Ancient bacteria go under the lens

Every fourth breath you take comes from cyanobac­teria, which pop­u­late the planet’s waters. Prog­en­i­tors of these micro­scopic, pho­to­syn­thetic organ­isms are believed to have been the first organ­isms to release oxygen into the atmos­phere. Their evo­lu­tion nearly 3 bil­lion years ago is thought to have enabled all aer­obic life on Earth.

But the same process that accounts for one quarter of the planet’s breath­able oxygen has also turned cyanobac­teria into one of the most poorly con­trolled forms of water pol­lu­tion, experts say. Rising ocean tem­per­a­tures and acidity have led to dev­as­tating blooms of marine cyanobac­teria around the globe, over­whelming other native species.

Despite these prob­lems, researchers still don’t have an easy way of studying cyanobac­teria through genetic analysis, according to Jacque­line Piret, an asso­ciate pro­fessor of mol­e­c­ular micro­bi­ology. Piret recently co-​​authored a research paper on the sub­ject in the journal Nature along with former stu­dent Desislava Raytcheva and col­leagues at the Mass­a­chu­setts Insti­tute of Tech­nology and the Baylor Col­lege of Medicine.

To over­come these chal­lenges, the research team is inves­ti­gating a virus called Syn5, which infects a cyanobac­te­rial species. “A bac­te­rio­phage virus offers an oppor­tu­nity to engi­neer a vector for car­rying out genetic manip­u­la­tion in the host organism,” Piret explained. By tweaking the host genome through con­trolled viral infec­tion, the researchers can tease out the func­tions of par­tic­ular genes, such as those involved in the har­vest of light energy for photosynthesis.

But in order to use the bac­te­rio­phage to their advan­tage, Piret’s team first needed to under­stand its struc­ture and behavior, as it was still unclear how the virus assem­bled and went on to infect its host.

For her doc­toral dis­ser­ta­tion, Raytcheva used painstaking exper­i­mental tech­niques to work out Syn5’s struc­ture, which turned out to be rather unique in that it has a horn pro­truding from the virus’ exte­rior shell. “Very few other viruses are known to have a sim­ilar struc­ture,” she explained.

In 2009, the researchers at North­eastern and MIT began col­lab­o­rating with their col­leagues at Baylor Col­lege of Med­i­cine, which had devel­oped an advanced microscopy tech­nique. The method allowed them to see in almost real-​​time and with striking clarity the Syn5 assembly process that Raytcheva had pieced together.

Piret noted that the imaging data com­ple­ments Raytcheva’s work, pointing to the two-​​pronged approach to get to the assembly process. “You need phys­ical evi­dence,” she said, “and then you need bio­chem­ical infor­ma­tion about the intermediates.”

This work is an impor­tant step toward under­standing how cyanophages infect and assemble inside their hosts. That knowl­edge, said Raytcheva, will be crit­ical for devel­oping methods for both studying and con­trol­ling cyanobacteria.

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