Genotypes of lucerne (Medicago sativa L.) show differential tolerance to manganese deficiency and toxicity when grown in bauxite residue sand

The physical and chemical characteristics of bauxite residue sand (BRS) affect the availability of a number of nutrients to plants, especially manganese (Mn). Lucerne (Medicago sativa L.) has been chosen as a BRS revegetation species because of its deep-rooting habit and tendency to tolerate moderately alkaline and saline soils, even though it is still prone to Mn deficiency stress. Sixteen commercially available lucerne genotypes were grown in BRS after addition of 5, 50 or 500 g Mn g^–1 BRS in a glasshouse. Manganese deficiency and toxicity symptoms were observed in 5 and 500 g g^–1 treatments, respectively. Symptom expression varied in severity between genotypes. Relative tolerance to Mn deficiency was defined by shoot dry weight at 5 g Mn g^–1 as a percentage of shoot dry weight at 50 g Mn g^–1. Salado, a genotype tolerant to Mn deficiency, and Sirosal, a genotype intolerant to Mn deficiency, were then grown with 0, 10, 20, 50, 100, 200 or 800 g Mn g^–1 BRS and found to have critical shoot Mn concentrations of 17.7 (Salado) and 26.6 g g^–1 (Sirosal). The use of genotypes with high relative Mn deficiency tolerance is recommended to help improve sustainability of BRS revegetation as well as to improve productivity on Mn-fixing agricultural soils.     

The effect of manganese supply on exudation of carboxylates by roots of lucerne (Medicago sativa)

Some low-molecular-weight carboxylates commonly found in plant root exudates have the potential to increase the availability of Mn in the rhizosphere. Release of various compounds into the rhizosphere by plant roots may also be a mechanism by which certain species and genotypes are able to tolerate conditions of low Mn availability better than others. Lucerne (Medicago sativa L.) plants of Salado, a genotype tolerant to Mn deficiency, and Sirosal, an intolerant genotype, were grown in solution culture with 0, 5 or 500 nM Mn (Mn-0, Mn-5 and Mn-500). Exudates of whole root systems were collected at 14, 24 and 36 d and analysed by HPLC. Oxalate, tartarate, L-malate, lactate, malonate, maleate, citrate and succinate were detected and quantified in exudates under all Mn treatments. Malonate, citrate and succinate accounted for the majority of carboxylates in the exudates. Exudation increased with plant age, but amounts of individual carboxylates remained constant in proportion to the total amount exuded. A significant increase in exudation of all carboxylates other than malonate and maleate resulted from omission of Mn from nutrient solutions. Salado exuded more oxalate, tartarate, L-malate, lactate, citrate and succinate than Sirosal at Mn-0, and more citrate and succinate than Sirosal at Mn-5. Genotypic differences in carboxylate exudation under Mn-0 were associated with production of roots with diameter <100 μm. Plant Mn concentrations and growth rates suggested carboxylate exudation differences were not the sole factor responsible for differential tolerance to Mn deficiency in the lucerne genotypes.     

Increased taxane accumulation in callus cultures of Taxus cuspidata and Taxus × media by some elicitors and precursors

In Taxus cuspidata callus, vanadyl sulfate (10 mg l^–1) induced a high (146 g g^–1 dry wt) production of 10-deacetylbaccatin III in comparison to 7 g g^–1 dry wt of the control. The content of paclitaxel in this species increased from 16 g g^–1 to 74 g g^–1 dry wt when 20 mg phenylalanine l^–1 was used. In T. media, p-aminobenzoic acid induced the highest content of 10-deacetylbaccatin III (481 g g^–1 dry wt) versus 181 g g^–1 in the control. Paclitaxel increased from 89 to 139 g g^–1 dry wt after adding chitosan (20 mg l^–1) to the cultures.     

Non-uniform distribution and seasonal variation of endogenous indol-3yl-acetic acid in the cambial region of Pinus contorta Dougl.

Endogenous, free indol-3yl-acetic acid (IAA) levels were measured in the main stem in the 10-year-old cambial zone, in the adjoining differentiating xylem, and in the adjoining mature xylem of 15–20-year-old Pinus contorta Dougl. by single-ion-current monitoring, combined gas chromatography — mass spectrometry, on several dates from early spring to early winter. Microscopy was used to determine the state of cambial activity on each harvest date. The IAA levels were found to be nearly constant at 1 g g^-1 DW in the cambial zone from March to July, then to increase to near 2 g g^-1 DW during the remainder of the growth season. No clear correlation was evident between number of fusiform cells per radial file and IAA content in the cambial zone. By contrast, the IAA content in differentiating xylem was higher than that in the adjoining meristematic zone on all harvest dates and also exhibited marked seasonal variation, peaking near 16 g g^-1 DW in mid summer, and declining to 1 g g^-1 DW in autumn. In mature xylem, IAA levels were very low and showed negligible variation. The fresh weight to dry weight ratio of differentiating xylem was greater than that of the cambial zone, and greater in the cambial zone than in mature xylem.     

Influence of added manganese on nitrification in a low-manganese soil

Summary Nitrification was studied in a Leefield sand, sufficiently low in Mn to produce severe Mn deficiency in soybeans. The soil was treated with 100 g/g NH₄ ⁺-N, 0, 10, 100 and 1000 g/g Mn, and incubated at field capacity for six weeks at 30°C. Weekly determinations of (NO₃ ^-+NO₂ ^-)-N and NH₄ ⁺-N revealed that nitrification was not increased above the control level by any of the Mn rates. In the control, the decrease in soil pH associated with nitrification caused an increase in extractable Mn from 0.12 to 1.56 g/g during the experimental period. The 1000 g/g rate of Mn completely inhibited nitrification for the first five weeks of the experiment, but nitrification began to occur during the sixth (last) week. It is postulated that Mn was being converted to unavailable forms such that by the sixth week the level of active Mn had been reduced sufficiently to permit nitrification to begin. re]19760512     

Determination of the minimal inhibitory concentration of Amphotericin B and Miconazole for 21 strains of Aspergillus

The susceptibility of 21 strains ofAspergillus (11 ofA. fumigatus, 8 ofA. niger, and 2 ofA. flavus) isolated from human pathologic specimens to Amphotericin B and Miconazole has been comparatively studied. Determination of the minimal inhibitory concentration of both drugs in a liquid medium showed a noticeably variability for the different strains. The values obtained for Amphotericin B varied between 0.25g/ml (2 strains) and 1.25g/ml (5 strains) after 48 hours, and between 1.25g/ml (1 strain) and 50g/ml (1 strain) after 10 days. For Miconazole the results varied between 0.1g/ml (1 strain) and 25g/ml (1 strain) after 48 hours of incubation, and between 0.5g/ml (5 strains) and > 100g/ml after 10 days. The variability of these results indicates the usefulness of carrying ourin vitro sensitivity studies whenever it is possible.     

Seedling responses of three Australian tree species to toxic concentrations of zinc in solution culture

A frequently desired outcome when rehabilitating Zn toxic sites in Australia is to establish a self-sustaining native ecosystem. Hence, it is important to understand the tolerance of Australian native plants to high concentrations of Zn. Very little is known about the responses of Australian native plants, and trees in particular, to toxic concentrations of Zn. Acacia holosericea, Eucalyptus camaldulensis and Melaleuca leucadendra plants were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Zn treatments viz., 0.5, 5, 10, 25, 50 and 100 M. The order of tolerance to toxic concentrations of Zn was E. camaldulensis> A. holosericea> M. leucadendra, the critical external concentrations being approximately 20, 12 and 1.5 M, respectively. Tissue Zn concentrations increased as solution Zn increased for all species. Root tissue concentrations were higher than shoot tissue concentrations at all solution Zn concentrations. The critical tissue Zn concentrations were approximately 85 and 110 g g^–1 DM for M. leucadendra, 115 and 155 g g^–1 DM for A. holosericea and 415 and 370 g g^–1 DM for E. camaldulensis for the youngest fully expanded leaf and total shoots, respectively. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the rehabilitation of potentially Zn toxic sites.     

The effect of triacontanol on micropropagation of Capsicum frutescens and Decalepis hamiltonii W & A

We studied the effect of triacontanol (TRIA) on shoot multiplication and rooting of in vitro derived shoot tips of Capsicum frutescens and Decalepis hamiltonii W & A. In both shoot multiplication and rooting phases, TRIA was administered at 2-20 g l^–1. TRIA resulted in highest promotion of axillary shoot proliferation at 2 g l^–1 in Capsicum frutescens and 20 g l^–1 in Decalepis hamiltonii while rooting was maximum at 5 and 10 g l^–1 for Capsicum frutescens and Decalepis hamiltonii respectively. TRIA enhanced shoot growth and chlorophyll content of leaves and also influenced root induction and supported growth of the roots. This work reveals that TRIA can be used as an effective growth regulator in the micropropagation of Capsicum frutescens and Decalepis hamiltonii, an endangered shrub of Deccan peninsular India.     

Effect of dilution rate on the release of pertussis toxin and lipopolysaccharide ofBordetella pertussis

Summary The kinetics ofBordetella pertussis growth was studied in a glutamate-limited continuous culture. Growth kinetics corresponded to Monod's model. The saturation constant and maximum specific growth rate were estimated as well as the energetic parameters, theoretical yield of cells and maintenance coefficient. Release of pertussis toxin (PT) and lipopolysaccharide (LPS) were growth-associated. In addition, they showed a linear relationship between them. Growth rate affected neither outer membrane proteins nor the cell-bound LPS pattern.Nomenclature X cell concentration (g L^–1) - specific growth rate (h^–1) - _m maximum specific growth rate (h^–1) - D dilution rate (h^–1) - S concentration of growth rate-limiting nutrient (glutamate) (mmol L^–1 or g L^–1) - Ks substrate saturation constant (mol L^–1) - m_s maintenance coefficient (g g^–1 h^–1) - Y_x/s theoretical yield of cells from glutamate (g g^–1) - Y_x/s yield of cells from glutamate (g g^–1) - Y_PT/s yield of soluble PT from glutamate (mg g^–1) - Y_KDO/s yield of cell-free KDO from glutamate (g g^–1) - Y_PT/x specific yield of soluble PT (mg g^–1) - Y_KDO/x specific yield of cell-free KDO (g g^–1) - q_PT specific soluble PT production rate (mg g^–1 h^–1) - q_KDO specific cell-free KDO production rate (g g^–1 h^–1)     

Seedling responses of four Australian tree species to toxic concentrations of manganese in solution culture

Little is known about the responses of Australian plants to excess metal, including Mn. It is important to remedy this lack of information so that knowledgeable decisions can be made about managing Mn contaminated sites where inhabited by Australian vegetation. Acacia holosericea, Melaleuca leucadendra, Eucalyptus crebra and Eucalyptus camaldulensis were grown in dilute solution culture for 10 weeks. The seedlings (42 days old) were exposed to six Mn treatments viz., 1, 8, 32, 128, 512 and 2048 M. The order of tolerance to toxic concentrations of Mn was A. holosericea E. crebra < M. leucadendra < E. camaldulensis, the critical external concentrations being approximately 5.1, 5.0, 21 and 330 M, respectively. The critical tissue Mn concentrations for the youngest fully expanded leaf and total shoots were, respectively, 265 and 215 g g^–1 DM for A. holosericea, 445 and 495 g g^–1 DM for M. leucadendra, 495 and 710 g g^–1 DM for E. crebra and 7230 and 6510 g g^–1 DM for E. camaldulensis. The high tolerance of E. camaldulensis (as opposed to the sensitivity of E. crebra) to excess Mn raises concern about fauna feeding on the plant and is consistent with hypotheses suggesting the Eucalyptus subgenus Symphomyrtus is particularly tolerant of stress, including excess Mn. The results from this paper provide the first comprehensive combination of growth responses, critical external concentrations, critical tissue concentrations and plant toxicity symptoms for three important Australian genera, viz., Eucalyptus, Acacia and Melaleuca, for use in the management of Mn toxic sites.     

Seasonal variability in mercury inputs into the Ria de Aveiro,Portugal

Water, suspended particulate matter (SPM) and sediments were collected from the Esteiro de Estarreja (Ria de Aveiro, Portugal), which receives considerable quantities of waste mercury from a chlor-alkali plant. Dissolved and particulate Hg concentrations in the effluent ranged between 4 –167 g I^–1 and 141–3144 g g^–1, respectively, at pH values of >10. The effluent plume undergoes significant chemical changes during advection downestuary. The evidence suggested that adsorption of dissolved Hg onto organic-rich SPM was an important process. A maximum sediment Hg concentration of 500 g g^–1 was found about 1.5 km from the discharge, as a result of the settling of Hg-rich SPM. Downestuary Hg concentrations in sediments decline to about 100 g g^–1 at the mouth of the Esteiro. The particle-water interactions are discussed in terms of the transport of dissolved and particulate Hg into the Ria de Aveiro.     

Interactions of water,mulch and nitrogen on sorghum in Niger

We tested the hypothesis that plants only stimulate net mineralization of N when intense competition for N exists between plants and heterotrophs. Nitrogen mineralization in the soil used was insensitive to the range of moisture fluctuations that were inevitable during plant growth. Pots were planted to wheat (Triticum aestivum L.) or left unplanted and received no straw, straw added in one central layer, or straw added uniformly through the whole soil volume. Through the addition of¹⁵ N-labelled nitrate, initial soil inorganic N was increased to 17 g g^–1 in unplanted treatments and to 17 g g^–1 and 72 g g^–1 in planted treatments. Straw addition increased microbial immobilization of labelled N (soil inorganic N at planting), but did not reduce net mineralization of unlabelled soil N (soil organic N at planting), indicating that straw decomposers immobilized N early in the growth period. Plant growth did not reduce immobilization of N by straw decomposers. Net mineralization of N was not affected by plant growth at the low rate of N addition, but was reduced at the high rate of N addition. We conclude that the influence of wheat growth on net mineralization of N depends on soil N availability, with reductions in net mineralization at high N levels due to increased immobilization.     

Effect of calcium-binding protein regucalcin on hepatic protein synthesis: Inhibition of aminoacyl-tRNA synthetase activity

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, onin vitro protein synthesis in the 5500g supernatant fraction of rat liver homogenate was investigated. Addition of Ca²⁺ up to 5.0 M in the reaction mixture caused a significant decrease in protein synthesis. This decrease was saturated at 10 M Ca²⁺. The Ca²⁺ effect was not reversed by the presence of regucalcin (2.0 M); the protein caused a remarkable decrease in hepatic protein synthesis, and it enhanced significantly the Ca^2– effect. Meanwhile, calmodulin (2.5-20 g/ml), a calcium-binding protein, did not have an appreciable effect on the Ca²⁺ (10 M)-induced decrease in hepatic protein synthesis. [³H]Leucyl-tRNA synthetase activity in the 105000g supernatant fraction (cytosol) of liver homogenate was markedly decreased by addition of Ca²⁺ (1.0–50 M). This decrease was not reversed by the presence of regucalcin (2.0 M); the protein (1.0–2.0 M) caused a remarkable decrease in the enzyme activity. The present results suggest that regucalcin can regulate protein synthesis in liver cells.     

SelectingRhizobium phaseoli strains for use with beans (Phaseolus vulgaris L.) in Kenya: Tolerance of high temperature and antibiotic resistance

Forty one strains ofRhizobium phaseoli were screened for the ability to multiply at high temperatures on yeast extract-mannitol agar. Most strains were tolerant of 30°C, eight strains were tolerant of 45°C and two of 47°C although the rate of multiplication was reduced at 45–47°C. The high temperature-tolerant strains were isolated from Kenyan soils and were fast-growing. Seven of the eight strains tolerant of 45–47°C lost their infectiveness after incubation at high temperature but four strains tolerant of 40°C remained infective after incubation at that temperature.Thirty six strains were resistant to 200 g ml^–1 streptomycin sulphate and 29 strains to 200 g ml^–1 spectinomycin dihydrochloride. Eight strains were resistant to both antibiotics each at 200 g ml^–1. Two of the double-labelled antibiotic-resistant mutants lost their infectiveness onPhaseolus vulgaris. The response to acidity was unaltered and two of the mutants showed a decrease in temperature tolerance. The doublelabelled mutants were recoverable from two Kenyan soils.     

Is birch a suitable reference in estimating dinitrogen fixation in alders by isotope dilution?

Seedlings ofAlnus incana (nodulated and non-nodulated) andBetula papyrifera were fertilized with varying amounts (0, 10, 25, 50, 100, 250 and 500 g N g^–1 soil) of labelled ammonium-N or nitrate-N ( 5.2 A% excess¹⁵N as ammonium sulphate or potassium nitrate). After 4 months in the greenhouse,¹⁵N excess in the plants were determined and an isotope dilution equation was applied to determine the percent of biomass N fixed by theA. incana/Frankia system. When ammonium was used as the sole N source and birch as the non-fixing reference, N-fixation accounted for 95%, 87% and 60% of the plant nitrogen yields with 10, 25 and 50 g N g^–1 rates, additions respectively. At the 100 g N g^–1 fertilization and above N-fixation accounted for less than 10% of the N yield. Similar results were obtained when non-nodulatedA. incana was used as non-fixing reference. With nitrate as the sole N source, N-fixation accounted for 98%, 97%, 97%, 86%, 56% and 12% of N yield with 10, 25, 50, 100, 250 and 500 g N g^–1 additions respectively. These values were similar for both types of reference plants. The direct isotope dilution method was compared to that of the total nitrogen difference method. There was good agreement between the two methods up to 50 g N g^–1 for ammonium and up to 100 g N g^–1 for nitrate. The difference method produced negative values at high concentrations of nitrogen fertilization. Again similar results were obtained by the two reference plants. The results indicate that birch can be used as a non-fixing control in isotope dilution studies but that care must be exercised in selecting the type and quantity of labelled nitrogen fertilizer.     

Growth and nutrition of small Betula pendula plants at different relative addition rates of iron

Summary Small birch plants (Betula pendula Roth.) were cultivated in a hydroponic spray solution where the relative addition rate of iron (R_Fe; g g^–1 day^–1), was the growth-controlling variable. All other elements were added in free access. An additional treatment was performed where all nutrients, including iron, were in free access (FA). The plants showed deficiency symptoms at steady-state growth and severe limitation of iron, R_Fe 0.05 and 0.10 day^–1. There were few symptoms at R_Fe of 0.15 or above. Plant relative growth rate (R_G; g g^–1 day^–1), equalled the relative rate of increase in iron supply, R_Fe. Internal iron concentration of the plants ranged from 40 to 70 g g^–1 dry weight (DW) over the range for which iron supply was limiting growth. At FA, the internal concentration was approximately 200 g g^–1 DW without further increase in R_G, demonstrating that iron may be taken up in excess without affecting growth. Internal concentrations of macronutrients were stable at the different R_Fe, except for Ca and Mg in shoots which were higher at low iron supply. Uptake rates of iron, calculated per root growth rate (mol g^–1 root DW), were approximately twice as high at R_Fe 0.20 as at 0.05 day^–1. The effect of iron limitation on dry matter allocation to leaves was small, with increases in the root fraction being largely at the expense of the stem. Leaf area ratio was constant regardless of R_Fe and the specific leaf area tended to increase with increasing iron limitation. Net assimilation rate decreased by a factor of 6 from free access to severe iron limitation, largely accounting for the differences in plant R_G.     

Concentrations of heavy metals and related trace elements in some Ethiopian rift-valley lakes and their in-flows

Concentrations of heavy metals commonly known to impact the environment and other related trace elements were quantified in the water bodies of nine Ethiopian rift-valley lakes and six rivers (their inflows) as well as in effluents from two factories. In about half of the samples the concentrations of As was 10–700 g l^–1 and Se, ranged from 10 to 28 g l^–1, were much higher than the maximum permissible level (MPL) according to international standards for drinking water. Mercury (Hg) was detected in four lakes and one river with high values ranging from 2 to 165 g l^–1. Concentrations of Mo in three soda lakes were as high as 544–2590 g l^–1. Iron (Fe) was found in high concentrations (567–4969 g l^–1) in three lakes, which are known to be discolored from inorganic colloids. Levels of Cd, Pb, and Cr ranged between 5 and 9, 12 and 20 and 104 and 121 g l^–1, respectively. The rest of the heavy metals analyzed, Ba, Cu, Mn, Ni and Zn, were either not detected in the samples or were found in much lower concentrations than the MPL for drinking water. Effluent from a tannery contained about 15, 141, 523, and 19 g l^–1 of As, Cr, Fe, and Se, respectively, and effluent from a textile factory contained high concentrations of As (10.6), Hg (3.8) and Se (20) g l^–1. Compared to more industrialized regions and other African lakes the concentrations of heavy metals in Ethiopian rift-valley lakes (with the exception of the soda lakes) and their inflows were low.     

Effects of GNA and other mannose binding lectins on development and fecundity of the peach-potato aphid Myzus persicae

Three mannose-binding lectins were assayed in artificial diets for their toxic and growth-inhibitory effects on nymphal development of the peach-potato aphid Myzus persicae. The snowdrop (Galanthus nivalis) lectin GNA was the most toxic, with an induced nymphal mortality of 42% at 1500 g ml^–1 (30 M) and an IC₅₀ (50% growth inhibition) of 630 g ml^–1 (13 M). The daffodil (Narcissus pseudonarcissus) lectin NPA and a garlic (Allium sativum) lectin ASA induced no significant mortality in the range 10–1500 g ml^–1, but did result in growth inhibition of 59% (NPA) and 26% (ASA) at 1500 g ml^–1 (40 M for NPA, 63 M for ASA). All three lectins were responsible for a slight but significant growth stimulation when ingested at 10 g ml^–1, reaching +26%, +18% and +11% over the control values for the garlic lectin, the daffodil lectin and the snowdrop lectin, respectively. GNA, as well as the glucose/mannose binding lectin Concanavalin A, were also provided at sublethal doses throughout the life cycle of the aphids, and effects on adult performance were monitored. Adult survival was not significantly altered, but both lectins adversely affected total fecundity and the dynamics of reproduction, resulting in significant reduction in calculated r _ms (population intrinsic rate of natural increase) on lectin-containing diets. These effects are discussed in relation to the use of transgenic plants expressing these toxic lectins for potential control of aphid populations.     

Phosphate in the sediments of the Gulf of Lions (NW Mediterranean Sea), relationship with input by the river Rhone

We investigated P-input by the Rhone river into the Mediterranean Sea taking into account P trapped in the surface sediment of the Gulf of Lions. Total phosphate concentration was determined every cm in the upper 10 cm-layer of sediments sampled at 11 stations in the Gulf of Lions during two cruises (March 1998 and January 1999). Two low downward gradients, one East–West and another North–South, with distance to the Rhone river mouth were found. Except at one station, total phosphate concentration in surface sediments was found to be constant with depth down to 10 cm. Values for individual stations ranged between 400 and 700 g g^–1 with an average value of 547 g g^–1 (st. dev. = 63 g g^–1) for the whole gulf. The low variability in total-P concentration in sediments is in contrast to the large variability in suspended matter load of the river Rhone and suggests the dominance of authigenic P removal mechanisms in P burial. The total P-pool in the upper 10 cm-layer of the sediments in the gulf was estimated at 562 kt, with about 80% trapped into the shelf and 20% into the slope. Annual P-deposition was estimated as 7.2–12.4 kt y^–1, from the P-pool in the sediment and the sedimentation rates. This is equivalent to a previous estimation of the river Rhone input, estimated to be about 6.5–12.2 kt y^–1. As the Rhone is the major river flowing into the Mediterranean Sea, total P in surface sediments of the Gulf of Lions should be taken into account in P-budgets at the scale of the Mediterranean Sea.     

Soil microbial population dynamics following bioaugmentation with a 3-chlorobenzoate-degrading bacterial culture

Changes in microbial populations were evaluated following inoculation of contaminated soil with a 3-chlorobenzoate degrader. Madera sandy loam was amended with 0, 500, or 1000 g 3-chlorobenzoate g^-1 dry soil. Selected microcosms were inoculated with the degrader Comamonas testosteroni BR60. Culturable bacterial degraderswere enumerated on minimal salts media containing 3-chlorobenzoate. Culturableheterotrophic bacteria were enumerated on R2A. Isolated degraders were grouped by enterobacterial repetitive intergenic consensus sequence-polymerase chain reaction fingerprints and identified based on 16S ribosomal-DNA sequences. Bioaugmentation increased the rate of degradation at both levels of 3-chlorobenzoate. In both the 500 and 1000 g 3-chlorobenzoate g^-1 dry soil inoculated microcosms, degradersincreased from the initial inoculum and decreased following degradation of 3-CB.Inoculation delayed the development of indigenous 3-chlorobenzoate degrading populations. It is unclear if inoculation altered the composition of indigenous degrader populations. In the uninoculated soil, degraders increased from undetectable levels to 6.6 × 10⁷ colony-forming-units g^-1 dry soil in the 500 g 3-chlorobenzoate g^-1 dry soil microcosms, but none were detected in the 1000 g 3-chlorobenzoate g^-1 dry soil microcosms. Degraders isolated from uninoculated soil were identified as one of two distinct Burkholderia species.In the uninoculated soil, numbers of culturable heterotrophic bacteria initially decreased following addition of 1000 g 3-chlorobenzoate g^-1 dry soil. Inoculation with C. testosteroni reduced this negative impact on culturable bacterial numbers. The results indicate that bioaugmentation may not only increase the rate of 3-chlorobenzoate degradation but also reduce the deleterious effects of 3-chlorbenzoate on indigenous soil microbial populations.