William T. Frankenberger

Plant growth-regulating substances in the rhizosphere: microbial production and functions

Publisher Summary The chapter presents a discussion on plant growth-regulating (PGR) substances in the rhizosphere, with emphasis on microbial production and functions. The chapter discusses the rhizosphere as a site of plant-microbe interactions; plant growth-regulating substances and their sources; biochemistry of microbial production of PGRs; production of PGRs by rhizosphere microorganisms; metabolism of PGRs in soil; and ecological significance of PGRs produced in the rhizosphere. The chapter provides a better understanding of the mechanisms of actions of microbially derived PGRs and their interactions with plants. Moreover, development of hormone-deficient plant mutants can provide opportunities to clearly define the role of microbially produced PGRs in plan-microbe interactions. An understanding of these aspects can aid in the utilization of microbial PGRs for the betterment and benefit of sustainable agriculture.

Enhanced degradation of polycyclic aromatic hydrocarbons in soil treated with an advanced oxidative process — Fenton's Reagent

Abstract Polycyclic aromatic hydrocarbons (PAHs) are resistant to present bioremediation practices. This study was conducted to determine if pretreatment with an advanced oxidative process (Fentons reagent; H2O2 + FeSO4) could enhance PAH degradation in soil that had previously been exposed to crude oil. PAHs were more readily degraded after incubation for 56 d when treated with H2O2 (2.8 M) plus FeSO4 (0.1 M) compared with degradation rates without the addition of Fentons reagent during the same time period. Overall, the use of Fentons reagent as a pretreatment promoted the mineralization of the nine spiked PAHs by an average of 87%. Degradation of native PAH parent compounds (180 to 840 μg of PAH per kilogram of soil) in the same soil incubated with Fentons reagent for 7 d was enhanced 44 and 39% for phenanthrene and fluoranthene, respectively, but only 5 and 1% for pyrene and chrysene, respectively, when compared with no addition of Fentons reagent. Pretreatment of the soil with a surfactant (10 m...

Long-term depletion of selenium from Kesterson dewatered sediments

Abstract Microbial methylation of selenium (Se) to volatile (CH3)2Se may contribute to a considerable loss of the Se inventory from seleniferous soils over time. A field experiment was carried out to assess microbial volatilization of Se as a bioremediation approach to dissipate Se. Field plots of size of 3.7 × 3.7 m2 were established at the Kesterson Reservoir, California. To enhance microbial activity, the plots were treated with different C and protein amendments and were periodically tilled and irrigated. Over a period of 100 months, 68–88% of the total amount of Se dissipated from the topsoil (0–15 cm). The pattern of Se depletion in soil was not correlated with rainfall events nor with temperature. As most of the rainfall occurred during the cold winter months, it is likely that leaching dominated the Se depletion in winter whereas volatilization prevailed in summer. The highest amount of Se depletion occurred with the amendment of the protein casein. However, there was no statistically significant difference in Se removal from the different treatments compared to the case where there was no C or protein amendment. Tillage and irrigation presumably prevailed over the effects of the amendments. A two-compartment model was superior to a one-compartment model for describing the long-term kinetics of Se depletion in soil. The rate of Se dissipation was initially faster than at later times. This indicates that the rate-limiting mechanisms have changed during the time of the study.

Molecular analysis of a perchlorate reductase from a perchlorate-respiring bacterium Perc1ace

Perchlorate (ClO4-) is a major ground water pollutant of public health concern. ClO4- reductase is the key enzyme in the pathway of ClO4- breakdown. ClO4- reductase from cell-free extracts of the ClO4- -respiring bacterium perc lace was purified 10-fold by ion-exchange and molecular exclusion fast protein liquid chromatography (FPLC). The ClO4- reductase catalyzed the reduction of ClO4- at a Vmax and Km of 4.8 U mg protein(-1) and 34.5 microM, respectively. ClO4- reduction was achieved in the temperature range of 20 to 40 degrees C and with optimum activity at 25 degrees C to 30 degrees C and pH 7.5 to 8.0. Molecular masses of two subunits of ClO4- reductase were determined by SDS-PAGE to be 35 kDa and 75 kDa. MALDI-TOF/MS analysis of a trypsin digest of the 35 kDa subunit, revealed several tryptic peptides. Amino acid sequences of 22 tryptic peptides of the 35 kDa ClO4- reductase subunit were obtained by electrospray mass spectrometry. GenBank protein Blast analysis of the amino acid sequences revealed relevant similarity to reductases, dehydrogenases and heme proteins. Data obtained are useful towards the identification of the overall genetic determinants of ClO4- reduction and specific in situ detection of ClO4- as well as NO3-reducing bacteria in ground water.

Speciation of selenium in plant water extracts by ion exchange chromatography-hydride generation atomic absorption spectrometry

Determination of selenium (Se) speciation in plants is important in studying the bioavailability and toxicity of Se in Se-contaminated soil/sediment. In this study, we used an anion exchange resin (Dowex 1-10X) to separate Se into non-amino acid organic Se, Se-amino acids, selenite (Se [IV]) and selenate (Se [VI]) in a plant (Stanleya pinnata) extract. The hydride generation atomic absorption spectrometry (HGAAS) was used to determine concentrations of these Se compounds in plant extracts. Results showed that Se compounds can be quantitatively separated by the resin column. Recovery of five spiked standard Se compounds (trimethylselenonium ion (TMSe+), dimethylselenoxide (DMSeO), selenomethionine (Semet), Se [IV] and Se [VII]) in the plant extract ranged from 92.9 to 103%. Water extractable Se accounted for 60.4-72.6% of the total Se in the plant. Among the soluble Se compounds in the plant extract, Se-amino acids were 73-85.5%, Se [VI] ranged from 7.5 to 19.5% and non-amino acid organic Se was less than 7%. Se [IV] in most samples was below the detection limit (1 microg/g). This study showed that considerable amounts of the accumulated Se [VI] in the plant was metabolized to Se-amino acids during growth of the plant.

Biodegradation of methyl tertiary butyl ether (MTBE) by a bacterial enrichment consortia and its monoculture isolates

Methyl tertiary butyl ether (MTBE), an important gasoline additive, is a recalcitrant compound posing serious environmental health problems. In this study, MTBE-degrading bacteria were enriched from five environmental samples. Enrichments from Stewart Lake sediments and an MTBE contaminated soil displayed the highest rate of MTBE removal; 29.6 and 27.8% respectively, in 28 days. A total of 12 bacterial monocultures isolated from enrichment cultures were screened for MTBE degradation in liquid cultures. In a nutrient-limited medium containing MTBE as the sole source of carbon and energy, the highest rate of MTBE elimination was achieved with IsoSL1, which degraded 30.6 and 50.2% in 14 and 28 days, respectively. In a nutrient-rich medium containing ethanol and yeast extract, the bacterium (Iso2A) substantially removed MTBE (20.3 and 28.1% removal in 14 and 28 days, respectively). Based upon analysis of the 16s rRNA gene sequence and data base comparison, IsoSL1 and Iso2A were identified as a Streptomyces sp. and Sphingomonas sp., respectively. The Streptomyces sp. is a new genera of bacteria degrading MTBE and could be useful for MTBE bioremediation.

Measurement of selenite in sediment extracts by using hydride generation atomic absorption spectrometry

Abstract Measurement of selenite (Se [IV]) is the most important step to determine selenium (Se) speciation in water, and in soil–sediment extracts by using hydride generation atomic absorption spectrometry (HGAAS). Determination of Se [IV] commonly involves sample acidification and application of XAD resins for removal of sample organic interference. The effects of sample acidification and application of XAD resins on determination of Se [IV] in sediment samples have not been evaluated in detail. In this study, we evaluated these effects by examining Se concentrations in six different extracts (0.01 M HCl, de-ionized water, 0.1 M NaOH, 0.1 M NaH 2 PO 4 , 0.1 M Na 2 HPO 4 , and 0.1 M Na 2 HPO 4 +0.1 M NaOH) from three seleniferous sediments. Results showed that the amount of extracted Se [IV] was pH-dependent, and was 3–15 times higher in a 0.1 M NaOH extract than in 0.01 M HCl and de-ionized water extracts. Phosphate can replace Se [IV] for adsorption sites, thus resulting in an increase in extracted Se [IV]. Acidification of a humic substance (HS)-containing sample caused a significant loss of free Se [IV], especially in 6 N HCl, due to a complexion of HS-Se [IV]. Hydrophobic and hydrophilic characteristics of HS-Se [IV] were found in these sediment extracts, resulting in the accumulation of HS-Se [IV] on XAD resins when the pH 2 extracts were allowed to pass through XAD-7 columns and a significant loss of spiked Se [IV] in the pH 2 extract elutes. These results suggest that determination of Se [IV] in a HS-containing sample by using HGAAS must be evaluated with caution during acidification and application of XAD resins for removal of sample organic interferences.

Factors affecting the volatilization of dimethylselenide by Enterobacter cloacae SLD1a-1

Abstract The facultative anaerobic bacterium Enterobacter cloacae SLD1a-1 (ATCC 700258), capable of reducing selenate (SeO 4 2− ) and selenite (SeO 3 2− ) to elemental selenium (Se 0 ), was found to volatilize dimethylselenide (DMSe) in the presence of SeO 3 2− . The effect of temperature, pH and electrical conductivity (EC) on the ability of E. cloacae SLD1a-1 to methylate selenium (Se) were investigated in a liquid medium of tryptic soy broth containing 10 μM SeO 3 2− . Optimum Se volatilization occurred at a pH, temperature and EC of 6.5, 35°C and 11 dS m −1 , respectively. Volatilization of Se was also found to be concentration dependent, as E. cloacae SLD1a-1 produced 11.3 times more DMSe at a SeO 3 2− concentration of 10 μM than at 1.0 μM. By determining the optimum environmental conditions which stimulate Se volatilization, it may be possible to design a strategy to remediate seleniferous water.

Determination of Selenium Fractionation and Speciation in Wetland Sediments by Parallel extraction

Selenium (Se) fractionation and speciation of wetland sediments is very important in understanding the bioavailability and bioaccumulation of Se in wetland systems. Sequential extraction of Se in sediments is often used in fractionation and speciation studies. Because of the difficulty to accurately determine Se fractions and species in sediment samples containing relatively low concentrations, high light materials and high clay texture by using a sequential extraction procedure, an alternative method was developed by parallel extraction of Se in sediments with deionized (DI) water, NaOH, Na 2 SO 3 and H 2 O 2 -HCl, and determination of Se species by differences. Results showed that adsorbed Se from spiked Se in sediments during DI water extraction can be quantitatively recovered with 0.1 M NaOH and 1 M Na 2 SO 3 . Mass recovery of Se from sediments between the parallel extraction and a sequential extraction was very close, indicating that sequential extraction can be replaced by parallel extraction in Se fractionation and speciation studies. Selenite [Se(IV)], elemental Se [Se(0)], organic material-related Se (OM-Se) and organic Se were the major forms of Se, respectively accounting for 31.2, 24.4, 25.2, and 11.6% of the total Se in Tulare Lake Drainage District wetland and Stewart Lake sediments. Reduction of selenate [Se(VI)] to reduced Se [Se(IV) + Se(0)] and Se uptake by wetland organisms with incorporation of these organisms into the sediment are two major immobilization processes that accumulate Se in wetland sediments.

Determination of aminosaccharides by high-performance anion-exchange chromatography with pulsed amperometric detection

High-performance anion-exchange chromatography (HPAC) was used for the determination of aminosaccharides in microbial polymers, chitin, animal waste, sewage sludge, plant residues and soil. The aminosaccharides, galactosamine, mannosamine and glucosamine were separated on a strong anion-exchange column with 1OmM sodium hydroxide as the eluent and determined by pulsed amperometric detection (PAD). The HPAC-PAD methodology was compared with high-performance liquid chromatography (HPLC) with refractive index detection (RI) in terms of selectivity and sensitivity for aminosaccharides. The results indicate that HPAC-PAD required less sample preparation, and was more precise and nearly two orders of magnitude more sensitive than HPLC-RI. HPAC-PAD was not subject to matrix interferences and was highly selective for aminosaccharides. More than 3% of the total nitrogen in alfalfa, and 20% of that in straw, was found to be present as aminosaccharides.