant substance in the universe. It dissolves more materials than any other solvent. It stores incredible amounts of energy. Life as we know it would not be possible without it. And although it covers ...

New method facilitates research on fuel cell catalysts

October 8, 2015

While the cleaning of car exhausts is among the best known applications of catalytic processes, it is only the tip of the iceberg. Practically the entire chemical industry relies on catalytic reactions. Therefore, catalyst ...

Trio wins Nobel Prize for mapping how cells fix DNA damage

October 7, 2015

Tomas Lindahl was eating his breakfast in England on Wednesday when the call came—ostensibly, from the Royal Swedish Academy of Sciences. It occurred to him that this might be a hoax, but then the caller started speaking ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.