Unveiling genome sequence of Bacillus safensis strain WOB7 KX774196, a linamarin-utilizing bacterium (LUB) isolated from cassava wastewater (CWW) in Lagos State, Nigeria.

Bacillus safensis strain WOB7 is a linamarin-utilizing bacterium (LUB) that was isolated from cassava wastewater obtained from a processing factory. We present here the draft genome sequence of the strain (WOB7). These data provide valuable information on the prospects of the linamarase and other genes of importance associated with cyanogen detoxification.

Draft genome sequence of Bacillus safensis strain WOIS2 KX774194, a nitrile-metabolizing bacterium isolated from solid waste leachates at Olusosun dumpsite, Ojota, Lagos State, Nigeria.

Bacillus safensis strain WOIS2, a nitrile-metabolizing bacterium, was isolated from solid waste leachates at the Olusosun dumpsite, Ojota, Lagos State, Nigeria. Here, we present the draft genome sequence of strain WOIS2. These data provide valuable information on the bioprospecting of B. safensis nitrilase and other intriguing genes of interest.

Chromium contamination accentuates changes in the microbiome and heavy metal resistome of a tropical agricultural soil.

The impacts of hexavalent chromium (Cr) contamination on the microbiome, soil physicochemistry, and heavy metal resistome of a tropical agricultural soil were evaluated for 6 weeks in field-moist microcosms consisting of a Cr-inundated agricultural soil (SL9) and an untreated control (SL7). The physicochemistry of the two microcosms revealed a diminution in the total organic matter content and a significant dip in macronutrients phosphorus, potassium, and nitrogen concentration in the SL9 microcosm. Heavy metals analysis revealed the detection of seven heavy metals (Zn, Cu, Fe, Cd, Se, Pb, Cr) in the agricultural soil (SL7), whose concentrations drastically reduced in the SL9 microcosm. Illumina shotgun sequencing of the DNA extracted from the two microcosms showed the preponderance of the phyla, classes, genera, and species of Actinobacteria (33.11%), Actinobacteria_class (38.20%), Candidatus Saccharimonas (11.67%), and Candidatus Saccharimonas aalborgensis (19.70%) in SL7, and Proteobacteria (47.52%), Betaproteobacteria (22.88%), Staphylococcus (16.18%), Staphylococcus aureus (9.76%) in SL9, respectively. Functional annotation of the two metagenomes for heavy metal resistance genes revealed diverse heavy metal resistomes involved in the uptake, transport, efflux, and detoxification of various heavy metals. It also revealed the exclusive detection in SL9 metagenome of resistance genes for chromium (chrB, chrF, chrR, nfsA, yieF), cadmium (czcB/czrB, czcD), and iron (fbpB, yqjH, rcnA, fetB, bfrA, fecE) not annotated in SL7 metagenome. The findings from this study revealed that Cr contamination induces significant shifts in the soil microbiome and heavy metal resistome, alters the soil physicochemistry, and facilitates the loss of prominent members of the microbiome not adapted to Cr stress.

Heavy metals assessment of ecosystem polluted with wastewaters and taxonomic profiling of multi-resistant bacteria with potential for petroleum hydrocarbon catabolism in nitrogen-limiting medium.

The coexistence of heavy metals (HMs) and petroleum hydrocarbons (PHs) exacerbates ecotoxicity and impair the drivers of eco-functionalities that stimulate essential nutrients for the productivity of the impacted environment. Profiling the bacteria that stem the ecological impact via HMs sequestration and PHs catabolism with nitrogen fixation is imperative to bioremediation of the polluted sites. The sediment of site that was consistently contaminated with industrial wastewaters was analysed for ecological toxicants and the bacterial strains that combined HMs resistance with PHs catabolism in a nitrogen-limiting system were isolated from the sediment and characterized. The geochemistry of the samples revealed the co-occurrence of the above-benchmark concentrations of HMs with the derivatives of hydrocarbons. Notwithstanding, nickel and mercury (with 5% each of the total metal concentrations in the polluted site) exhibited probable effect concentrations on the biota and thus hazardous to the ecosystem. Approx. 31% of the bacterial community, comprising unclassified Planococcaceae, unclassified Bradyrhizobiaceae, Rhodococcus, and Bacillus species, resisted 160 µmol Hg2+ in the nitrogen-limiting system within 24 h post-inoculation. The bacterial strains adopt volatilization, and sometimes in combination with adsorption/bioaccumulation strategies to sequester Hg2+ toxicity while utilizing PHs as sources of carbon and energy. Efficient metabolism of petroleum biomarkers (> 87%) and Hg2+ sequestration (≥ 75% of 40 µmol Hg2+) displayed by the selected bacterial strains portend the potential applicability of the bacilli for biotechnological restoration of the polluted site.

Complete Genome Sequence of Cluster C Mycobacteriophage McGee.

Mycobacteriophage McGee is a myovirus isolated from a wet soil sample collected at Manassas, VA, using Mycobacterium smegmatis mc2155. McGee has a genome 156,008 bp long, containing 237 protein-coding genes, 31 tRNA genes, and 1 transfer-messenger RNA (tmRNA) gene. McGee shares high gene content similarity to phages in actinobacteriophage cluster C1.

Complete Genome Sequences of Cluster A Mycobacteriophages Kenmech and Peterson and Cluster F Mycobacteriophage Rockne.

Kenmech, Peterson, and Rockne are bacteriophages that infect Mycobacterium smegmatis mc2 155. Both Kenmech and Peterson genomes are ~52 kbp long and contain 1 tRNA as well as 92 and 89 protein-coding genes, respectively. Rockne has a 56,704-bp genome with 108 protein-coding genes and no tRNA.

Comparative geochemical evaluation of toxic metals pollution and bacterial communities of industrial effluent tributary and a receiving estuary in Nigeria.

Toxic metals/metalloid contaminations of estuarine sediments due to compromised tributaries arouse significant interest in studying bacterial community that triggers natural attenuation processes. Geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), and Hakanson potential ecological risk index (RI) as a sum of risk factors (Er) were used to quantify toxic metal/metalloid-pollution status of Lagos Lagoon (2W) and 'Iya-Alaro' tributary (4W) sediments in comparison with pristine 'Lekki Conservation Centre' sediment (L1-B). Bacteriology of the ecosystems was based on culture-independent analyses using pyrosequencing. 2W and 4W were extremely contaminated with mercury (Igeo > 7), whereas, cadmium contamination was only observed in 4W. The two ecosystems were polluted with toxic metal based on PLI, where mercury (Er = 2900 and 1900 for 4W and 2W, respectively) posed very high ecological risks. Molecular fingerprinting revealed that Proteobacteria, Firmicutes, and Acidobacteria predominately contributed the 20 most abundant genera in the two ecosystems. The 240 and 310 species present in 2W and 4W, respectively, but absent in L1-B, thrive under the metal concentrations in the polluted hydrosphere. Whereas, the 58,000 species missing in 2W and 4W but found in L1-B would serve as indicators for systems impacted with metal eco-toxicity. Despite toxic metal pollution of the ecosystems understudied, bacterial communities play vital roles in self-recovery processes occurring in the hydrosphere.

Carbazole degradation in the soil microcosm by tropical bacterial strains.

In a previous study, three bacterial strains isolated from tropical hydrocarbon-contaminated soils and phylogenetically identified as Achromobacter sp. strain SL1, Pseudomonas sp. strain SL4 and Microbacterium esteraromaticum strain SL6 displayed angular dioxygenation and mineralization of carbazole in batch cultures. In this study, the ability of these isolates to survive and enhance carbazole degradation in soil were tested in field-moist microcosms. Strain SL4 had the highest survival rate (1.8 x 107 cfu/g) after 30 days of incubation in sterilized soil, while there was a decrease in population density in native (unsterilized) soil when compared with the initial population. Gas chromatographic analysis after 30 days of incubation showed that in sterilized soil amended with carbazole (100 mg/kg), 66.96, 82.15 and 68.54% were degraded by strains SL1, SL4 and SL6, respectively, with rates of degradation of 0.093, 0.114 and 0.095 mg kg-1 h-1. The combination of the three isolates as inoculum in sterilized soil degraded 87.13% carbazole at a rate of 0.121 mg kg-1 h-1. In native soil amended with carbazole (100 mg/kg), 91.64, 87.29 and 89.13% were degraded by strains SL1, SL4 and SL6 after 30 days of incubation, with rates of degradation of 0.127, 0.121 and 0.124 mg kg-1 h-1, respectively. This study successfully established the survivability (> 106 cfu/g detected after 30 days) and carbazole-degrading ability of these bacterial strains in soil, and highlights the potential of these isolates as seed for the bioremediation of carbazole-impacted environments.

Carbazole degradation in the soil microcosm by tropical bacterial strains

In a previous study, three bacterial strains isolated from tropical hydrocarbon-contaminated soils and phylogenetically identified as Achromobacter sp. strain SL1, Pseudomonas sp. strain SL4 and Microbacterium esteraromaticum strain SL6 displayed angular dioxygenation and mineralization of carbazole in batch cultures. In this study, the ability of these isolates to survive and enhance carbazole degradation in soil were tested in field-moist microcosms. Strain SL4 had the highest survival rate (1.8 x 107 cfu/g) after 30 days of incubation in sterilized soil, while there was a decrease in population density in native (unsterilized) soil when compared with the initial population. Gas chromatographic analysis after 30 days of incubation showed that in sterilized soil amended with carbazole (100 mg/kg), 66.96, 82.15 and 68.54% were degraded by strains SL1, SL4 and SL6, respectively, with rates of degradation of 0.093, 0.114 and 0.095 mg kg−1 h−1. The combination of the three isolates as inoculum in sterilized soil degraded 87.13% carbazole at a rate of 0.121 mg kg−1 h−1. In native soil amended with carbazole (100 mg/kg), 91.64, 87.29 and 89.13% were degraded by strains SL1, SL4 and SL6 after 30 days of incubation, with rates of degradation of 0.127, 0.121 and 0.124 mg kg−1 h−1, respectively. This study successfully established the survivability (> 106 cfu/g detected after 30 days) and carbazole-degrading ability of these bacterial strains in soil, and highlights the potential of these isolates as seed for the bioremediation of carbazole-impacted environments.

Catabolic plasmid specifying polychlorinated biphenyl degradation in Cupriavidus sp. strain SK-4: mobilization and expression in a pseudomonad.

Strain SK-4, a polychlorinated biphenyl (PCB) degrader previously reported to utilize di-ortho-substituted biphenyl, was genotypically re-characterized as a species of Cupriavidus. The bacterium harbored a single plasmid (pSK4), which resisted curing and which, after genetic marking by a transposon (SK4Tn5), could be mobilized into a pseudomonad. Analysis of pSK4 in both the transconjugant and the wild type revealed that it specifies the genes coding for 2-hydroxy-2,4-pentadienoate degradation in addition to those of the upper biphenyl pathway. Expression of the benzoate metabolic pathway in the transconjugant is evidence suggesting that the benzoate catabolic genes are also localized on the plasmid. This implies that pSK4 codes for all the genes involved in biphenyl mineralization. It is therefore reasonable to propose that the plasmid is the determinant for the unique metabolic capabilities known to exist in Cupriavidus sp. strain SK-4.

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.

Bacteria with dual resistance to elevated concentrations of heavy metals and antibiotics in Nigerian contaminated systems.

Samples of soil, water, and sediments from industrial estates in Lagos were collected and analyzed for heavy metals and physicochemical composition. Bacteria that are resistant to elevated concentrations of metals (Cd(2+), Co(2+), Ni(2+), Cr(6+), and Hg(2+)) were isolated from the samples, and they were further screened for antibiotic sensitivity. The minimum tolerance concentrations (MTCs) of the isolates with dual resistance to the metals were determined. The physicochemistry of all the samples indicated were heavily polluted. Twenty-two of the 270 bacterial strains isolated showed dual resistances to antibiotics and heavy metals. The MTCs of isolates to the metals were 14 mM for Cd(2+), 15 mM for Co(2+) and Ni(2+), 17 mM for Cr(6+), and 10 mM for Hg(2+). Five strains (Pseudomonas aeruginosa, Actinomyces turicensis, Acinetobacter junni, Nocardia sp., and Micrococcus sp.) resisted all the 18 antibiotics tested. Whereas Rhodococcus sp. and Micrococcus sp. resisted 15 mM Ni(2+), P. aeruginosa resisted 10 mM Co(2+). To our knowledge, there has not been any report of bacterial strains resisting such high doses of metals coupled with wide range of antibiotics. Therefore, dual expressions of antibiotics and heavy-metal resistance make the isolates, potential seeds for decommissioning of sites polluted with industrial effluents rich in heavy metals, since the bacteria will be able to withstand in situ antibiosis that may prevail in such ecosystems.

Differential degradation of crude oil (Bonny Light) by four Pseudomonas strains.

Four hydrocarbon degraders isolated from enriched oil- and asphalt-contaminated soils in Lagos, Nigeria, were tested for their petroleum degradation potentials. All the isolates were identified as species of Pseudomonas. Pseudomonas putida P11 demonstrated a strong ability to degrade kerosene, gasoline, diesel, engine oil and crude oil while P. aeruginosa BB3 exhibited fair degradative ability on crude oil, gasoline, engine oil, anthracene and pyrene but weak on kerosene, diesel and dibenzothiophene. Pseudomonas putida WL2 and P. aeruginosa MVL1 grew on crude oil and all its cuts tested with the latter possessing similar polycyclic aromatic potentials as P11. All the strains grew logarithmically with 1-2 orders of magnitude and with generation time ranging significantly between 3.07 and 8.55 d at 0.05 level of confidence. Strains WL2 and MVL1 utilized the oil substrate best with more than 70% in 6 d experimental period, whereas the same feat was achieved by P11 in 12 d period. BB3 on the other hand degraded only 46% within 6 d. Interestingly, data obtained from gas chromatographic analysis of oil recovered from the culture fluids of MVL1 confirmed near-disappearance of major peaks (including aliphatics and aromatics) in the hydrocarbon mixture.

Growth and biosurfactant synthesis by Nigerian hydrocarbon-degrading estuarine bacteria

The ability of microorganisms to degrade petroleum hydrocarbons is important for finding an environmentally-friendly method to restoring contaminated environmental matrices. Screening of hydrocarbon-utilizing and biosurfactant-producing abilities of organisms from an estuarine ecosystem in Nigeria, Africa, resulted in the isolation of five microbial strains identified as Corynebacterium sp. DDv1, Flavobacterium sp. DDv2, Micrococcus roseus DDv3, Pseudomonas aeruginosa DDv4 and Saccharomyces cerevisae DDv5. These isolates grew readily on several hydrocarbons including hexadecane, dodecane, crude oil and petroleum fractions. Axenic cultures of the organisms utilized diesel oil (1.0 % v/v) with generation times that ranged significantly (t-test, P < 0.05) between 3.25 and 3.88 day, with concomitant production of biosurfactants. Kinetics of growth indicates that biosurfactant synthesis occurred predominantly during exponential growth phase, suggesting that the bioactive molecules are primary metabolites. Strains DDv1 and DDv4 were evidently the most metabolically active in terms of substrate utilization and biosurfactant synthesis compared to other strains with respective emulsification index of 63 and 78 %. Preliminary biochemical characterization indicates that the biosurfactants are heteropolymers consisting of lipid, protein and carbohydrate moieties. The hydrocarbon catabolic properties coupled with biosurfactant-producing capabilities is an asset that could be exploited for cleanup of oil-contaminated matrices and also in food and cosmetic industries. Rev. Biol. Trop. 56 (4): 16031611. Epub 2008 December 30.

La capacidad de los microorganismos para degradar hidrocarburos del petróleo es de gran importancia para hallar un método aceptable y ambientalmente amigable para la restauración de terrenos ambientalmente contaminados. Al investigar las capacidades de los organismos de un ecosistema de estuario que utilizan hidrocarburos y producen biosurfactantes, se produjo como resultado el aislamiento de cinco cepas microbianas identificadas como Corynebacterium sp. DDv1, Flavobacterium sp. DDv2, Micrococcus roseus DDv3, Pseudomonas aeruginosa y DDv4 Saccharomyces cerevisiae DDv5. Estas cepas crecieron fácilmente en varios hidrocarburos incluyendo hexadecanos, dodecanos, petróleo crudo y fracciones de petróleo. Los cultivos axénicos de organismos utilizaron diesel (1.0% v/v) con períodos por generación con ámbitos significativos (t-test, P <0.05) de entre 3.25 y 3.88 días, con la consiguiente producción de bio-surfactantes. La cinética del crecimiento indica que la síntesis de bio-surfactante se produjo principalmente durante la fase de crecimiento exponencial, lo que sugiere que las moléculas bioactivas son metabolitos primarios. Las cepas DDv1 y DDv4 fueron evidentemente las más metabólicamente activas en términos de utilización del sustrato y la síntesis de bio-surfactantes en comparación con otras cepas con índices respectivos de emulsificación de 63 y 78%. La caracterización bioquímica preliminar indica que los bio-surfactantes son heteropolímeros constituidos de fracciones de lípidos, proteínas y carbohidratos. Las propiedades catabólicas de los hidrocarburos, junto con las capacidades de producción de bio-surfactantes, es una ventaja que puede ser aprovechada para la limpieza de terrenos contaminados con petróleo y también en la industria alimentaria y cosmética.

Extensive biodegradation of polychlorinated biphenyls in Aroclor 1242 and electrical transformer fluid (Askarel) by natural strains of microorganisms indigenous to contaminated African systems.

Evidence for substantial aerobic degradation of Aroclor 1242 and Askarel fluid by newly characterized bacterial strains belonging to the Enterobacter, Ralstonia and Pseudomonas genera is presented. The organisms exhibited degradative activity in terms of total PCB/Askarel degradation, degradation of individual congeners and diversity of congeners attacked. Maximal degradation by the various isolates of Askarel ranged from 69% to 86% whereas, Aroclor 1242, with the exception of Ralstonia sp. SA-4 (9.7%), was degraded by 37% to 91%. PCB analysis showed that at least 45 of the representative congeners in Aroclor 1242 were extensively transformed by benzoate-grown cells without the need for biphenyl as an inducer of the upper degradation pathway. In incubations with Aroclor 1242, no clear correlation was observed between percentage of congener transformed and the degree of chlorination, regardless of the presence or absence of biphenyl. Recovery of significant but nonstoichiometric amounts of chloride from the culture media showed partial dechlorination of congeners and suggested production of partial degradation products. Addition of biphenyl evidently enhanced dechlorination of the mixture by some isolates. With the exception of Ralstonia sp. SA-5, chloride released ranged from 24% to 60% in the presence of biphenyl versus 0.35% to 15% without biphenyl.

Evidence of aerobic utilization of di-ortho-substituted trichlorobiphenyls as growth substrates by Pseudomonas sp. SA-6 and Ralstonia sp. SA-4.

Robust and effective bioremediation strategies have not yet been developed for polychlorinated biphenyl (PCB)-contaminated soils. This is in part a result of the fact that ortho- or ortho- and para-substituted congeners, frequent dead-end products of reductive dechlorination of PCB mixtures, have greatly reduced aerobic biodegradability. In this study, we report substantial evidence of utilization of diortho-substituted trichlorobiphenyls (triCBs) as growth substrates by Ralstonia sp. SA-4 and Pseudomonas sp. SA-6 in which ortho-substitution resulted in no obvious patterns of recalcitrance. These stains exhibited unusual preferences for growth on congeners chlorinated on both rings. Substrate uptake studies with benzoate-grown cells revealed that the isolates attacked the 2-chlorophenyl rings of 2,2',4- and 2,2',5-triCB. Between 71% and 93% of the initial 0.23-0.34 mM dose of congeners were transformed in less than 261 h concomitant with non-stoichiometric production of respective dichlorobenzoates and chloride ion. In enzyme assays, activity of 2,3-dihydroxybiphenyl-1,2-dioxygenase was constitutive. Additionally, these strains harboured no detectable plasmids which, coupled with exponential growth on the two triCB congeners, suggested chromosomal location of PCB degradative genes. In addition to the fact that there is a paucity of information on degradation of PCBs by tropical isolates, growth on triCBs as a sole carbon and energy source has never been demonstrated for any natural or engineered microorganisms. Such isolates may help prevent accumulation of ortho-substituted congeners in natural systems and offer the hope for development of effective bioaugmentation or sequential anaerobic-aerobic bioremediation strategies.

Growth and biosurfactant synthesis by Nigerian hydrocarbon-degrading estuarine bacteria.

The ability of microorganisms to degrade petroleum hydrocarbons is important for finding an environmentally-friendly method to restoring contaminated environmental matrices. Screening of hydrocarbon-utilizing and biosurfactant-producing abilities of organisms from an estuarine ecosystem in Nigeria, Africa, resulted in the isolation of five microbial strains identified as Corynebacterium sp. DDV1, Flavobacterium sp. DDV2, Micrococcus roseus DDV3, Pseudomonas aeruginosa DDV4 and Saccharomyces cerevisae DDV5. These isolates grew readily on several hydrocarbons including hexadecane, dodecane, crude oil and petroleum fractions. Axenic cultures of the organisms utilized diesel oil (1.0% v/v) with generation times that ranged significantly (t-test, P < 0.05) between 3.25 and 3.88 day, with concomitant production of biosurfactants. Kinetics of growth indicates that biosurfactant synthesis occurred predominantly during exponential growth phase, suggesting that the bioactive molecules are primary metabolites. Strains DDV1 and DDV4 were evidently the most metabolically active in terms of substrate utilization and biosurfactant synthesis compared to other strains with respective emulsification index of 63 and 78%. Preliminary biochemical characterization indicates that the biosurfactants are heteropolymers consisting of lipid, protein and carbohydrate moieties. The hydrocarbon catabolic properties coupled with biosurfactant-producing capabilities is an asset that could be exploited for cleanup of oil-contaminated matrices and also in food and cosmetic industries.

Degradation and mineralization of 2-chloro-, 3-chloro- and 4-chlorobiphenyl by a newly characterized natural bacterial strain isolated from an electrical transformer fluid-contaminated soil.

A bacterium classified as Achromobacter xylosoxidans strain IR08 by phenotypic typing coupled with 16S rRNA gene analysis was isolated from a soil contaminated with electrical transformer fluid for over sixty years using Aroclor 1221 as an enrichment substrate. The substrate utilization profiles revealed that IR08 could grow on all three monochlorobiphenyls (CBs), 2,4'- and 4,4'-dichlorobiphenyl as well as 2-chlorobenzoate (2-CBA), 3-CBA, 4-CBA, and 2,3-dichlorobenzoate. Unusually, growth was poorly sustained on biphenyl and benzoate. In growth experiments, IR08 degraded all CBs (0.27 mmol/L) in less than 96 h with concomitant stoichiometric release of inorganic chloride and growth yields were 2-3 times higher than those observed on biphenyl. In contrast to most of the chlorobiphenyl-degrading strains described in the literature, which are reported to form CBA, no metabolite was identified in the culture broth by HPLC analysis. When co-incubated with respective CBs and biphenyl, strain IR08 preferentially utilized the chlorinated analogues in less than 96 h while it took another 264 h before 90% of the initially supplied biphenyl could be degraded. The promotion of co-metabolic transformation of halogenated substrates by the inclusion of their non-halogenated derivatives may not therefore, result in universal benefits.

Metabolism of chlorinated biphenyls: use of 3,3'- and 3,5-dichlorobiphenyl as sole sources of carbon by natural species of Ralstonia and Pseudomonas.

Ralstonia sp. SA-3, Ralstonia sp. SA-4 and Pseudomonas sp. SA-6 are natural strains with a novel capacity to utilize meta-substituted dichlorobiphenyls (diCBs) hitherto not known to serve as a sole source of carbon and energy for polychlorobiphenyl-degraders. In growth experiments, axenic cultures of isolates grew logarithmically on 3,3'-diCB with generation times that ranged insignificantly (t-test, P>0.05) from 30.4 to 33.8 h. Both 3-chlorobenzoate (3-CBA) and chloride produced as metabolites were recovered in non-stoichiometric quantities. The release of chloride by the cultures lagged substantially, indicating that the initial dioxygenase attack preceded cleavage of carbon-chloride bonds and that chloride must have been released from the chlorinated hydroxypentadienoate. In the case of 3,5-diCB, SA-3 and SA-6 metabolised this substrate primarily to 3,5-CBA. The lack of chloride in the culture media coupled with stoichiometric recovery of 3,5-CBA suggests that growth by these strains occurred predominantly at the expense of the unsubstituted phenyl ring. The unique metabolic properties of these three aerobic isolates point to their potential usefulness as seeds for bioremediation of PCBs polluted environments without the need for repeated inoculation or supplementation by a primary growth substrate such as biphenyl.

Characterization of multiple novel aerobic polychlorinated biphenyl (PCB)-utilizing bacterial strains indigenous to contaminated tropical African soils.

Contaminated sites in Lagos, Nigeria were screened for the presence of chlorobiphenyl-degrading bacteria. The technique of continual enrichment on Askarel fluid yielded bacterial isolates able to utilize dichlorobiphenyls (diCBs) as growth substrates and six were selected for further studies. Phenotypic typing and 16S rDNA analysis classified these organisms as species of Enterobacter, Ralstonia and Pseudomonas. All the strains readily utilized a broad spectrum of xenobiotics as sole sources of carbon and energy. Growth was observed on all monochlorobiphenyls (CBs), 2,2'-, 2,3-, 2,4'-, 3,3'- and 3,5-diCB as well as di- and trichlorobenzenes Growth was also sustainable on Askarel electrical transformer fluid and Aroclor 1221. Time-course studies using 100 ppm of 2-, 3- or 4-CB resulted in rapid exponential increases in cell numbers and CB transformation to respective chlorobenzoates (CBAs) within 70 h. Significant amounts of chloride were recovered in culture media of cells incubated with 2-CB and 3-CB, suggesting susceptibilities of both 2- and 3-chlorophenyl rings to attack, while the 4-CB was stoichiometrically transformed to 4-CBA. Extensive degradation of most of the congeners in Aroclor 1221 was observed when isolates were cultivated with the mixture as a sole carbon source. Aroclor 1221 was depleted by a minimum of 51% and maximum of 71%. Substantial amounts of chloride eliminated from the mixture ranged between 15 and 43%. These results suggest that some contaminated soils in the tropics may contain exotic micro-organisms whose abilities and potentials are previously unknown. An understanding of these novel strains therefore, may help answer questions about the microbial degradation of polychlorinated biphenyls (PCBs) in natural systems and enhance the potential use of bioremediation as an effective tool for cleanup of PCB-contaminated soils.