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Biothreat specialist

Nov. 23, 2020: A molecular biologist cultures an ecological perspective of biothreats in his new role at the Emerging Pathogens Institute.

Biothreat specialist

Bacillus anthracis spores shown in a colored scanning electron micrograph. (Restricted use image. © NIBSC/SCIENCE PHOTO LIBRARY)

A UF molecular biologist and bioengineer, Mike Norris, employs the tiny yet expansive microcosms of molecular biology and bioengineering to probe ecological questions of how disease agents function within landscapes, and how we can best protect society against bioterrorism. 

Norris studies tiny bacteria that are among the world's most lethal. Burkholderia mallei, Burkholderia pseudomallei and Bacillus anthracis are the causative agents of glanders, melioidosis and anthrax. The trio form the axis of his career.

"I have spent a lot of time understanding how these organisms interact with a host during infection," Norris says.

All three pathogens occur naturally in the environment or within mammalian hosts and require only a small infectious dose to kill their host—infection results from accidental inhalation, consumption or contamination of an open wound.

All three share the potential to be weaponized as biothreats.

Norris, who is a research assistant professor of medical geography in global health at UF's College of Liberal Arts and Sciences, works with these microorganisms in high-containment labs at the Emerging Pathogens Institute. He also seeks to understand how these pathogens persist, grow, and cause disease in their natural environments.

His work moves seamlessly from cell cultures to landscapes.

Melioidosis and glanders

Norris was hired jointly by the College of Liberal Arts and Sciences Department of Geography and the Emerging Pathogens Institute in late 2018. He previously received EPI seed funding for an investigation of how diversity within B. pseudomallei strains affect the disease process within infected hosts. Norris also formally joined the Spatial Epidemiology and Ecology Research Laboratory as an associate director. His postdoctoral adviser, Apichai Tuanyok, is also an EPI member and guided Norris’ early studies of melioidosis and glanders.

Burkholderia mallei and B. pseudomallei are a little unusual in the bacterial world. They lead an intracellular lifestyle where they invade host cells and reproduce within them. They then spread rapidly from cell to cell. But they can also live outside a host. Both species are resistant to many antibiotics. The mortality rate of melioidosis approaches or exceeds 50 percent even when its victims receive a proper diagnosis and treatment. For glanders, the mortality rate can be as high as 95 percent in untreated cases or as low as 20 percent when people receive therapeutic drugs.

Burkholderia pseudomallei SEM with colorization

Colored scanning electron micrograph of Burkholderia pseudomallei. (Restricted use image. © Dennis Kunkel Microscopy/SCIENCE PHOTO LIBRARY)

Melioidosis is endemic in at least 79 countries, and it is estimated to cause roughly 165,000 human infections and 89,000 deaths annually. Most of these infections occur in tropical and subtropical locations where the bacteria reside in the soil's uppermost root zone. It also occurs in water.

Because the Centers for Disease Control and Prevention classify both B. pseudomallei and B. mallei as Tier-1 agents, part of Norris' efforts involve widening the toolkit of organisms that researchers can safely study. Some B. pseudomallei strains do not produce disease in people due to mutations within a large molecule in the bacteria's outer membrane called lipopolysaccharide, or LPS. This molecule is essential for how pathogenic Burkholderia species produce disease.

In a paper published in BMC Microbiology, Norris' team reported on the creation of a new biosafe strain of Burkholderia, named 576mn, which is suitable for lab studies. It is incapable of replicating within human cells and doesn’t cause disease in mice. In comparison to pathogenic strains, lab strains such as 576mn are safer for researchers to use in projects that seek to develop preventative therapies and melioidosis treatments.

In other work, published in the American Journal of Tropical Medicine, Norris contributed to the development of a new assay, or lab test, which can differentiate between the two major types of lipopolysaccharide molecules found on B. pseudomallei. These are type A, or typical LPS; and type B, which is composed of atypical LPS, types B and B2, and rough LPS. Although lab studies show that the LPS type likely affects disease severity, researchers are still trying to understand if there are links between each LPS type and the severity of disease clinically observed. The assay developed by Norris' research group is 98.8 percent effective at differentiating the type A and B Burkholderia LPS forms.

The two types also have geographic inferences. Type A dominates as the typical form in most places except India where nearly 40 percent of infections are type B. The less common B type shows up in only 3 percent of Southeast Asia’s cases and 15 percent of Australia’s, which are both focal regions of Norris’s research.

"When there are different types of lipopolysaccharide which coat the outside of the organism, that is a powerful diagnostic target, so people who have this disease, or who have been exposed in the past, have antibodies to these particular types of antigens," Norris says. "My seed funding from EPI was a project where we investigated if the host response differed between type A and type B. We found that they are different, and now we frequently create diagnostics to use in the serosurveillance of those two types of exposures."

Along with a team of collaborators, Norris contributed to a new understanding that infections with either type A or B led to different immune responses. Prior to this work, it had been thought that the LPS of B. pseudomallei produced only a weak immune response. But results from a study he led showed that in a mouse animal model, several of the type B strains induced strong innate immune reactions — which differs from what unfolds with infections caused by type A forms.

In addition to engineering safer ways to study Burkholderia, and type its strains, Norris has also contributed to searching for compounds that could be useful in new melioidosis drugs. Last year, he helped develop a cell-based phenotypic assay that was then used to identify two, novel, small molecules with therapeutic promise. In this project, his research teammates used a closely related lab-safe surrogate, B. thailandensis, to screen for molecules that could disrupt the bacteria's intracellular spread. They initially turned up 268 leads, but this narrowed to just two that demonstrated cross-species activity against both B. pseudomallei and B. mallei.

Anthrax, and disease ecology

Norris brings to the SEER Lab an in-depth knowledge of cell cultures, animal models, bacterial genetics, and gene expression techniques. In his new position, he collaborates with the lab's director, Jason Blackburn, who is an associate professor of medical geography at UF's College of Liberal Arts and Sciences. Blackburn specializes in studying the ecological processes of anthrax outbreaks. While their academic backgrounds differ, their partnership speaks to the multidisciplinary approach that the EPI fosters to solve complex problems.

"I’m a molecular biologist, and Jason is a medical geographer," Norris says. "Working with Jason, my focus has moved into pathogen ecology and how that drives virulence, disease, detection and vaccine development and efficacy. It’s a broad platform. We call our method the bookend approach to melioidosis, anthrax and glanders."

Before joining the SEER Lab, Norris focused on the nature of interactions between a host and an organism. But he soon learned his perspective was limited to the scale of bacterial infections and individuals. Suddenly he was steeped in the lingo of ecology, disease surveillance and the value of remote sensing for studying landscapes.

"My attention has shifted to pathogen ecology and how this drives virulence, disease, detection, and vaccine development and efficacy," Norris says.

The SEER Lab has a strong focus on understanding anthrax outbreaks, which are caused by Bacillus. anthracis, and also understanding what factors drive the bacteria’s virulence. B. anthracis occurs naturally in the environment. It has a complex relationship with soil, weather and grazing animals and Norris had to shift from a lab mentality to a perspective that incorporated ecological relationships beyond the host and pathogen.

“The most interesting aspect of this work has been the focus on integrating and understanding the pathogenesis of the organism with the ecology of the organism,” Norris says. “Understanding how animal and human interactions with the environment can lead to pathogen evolution.”

In one example of how Norris’ lab expertise compliments the SEER Lab’s ecological investigations, Norris devised a molecular technique to illuminate key B. anthracis metabolic processes. He used plasmids—which are tiny, circular strands of DNA that can be used to deliver genes to bacteria—to genetically engineer a B. anthracis strain to luminesce, or glow, when it either secretes toxins or generates spores. He then detected the glowing marker in various lab experiments that employed fluorescent microscopy and fluorescent time-lapse imaging. This allowed the SEER lab researchers to better understand how B. anthracis grows in the soil, and produces disease in a host.

Norris has also contributed to work that links lab experiments with fieldwork. He recently helped verify different growth rates in lab media for wild B. anthracis strains versus lab strains. The results were published in PLOS-ONE, and have implications for how to interpret findings from lab studies that use these strains and make inferences about how sporulation or disease may occur in the wild.

“A lab scientist will take a strain that’s been in the lab for decades and try to characterize how growth rates and sporulation rates could affect host infection,” Norris explains. “But what they don’t realize is that what they are looking at is not representative of what is happening in the wild. What we showed is that strains which are newly isolated from outbreaks behave differently than lab strains.”

Norris and Blackburn showcased their lab-to-field collaboration in a paper published in the International Journal of Environmental Research and Public Health. “We wanted to show our colleagues how we have linked geospatial and lab analyses,” Norris says. “In this project, we discussed what happens to Bacillus when it sits in soil and what factors come into play when there is a natural outbreak.”

The pair examined global trends in rainfall, vegetation, mineral levels and soil pH then explored an outbreak case study in Australia. Norris’ portion involved designing lab experiments that utilized luminescent tagging to examine prime conditions under which engineered B. anthracis undergoes sporulation and toxin excretion. He found that a pH level of between 6.5 and 8.5 enhanced both sporulation and toxin production, and the spore’s longevity in the soil. Norris also manipulated calcium and pH levels and found that adding calcium could buffer growing conditions that were otherwise too basic, providing short term gains in B. anthracis growth. The lab results closely mirrored pH and calcium conditions found in Kruger National Park, South Africa.

“Our results from this study extend current understanding of the ecology of anthrax,” Norris says. “And they have special implications for understanding the triggers of anthrax outbreaks in the real world.” 

In his latest work, Norris’ attention is turning to understanding the genetic and evolutionary drivers of pathogenesis in strains of B. anthracis that can drop anthrose, a sugar, from the bacterial spore surface. Although the first known anthrose-deficient strain was originally thought to be confined to West Africa, Norris was involved in work that documented a distantly related anthrose-deficient strain in Poland. He used allelic recombination techniques to knock out anthrose-encoding genes in order to develop a new lab assay that identifies B. anthracis strains containing mutations in their DNA that lead to anthrose deficiency.

He and Blackburn are also training their sights on testing anti-toxin treatments for anthrax. In a recent commentary published in The Lancet Infectious Diseases, the pair called for a drug named raxibacumab to be tested against not only conventional lab strains of B. anthracis but also all of its various types, even the new anthrose-deficient forms.

Norris’ ultimate goal is to develop a next-generation anthrax vaccine, and to increase scientific understanding of the environmental ecology of Burkholderia.

“The SEER Lab has done a lot of good work understanding where these pathogens are and their diversity, so now we will look at what happens next,” Norris says. “Are there patterns of infectivity, are there questions about genomic diversity that we can answer? And can we use any of this information to develop new diagnostics, so that we can better understand the prevalence of exposure, or prevalence of disease?”


Written by DeLene Beeland