Bacteria tracked feeding nitrogen to nutrient-starved plants

With rising populations and changing climate conditions, the need for resilient and reliable crops has never been greater. Nitrogen -- an essential element for plant growth -- is often woefully absent in heavily farmed land. Earth's atmosphere offers an overabundance of nitrogen, but how can it be safely and sustainably transferred into the soil? Nitrogen-eating bacteria may be the answer.

An international team of researchers, including three from the U.S. Department of Energy's Brookhaven National Laboratory, has tracked nitrogen as soil bacteria pull it from the air and release it as plant-friendly ammonium. This process -- called biological nitrogen fixation, or BNF -- was found to substantially promote growth in certain grass crops, offering new strategies for eco-friendly farming.

"Our results show that healthy growth can be achieved by combining certain soil bacteria with grasses, even when plants are grown in extremely nitrogen-deprived soil," said study coauthor Richard Ferrieri, director of Brookhaven Lab's Radiochemistry and Biological Imaging Program. "We plan to apply this method to other crop systems, including bioenergy grasses like sorghum, switchgrass, and miscanthus, and even to food crops like corn and wheat."

The scientists measured the effects of two BNF soil bacteria -- Azospirillum brasilense and Herbaspirillum seropedicae -- on growth of the grass Setaria viridis. The study shows the first direct evidence of BNF by tracking the presence of a nitrogen radiotracer as it was absorbed first by the bacteria and then moved through the plant. The results, published in the March issue of The Plant Journal, revealed substantial increases in height, weight, and root length.

The collaboration also included scientists from Brazil's Federal University of ParanĂ¡ and Federal University of Santa Catarina, the State University of New York's College of Environmental Science and Forestry, and the University of Missouri.

"The bacteria we are using are currently among those sold as crop inoculants in South America, but this technology is not widely applied in the U.S.," said study coauthor Gary Stacey, a scientist at the University of Missouri. "We hope that our findings will stimulate others to look at this area, which we believe holds real promise for promoting more sustainable agriculture, especially with regard to biofuel crops."

Nitrogen -- chemically bound as dinitrogen gas -- is the most abundant element in the atmosphere. Unfortunately, plants can only absorb it after it is integrated into the soil as nitrate and ammonium. This process often happens through natural cycles of plant and animal decay, which can take too long to be commercially viable. Instead, fertilizers are typically introduced to maintain high crop yields.

"Many commercial fertilizers focus primarily on infusing soil with chemical forms of nitrogen," Ferrieri said. "However, this is a costly process that can result in excessive nitrogen runoff into waterways, sometimes causing severe ecological damage."

Certain bacteria, however, can restrict their activities to specific root systems and use abundant, airborne nitrogen. The soil becomes locally enriched after BNF inoculation, avoiding the risks of large-scale chemical intervention.

The scientists used Brookhaven's Cyclotron -- a small accelerator dedicated to isotope production -- to produce the nitrogen radiotracer, which was then introduced to the soil in a stream of air. Once absorbed, the radioactive nitrogen emitted bursts of antimatter particles that were detected by phosphor plates, which behave like photosensitive film. The team then used a simple radiation detector to track the movement of radiotracers into the plant's shoots and leaves. Then, to map metabolic turnover, the team dissected plant tissue to reveal the nitrogen within photosynthesis proteins.

"This radiotracer only has a half-life of 10 minutes, meaning it becomes inactive and undetectable very quickly," Ferrieri said. "Gathering biological data within such a short time was one of our biggest challenges."

"The leaf biochemistry of the S. viridis grass closely matches bioenergy crops, which may facilitate the practical applications of the study," Stacey said. "My colleagues and I tested 30 candidate grass genotypes, identifying three that responded to BNF and one in particular -- called A10.1 -- that was very active."

That targeted genotype was also sequenced by the Joint Genome Institute, a DOE Office of Science User Facility, which will eventually give scientists the molecular information needed to pinpoint the mechanisms regulating BNF.

One particular kind of bacteria -- a mutant strain of A. brasilense developed by the Brazilian scientists -- also produced surprisingly strong growth, suggesting great practical potential.

"We're bringing all guns to bear on this system to tease out any physiological, metabolic, proteomic, or transcriptional basis for BNF," Ferrieri said. "Brookhaven's radiotracer tools offer a singular window into plant metabolism and plant-microbe interactions."

Ferrieri and Stacey will continue this work at another DOE Office of Science User Facility, Pacific Northwest National Laboratory's Environmental and Molecular Science Laboratory, where two research proposals were recently approved. The two scientists will probe changes in plant proteins and metabolites under a variety of growth conditions. Stacey's group is also actively working to isolate genetic commonalities and differences in these plants to accelerate research and reveal the molecular BNF mechanism.

Clinton To Make Gender Issues Key to Presidential Bid

Hillary Clinton gives the keynote speech at a conference in Santa Clara, Feb 24, 2015. Hillary Clinton gives the keynote speech at a conference in Santa Clara, Feb 24, 2015. Marla Aufmuth/Getty Images

Ending years of speculation, Hillary Clinton has confirmed that she will run for president in 2016.

Like Republican candidates Rand Paul and Ted Cruz, the former Secretary of State announced the news online. In a YouTube video posted on her website, Clinton lays out her priorities for the coming election season.

“Americans have fought their way back from tough economic times, but the deck is still stacked in favor of those at the top,” Clinton says in the video. “Everyday Americans need a champion, and I want to be that champion, so you can do more than just get by. You can get ahead, and stay ahead, because when families are strong, America is strong.”

As Clinton takes another shot at becoming the country’s first female president, it is already clear that this time around, she plans to put women’s issues front and center in an attempt to appeal to female voters. Among the many Americans profiled in the video, the majority are women, from working mothers to expectant ones, signaling that Clinton plans to make issues of gender inequality, which she has been working on since stepping down as Secretary of State in 2013, key to her campaign.

In recent years, Clinton has been an outspoken advocate of the need to close the gender gap that still exists in the US workforce. That gap is particularly wide in the tech industry, where women make up a small fraction of the staff at leading businesses like Facebook and Google. Now, as a presidential candidate and the likely Democratic nominee, Clinton is uniquely poised to push this conversation, which has been slowly building in Silicon Valley, into the spotlight on a national and global stage.

Over the last year, speaking on behalf of The Clinton Foundation, Clinton has frequently decried the gender wage gap in the United States, in which women earn on average 78.3 cents less than their male counterparts. Clinton has also been actively promoting the need for more women in tech, noting in a recent conversation with tech journalist Kara Swisher that the number of women graduating with computer science degrees has actually dropped since the 1980s from 38 percent to just 18 percent. “We’re going backwards in a field that’s supposed to be all about going forward,” Clinton said.

She has also openly supported policies like free preschool programs and guaranteed paid parental leave, which would make it easier to be a working mom. “Those are not just nice luxuries for women,” Clinton argued on stage at The Clinton Global Initiative in September. “They would fundamentally free up women to be in the workforce if they had the skills and desire to do so.”

Mining the Data

Along with her daughter Chelsea, meanwhile, Clinton has been heavily involved in several data-mining projects that aim to highlight where the gender gaps are widest both in the US and around the world. Through the No Ceilings project, the Clinton Foundation has aggregated 850,000 data points that have been collected since 1995 related to the status of women around the world.

In an interview with WIRED last month, Chelsea Clinton said that this data “enables us to make the most powerful case ultimately for why investing in women and girls isn’t just the morally right thing to do, but the smart thing to do.”

“The evidence really shows that where countries have invested in women and girls, societies are safer, and a rising tide really lifts all boats,” she said.

The former first lady has also been working with the United Nations Foundation on a data collection project called Data2X, which will gather even more information on the status of women and girls where it doesn’t already exist. “I’m not sure we have the best data we need in our own country. What’s really behind the stagnation in wages and in workforce participation? We have some very educated guesses, but I’m not sure we really know,” Clinton said at the Clinton Global Initiative. “We need to do much more to understand.”

During her primary run against President Barack Obama back in 2008, Clinton was notably close-lipped about issues related to gender. This time around, it seems all that will change. And whether she ultimately wins or loses, the attention her campaign will likely bring to these issues—and the discussions her rivals will also have to engage with—is already a win for women everywhere.