Powering proteins in cyanobacteria

Researchers at IIT-Bombay have modified DNA in cyanobacteria — a type of single-celled bacteria found everywhere — to boost protein production. This work can eventually be a big help in the industrial production of a range of proteins.

Most of us know proteins as the substance that helps build our body. However, it is a common term for a huge range of biochemicals made up of amino acids, which are chains of molecules that contain carbon, oxygen (carboxyl or COOH) and nitrogen and hydrogen (NH2). Insulin and cobra poison are proteins.

Cyanobacteria make their own food (proteins) with carbon in sunlight. So, the aim is to culture cyanobacteria, let them make their food and then steal it. But it is not so simple, of course. First, for industrial scale production of proteins, you need carbon in an edible form — that is, glucose. This costs money. Second, there are some genes in cyanobacteria that suppress food production in sunlight.

The team of researchers led by Professor Pramod Wangikar manipulated the genes of cyanobacteria to kick-out the problematic genes and introduce helpful ones, so as to enable the bacteria to produce only those proteins that are needed, as and when required, and in a less expensive manner.

Like all organisms, bacteria, too, have in their cells DNA, the spiral staircase-like arrangement of sugars, and nitrogen and phosphate groups (ultimately, only carbon, nitrogen, oxygen, hydrogen and phosphorus), the combinations of which determine what each living thing is. Certain combinations — genes — contain ‘instructions’ on how to develop, survive and reproduce.

The process of making food in cyanobacteria is kick-started by sections of DNA called ‘promoters’. Some external chemicals, called inducers, help boost production. Wangikar’s team wanted to do away with the expensive inducers, and manipulate the promoters to gain productivity.

For this, they selected two promoters native to cyanobacteria. Called P rbcL and P cpcB, these are known to boost protein production. However, the former contains certain parts that repress protein production under carbon dioxide; the latter has some that does so under sunlight. The researchers’ job was to eliminate the undesirable elements.

Using ‘gene editing’ techniques, they developed variations (mutants) of both P rbcL and P cpcB — 36 mutants of the former and 12 of the latter. “We have 48 tunable, portable, inducer-free promoters,” Wangikar told Quantum. They tested these in a strain of cyanobacteria called synechococcus elongatus.

These 48 mutant promoters are tools for the industry to play with. Potentially, a biotechnology unit can, for instance, choose any of these that suits its needs. All it needs to do is to pick up the right promoter and inject it into the bacterial cell for the desired property. For instance, you can inject a promoter in Escherichia coli (which also lives in human intestines) to boost insulin production in a factory.

Or, with another promoter, you could use carbon dioxide from thermal power plants as the bacterial feed. “Right now, we are testing how well promoters from one cyanobacteria work in other cyanobacteria,” says Wangikar.