Faster growth: Washington University researchers find record-setting growth rates from a long-lost bacterial strain 

In Missouri, scientists have re-discovered a fast-growing bacterial strain first described in 1955.

Although most cyanobacteria grow slowly, in 1955 two scientists at the University of Texas at Austin described a fast-growing cyanobacterial strain collected from a campus creek.

Whereas most strains grew by 5 to 8 percent per hour, this strain grew by 30 percent per hour. What’s more, it grew fastest at the relatively high temperature of 38 degrees C (104 degrees F). This strain was eventually deposited in the UTEX algae culture collection as Synechococcus leopoliensis UTEX 625.

However, at some point the UTEX 625 strain was contaminated and lost its rapid growth property. Now, a group of scientists led by Himadri B. Pakrasi, PhD, the Myron and Sonya Glassberg/Albert and Blanche Greensfelder Distinguished University Professor in Arts & Sciences at Washington University in St. Louis, reported in the Sept. 30 issue of Scientific Reports that they obtained a frozen sample of the UTEX strain, and by careful coaxing under appropriate conditions, recovered a pure, fast-growing strain from the mixed culture of the deposited algae.

Under favorable conditions, the newly isolated strain grows at more than 50 percent per hour, the highest growth rate reported to date for any cyanobacterial strain, and almost twice as fast as a widely studied close relative. Since the new strain may not be the one that was described in 1955, the scientists deposited it in the UTEX algae collection as Synechococcus elongatus UTEX 2973.

Rapid growth may allow this cyanobacterial strain to outcompete contaminating ones and eventually to synthesize larger quantities of biofuel or other valuable products. The scientists also showed that the genome of the new strain can be easily manipulated, a characteristic essential to its use as a host for projects in synthetic biology.

To the scientists’ surprise, the new strain turned out to be remarkably similar to a widely studied cyanobacterium, Synechococcus elongatus PCC 7942, originally discovered far away from Texas (in lakes in California), that grows only half as fast.  Since the genome sequences of the two strains are 99.8 percent identical, the genetic determinants of rapid growth almost certainly lie in the remaining 0.2 percent.

“What intrigues me most about these microbes is their ingenuity,” Pakrasi said. “They have somehow figured out how to multiply rapidly by using sunlight and carbon dioxide very efficiently.”

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