Milena Colombo

Arsenic-resistant bacteria associated with roots of the wild Cirsium arvense (L.) plant from an arsenic polluted soil, and screening of potential plant growth-promoting characteristics

A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growing in an arsenic polluted soil, was studied by fluorescence in situ hybridization (FISH) analysis in conjunction with cultivation-based methods. In the bulk, rhizosphere, and rhizoplane fractions of the soil, the qualitative picture obtained by FISH analysis of the main phylogenetic bacterial groups was similar and was predominantly comprised of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The arsenic-resistant isolates belonged to 13 genera, the most abundant being those of Bacillus, Achromobacter, Brevundimonas, Microbacterium, and Ochrobactrum. Most bacteria grew in the presence of high arsenic concentrations (over 100mM arsenate and 10mM arsenite). Most strains possessed the ArsC, ArsB and ACR3 genes homologous to arsenate reductase and to the two classes of arsenite efflux pumps, respectively, peculiar to the ars operon of the arsenic detoxification system. ArsB and ACR3 were present simultaneously in highly resistant strains. An inconsistency between 16S rRNA phylogenetic affiliations and the arsenate reductase sequences of the strains was observed, indicating possible horizontal transfer of arsenic resistance genes in the soil bacterial community. Several isolates were able to reduce arsenate and to oxidise arsenite. In particular, Ancylobacter dichloromethanicum strain As3-1b possessed both characteristics, and arsenite oxidation occurred in the strain also under chemoautotrophic conditions. Some rhizobacteria produced siderophores, indole acetic acid and 1-amino-cyclopropane-1-carboxylic acid deaminase, thus possessing potential plant growth-promoting traits.

Distribution of catabolic pathways in some hydrocarbon-degrading bacteria from a subsurface polluted soil

Enrichment cultures on naphtha solvent were used to select aromatic hydrocarbon-degrading bacteria from a BTEX (benzene, toluene, ethylbenzene, xylene)-contaminated subsoil obtained from beneath a paint factory located in Milan, Italy. Fifteen isolated strains were studied for their different biodegradative capacities. Among these, 13 were able to grow on naphtha solvent. Ten were identified as Pseudomonas putida and three as Pseudomonas aureofaciens. Two other degraders were identified as Pseudomonas aeruginosa and Alcaligenes xylosoxidans subsp. denitrificans. Further molecular characterization of the isolates was carried out by randomly amplified polymorphic DNA analysis to ascertain that all the studied strains belonged to different haplotypes. The isolates were characterized for the presence of genes encoding for toluene dioxygenase, xylene monooxygenase and catechol 2,3-dioxygenase by polymerase chain reaction analysis and by Southern analysis. P. putida strain CM23, which showed homology with xylA,M, xylE and todC1C2BA genes, possessed multiple pathways which enabled the strain to grow on benzene, toluene and m-xylene.

Anaerobic digestion of winery wastewaters derived from different wine making processes

Abstract Anaerobic digestion of winery effluents derived from two different wine making processes was compared in a laboratory scale upflow filter. White winery effluents (WWE) were more easily degradable (average soluble COD removal=92%) than red winery effluents (RWE) (average soluble COD removal = 85%). Differences in the reactor microbial populations for the two effluents were also observed. Both aceticlastic and hydrogenotrophic methanogens in the circulating fractions were significantly higher during the treatment of WWE than during that of RWE. With both wastewaters, the reactor promptly reacted to volumetric organic load (Bv) stress (tripling from 4 to 12 g COD L‐1 d‐1). Following the Bv perturbation, COD removal decreased to 50%. However, after two weeks the COD removal values were as before perturbation. Volatile fatty acids, especially total VFAs and butyrate measured on the second day after the imposed Bv perturbation, were good indicators of process imbalance. Coenzyme F420 determination and ...

Characterization of a biofilter treating toluene contaminated air

The removal of toluene from an experimental gas-stream was studied in an industrial biofilter filled with poplar wood bark. Toluene degradation, approximately 85% through the operating period, resulted in low levels of toluene in the off-gas effluent. For a toluene load of 6.7 g m-3 h-1 the elimination capacity of the biofilter was found to be 6.0 g m-3 h-1. Toluene removal was due to biodegradative activity of microorganisms in the filter bed; the most probable number counts of toluene degraders increased from 2.4×102 to 6.4×107 MPN/g dry packing material in about seven months of air-toluene supply. The degradative capacity of a Burkholderia (Pseudomonas) cepacia strain, isolated from the biofilter material, as an example of the effectiveness of microbial toluence removal was tested in batch culture. The microorganism degraded completely 250 ppm of toluence supplied as sole carbon source in 24 hours. The high performance demonstrated for a long period and the mechanical and physico-chemical stability of the biofilter favour its use in industrial full-scale off-gas control.

Enzymatic and genetic profiles in environmental strains grown on polycyclic aromatic hydrocarbons

The possible generation of oxidative stress induced by aromatic hydrocarbon degradation suggests that ancillary enzyme activities could facilitate the utilization of polycyclic aromatic hydrocarbons as sole carbon source. To investigate the metabolic profiles of low molecular weight polycyclic aromatic hydrocarbon-degrading strains of Sphingobium chlorophenolicum, Rhodococcusaetherovorans, Rhodococcus opacus and Mycobacterium smegmatis, the determination of the activity of putative detoxifying enzymes (rhodanese-like and glutathione S-transferase proteins) was combined with genetic analyses. All the studied strains were able to utilize phenanthrene or naphthalene. Glutathione S-transferase activity was found in S. chlorophenolicum strains grown on phenanthrene and it was related to the presence of the bphK gene, since modulation of glutathione S-transferase activity by phenanthrene paralleled the induction of glutathione S-transferase transcript in the S. chlorophenolicum strains. No glutathione S-transferase activity was detectable in R.aetherovorans, R. opacus and in M. smegmatis strains. All strains showed 3-mercaptopyruvate:cyanide sulfurtransferase activity. A rhodanese-like SseA protein was immunodetected in R.aetherovorans, R. opacus and in M. smegmatis strains, where increase of 3-mercaptopyruvate:cyanide sulfurtransferase activity was significantly induced by growth on phenanthrene.

Bioventing of hydrocarbon ‐ contaminated soil and biofiltration of the off ‐ gas: Results of a field scaleinvestigation

Abstract Bioremediation through venting, biodegradation and biofiltration was considered to be a feasible approach to remediate a hydrocarbon‐contaminated soil from a site underneath a paint factory. Before the field‐scale treatment process was designed, a microbial enumeration study was performed to estabilish the existence of an indigenous population of microorganisms capable of degrading naphtha in the impacted soil. A significant remediation of a limited area contaminated with approximately 100 Kg of naphtha, toluene and xylenes was achieved in a 2 month treatment in which the soil was remediated to conform with local soil quality regulations. The bulk of soil removal of contaminants was achieved by vapour extraction (about 70 kg). Biodegradation also provided a significant contaminant removal (about 18 Kg). The hydrocarbons removed from the vent system were successfully biofiltered and outlet gas stream concentrations were acceptable under Italian national law. The biodegradative capacity of a mixed ...

Anaerobic expanded‐bed laboratory digester for the treatment of swine slurries. COD removal and methane generation

The performance of a digester, fed with swine slurries, under different COD specific load rates (2.1-30.3 Kg/m{sup 3}.d) and HRT (60-14 h) during start-up and steady-state periods were evaluated. The reactor (6.01 useful volume, 100 cm height, 0.2-12 cm diameter) was filled at 20% (v/v) with marl sand (30/60 mesh) selected among four different materials, after preliminary tests carried out in batch. The expansion of the granular bed up to 30% of useful the volume was obtained recycling the slurries with a peristaltic pump. During the experimental trial, COD influent increased from 5.4 Kg/m{sup 3} to 17.7 Kg/m{sup 3}, while HRT decreased from 60 to 14 h. COD remotion, CH{sub 4} yield and coenzyme F{sub 420} content in biofilm attached to inert matrices were monitored. The best results in COD remotion (72%) were obtained with a specific load of 6.2 Kg COD/m{sup 3}.d and the highest specific methane production (0.2 m{sup 3}/Kg COD rem) with a specific load of 2.2 KgCOD/m{sup 3}.d. The digester continued to run also when HRT was rapidly reduced but went through serious difficulties when specific load was increased up to 70.8 KgCOD/m{sup 3}.d. 29 refs., 4 figs., 4 tabs.