Biological Remediation of Groundwater Containing Both Nitrate and Atrazine

Due to its high usage, mobility, and recalcitrant nature, atrazine is a common groundwater contaminant. Moreover, groundwaters that are contaminated with atrazine often contain nitrate as well. Nitrate interferes with the biological degradation of atrazine and makes it more difficult to use in situ biological methods to remediate atrazine contaminated groundwater. To solve this problem we used two reactors in sequence as models of in situ biobarriers; the first was a vegetable-oil-based denitrifying biobarrier and the second an aerobic reactor that oxygenated the denitrifying reactor’s effluent. The reactors were inoculated with an atrazine-degrading microbial consortium and supplied with water containing 5 mg l⁻¹ nitrate–N and 3 mg l⁻¹ atrazine. Our hypothesis was that the denitrifying barrier would remove nitrate from the flowing water and that the downstream reaction would remove atrazine. Our hypothesis proved correct; the two reactor system removed 99.9% of the atrazine during the final 30 weeks of the study. The denitrifying barrier removed ~98% of the nitrate and ~30% of the atrazine while the aerobic reactor removed ~70% of the initial atrazine. The system continued to work when the amount of nitrate–N in the influent water was increased to 50 mg l⁻¹. A mercury poisoning study blocked the degradation of atrazine indicating that biological processes were involved. An in situ denitrifying barrier coupled with an air injection system or other oxygenation process might be used to remove both nitrate and atrazine from contaminated groundwater or to protect groundwater from an atrazine spill.     

Rapid atrazine mineralisation in soil slurry and moist soil by inoculation of an atrazine-degrading Pseudomonas sp. strain

The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria added to the soil. In soil slurry, 6 mg atrazine kg soil⁻¹ was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil⁻¹ and within 5 days when 0.003 g kg soil⁻¹ was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil⁻¹ was eliminated within 2 days by 1 g biomass kg soil⁻¹ and within 25 days when 0.01 g biomass kg soil⁻¹ was used. In unsaturated soil, about 60% [U-ring-¹⁴C]atrazine was converted to ¹⁴CO₂ within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were still active after a starvation period of 240 days: 15 mg newly added atrazine kg soil⁻¹ was eliminated within 5 days. Received: 31 October 1997 / Received revision: 16 January 1998 / Accepted: 18 January 1998     

Atrazine degradation by a simple consortium of <Emphasis Type="Italic">Klebsiella</Emphasis> sp. A1 and <Emphasis Type="Italic">Comamonas</Emphasis> sp. A2 in nitrogen enriched medium

A simple consortium consisted of two members of Klebsiella sp. A1 and Comamonas sp. A2 was isolated from the sewage of a pesticide mill in China. One member of Klebsiella sp. A1 is a novel strain that could use atrazine as the sole carbon and nitrogen source. The consortium showed high atrazine-mineralizing efficiency and about 83.3% of 5 g l⁻¹ atrazine could be mineralized after 24 h degradation. Contrary to many other reported microorganisms, the consortium was insensitive to some nitrogenous fertilizers commonly used, not only in presence of 200 mg l⁻¹ atrazine but also in 5 g l⁻¹ atrazine mediums. After 24 h incubation, 200 mg l⁻¹ atrazine was completely mineralized despite of the presence of urea, (NH₄)₂CO₃ and (NH₄)₂HPO₄ in the medium. Very minor influence was observed when NH₄Cl was added as additional nitrogen source. Advantages of the simple consortium, high mineralizing efficiency and insensitivity to most of exogenous nitrogen sources, all suggested application potential of the consortium for the bioremediation of atrazine-contaminated soils and waters.     

Bioreduction of Cu(II) by Cell-Free Copper Reductase from a Copper Resistant <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. NA

Environmental copper contamination is a serious human health problem. Copper reductase is produced by microorganisms to facilitate copper uptake by ATPases into the cells increasing copper biosorption. This study assessed the reduction of Cu(II) by cell-free extracts of a highly copper-resistant bacterium, Pseudomonas sp. strain NA, isolated from vineyard soil contaminated with copper. Both intact cells and cell-free extract of Pseudomonas sp. strain NA displayed substantial reduction of Cu(II). Intact cells reduced more then 80 mg L⁻¹ of Cu(II) from medium amended with 200 mg L⁻¹ of copper after 24 h of incubation. Cell-free extract of the isolate reduced more than 65% of the Cu(II) at initial copper concentration of 200 mg L⁻¹ after 24 h. Soluble protein production was high at 72 h of incubation at 100 mg L⁻¹ of copper, with more then 60 μg L⁻¹ of total soluble protein in cell-free extract recorded. Cu(II) reduction by isolate NA was increased when copper concentration increased for both intact cells and cell-free extract. Results indicate that Pseudomonas sp. strain NA produces copper reductase enzyme as the key mechanism of copper biotransformation.     

4-Chlorophenol degradation by a bacterial consortium: development of a granular activated carbon biofilm reactor

A bacterial consortium that can degrade chloro- and nitrophenols has been isolated from the rhizosphere of Phragmitis communis. Degradation of 4-chlorophenol (4-CP) by a consortium attached to granular activated carbon (GAC) in a biofilm reactor was evaluated during both open and closed modes of operation. During the operation of the biofilm reactor, 4-CP was not detected in the column effluent, being either adsorbed to the GAC or biodegraded by the consortium. When 4-CP at 100 mg l⁻¹ was fed to the column in open mode operation (20 mg g⁻¹ GAC total supply), up to 27% was immediately available for biodegradation, the rest being adsorbed to the GAC. Biodegradation continued after the system was returned to closed mode operation, indicating that GAC bound 4-CP became available to the consortium. Biofilm batch cultures supplied with 10–216 mg 4-CP g⁻¹ GAC suggested that a residual fraction of GAC-bound 4-CP was biologically unavailable. The consortium was able to metabolise 4-CP after perturbations by the addition of chromium (Cr VI) at 1–5 mg l⁻¹ and nitrate at concentrations up to 400 mg l⁻¹. The development of the biofilm structure was analysed by scanning electron microscopy and confocal laser scanning microscopy (CLSM) techniques. CLSM revealed a heterogeneous structure with a network of channels throughout the biofilm, partially occupied by microbial exopolymer structures. Received: 17 March 1999 / Received revision: 27 May 1999 / Accepted: 28 May 1999     

Atrazine degradation in saline wastewater by Pseudomonas sp strain ADP

Wastewater from atrazine manufacturing plants contains large amounts of residual atrazine and atrazine synthesis products, which must be removed before disposal. One of the obstacles to biological treatment of these wastewaters is their high salt content, eg, up to 4% NaCl (w/v). To enable biological treatment, bacteria capable of atrazine mineralization must be adapted to high-salinity conditions. A recently isolated atrazine-degrading bacterium, Pseudomonas sp strain ADP, originally isolated from contaminated soils was adapted to biodegradation of atrazine at salt concentrations relevant to atrazine manufacturing wastewater. The adaptation mechanism was based on the ability of the bacterium to produce trehalose as its main osmolyte. Trehalose accumulation was confirmed by natural-abundance ¹H NMR spectral analysis. The bacterium synthesized trehalose de novo in the cells, but could not utilize trehalose added to the growth medium. Interestingly, the bacterium could not produce glycine betaine (a common compatible solute), but addition of 1 mM of glycine betaine to the medium induced salt tolerance. Osmoregulated Pseudomonas sp strain ADP, feeding on citrate decreased the concentration of atrazine in non-sterile authentic wastewater from 25 ppm to below 1 ppm in less than 2 days. The results of our study suggest that salt-adapted Pseudomonas sp strain ADP can be used for atrazine degradation in salt-containing wastewater. Received 26 August 1997/ Accepted in revised form 06 December 1997     

Metabolic ability and gene characteristics of Arthrobacter sp. strain DNS10, the sole atrazine-degrading strain in a consortium isolated from black soil

Strain DNS10 was the only member that could utilize atrazine as the sole nitrogen source for growth in an atrazine-degrading consortium which was isolated from black soil previously in our laboratory. It belongs to the genus Arthrobacter according to the sequence of 16S rRNA gene and is designated as Arthrobacter sp. DNS10. 16S rRNA gene phylogenetic analysis showed that strain DNS10 was located in a different evolutionary branch comparing with other Arthrobacter sp. atrazine-degrading strains. The degrading genes such as trzN, atzB and atzC harbored in strain DNS10 revealed high sequence similarity with those in Arthrobacter aurescens TC1 and Pseudomonas sp. ADP. These genes enabled the strain DNS10 to decompose atrazine to cyanuric acid. This was further proved by the results that the strain DNS10 (10⁸ CFU mL⁻¹) could degrade the whole atrazine (100 mg L⁻¹) in the medium within 24 h at 30 °C and there was 66.13 ± 2.11 mg L⁻¹ cyanuric acid accumulated at 24 h. These results imply that the strain DNS10 seems to be an excellent atrazine-degrading strain. Furthermore, this paper helps us in the better understanding of the strain evolution by comparing the metabolic ability and gene characteristics of strain DNS10 with other geographically distinct atrazine-degrading strains.     

Anaerobic biodegradation of pentachlorophenol in a contaminated soil inoculated with a methanogenic consortium or with Desulfitobacterium frappieri strain PCP-1

Anaerobic biodegradation of pentachlorophenol (PCP) in a contaminated soil from a wood-treating industrial site was studied in soil slurry microcosms inoculated with a PCP-degrading methanogenic consortium. When the microcosms containing 10%–40% (w/v) soil were inoculated with the consortium, more than 90% of the PCP was removed in less than 30 days at 29 °C. Less-chlorinated phenols, mainly 3-chlorophenol were slowly degraded and accumulated in the cultures. Addition of glucose and sodium formate to the microcosms was not necessary, suggesting that the organic compounds in the soil can sustain the dechlorinating activity. Inoculation of Desulfitobacterium frappieri strain PCP-1 along with a 3-chlorophenol-degrading consortium in the microcosms also resulted in the rapid dechlorination of PCP and the slow degradation of 3-chlorophenol. Competitive polymerase chain reaction experiments showed that PCP-1 was present at the same level throughout the 21-day biotreatment. D. frappieri, strain PCP-1, inoculated into the soil microcosms, was able to remove PCP from soil containing up to 200 mg PCP/kg soil. However, reinoculation of the strain was necessary to achieve more than 95% PCP removal with a concentration of 300 mg and 500 mg PCP/kg soil. These results demonstrate that D. frappieri strain PCP-1 can be used effectively to dechlorinate PCP to 3-chlorophenol in contaminated soils. Received: 14 November 1997 / Received revision: 29 January 1998 / Accepted: 24 February 1998     

Permissible Value for Vanadium in Allitic Udic Ferrisols Based on Physiological Responses of Green Chinese Cabbage and Soil Microbes

Greenhouse experiments were conducted to study the permissible value of vanadium (V) based on the growth and physiological responses of green Chinese cabbage (Brassica chinensis L.), and effects of V on microbial biomass carbon (MBC) and enzyme activities in allitic udic ferrisols were also studied. The results showed that biomass of cabbage grown on soil treated with 133 mg V kg⁻¹ significantly decreased by 25.1% compared with the control (P < 0.05). Vanadium concentrations in leaves and roots increased with increasing soil V concentration. Contents of vitamin C (Vc) increased by 10.3%, while that of soluble sugar in leaves significantly decreased by 54.0% when soil V concentration was 133 mg kg⁻¹, respectively. The uptake of essential nutrient elements by cabbage was disturbed when soil V concentration exceeded 253 mg kg⁻¹. Soil MBC was significantly stimulated by 15.5%, while dehydrogenase activity significantly decreased by 62.8% and urease activity slightly changed at treatment of 133 mg V kg⁻¹ as compared with the control, respectively. Therefore, the permissible value of V in allitic udic ferrisols is proposed as 130 mg kg⁻¹.     

Accelerated biodegradation of atrazine by a microbial consortium is possible in culture and soil

A mixed enrichment culture of microorganisms capable of accelerated mineralization of atrazine was isolated from soil treated with successive applications of the herbicide. Liquid cultures of this consortium, in the presence of simple carbon sources, mineralized 96% of the applied atrazine (0.56 mM) within 7 days. Atrazine mineralization in culture is initiated with the formation of the metabolite hydroxyatrazine. In soil treated with atrazine at a concentration of 0.14 mM (concentration is based on total soil mass), and then inoculated with the microbial consortium, the parent compound was completely transformed in 25 days. After 30 days of incubation, 60% of the applied atrazine was accounted for as¹⁴CO₂. As was found with the liquid cultures, hydroxyatrazine was the major metabolite. After 145 days, soil extractable hydroxyatrazine declined to zero and 86% of the applied atrazine was accounted for as¹⁴CO₂. No metabolites, other than hydroxyatrazine, were recovered from either the liquid culture or soil inoculated with the consortium. The use of the mixed microbial culture enhanced mineralization more than 20 fold as compared to uninoculated soil.     

A novel method for characterisation of microbial growth kinetics on volatile organic compounds

A novel method for the determination of microbial growth kinetics on hydrophobic volatile organic compounds (VOC) has been developed. A stirred tank reactor was operated as a fed-batch system to which the VOC was continuously fed via the gas phase, assuring a constant VOC concentration in the mineral medium. A flow of air was saturated with the VOC, and then mixed with a further flow of air, to obtain a predetermined VOC concentration. Thus, different VOC concentrations in the mineral medium could be obtained by altering the VOC concentration in the feed gas. The growth kinetics of Xanthobacter autotrophicus GJ10 on 1,2-dichloroethane (DCE) and of Pseudomonas sp. strain JS150 on MonoChloroBenzene (MCB) were assessed using this method. The growth of strain JS150 was strongly inhibited at MCB concentrations higher than 160 mg l⁻¹, and the results were fitted using a piecewise function. The growth kinetics of strain GJ10 were described by the Luong model where maximum growth rate μ_max = 0.12 h⁻¹, substrate saturation constant K _S = 7.8 mg l⁻¹, and maximum substrate concentration S _m (above which growth is completely inhibited) = 1080 mg l⁻¹. Varying nitrogen and oxygen flows enabled the effect of oxygen concentration on the growth kinetics of Pseudomonas JS150 to be determined. Received: 30 November 1998 / Received revision: 19 March 1999 / Accepted: 20 March 1999     

Bioremediation of diesel-oil-contaminated alpine soils at low temperatures

Bioremediation of two diesel-oil-contaminated alpine subsoils, differing in soil type and bedrock, was investigated in laboratory experiments at 10 °C after supplementation with an inorganic fertilizer. Initial diesel oil contamination of 4000 mg kg⁻¹ soil dry matter (dm) was reduced to 380–400 mg kg⁻¹ dm after 155 days of incubation. In both soils, about 30 % of the diesel oil contamination (1200 mg kg⁻¹ dm) was eliminated by abiotic processes. The residual decontamination (60 %–65 %) could be attributed to microbial degradation activities. In both soils, the addition of a cold-adapted diesel-oil-degrading inoculum enhanced biodegradation rates only slightly and temporarily. From C/N and N/P ratios (determined by measuring the contents of total hydrocarbons, NH₄ ⁺ N, NO₃ ⁻ N and PO₄ ³⁻ P) of soils␣it could be deduced that there was no nutrient deficiency during the whole incubation period. Soil biological activities (basal respiration and dehydrogenase activity) corresponded to the course of biodegradation activities in the soils. Received: 9 September 1996 / Accepted: 7 December 1996     

An elite protocol for accelerated quality-cloning in <Emphasis Type="Italic">Gerbera jamesonii</Emphasis> Bolus cv. Sciella

A novel, efficient, and simple protocol was developed on in vitro mass propagation and acclimatization of Gerbera jamesonii Bolus cv. Sciella, an ornamental plant with attractive flowers. Shoot tip was used as the primary explant for in vitro establishment in which Murashige and Skoog (MS) medium supplemented with a low level of NAA (0.5 mg l⁻¹) and BAP (1.5 mg l⁻¹) promoted earliest axillary bud initiation within 5 d in 91.6% of the inoculants. Five axillary buds were initiated from a single explant within 13 d after inoculation. A very high rate of shoot multiplication (14 shoots per inoculated axillary bud) and proliferation was achieved when MS medium was fortified with a relatively higher level of BAP (2 mg l⁻¹) and 60 mg l⁻¹ ADS within 27 d of multiple shoot culture. A maximum number of well-developed roots per plant was observed in MS medium with 0.5 mg l⁻¹ IAA in the next 26 d. In the easy low-cost acclimatization process of 20 d, a combination of sand, soil, cow urine, and tea leaves extract (1:1:1:1; v/v) ensured 95% survival rate. Sixty-one well-acclimatized plants were obtained from a single shoot tip within 86 d. The sustained multiple shoot culture for 15 mo paved the way toward the conservation of genetic resources as well as beneficial economics. The clonal fidelity study of micropropagated and sustained cultured clones using ISSR primers ensured the continuous supply of quality propagules retaining genetic uniformity. The in vitro-generated plants performed better over conventionally propagated plants in the field condition.     

Comparative analysis of the digestive efficiency and nitrogen and energy requirements of the phyllostomid fruit-bat (Artibeus jamaicensis) and the pteropodid fruit-bat (Rousettus aegyptiacus)

Nitrogen (N) and energy (E) requirements of the phyllostomid fruit bat, Artibeus jamaicensis, and the pteropodid fruit bat Rousettus aegyptiacus, were measured in adults that were fed on four experimental diets. Mean daily food intake by A. jamaicensis and R. aegyptiacus ranged from 1.1–1.6 times body mass and 0.8–1.0 times body mass, respectively. Dry matter digestibility and metabolizable E coefficient were high (81.1% and 82.4%, respectively) for A. jamaicensis and (77.5% and 78.0%, respectively) for R. aegyptiacus. Across the four diets, bats maintained constant body mass with mean metabolizable E intakes ranging from 1357.3 kJ · kg^−0.75 · day⁻¹ to 1767.3 kJ · kg^−0.75 · day⁻¹ for A. jamaicensis and 1282.6–1545.2 kJ · kg^−0.75 · day⁻¹ for R. aegyptiacus. Maintenance E costs were high, in the order of 3.6–5.4 times the basal metabolic rate (BMR). It is unlikely that the E intakes that we observed represent a true measure of maintenance E requirements. All evidence seems to indicate that fruit bats are E maximizers, ingesting more E than required and regulating storage by adjusting metabolic output. We suggest that true maintenance E requirements are substantially lower than what we observed. If it follows the eutherian norm of two times the BMR, fruit bats must necessarily over-ingest E on low-N fruit diet. Dietary E content did affect N metabolism of A. jamaicensis. On respective low- and high-E diets, metabolic fecal N were 0.492 mg N · g⁻¹ and 0.756 mg N · g⁻¹ dry matter intake and endogenous urinary N losses were 163.31 mg N · kg^−0.75 · day⁻¹ and 71.54 mg N · kg^−0.75 · day⁻¹. A. jamaicensis required 332.3 mg · kg^−0.75 · day⁻¹ and 885.3 mg · kg^−0.75 · day⁻¹ of total N on high- and low-E diets, respectively, and 213.7 mg · kg^−0.75 · day⁻¹ of truly digestible N to achieve N balance. True N digestibilities were low (29% and 49%) for low- and high-E diets, respectively. For R. aegyptiacus, metabolic fecal N and endogenous urinary N losses were 1.27 mg N · g⁻¹ dry matter intake and 96.0 mg N · kg^−0.75 · day⁻¹, respectively, and bats required 529.8 mg · kg^−0.75 · day⁻¹ (total N) or 284.0 mg · kg^−0.75 · day⁻¹ (truly digestible N). True N digestibility was relatively low (50%). Based on direct comparison, we found no evidence that R. aegyptiacus exhibits a greater degree of specialization in digestive function and N retention than A. jamaicensis. When combined with results from previous studies, our results indicate that all fruit bats appear to be specialized in their ability to retain N when faced with low N diet. Accepted: 24 November 1998     

Low-temperature bioremediation of a waste water contaminated with anionic surfactants and fuel oil

We conducted a laboratory study at 10 °C on the biological decontamination of the waste water from a garage and car-wash that was contaminated with anionic surfactants (57 mg l⁻¹) and fuel oil (184 mg hydrocarbons l⁻¹). The indigenous microorganisms degraded both contaminants efficiently after biostimu- lation by an inorganic nutrient supply. After 7 days at 10 °C, the residual contaminations were 11 mg anionic surfactants l⁻¹ and 26 mg hydrocarbons l⁻¹. After 35 days, only the anionic surfactants had been further reduced to 3 mg l⁻¹. Bioaugmentation of the unfertilized waste water with a cold-adapted inoculum, able to degrade both hydrocarbons (diesel oil) and anionic surfactants (sodium dodecyl sulphate), resulted in a significant increase of the hydrocarbon biodegradation during the first 3 days of decontamination, whereas biodegradation of anionic surfactants was inhibited during the first 21 days following inoculation. Bioaugmentation of the nutrient-amended waste water was without any effect. Received: 14 November 1997 / Accepted: 29 November 1997     

Effects of Corn Steep Liquor on Growth Rate and Pyrene Degradation by Pseudomonas strains

The growth rates and pyrene degradation rates of Pseudomonas sp. LP1 and Pseudomonas aeruginosa LP5 were increased in corn steep liquor (CSL) supplemented. On pyrene alone the highest specific growth rate of LP1 was 0.018 h⁻¹, while on CSL-supplemented pyrene MSM, the value was 0.026 h⁻1. For LP5 the highest growth rate on CSL-supplemented pyrene-MSM was 0.034 h⁻¹. Conversely, on pyrene alone the highest rate was 0.024 h⁻¹. CSL led to marked reduction in residual pyrene. In the case of Pseudomonas sp. LP1 values of residual pyrene were 58.54 and 45.47%, respectively, for the unsupplemented and supplemented broth cultures, showing a difference of 13.09%. For LP5 the corresponding values were 64.01 and 26.96%, respectively, showing a difference of 37.05%. The rate of pyrene utilization by LP1 were 0.08 and 0.11 mg l⁻¹ h⁻¹ on unsupplemented and supplemented media, respectively. The corresponding values for LP5 were 0.07 and 0.015 mg l⁻¹ h⁻¹, respectively. These results suggest that CSL, a cheap and readily available waste product, could be very useful in the bioremediation of environments contaminated with pyrene.     

Agrobacterium-mediated genetic transformation of California poppy, Eschscholzia californica Cham., via somatic embryogenesis

 An efficient Agrobacterium-mediated protocol for the stable genetic transformation of Eschscholzia californica Cham. (California poppy) via somatic embryogenesis is reported. Excised cotyledons were co-cultivated with A. tumefaciens strain GV3101 carrying the pBI121 binary vector. Except for the co-cultivation medium, all formulations included 50 mg l⁻¹ paromomycin as the selective agent and 200 mg l⁻¹ timentin to eliminate the Agrobacterium. Four to five weeks after infection, paromomycin-resistant calli grew on 80% of explants in the presence of 2.0 mg l⁻¹ 1-naphthaleneacetic acid (NAA) and 0.1 mg l⁻¹ 6-benzylaminopurine (BAP). Calli were cultured on somatic embryogenesis induction medium containing 1.0 mg l⁻¹ NAA and 0.5 mg l⁻¹ BAP, and somatic embryos were visible on 30% of the paromomycin-resistant calli within 3–4 weeks. Three to four weeks after the somatic embryos were transferred to phytohormone-free plant regeneration medium, 32% converted to paromomycin-resistant plants. Detection of the neomycin phosphotransferase gene and high levels of β-glucuronidase (GUS) mRNA and enzyme activity, and the cytohistochemical localization of GUS activity in all plant tissues confirmed the integrative transformation of the regenerated plants. The normal alkaloid profile of California poppy was unaffected by the transformation process; thus, the reported protocol could serve as a valuable tool to investigate the molecular and metabolic regulation of the benzophenanthridine alkaloid pathway. Received: 27 October 1999 / Revision received: 6 December 1999 / Accepted: 11 January 2000     

Evidence of atrazine mineralization in a soil from the Nile Delta: Isolation of Arthrobacter sp. TES6, an atrazine-degrading strain

The s-triazine herbicide atrazine was rapidly mineralized (i.e., about 60% of ¹⁴C-ring-labelled atrazine released as ¹⁴CO₂ within 21 days) by an agricultural soil from the Nile Delta (Egypt) that had been cropped with corn and periodically treated with this herbicide. Seven strains able to degrade atrazine were isolated by enrichment cultures of this soil. DNA fingerprint and phylogenetic studies based on 16S rRNA analysis showed that the seven strains were identical and belonged to the phylogeny of the genus Arthrobacter (99% similarity with Arthrobacter sp. AD38, EU710554). One strain, designated Arthrobacter sp. strain TES6, degraded atrazine and mineralized the ¹⁴C-chain-labelled atrazine. However, it was unable to mineralize the ¹⁴C-ring-labelled atrazine. Atrazine biodegradation ended in a metabolite that co-eluted with cyanuric acid in HPLC. This was consistent with its atrazine-degrading genetic potential, shown to be dependent on the trzN, atzB, and atzC gene combination. Southern blot analysis revealed that the three genes were located on a large plasmid of about 175 kb and clustered on a 22-kb SmaI fragment. These results reveal for the first time the adaptation of a North African agricultural soil to atrazine mineralization and raise interesting questions about the pandemic dispersion of the trzN, atzBC genes among atrazine-degrading bacteria worldwide.     

Selection of functional consortium for crude oil-contaminated soil remediation

Microorganisms with high oil-degrading performance are essential for bioremediation of soil contaminated with crude oil. A positive end dilution method was employed for the selection of crude oil-degrading functional consortium from contaminated soil. The selected consortium was consisted of Rhizobiales sp., Pseudomonas sp., Brucella sp., Bacillus sp., Rhodococcus sp., Microbacterium sp. and Roseomonas sp. and removed nearly 52.1% of crude oil at initial concentration of 10,000 mg l⁻¹ at 30 °C within 7 days, with removal of aliphatic hydrocarbons by 71.4% and aromatic hydrocarbons by 36.0%, respectively. The effectiveness of the consortium for bioaugmentation was confirmed with microcosm test by contaminated soil (1.0 kg) from Karemary Oilfield, China. The removal efficiency of crude oil was enhanced to >50% in microcosms with the consortium compared with 8-13% or lower in controls over a 60 day period. The crude oil removal reaction was probably first order reaction and the rate was greatly enhanced by bioaugmentation. Supplementation of nitrogen and phosphate sources had limited effect on the oil removal in the tested soil.     

A bioprocessing strategy that allows for the selection of Cr(VI)-reducing bacteria from soils

Anaerobic bacteria that reduce hexavalent chromium [Cr(VI)] to trivalent [Cr(III)] are common in soils and were used to develop a bioprocess employing a selection strategy. Indigenous Cr(VI)-reducers were enriched from Cr(VI)-contaminated soil under anaerobic conditions. The mixed culture was then tested for Cr(VI)-reducing activity in a chemostat, followed by transfer to a 1-L packed-bed bioreactor operated at 30°C for additional study. The support material used in the reactor consisted of 6-mm porcelain saddles. Cr(VI) concentrations in the liquid ranged from 140–750 mg L⁻¹. Cr(VI)-reducing bacteria were the dominant population with Cr(VI)-reduction rates of approximately 0.71 mg g⁻¹ dry cells h⁻¹ achieved at Cr(VI) concentrations of 750 mg L⁻¹. These results indicate a potential for selecting and maintaining indigenous Cr(VI)-reducers in a bioreactor for Cr(VI)-remediation of groundwater or soil wash effluents. Received 09 January 1996/ Accepted in revised form 15 November 1996