Microbiologists at Fresno State are searching for a two-for-one bacterial bargain that will help the natural environment recover more quickly from chemical contamination of the soil.
Dr.Alice Wright and Dr. Mamta Rawat, both biology professors, recently completed a faculty-student study of bacteria capable of simultaneously detoxifying mercury and 2, 4-D, two chemicals that have accumulated to higher-than-desirable levels in some California soils.
Mercury is a naturally occurring metal but has been found concentrated in soils adjacent to mining operations. It was mined and used extensively in both the Coast and Sierra Nevada mountain ranges to purify ore deposits during gold-mining operations.
“There is a lot of concern now about
If mercury leaches into groundwater and eventually is ingested by humans, it can cause an assortment of adverse reactions, affecting major organs and the nervous system.
The phrase “mad as a hatter” is thought to explain the odd behavior of 19th-century hatmakers who used mercury in their craft, Rawat noted. Their symptoms included dementia, moodiness, loss of coordination and shaking.
According to Wright, some bacteria can reduce organic mercury into an inorganic form that is more volatile but less toxic.
2, 4-D (2, 4-dichlorophenoxy acetic acid) is a widely-used herbicide that some microbes are able to break down in the soil, changing it to carbon dioxide and water. However, health problems can arise when people are exposed to concentrated amounts of 2, 4-D. Acute symptoms include weakness and problems of the eyes, skin, and mouth.
“Many bacteria are known to degrade 2, 4-D, and likewise, others are known to detoxify mercury,” Rawat said.
This study examined the potential of selected microorganisms to detoxify soils co-contaminated with mercury and 2, 4-D. The study focused on two bacterial species (Cupriavidus necator and Arthrobacter fluorenscens) commonly found in soil.
Multiple tests using different concentrations of mercury, 2, 4-D, and the bacteria were conducted. Results were encouraging, but not optimal, Wright reported.
“Although bacterial growth was slowed when both toxins were added to the soil, the combined toxins were toxic at lower concentrations than the two toxins alone. So comprehensively it was a positive result. The bacteria will detoxify the metal and the organic pesticide at the same time,” Rawat said.
The study also has provided new information about how certain bacterial genes are expressed when both pesticides and metals are present during metabolism. The results have been presented to the California State University Program for Education and Research in Biotechnology and Central California Research Symposium as well as the national Society for the Advancement of Chicanos and Native Americans in Science, Wright said.
Additional research is warranted when funding is available, Wright said. The project was conducted with partial financial support from the California State University Agricultural Research Institute, the U.S. Department of Agriculture and Envirnonmental Protection Agency, and Dow Agrosciences.
Collaborating with Wright and Rawat in the work were five Fresno State students who have gained experience working with contaminants at the molecular level.
“We had very talented and hardworking students work on the project, and after this work they have gone on to do great things,” Wright said.
Michelle Davison is attending graduate school at Stanford University; Yaw Anane works at an east coast biotechnology company; Leslie Dominguez works at the Dried Fruit Association; Chantale Johnson is a manager at Food Safety; and Denise Lopez is the head of education for the Tulare County Public Health Department.
For more information on this study, contact Wright at awright@csufresno.edu.
(Text by Steve Olson, publications editor of the California Agricultural Technology Institute)
