Peter G. Hartel

Deer diet affects ribotype diversity of Escherichia coli for bacterial source tracking

Ribotyping is one of a number of genotypic methods for bacterial source tracking. This method requires a host origin database of one bacterial species be established in order to identify environmental isolates. Researchers establishing these databases have observed considerable ribotype diversity within a specific bacterial species. One source of this diversity may be diet. We determined the effect of diet on ribotype diversity for Escherichia coli in penned and wild deer (Odocoileus virginianus) in a 13-ha forested watershed. A total of 298 E. coli isolates was obtained, 100 from penned deer, 100 from wild deer, and 98 from the stream in the watershed to which all deer had access. The wild deer had significantly more ribotypes (35) than the penned deer (11 ribotypes, p = 0.05). This result suggests that diet affected ribotype diversity, and that a host origin database for bacterial source tracking should contain bacterial isolates from wild rather than from captive animals. Also, 42 of 98 (42.9%) environmental isolates matched penned and wild deer ribotypes. If bacterial source tracking determines that fecal contamination is predominantly from wildlife, then it may be unnecessary to monitor these watersheds because control over wildlife is difficult.

17β-Estradiol and testosterone in drainage and runoff from poultry litter applications to tilled and no-till crop land under irrigation.

Thirteen million [corrected] metric tons of poultry litter are produced annually by poultry producers in the U.S. Poultry litter contains the sex hormones estradiol and testosterone, endocrine disruptors that have been detected in surface waters. The objective of this study was to evaluate the potential impact of poultry litter applications on estradiol and testosterone concentrations in subsurface drainage and surface runoff in irrigated crop land under no-till and conventional-till management. We conducted an irrigation study in fall of 2001 and spring of 2002. Four treatments, no-till plus poultry litter, conventional-till plus poultry litter, no-till plus conventional fertilizer, and conventional-till plus conventional fertilizer, were evaluated. Flow-weighted concentration and load ha(-1) of the two hormones were measured in drainage and runoff. Soil concentrations of estradiol and testosterone were measured. Based on comparisons to the conventional fertilizer (and control) treatments, poultry litter did not add to the flow-weighted concentration or load ha(-1) of either estradiol or testosterone in subsurface drainage or surface runoff. Significant differences were, however, observed between tillage treatments: flow-weighted concentrations of estradiol were greater for no-till than conventional-till plots of the June irrigation; and runoff loads of both estradiol and testosterone were less from no-till than conventional-till plots for the November irrigation. Although the differences between no-till and conventional-tillage appeared to affect the hydrologic transport of both hormones, the differences appeared to have inconsequential environmental impact.

Evaluating an Environmental Literacy Requirement Chosen as a Method to Produce Environmentally Literate University Students.

Purpose – Few US universities choose an environmental literacy requirement (ELR) as a method to increase student environmental literacy. Even fewer universities have evaluated their ELRs. The paper aims to assess the ELR at the University of Georgia (UGA) in Fall 2005 and Spring 2006 semesters.Design/methodology/approach – A total of 7,268 of the 13,740 students (53 percent) currently taking an ELR course and the 86 of 100 faculty teaching ELR courses were surveyed with a voluntary questionnaire on their awareness, support, and satisfaction for the requirement. The assessment involved 58 courses with 120 sections.Findings – Although a majority of faculty (87 percent) was aware of the ELR, a majority of students (68 percent) was not. In spite of their awareness, most faculty (81 percent) did not know the specifics of the two ELR criteria. Both a majority of faculty (89 percent) and students (84 percent) supported the idea of an ELR. The ELR increased student knowledge (76 percent) and concern (65 percent) ...

Rhizobium meliloti inoculation of alfalfa selected for tolerance to acid, aluminium-rich soils

Alfalfa (Medicago sativa L.) growth and nodulation is reduced in acid soil because the plant and its bacterial symbiont Rhizobium meliloti cannot tolerate acid, Al-rich soil. A two-year field study was conducted to determine if the ‘Acid-Tolerant’ (AT) alfalfa germplasm could be combined with relatively acid-tolerant R. meliloti strains for the establishment of alfalfa in moderately acid, Al-rich soils. In the first year, inoculated ‘Acid-Sensitive’ (AS) and AT germplasms had significantly greater nodule numbers, nodule weight, and acetylene reduction values than the uninoculated controls in an acid soil (pH 5.0; Al ⩾ 0.25 cmol(+) kg−1). These differences were not observed in the second year because of plot cross contamination. In the first year no significant differences (P < 0.05) in plant top weights were observed within the unlimed treatments; however, in the second year the inoculated AT germplasm had greater plant top weights than the inoculated AS germplasm. The reason for the significant rhizobia X germplasm interaction in the second year was probably a result of heavy rainfall, reducing soil fertility. In the second year plant top weights of the inoculated AT and AS germplasms in unlimed soil were 71 and 16% of the inoculated plant top weights in limed soil, respectively. Nodule occupancy of the AT and AS germplasms in limed and unlimed soil by the introduced R. meliloti strains ranged from 88 to 99%. The results show the importance of combining an acid- and aluminium-tolerant alfalfa germplasm with acid-tolerant R. meliloti where liming is not practical or economically feasible.

Improving fluorometry as a source tracking method to detect human fecal contamination

In a continuing effort to develop inexpensive source tracking methods to detect human fecal contamination in environmental waters, targeted sampling was combined with fluorometry. Targeted sampling works by identifying hot spots of fecal contamination through multiple samplings over ever-decreasing distances. Fluorometry identifies human fecal contamination by detecting optical brighteners, primarily from laundry detergents. Because organic matter fluoresces and interferes with fluorometry, two locations were chosen for sampling: waters relatively low in organic matter at Mayagüez Bay, Puerto Rico, and waters relatively high in organic matter at St. Simons Island, Georgia. In Puerto Rico, targeted sampling and fluorometry quickly and easily identified two hot spots of human fecal contamination in the Yagüez River, which flows through the city of Mayagüez. Another source tracking method, detection of theesp gene, confirmed their human origin. On St. Simous Island, targeted sampling and fiuorometry identified two hot spots of potential human fecal contamination. Detection of theesp gene confirmed the human origin of one site but not the other, most likely because background organic matter fluorescence interfered with fhiorometry. A separate experiment showed that adding a 436-um emission filter to the fluorometer reduced this background fluorescence by > 50%. With the 436-nm Filter in place, another sampling was conducted on St. Simons Island, and the second hot spot was identified as fecal contamination from birds. As long as the fluorometer was equipped with a 436-nm filter and organic matter concentrations were considered, targeted sampling combined with fluorometry was a relatively inexpensive method for identifying human fecal contamination in water.

Effects of potential plant CS2 emissions on bacterial growth in the rhizosphere

Abstract Carbon disulfide (CS2) is a volatile, flammable, foul-smelling liquid with bacteriostatic, fungicidal, nematicidal and insecticidal properties. Some plants emit CS2. The present study was designed to determine if CS2 emissions from Mimosa pudica could inhibit the rhizosphere growth of six different bacterial species. Albizia julibrissin, a plant that does not emit CS2 and is closely related to M. pudica, was used as a negative control. Two pseudomonads, streptomycetes and rhizobia were each inoculated at a concentration of 105 colony-forming units (CFU) plant−1 into assemblies with and without a gnotobiotically grown M. pudica or A. julibrissin plant. Roots of M. pudica and A. julibrissin had a variable effect on bacterial growth. Neither plant inhibited pseudomonad nor rhizobial growth on the rhizoplane or in the rhizosphere, but both plants inhibited streptomycete growth on the rhizoplane and in the rhizosphere. However, the inhibition of streptomycete growth was temporary and after 7 days, little difference in streptomycete numbers was observed between assemblies with a plant and assemblies without a plant but with an added carbon source. Similar results were observed in a competition study between a rhizobium and a streptomycete on the rhizoplane and in the rhizosphere of M. pudica except the streptomycete counts did not recover to the same extent after 7 days. In CS2 studies, the growth of all six bacterial species was inhibited by 155 ng CS2 ml−1, and with two exceptions, to a lesser extent by 1.9 ng CS2 ml−1. It is unlikely that CS2 inhibited streptomycete growth because the streptomycetes were inhibited by A. julibrissin (which does not emit CS2), and little relationship was observed between the inhibition of streptomycete growth in assemblies with M. pudica plants and in assemblies with CS2. It is likely that other compounds on the rhizoplane and in the rhizosphere of M. pudica and A. julibrissin are responsible for the inhibition of streptomycete growth.

Effect of Xanthobacter, isolated and characterized from rice roots, on growth of wetland rice

With an autotrophic, N-free medium, Xanthobacter populations were isolated from the roots of wetland rice grown under field conditions. Xanthobacter populations ranged from 3.2×104 to 5.1×105 colony-forming units (cfu) g-1 of root and averaged 47-fold higher on the root or rhizoplane than in the neighbouring nonrhizosphere. Characterization studies indicated dissimilarities in carbon utilization and motility among the isolated Xanthobacter strains and other recognized Xanthobacter species. Under gnotobiotic conditions, the population of one isolate, Xanthobacter sp. JW-KR1, increased from 105 to 107 cfu plant-1 1 d after inoculation when a rice plant was present, but declined to numbers below the limit of detection (<104 cfu assembly-1) after 3 d in the absence of a plant. Scanning electron microscopy revealed Xanthobacter as pleomorphic forms on the rhizoplane. To assess the effect of Xanthobacter on plant growth, rice plants were grown under greenhouse conditions in plant assemblies containing sand and half-strength Hoaglands nutrient solution with and without nitrogen. Plants were either inoculated with 105 cfu Xanthobacter g-1 of sand or left uninoculated. After 40 d, plants without nitrogen showed no significant differences in top or root dry weight, plant height, root length, or number of tillers or leaves, whether the plants were inoculated or uninoculated. However, when nitrogen was added, inoculated plants had a significantly larger top dry weight (15%) and number of leaves (19%) than uninoculated plants. Under conditions of added and no added nitrogen, acetylene reduction assays showed Xanthobacter sp. JW-KR1 produced <0.1 (below detection limit) and 7 nmol C2H4 plant-1 h-1, respectively. Under the conditions studied, the results suggest that both Xanthobacter and wetland rice derive some benefits from their association.

Growth of genetically-engineered Pseudomonas aeruginosa and Pseudomonas putida in soil and rhizosphere

The effect of the addition of a recombinant plasmid containing the pglA gene encoding an alpha-1,4-endopolygalacturonase from Pseudomonas solanacearum on the growth of Pseudomonas aeruginosa and Pseudomonas putida in soil and rhizosphere was determined. Despite a high level of polygalacturonase production by genetically engineered P. putida and P. aeruginosa, the results suggest that polygalacturonase production had little effect on the growth of these strains in soil or rhizosphere.

Production of carbon disulfide (CS2) from L-djenkolic acid in the roots of Mimosa pudica L.

CS2 is a volatile liquid with bacteriostatic, fungicidal, nematicidal and insecticidal properties. The roots of some plants, particularly those in the subfamily Mimosoideae, produce CS2. These plants may have an agronomic use in crop rotations or intercropping because root-produced CS2 may act as a deterrent to soil pathogens. The biochemical pathway leading to the production of CS2 from mimosoid roots is unclear. Presumably, S-alkyl cysteine lyases present in mimosoid seedlings hydrolyze L-djenkolic acid, a unique, non-protein, sulfur-containing amino acid, to pyruvate, ammonia and methylene dithiol. Because methylene dithiol has never been detected from mimosoid roots, we hypothesized that CS2 is produced instead. Mimosa pudica, a species which produces CS2 in its roots, was used as a model plant. To eliminate CS2 production from microbial sources, all plants were grown gnotobiotically. S-alkyl cysteine lyase activity was confirmed in M. pudica when PbS formed on injured roots treated with L-cysteine and lead acetate. When injured roots were wetted, CS2 production increased significantly compared to non-wetted roots. When L-djenkolic was applied to injured roots, CS2 production increased significantly compared to controls. Both thin-layer paper chromatography and high performance liquid chromatography showed the presence of L-djenkolic acid in root tissues of M. pudica. These findings suggest CS2 production in roots of M. pudica occurs via the hydrolysis of L-djenkolic acid by S-alkyl cysteine lyase.

Factors affecting production of COS and CS2 in Leucaena and Mimosa species

Carbon disulfide (CS2) and carbonyl sulfide (COS) are colorless, foul-smelling, volatile sulfur compounds with biocidal properties. Some plants produce CS2 or COS or both. When used as an intercrop or forecrop, these plants may have agronomic potential in protecting other plants. Most of the factors which affect production of these plant-generated organic sulfides are unknown. We determined the effects of sulfate concentration, plant age, nitrogen fixation, drought stress, root injury (through cutting), and undisturbed growth on COS production in Leucaena retusa or Leucaena leucocephala and the effect of some of these factors on CS2 production in Mimosa pudica. In addition, we determined if organic sulfides were produced in all Leucaena species. When L. retusa and M. pudica seedlings were grown in a plant nutrient medium with different sulfate concentrations (50 to 450 mg SL-1), COS or CS2 from crushed roots generally increased with increasing sulfate concentration. COS production was highest (≤74 ng mg-1 dry root) for young L. retusa seedlings and declined to low amounts (<5 ng mg-1 dry root) for older seedlings. Nitrogen fixation reduced the amounts of COS or CS2 produced in L. leucocephala and M. pudica. Under conditions of undisturbed growth, root cutting, or drought stress, no COS production was detected in 4-to 8-weeks-old L. retusa plants. COS or CS2 or both was obtained from crushed roots or shoots of all 13 known Leucaena species.