Progress 04/01/24 to 03/31/25

Outputs
Target Audience:Target audiences include students, faculty, and staff at Texas A&M International University (TAMIU), USDA-ARS Agricultural Water Efficiency and Salinity Research Unit, extension specialists at Texas A&M Agri Life, and the scientific community. At Texas A&M International University, a total of 33 (21 students in the Environmental Science course, one graduate student, and 12 undergraduate students that include 7 Honors thesis students) were trained in the classroom and research protocols within chemistry, environmental science, microbiology, and agricultural sciences. Our purpose in working with and training students was to 1) introduce students to the regional issue of water quality of the Rio Grande; 2) train students to address research questions that connect regional scientific interests in antimicrobial resistance and scientific inquiry; and 3) prepare young scholars for careers in agriculture, natural resource management, analytical chemistry, and microbiology. In addition, 10 faculty, 4 staff members, and 30 students were introduced to the goals and outcomes of our project to communicate 1) scientific interests in the region, 2) water quality and availability issues affecting the food quality of the most important agricultural region of Texas, the Rio Grande Valley, and 3) community activities and potential solutions to the agricultural resistance development. Our relationship with scientists at USDA-ARS Agricultural Water Efficiency and Salinity Research Unit and the extension specialists at Texas A&M Agri-Life was to 1) inform multiple stakeholders of the regional water quality issues related to antimicrobial resistance development and its impact on agricultural resources; and 2) expand the knowledge base of the Rio Grande water quality issues in an effort to build on the scientific expertise of agricultural scientists. Changes/Problems:Drought conditions in the Rio Grande Valley and water restrictions limited the availability of fields during our 2024 reporting period. We were unable to access the same farms as we did during the 2023 crop season, and we were only limited to an onion farm to compare to the 2023 season. Our analysis of the antimicrobials was delayed due to equipment issues, but we have obtained a new GC-MS for analysis and have adjusted methods accordingly. Final quantification of the antimicrobial data has been delayed; however, we are finalizing these numbers. We have also addressed our greenhouse accessibility issue which will be available for us by the end of Summer 2025. What opportunities for training and professional development has the project provided?Students mentored during the project were trained in chemistry, microbiology, agricultural and professional skills. Training opportunities included agricultural field sampling, water quality analysis, soil, water and plant chemical extractions, microbial analysis, and microbial culturing techniques. Trainees are more competitive for national summer research programs and admission into post-graduate programs, specifically in agricultural science or a related field. Twelve student trainees (eleven undergraduates and one graduate student) developed a poster presentation for a regional and/or national scientific conference: two students for the national meeting for the American Society for Microbiology; three students for the Texas Branch meeting of the American Society for Microbiology; and five students for the American Chemical Society's national meeting. In addition, 21 students in our Environmental Science course participated in a preliminary study and learned experimental design, seed sowing and plant growth monitoring and assessment. Trainees learned how to statistically analyze microbial data. Trainees that have learned chemical extractions have also gained experience in instrumental analysis of chemical extracts, a skill that can transition them into a career or graduate program. At least 11 trainees will be co-authors on future manuscripts. How have the results been disseminated to communities of interest?Results of the project have been communicated through four avenues: the national meeting for the American Society for Microbiology, the Texas Branch meeting for the American Society for Microbiology, the American Chemical Society, and the Texas A&M International University's Research Seminar Series. In addition, we have communicated results to our collaborators at the USDA-ARS's Salinity Research Unit and the Texas A&M Agri-Life Research Station. What do you plan to do during the next reporting period to accomplish the goals?We are currently completing chemical analyses and soil bacterial counts along with drafting a manuscript for submission (Objective 1). During Summer 2025, we will be completing DNA extractions, quantification of antimicrobials in farm samples, identification of screened isolates for final selection and preliminary degradation assays to prepare for the final experiment (Objective 2). Biosafety protocols for our greenhouse study will also be submitted for approval prior to Fall 2025. Within the next six months, we will be submitting at least two manuscripts. During Fall 2025 (Objective 2), we will be collecting field soil and water samples for the greenhouse study and setting up a greenhouse study. DNA extractions of all matrices will continue during Fall 2025 and Spring 2026 for greenhouse study. DNA extractions will be submitted for microbiome analysis and antimicrobial resistant gene marker analysis, and our third manuscript will be prepared and submitted at the end of our funding year.

Impacts
What was accomplished under these goals? Rio Grande waters are the primary source of irrigation for South Texas and recharged with chemicals of emerging concern from binational sources of recycled waters and sewage outfalls (up to 15 million gallons per day). Although this is unique to border regions, elevated contaminant levels will become similar in the U.S. with increasing water deficits, and border region crops are distributed nationally for human consumption. This project aims to 1) assess the contribution of recycled water to antimicrobial resistance in agricultural fields and 2) to mitigate soil and crop contamination using plant beneficial bacteria to degrade antimicrobials. Outcomes of this project include training undergraduate and graduate students for agricultural research careers, and providing scientists and extension specialists applied knowledge for agroecosystem management and research. Ultimately, this work will offer insights into strategies for protecting human health from long-term risks of antimicrobial resistance associated with reused irrigation water in agricultural production. For Objective 1 of this study, chemical and microbial analyses were performed on irrigation waters, soils, and crops (onions, cilantro, and Swiss Chard) collected at three separate locations within a field relative to the irrigation source (nearest, midpoint, and farthest) in the Rio Grande Valley at three time points during the growing season. We also collected additional water, soil and onion samples from a commercial farm at two sampling times during an additional growing season (early season and late season). The highest levels of antimicrobial and metal contamination were found in a bulb crop. The major antimicrobial found in field samples was triclosan, an antimicrobial banned from over-the-counter antimicrobial soaps in the U.S. Between three different commercial crop fields, onions were the highest bioaccumulators of triclosan (2,000-fold that of levels found in irrigation waters), cilantro was second with 229-fold water levels, and Swiss chard with 57-fold water levels. The most predominant metals in irrigation waters were arsenic, lead, and antimony. Onion bulbs accumulated all three metals at two to four times that found in soils. We confirmed that bacterial populations examined in our study were primarily triclosan-resistant, coinciding with our chemical data showing that triclosan is the most prevalent antimicrobial tested. Non-pathogenic bacteria (heterotrophic bacteria) were at higher levels than total coliform bacteria with a minimal presence of E. coli in the crop-soil systems. Heterotrophic bacteria detected in water were relatively low in number compared to other farm matrices with a trend of < 200 CFUs/mL of antimicrobial resistant bacteria. During Y1 & Y2 of the study, triclosan-resistant heterotrophic bacteria and total coliforms composed the highest proportion of bacteria, which corresponds to elevated levels of triclosan detected in waters. E. coli numbers were a mean of 22 MPNs/100mL, below the FDA Food Safety Modernization Act (FSMA) Produce Safety Rule's guidelines for pre-harvest agricultural waters used for covered crops. In bulk soil samples and on onion bulbs, antimicrobial resistant bacterial numbers were generally highest nearest the irrigation source, indicating that irrigation waters are likely depositing antimicrobial residues and antimicrobial resistant bacteria along with antimicrobial resistant genes. Bulk soil had the highest number of antimicrobial resistant bacteria compared to leaf/bulb or rhizosphere microbiomes; therefore, soil is serving as the reservoir for these populations. Despite the absence of E. coli on crop plants, the decrease in total coliforms on onion bulbs farther away from the irrigation pipe indicates a higher potential for fecal contamination nearest the discharge point for irrigation. For Objective 2 of this study, we screened bacteria from crop plants to screen for abilities to degrade antimicrobials and promote plant growth. Out of a collection of 95 isolates from onion, cilantro and Swiss Chard, we found 23 of these isolates were able to grow using triclosan as their only food source, an indicator of degradation abilities. All bacteria had resistance to ampicillin and either tetracycline or triclosan, indicating a cross-resistance mechanism common to ampicillin resistance. Ampicillin- and tetracycline- resistant bacteria were more likely to produce high levels of siderophores, a compound that increases iron availability for plants. Triclosan resistant isolates had higher levels of phosphate solubility, potentially allowing for greater levels of phosphate release in soils. Preliminary data suggests that despite the presence of antimicrobial-resistant bacteria, they are still providing beneficial functions for crop growth. Selected isolates will be used for the greenhouse study to complete Objective 2. Our study identifies chemical and microbial factors needing to be addressed in irrigation and cropping management. Antimicrobial contamination, in particular triclosan contamination, of soils and crops is particularly problematic in bulb crops. Given that metal bioaccumulation was also elevated in onions, there may be an interplay between antimicrobial and metal contamination of crop products and the influence of these factors on antimicrobial resistance development. The primary population of antimicrobial resistant bacteria in agroecosystems will be bacteria that are non-pathogenic but provide a potential for transmission of antimicrobial resistance mechanisms to pathogenic bacteria. Despite the bacterial population that we examined, triclosan-resistant bacteria are the most prevalent. We have tracked total coliforms and E. coli in waters during two crop seasons, providing a baseline for South Texas farmers monitoring bacterial contamination of agricultural waters at the pre-harvest stage. Further, based on E. coli numbers alone, bacterial numbers did not exceed the FSMA's Product Safety Rule guidelines. Our study fills a gap in knowledge on presence of fecal contamination indicators in South Texas agricultural waters along with antimicrobial resistance of plant surface bacteria, particularly in crops. We have identified antimicrobial resistant members on crop surfaces and their potential to degrade antimicrobials, the main stressor driving antimicrobial resistance development. We have also trained undergraduate and graduate students in field sampling, chemical analyses, microbial analyses, biochemical assays, and statistical analyses that increase their competitiveness for graduate programs and careers in agricultural sciences.

Publications

• Type: Conference Papers and Presentations Status: Other Year Published: 2024 Citation: Mendez, M.O., D.E. Tarver, F. Montaner, A. Elizaldi, F. Castillo, A. Addo-Mensah, A.M. Ibekwe, and J. Anciso. 2024 Mitigation and Risk Assessment of Antimicrobial Resistance in Recycled Irrigation Water. USDA-NIFA AFRIs Foundational Food Safety Programs, Mitigating Antimicrobial Resistance Across the Food Chain and Food Safety and Defense Project Directors Meeting. Long Beach, CA, Jul 13.
• Type: Conference Papers and Presentations Status: Published Year Published: 2025 Citation: Velez Rivera, M., Lomelin, C., Cuadra, L., Ancisco, J., Mendez, M.O., Addo-Mensah, A., 2025. Assessment of trace metals in irrigation water, soil, and vegetables and their health risks. American Chemical Societys Annual Meeting, Spring 2025. doi:10.1021/scimeetings.5c11226
• Type: Conference Papers and Presentations Status: Published Year Published: 2025 Citation: Alarcon, A., Garcia, V., De La Fuente, H., Anciso, J., Mendez, M.O., Addo-Mensah, A., 2025. Assessment of triclosan in recycled irrigation water, soil, and vegetables and their health risks. American Chemical Societys Annual Meeting, Spring 2025. doi:10.1021/scimeetings.5c11224
• Type: Conference Papers and Presentations Status: Other Year Published: 2025 Citation: Elizaldi, A., F. Castillo, D.E. Tarver, F. Montaner, K. Hamlin, A. Addo-Mensah, J. Anciso, and M.O. Mendez. 2025. Biodegradation of triclosan: the role of plant-associated bacteria. Texas Branch American Society for Microbiology 2025 Spring Meeting. Mar 27-29, 2025.
• Type: Conference Papers and Presentations Status: Other Year Published: 2025 Citation: Diana E. Tarver, F. Montaner, A. Espinoza, K. Hamlin, A. Elizaldi, F. Castillo, A. Addo-Mensah, J. Anciso, and M.O. Mendez. 2025. The impact of Rio Grande irrigation waters on antimicrobial resistance of cilantro-associated bacteria. Biodegradation of triclosan: the role of plant-associated bacteria. Texas Branch American Society for Microbiology 2025 Spring Meeting. Mar 27-29, 2025.

Progress 04/01/23 to 03/31/24

Outputs
Target Audience:Target audiences include students at Texas A&M International University (TAMIU), USDA-ARS Agricultural Water Efficiency and Salinity Research Unit, extension specialists at Texas A&M Agri Life. At Texas A&M International University, 20 graduate students and two faculty of the Harvard University School of Design, and the Rio Grande International Study Center. At TAMIU, a total of 18 Hispanic undergraduate students (at least 50% first-generation and qualified for financial assistance) and one Hispanic first-generation graduate student were targeted for training in agricultural sciences. Six of the undergraduate students were graduating seniors (5 Biology majors and 1 Chemistry major) and 12 of the students had a sophomore standing during the reporting period. One of the graduating senior students is now a graduate student, currently being funded as a graduate research assistant through this grant funding. One undergraduate was a paid participant and a University Honors Program student, 11 students obtained academic credits for our undergraduate research course, and 6 additional undergraduates were University Honors Program students. Another 24 undergraduates (23 Hispanic and 1 African-American student) were targeted in the Environmental Chemistry course at TAMIU. During the April 2023 to March 2024 reporting period, components of the project were used for experiential learning experiences through our Undergraduate Research course and University Honors Program. Components of the project were used to develop Honors thesis projects and short-term undergraduate research projects that investigated the concentrations of contaminants in soil, water, and plant tissues along with microbial enumeration and antimicrobial resistant bacterial numbers in the same matrices. During the experiential learning experiences and the Environmental Chemistry course, project goals and design were used to provide context of a regional water quality and food security issue: metal and antimicrobial fate and transport from the Rio Grande to the food chain and its contribution to antimicrobial resistance development. Additionally, two extension specialists were consulted during field research and results were communicated to extension specialists and a USDA-ARS scientist. Issues of the Rio Grande Valley water use and contamination potentials, including field data, were communicated informally at the TAMIU Faculty Panel on Current Research and Educational Initiatives with the Rio Grande International Study Center (RGISC), TAMIU faculty, and the Harvard University Graduate School of Designfor students designing pilot projects for water recycling and reuse systems. Changes/Problems:Our project was delayed due to accessibility to farms meeting our criteria of bulb and leafy crops. Drought conditions in the Rio Grande Valley prevented pre-planning activities, timing of collection, and consistent access to field sites. Water restrictions imposed on farmers and excessive heat delayed seeding events on onion and leafy green farms and limited the availability of field sites. We were able to access one onion farm, a Swiss Chard/beet farm, and an organic cilantro farm. This delayed our field study and did not allow us to sample multiple fields with the same crop or even consistently access fields during the time point we planned to sample. Additionally, we have had equipment and facility issues that have delayed our progress in completing our studies. New construction on campus has impeded access to our greenhouse for preliminary studies. Analytical equipment and repairs have delayed optimization and analysis of antimicrobials. We are currently working with administrators to remedy these situations. We have added metal analyses and additional microbial analyses to our project. As irrigation waters are influenced by industrial activities along the border, including mining near tributary waters for the Rio Grande, we have decided to also examine metal concentrations in irrigation waters, soils and plant tissues. Heavy metals may affect the presence and abundance of mobile genetic elements and antimicrobial resistance genes. We plan to determine if metal concentrations in our studies have a relationship with abundance of antimicrobial resistance genes. In considering food quality and contamination, we have added detection of E. coli and total coliforms to our data, including proportions of these populations that are antimicrobial-resistant in water, soil and plant samples. Taking these two populations into account will allow us to assess potential contamination of the samples by pathogenic populations and determine if there is a relationship with water and/or soil antimicrobial/metal contaminant levels. What opportunities for training and professional development has the project provided?Students mentored during the project were trained in chemistry, microbiology, agricultural and professional skills. Training opportunities included agricultural field sampling, water quality analysis, soil, water and plant chemical extractions, microbial analysis, and microbial culturing techniques. Trainees are more competitive for national summer research programs and admission into post-graduate programs, specifically in agricultural science or a related field. Two students (one undergraduate and one graduate student) developed a poster presentation and were both awarded first place in our university-wide research conference within their respective categories. The two trainees also prepared an abstract for a national conference, the American Society for Microbiology, and have learned how to statistically analyze microbial data. Trainees that have learned chemical extractions have also gained experience in instrumental analysis of chemical extracts, a skill that can transition them into a career or graduate program. At least 6 trainees will be co-authors on future manuscripts. How have the results been disseminated to communities of interest?Results of the project have been communicated through four avenues: a university-wide student conference (Lamar Bruni Vergara Conference) at Texas A&M International University, the Harvard University School of Design panel discussion at Texas A&M International University, and the USDA-Texas A&M Agri Life Future Community Forum. Two trainees presented at our student research conference. Two directors from the Rio Grande International Study Center, including the watershed director, attended the Harvard University School of Design panel discussion, an informal meeting on recycled water issues in South Texas, contamination issues of the Rio Grande and agricultural use of the river water. At the USDA Texas A&M Agri-Life Future Community Forum, Rio Grande water issues and agricultural issues were communicated to local ranchers, small and urban famers, and directly to a USDA representative at the meeting to prioritize USDA and Agri-Life extension efforts in South Texas. What do you plan to do during the next reporting period to accomplish the goals?We are currently completing chemical analyses and soil bacterial counts along with drafting a manuscript for submission (Objective 1). Within the next three months, we will be completing DNA extractions, screening of isolates for degradation and plant growth-promoting assays (Objective 2), and quantification of antimicrobials/metals in farm samples. During Summer 2024, results will be presented at the American Society for Microbiology. Within the next six months, we will be submitting at least two manuscripts. During Fall 2024 (Objective 2), we will be collecting field soil and water samples for the greenhouse study, setting up a greenhouse study, and sampling at least two fields to confirm our findings of the 2023-2024 crop season. DNA extractions of all matrices will continue during Fall 2024 and Spring 2024 for greenhouse study samples and the Fall 2024 & Spring 2024 field sampling. DNA extractions will be submitted for microbiome analysis and antimicrobial resistant gene marker analysis, and our third manuscript will be prepared and submitted at the end of our funding year.

Impacts
What was accomplished under these goals? Rio Grande waters are the primary source of irrigation for South Texas and recharged with chemicals of emerging concern from binational sources of recycled waters and sewage outfalls (up to 15 million gallons per day). Although this is unique to border regions, elevated contaminant levels will become similar in the U.S. with increasing water deficits, and border region crops are distributed nationally for human consumption. This project aims to 1) assess the contribution of recycled water to antimicrobial resistance in agricultural fields and 2) to mitigate soil and crop contamination using plant beneficial bacteria to degrade antimicrobials. Outcomes of this project include training undergraduate and graduate students for agricultural research careers, and providing scientists and extension specialists applied knowledge for agroecosystem management and research. Ultimately, this work will offer insights into strategies for protecting human health from long-term risks of antimicrobial resistance associated with reused irrigation water in agricultural production. For objective 1 of this study, we sampled irrigation water, soils, and crops (onions, cilantro, and Swiss Chard) at three separate locations within a field relative to the irrigation source (nearest, midpoint, and farthest) in the Rio Grande Valley at three time points during the growing season. We analyzed samples for contaminant levels (antimicrobials and metals), indicators of fecal contamination (E. coli and total coliforms) and bacteria resistant to antimicrobials (ampicillin, tetracycline, and triclosan). Preliminary data shows that the presence of antimicrobials in waters corresponds to our findings in soil samples. Triclosan, an antimicrobial banned from over-the-counter antimicrobial soaps in the U.S. was detected in samples. Our previous work has also supported elevated levels of triclosan compared to other rivers in the U.S., likely due to the continued use of triclosan in Mexico. Arsenic was detected in waters at elevated levels (50-100 parts per billion) compared to expected levels in surface waters (approximately 1 part per billion) and above limits for drinking water (10 parts per billion). Other contaminants detected in water and soil samples included the metals lead, chromium, cadmium, iron, antimony, and thallium. We are pending quantification of contaminants to determine if excessive levels are present in edible portions of crops. We found that harvesting methods, crop type, distance from an irrigation source, and sample type may have an influence on contamination and the presence of antimicrobial resistant bacteria. Cilantro is harvested multiple times throughout a growing season to allow for regrowth of cilantro leaves from the same plant. During our study, cilantro was harvested three times and was the only crop to have detectable E. coli numbers and only in samples collected nearest to the irrigation source. Ampicillin-resistant E. coli was also found on cilantro plants but at the minimum detection limit, indicating a low probability of antimicrobial-resistant E. coli on produce. Ampicillin-resistant total coliforms, however, were more abundant than E. coli. Numbers of antimicrobial resistant bacteria on cilantro leaves were also similar within fields during the late season, compared to the mid-season samples. This indicated that re-exposure to recycled water and soil between harvests could contribute to the development of antimicrobial resistance. Leafy greens can also harbor higher numbers of antimicrobial resistant bacteria compared to bulb crops. We found that up to 93% of total bacteria on leafy greens were ampicillin resistant, up to 21% were tetracycline-resistant, and up to 88% were triclosan resistant. However, root-associated soil had 2-4 times higher numbers of antimicrobial resistant bacteria than bulb/leaves, indicating a possible reservoir of antimicrobial resistant bacteria. Types of antimicrobial resistant bacteria were also different based on sample type with higher numbers of triclosan-resistant bacteria in water and root soil samples and primarily ampicillin-resistant bacteria on bulbs/leaves. Distance from the irrigation source was only important in the Swiss Chard field, where triclosan-resistant bacteria were highest near the irrigation source. So far, we have confirmed the presence of triclosan in water and soil samples, and other antimicrobials are currently being screened. For Objective 2 of this study, we isolated bacteria from crop plants to screen for abilities to degrade antimicrobials and promote plant growth. From onion and cilantro field samples, we selected 57 bacteria from plant surfaces (leaves and bulbs) and 38 bacteria from root soil samples. Two crop isolates, one from Swiss Chard and the other from cilantro, can use triclosan as their only food source, an indicator of degradation abilities, and produce enzymes that increase availability of phosphate, a nutrient, for plants. Spinach bacteria from a previous study are also being screened for degradation and plant growth-promoting activities. Three spinach bacteria were able to use triclosan as a food source, increase phosphate availability and affect the availability of iron, a plant nutrient. We are currently screening additional bacteria for other degradation abilities and identifying bacteria of interest. Preliminary data indicates that leaf-associated bacteria from cilantro and Swiss Chard have greater degradation abilities due to their exposure to antimicrobials from irrigation waters. Assessing data over a season for bulb and leafy crops increased our knowledge of the impact of recycled water irrigation on the microbiome of an agroecosystem. Despite levels of antimicrobials in irrigation waters, root soils can serve as a reservoir for antimicrobial resistant bacteria. The primary population of antimicrobial resistant bacteria in agroecosystems will be bacteria that are non-pathogenic but provide a potential for transmission of antimicrobial resistance mechanisms to pathogenic bacteria. Surprisingly, our study showed that leafy crops had higher levels of antimicrobial resistant bacteria than a bulb crop (onions). However, root soil bacteria can serve as a reservoir of antimicrobial resistant populations. Our study fills a gap in knowledge on antimicrobial resistance of plant surface bacteria, particularly in crops. We have identified antimicrobial resistant members on crop surfaces and their potential to degrade antimicrobials, the main stressor driving antimicrobial resistance development. We have also trained underrepresented (Hispanic, female, and/or first-generation) undergraduate and graduate students in field sampling, chemical analyses, microbial analyses, and statistical analyses that increase their competitiveness for graduate programs and careers in agricultural sciences.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Tarver-Ramos, D., A. Elizaldi, F. Montaner, S. Martinez, D. Warrick Jalomo, N. Zapata, A. Ortiz, and M.O. Mendez. 2023. Identification of triclosan-degrading spinach phyllosphere bacteria. Lamar Bruni-Vergara Research Conference, Laredo, TX. Oct.26. *First Place in STEM Graduate Students.
• Type: Conference Papers and Presentations Status: Submitted Year Published: 2023 Citation: Montaner, F., D. Hernandez, D. Tarver Ramos, R. Gonzalez, A. Elizaldi, and M.O. Mendez. 2023. Exploring the onset of triclosan-induced resistance and its potential links with antibiotic cross-resistance. Lamar Bruni-Vergara Research Conference, Laredo, TX. Oct.26. *First Place in STEM Undergraduate Students.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2024 Citation: " Montaner, F., D. Hernandez, D. Tarver Ramos, R. Gonzalez, A. Elizaldi, and M.O. Mendez. Investigating antibiotic cross-resistance resulting from chronic low-level triclosan exposure. American Society for Microbiology Annual Meeting, Atlanta, GA. June 13-17.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2024 Citation: Tarver-Ramos, D.E., F. Montaner, A. Elizaldi, F. Castillo, A. Addo-Mensah, A.M. Ibekwe, J. Anciso, and M.O. Mendez. Comparative analysis of antimicrobial resistance and degradation: lab-grown vs. field-grown irrigated crops. American S American Society for Microbiology Annual Meeting, Atlanta, GA. June 13-17.