Darakhshan Ahmad

Rhizospheric effects of alfalfa on biotransformation of polychlorinated biphenyls in a contaminated soil augmented with Sinorhizobium meliloti

Abstract The effects of plant–microbe–soil interactions on the biotransformation of polychlorinated biphenyls (PCBs) in a rhizosphere soil were investigated. Containers packed with 350 g of a soil contaminated with Aroclor 1242, 1248, 1254 and 1260, were planted with alfalfa ( Medicago sativa L.) and augmented with its symbiotic N 2 -fixing host rhizobium ( Sinorhizobium meliloti , strain A-025). The four treatment setups comprised a factorial combination of the presence/absence of alfalfa with the non-inoculation/inoculation of soil with S. meliloti in a completely randomized design with two replicates. Up to 44 days after planting, when the alfalfa was not fully developed, alfalfa and S. meliloti together were the most effective in PCB transformation/depletion, whereas alfalfa only was the least effective. However, by the last day of the experimental period (Day 270), when alfalfa growth was robust and full, alfalfa alone was the most effective, whereas S. meliloti alone was the least. In rhizobium-inoculated soil, soil hardness increased, soil moisture contents decreased, and both plant growth and yield were lowered, compared to non-inoculated soil. The depletion, loss or change in PCB levels may be attributed to either direct or indirect biotransformation, biotranslocation and adsorption of PCBs due to the presence of alfalfa and/or rhizobial inoculation. Either possibility underscores the possibility of using plant-rhizobacterial associations to phytoremediate soils contaminated with PCBs.

Sequencing of Comamonas testosteroni strain B-356-biphenyl/chlorobiphenyl dioxygenase genes: evolutionary relationships among Gram-negative bacterial biphenyl dioxygenases.

In a previous work, all three components of Comamonas testosteroni B-356 biphenyl (BPH)/chlorobiphenyls (PCBs) dioxygenase (dox) have been purified and characterized. They include an iron-sulphur protein (ISPBPH) which is the terminal oxygenase composed of two subunits (encoded by bphA and bphE), a ferredoxin (FERBPH) encoded by bphF and a reductase (REDBPH) encoded by bphG. bphG Is not located in the neighbourhood of bphAEF in B-356. We are reporting the cloning of B-356-bphG and the sequencing of B-356-BPH dox genes. Comparative analysis of the genes provided genetic evidence showing that two BPH dox lineages have emerged in Gram-negative bacteria. The main features of the lineage that includes B-356 are the location of bphG outside the bph gene cluster and the structure of REDBPH which is very distinct from all other aryl dioxygenase-reductases.

Are There Naturally Occurring Pleomorphic Bacteria in the Blood of Healthy Humans

ABSTRACT Dark-field microscopy of blood from healthy individuals revealed the existence of pleomorphic microorganisms. These bacteria exhibited limited growth and susceptibility to antibiotics and could be detected by fluorescent in situ hybridization and flow cytometry. They were further characterized by analysis of their 16S rRNA and gyrB genes.

Metabolism of hydroxybiphenyl and chloro-hydroxybiphenyl by biphenyl/chlorobiphenyl degradingPseudomonas testosteroni, strain B-356

SummaryA biphenyl (BP) and chlorobiphenyl (CBP) metabolizingPseudomonas testosteroni, strain B-356 was also capable of utilizing 2-, 3-, and 4-hydroxybiphenyl. Data presented here suggest that utilization of biphenyl and mono-subtituted biphenyls involves the enzymes of the same pathway. Chloro-hydroxybiphenyls were also metabolized by strain B-356. The unsubstituted ring is first hydroxylated in position 2 and 3 and then cleaved in ameta 1, and 2, position to ultimately generate the benzoic acid derivatives. Since strain B-356 was capable of utilizing benzoic acid and mono-hydroxybenzoic acids, the utilization of biphenyl, 2-, 3-, and 4-hydroxybiphenyl is complete at non-toxic concentrations of the substrates. Chlorobenzoic acids and chloro-hydroxybenzoic acids were not metabolized further by this strain. Studies usingPseudomonas putida, strain KT2440 carrying cloned BP/CBP genes from strain B-356 provided further evidence for the presence of a common pathway for the metabolism of the above compounds inP. testosteroni, strain B-356. Suggestions are made on significance of the broad substrate specificity of the enzymes of biphenyl/chlorobiphenyl pathway in regard to their possible origin and in relation to PCB mixture degradation.

Isolation and characterization of symbiotic N2-fixing Rhizobium meliloti from soils contaminated with aromatic and chloroaromatic hydrocarbons: PAHs and PCBs

Abstract Using plant modulation tests on Medicago sativa (alfalfa), the presence of a variety of strains of Rhizobium meliloti was demonstrated in soils contaminated with aromatic/chloroaromatic hydrocarbons and with no history of indigenous alfalfa presence. The contaminants were PAHs and PCBs which occurred as a result of long term (> 15 years) industrial use and/or spillage. We purified some of these strains and characterized their colony morphologies, antibiotic sensitivities, plasmid profiles, species-specific insertion element, insertion sequence IS Rm5 , genomic RFL (restriction fragment length) hybridization patterns and random primer generated DNA fragment amplification patterns with PCR (polymerase chain reaction). From these results it was concluded that the population of R. meliloti in each of these soils, is not homogeneous and is composed of several phenotypically and genetically distinct strains. Strains obtained from all three soils were all effective in symbiotic N 2 -fixation, irrespective of the nature or level of contamination, and their genomic DNAs hybridized strongly with a DNA fragment bearing bphABC genes from Comamonas testosteroni B-356. These findings indicate that at least some strains of R. meliloti are capable of inhabiting contaminated soils that have not been previously planted with a compatible host plant in the past, and suggest a possible role of rhizobia in decontamination and recycling of organic compounds; a role which could potentially use these agronomically important microbes for environmental clean up. To the best of our knowledge, this is first report on isolation of rhizobia from soils contaminated with aromatic and chloroaromatic compounds.

Cell surface properties of rhizobial strains isolated from soils contaminated with hydrocarbons: hydrophobicity and adhesion to sandy soil

Abstract Ten strains of Rhizobium meliloti and two non-rhizobial strains, Escherichia coli JM105 and Comamonas testosteroni B-356, were studied for their behaviour in soil and water matrices by determining their hydrophobicity, as measured by bacterial adherence to n -octane, and adhesion, as measured by their retention on sandy soil particles. The hydrophobicity values for the rhizobial strains were similar to that for E. coli (around 15%), whereas C. testosteroni , which belongs to the Pseudomonads group, showed a significantly higher level (33%). Both non-rhizobial strains, however, showed higher levels of adhesion, (85% and 78%, respectively) than did the rhizobial strains (≈55%). The cell surface properties of the rhizobial strains were influenced by the composition of the growth media used, being significantly higher with nutrient-rich media. The nature or level of contaminants in the soil from which these strains were originally isolated did not, however, influence these properties. These characteristics are important in determining the fate of bacteria in the unsaturated subsurface soil environment because of their influence on the vertical transport, distribution and survival. Information about these characteristics will be particularly useful in choosing strains for agricultural applications (e.g., as biofertilizers or biocontrol agents) or in situ soil environmental operations (e.g., bioaugmentation for bioremediation of pollutants).

Soil P-status and cultivar maturity effects on pea-Rhizobium symbiosis

In a green-house experiment, five cultivars of Pisum sativum L. grown on soils from 10 different locations in Tunisia, showed significant differences in nodulation, shoot dry matter (shDM) yield and shoot nitrogen content (shNC). The effect of soil on biological nitrogen fixation, as evidenced by the number and weight of nodules, was mainly attributable to the available phosphorus content. Cate-Nelson ANOVA analysis established a critical value of soil test phosphorus (STP) of 20 mg P kg−1 soil for nodule weight and number for the majority of cultivars. Within cultivars, nodulation varied with maturation period and was correlated with shoot NC. Thus, the overall interaction of soil-P content and cultivar-maturation period were correlated positively with nodulation and to symbiotic effectiveness of strains of Rhizobium leguminosarum bv. viceae indigenous to these soils. Based on an antibiotic susceptibility test and main variable factor analysis of the data obtained, 70 isolates of Rhizobia that nodulate pea, obtained from soils from agricultural sites throughout Tunisia, were identified as belonging to 18 distinct strains. These classes were identified on the basis of symbiotic efficiency parameters (shoot DM yield and shoot NC) as: ineffective (33 isolates), moderately effective (27 isolates), and efficient strains (10 isolates). This study shows that the Mateur site, an agricultural area for millennia in the northern region of Tunisia, harbors rhizobial strains that are highly efficient in fixing N2 with peas. These results also indicate the importance of strain-cultivar interrelationships and specificity.

EFFECT OF BIOAUGMENTATION ON MICROBIAL TRANSPORT, WATER INFILTRATION, MOISTURE LOSS, AND SURFACE HARDNESS IN PRISTINE AND CONTAMINATED SOILS

Three different soils, a clay, a pristine sandy loam and a PCB-contaminated sandy loam, were bioaugmented to determine the influence of clay content and contaminants on the transport of bacteria in unsaturated soils, using surface irrigation water as a transport medium. The results indicate that the transport of the implanted bacteria was influenced negatively more by the presence of PCBs than by the clay content of the soil. Transport was directly related to the frequency of irrigation and length of the intervals between irrigation periods, making these variables important factors to consider when applying bioaugmentation via downward percolating water. Other parameters measured after bacterial bioaugmentation were water infiltration, moisture loss, and surface hardness of these soils. Surface water infiltration was affected more by the soil clay content than by the hydrophobic contaminant. Infiltration was significantly but differently influenced by bioaugmentation, positively in clay, negatively in sandy loam, and negatively (to a lesser extent) in the PCB-contaminated sandy loam soils. Moisture loss was slower in the bioaugmented soil than in the control soils, with this difference being most pronounced in the PCB soil. High moisture loss in the bioaugmented clay soil rendered it the hardest soil for surface penetration.