A fast-growing bacterial strain found on the campus of The University of Texas at Austin in the 1950s might ultimately prove useful for carbon sequestration, biofuel production, biosynthesis of valuable chemicals and the search for novel pharmaceuticals, scientists announced in newly published paper.
Cyanobacteria, bacteria that obtain their energy through photosynthesis, are of considerable interest as bio-factories, organisms that could be harnessed to generate a range of industrially useful products.
Part of their appeal is that they can grow on sunlight and carbon dioxide alone and thus could contribute to lowering greenhouse gas emissions and moving away from a petrochemical-based economy.
However, familiar cyanobacterial strains grow more slowly than the bacterial and yeast bio-factories already in use, and their genetic and metabolic networks are not as well understood.
A group of scientists reported in the January 30 issue of Scientific Reports that they have identified a fast-growing cyanobacterial strain, called Synechococcus elongatus UTEX 2973. Authors on the paper include Himadri B. Pakrasi of Washington University in St. Louis; University of Texas at Austin co-author Jerry Brand, who is Director of the UTEX Culture Collection of Algae at UT Austin; and first author Jingjie Yu, a postdoctoral researcher in the Pakrasi lab and a former graduate student of Brand who received her Ph.D. from the College of Natural Sciences in 2011.
Rapid growth may allow this cyanobacterial strain to outcompete contaminating ones and eventually to synthesize larger quantities of biofuel or other valuable products.
It also has the more immediate benefit of making it easier to do the experimental work needed to understand the bacterium well enough that it can serve as a “chassis” that can be retooled for a variety of purposes. Because other cyanobacterial strains grow sluggishly, it takes significantly longer to perform experiments with them than with E. coli or yeast.
Jack E. Myers–Botanist, Zoologist, and Educator–Key to Waller Creek Find
Dr. Jack Myers was one of the orignal scientists who detected fast growth in a cyanobacterial strain collected in Waller Creek. He also had a long and fruitful career at UT Austin, which began when he joined the faculty in 1941.
During his tenure here, Myers received much recognition for his scientific and educational accomplishments. In addition to being named a National Academy of Sciences member and holding a National Institutes of Health Research Career Award, Dr. Myers published more than 135 articles during over 60 years of distinguished research of photobiology. He was inducted into the College of Natural Sciences’ Hall of Honor in 1993.
Jack considered all teaching very important whether of graduate students or children. This is reflected in his dedication as science editor of a magazine popular across the country, “Highlights for Children,” which was founded by Jack's parents. In this capacity, he answered hundreds of questions from children every year and wrote two children’s books, “What Makes Popcorn Pop?” and “What Happened to the Mammoths?” He later recalled that writing for children was “a challenge I hadn't counted on, but my Pop was of a mind that, ‘You can do this. You're a scientist’.” Jack always took the questions seriously and was particularly interested when the child had really thought about the question.
Dr. Jack Myers kept working, both in his research and as the science editor for Highlights, right up until he passed away in December of 2006.
The summary of Jack Myers’ life that we present here barely scratches the surface. You can read more about his illustrious career here, here and here.
Hiding in plain sight
Like the famous purloined letter, the cyanobacterial strain was hiding in plain sight — or to be precise, in the UTEX Culture Collection at UT Austin.
Although most cyanobacteria grow slowly, in 1955 two scientists at UT Austin, William Kratz and Jack Myers (see sidebar), described a fast-growing cyanobacterial strain collected from Waller Creek, which runs through the campus.
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 UTEX as Tx 20 Anacystis nidulans and later renamed as Synechococcusleopoliensis UTEX 625.
However, at some point over the decades the UTEX 625 strain mutated and lost its rapid growth property. Yu obtained a frozen sample of the UTEX strain, and by careful coaxing under appropriate conditions, isolated a pure, fast-growing mutant strain from the UTEX 625 culture.
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 is not identical to the one that was described in 1955, a new sample was deposited it in the UTEX algae collection as Synechococcus elongatus UTEX 2973.
The discovery of the mutated strain has sparked new research into the stability of cyanobacterial cultures over time.
“We are sequencing three strains, including the Waller Creek strain, in order to see how cyanobacteria may evolve after they are brought into culture, and how two identical starting cultures may diverge when separated and cultured in separate facilities for decades,” said Brand. “These studies are now well underway, in collaboration with scientists elsewhere.”
Kicking the tires on the new model
In order to characterize the new strain, Washington University sequenced its genome. 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.
The proteomes (the set of proteins produced by an organism) of both of these strains were analyzed at the Environmental Molecular Sciences Laboratory, a Department of Energy national scientific user facility located at Pacific Northwest National Laboratory in Richland, Wash. This data, which covers 68 percent of the proteins the microbes produce, will guide further work with both strains.
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.
“Cyanobacteria have the potential to be the ideal biofactories for sustainable carbon negative production of numerous compounds,” Pakrasi said. “This fast-growing strain should help to realize that dream.”
This post was adapted from a Washington University in St. Louis press release.
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