Grazia Baggi

Styrene Catabolism by a Strain of Pseudomonas fluorescens

A strain of Pseudomonas fluorescens, capable of growing on styrene as the sole C source was isolated from enrichment cultures. From the Pseudomonas cultures supplied with styrene, phenylacetic and o-hydroxyphenylacetic acids were isolated and identified, o-Hydroxyphenylacetic acid was also isolated from the cultures supplied with phenylacetate. Homogentisate 1,2-dioxygenase is induced in the cells grown either on styrene or phenylacetate or o-hydroxyphenylacetate. A pathway for styrene metabolism through the intermediary formation of phenylacetate and o-hydroxyphenylacetate which is further oxidized via homogentisate is suggested and discussed.

3-chloro-, 2,3- and 3,5-dichlorobenzoate co-metabolism in a 2-chlorobenzoate-degrading consortium: role of 3,5-dichlorobenzoate as antagonist of 2-chlorobenzoate degradation. Metabolism and co-metabolism of chlorobenzoates.

A study was made of the metabolic and co-metabolic intermediates of 2- and 3-chlorobenzoate, 2,3- and 3,5-dichlorobenzoate to elucidate the mechanism(s) involved in the negative effects observed on the growth of a chlorobenzoate-degrading microbial consortium in the presence of mixed chlorobenzoates. 2-Chloro-muconate accumulated as the end-product in the cultural broths of the microbial consortium during growth on 2-chlorobenzoate; the same 2-chloromuconate was identified in the reaction mixtures of resting cells pre-grown on 2-chlorobenzoate and exposed to 3-chloro- and 2,3-dichlorobenzoate, while in similar experiments 1,2-dihydroxy-3,5-dichloro-cyclohexa-3,5-dienoate was detected as dead-end product of 3,5-dichlorobenzoate co-metabolism. These results suggest an initial degradative attack by 2-chlorobenzoate induced dioxygenase(s). The role of 3,5-dichlorobenzoate as an antagonist of 2-chlorobenzoate degradation was also studied: in the presence of mixed 2-chloro- and 3,5-dichlorobenzoate, the 3,5-dichlorobenzoate preferential uptake by the resting cells of the chlorobenzoate-degrading consortium was observed. 2-Chlorobenzoate entered the cells only after the complete removal of the co-substrate. In growing cells experiments, the addition of 1,2-dihydroxy-3,5-dichloro-cyclohexa-3,5-dienoate, the 3,5-dichlorobenzoate co-metabolite, to 2-chlorobenzoate exerted the same antagonistic effect of the parent compound, inhibiting both the microbial growth and the degradative process. These data are discussed, allowing us to attribute the inhibitory effects observed to a substrate/co-substrate competition, though other additional causes may not be totally excluded.

Chlorophenol removal from soil suspensions: effects of a specialised microbial inoculum and a degradable analogue

Two soils of different contamination history were tested in slurry for their self-remediability towards mono-, di- and trisubstituted chlorophenols. The landfill soil showed poor ability in removing the compounds. Instead, the soil from the golf course, treated for many years with a 2,4,6-trichlorophenol derivative (Prochloraz), remediated different concentrations of the same 2,4,6TCP,2,4-dichlorophenol and monochlorophenol isomers, singly and in mixtures, at varying degradation rates. Ralstonia eutropha TCP, a specialised microorganism capable of degrading 2,4,6TCP, proved highly efficient in removing the compound from both tested soils. The same microbial inoculum allowed total removal of the ternary mixture of monochlorophenol isomers from the golf course soil, but it did not accelerate the removal of the same compounds when singly supplied. The addition of phenol as a degradable analogue was more effective in co-metabolically removing not only the single monochlorophenols, but also their mixtures, the removal occurring faster and independently of the presence of the microbial inoculum. From the golf course soil, a microorganism, phenotypically and genetically identical to R. eutropha TCP, was isolated and classified as R. eutropha TCP II.

Bacterial degradation of 6-aminocaproic acid polyamides (nylon 6) of low molecular weight

Abstract Three mixed cultures of aerobic bacteria were able to grow on 6-aminocaproic acid polyamides of low molecular weight (1400, 2100, 6800) as the only carbon and energy source. No growth was observed on polyamide of a molecular weight of 11000. Growth was accompanied by the utilization of cyclic and linear oligomers of up to eight monomeric units present in the polymeric matrix. The extent of the growth was higher on polyamides at lower molecular weight and depended on the amount of oligomers utilized.

Biotransformation of alkyl and aryl carbonates. Microbial degradation

SummaryAn enriched mixed culture was successfully grown on model alkyl and aryl carbonates. These compounds were degraded by microorganisms at different rates.P-Chlorophenyl-2-octyl carbonate andp-nitrobenzyl-2-octyl carbonate were metabolized through the formation ofp-chlorophenol andp-nitrobenzyl alcohol respectively. A strain ofAcinetobacter calcoacefcus isolated from the mixed culture utilized phenyl-2-octyl carbonate by an intracellular hydrolase to phenol and 2-octanol which were further metabolized.

Effects of the herbicide molinate on the metabolic activities of a degradative Streptomyces griseus strain

Abstract Cometabolic degradation of the herbicide molinate was tested using two microorganisms, Arthrobacter sp., strain M3 and Streptomyces griseus strain M2; the latter classified on the basis of the presence of the enzymatic cofactor SF‐420. The strains M3 and M2, inoculated in a basic salts medium with glucose as carbon source and added with 100 mg L‐1 of molinate, degraded respectively 35 and 51% of the herbicide in 36 days. Increasing concentrations of molinate, ranging from 50 to 200 mg L‐1 in glucose medium, did not affect the final ATP yield of the strain M2, but decreased the final growth yield and the ATP synthesis rate. Moreover, the onset of coenzyme SF‐420 synthesis was progressively delayed. In contrast, surprisingly, SF‐420 final yield and production rate were increased by progressive increasing concentrations of molinate in the mineral medium.

Microbial degradation of chlorobenzoates (CBAs): Biochemical aspects and ecological implications

Publisher Summary The behavior of chlorobenzoates (CBAs) in soils and waters has been carefully considered, as these compounds are used themselves as herbicides. The Chlorobenzoic acids from mono- to tri-substituted compounds, were shown susceptible to microbial attack, even if more chlorinated isomers and/or having chlorine atoms in ortho position were demonstrated more refractory to biodegradation. CBAs can be totally mineralized with stoichiometric release of the chlorine atoms, both in aerobic and anaerobic conditions, or can undergo only co-metabolic transformations giving dead-end products, which the other microorganisms could utilize for their growth. The bacterial strategies for CBA degradation, elucidated with pure cultures or in microbial consortia, turn around the detachment of chlorine atoms that may occur through: (i) oxygenolytic elimination in an early stage mediated by more or less specific 1,2- or 1,6-dioxygenases leading to the formation of catechol or chlorocatechols; (ii) spontaneous C1-release at a later stage, by lactonization of the ortho-ring fission product; (iii) initial dehalogenation through hydrolytic or oxidative reactions with the formation of corresponding hydroxy derivatives; and (iv) reductive dechlorinations, mostly occurring in anaerobic conditions, and on polychlorinated compounds, with the formation of the corresponding derivatives carrying n-1 chlorine substituents.

Biotransformation of alkyl and aryl carbonates: enantioselective hydrolysis

SummaryA strain ofAcinetobacter calcoaceticus hydrolysed phenyl-2-octyl carbonate (P-2-OC) by an inducible intracellular hydrolase to phenol and 2-octanol. Washed cells ofA. calcoaceticus grown on yeast extract produced 25% of 2-octanol with 54% enantiomeric excess of the R-enantiomer. The 2-octanol produced was oxidized to 2-octanone and then further degraded. Hydrolytic and oxidative activities, with an optimum pH of 7.0, appeared to be in the supernatant.

Microbial degradation of nitrogenous xenobiotics of environmental concern

Publisher Summary This chapter focuses on the broad and updated overview of the physiological, biochemical, and genetic basis of biodegradation of nitrogenous compounds by aerobic and anaerobic micro-organisms. Xenobiotic compounds have been used extensively in agriculture as herbicides and insecticides and in the manufacturing industry as surfactants, dyes, drugs, solvents, and so on. Aliphatic and aromatic organic nitrogen compounds represent an important fraction of these chemicals. Even if many of the nitrogenous compounds are highly toxic and often recalcitrant to microbial attack, the microorganisms exposed to these synthetic chemicals have developed the ability to utilize some of them. For every compound that has proven to be biodegradable, the load of environmental pollutants is reduced. The assessment of biodegradability opens the way for the development of microbiological methods for the clean-up of soils and waters, contaminated with synthetic compounds. As bioremediation has its basis in the physiology and ecology of micro-organisms, these methods have to be developed according to the capabilities of these micro-organisms to ensure an optimal performance in those habitats. Moreover, the development of genetic manipulation techniques gives us the possibility to construct new strains with the desired “capabilities” for the degradation of xenobiotics. The employment of these strains could enhance the possibilities to decontaminate polluted environments.

Inhibitory mechanisms by chlorobenzoate mixtures in chlorobenzoate-degrading microorganisms

Abstract]A microbial consortium selected on 2-chlorobenzoate was shown to be able to also utilise 4-chlorobenzoate and 2,5-dichlorobenzoate as sole carbon source. The consortium adapted to grow on 4-chlorobenzoate, degraded the carbon sourcevia protocatechuate, whereas the same consortium degraded 2-chlorobenzoate and 2,5-dichlorobenzoate via 1,2- or 1,6-dioxygenation of the chlorinated ring. Moreover, no significant effects on the microbial growth due to the presence of chlorobenzoate mixtures were observed when 4-chlorobenzoate was the carbon source. Instead, when mete-substituted chlorobenzoates were added as co-substrates to 2,5-dichlorobenzoate, the growth of the consortium was totally inhibited, just as when the culture utilised for growth 2-chlorobenzoate. Uptake experiments with 2-chlorobenzoate-grown resting cells showed that 3-chlorobenzoate, 2,3-dichlorobenzoate and 2,3,5-trichlorobenzoate competed with 2-chlorobenzoate, entering the resting cells both preferentially and faster than the growth substrate, that was also impeded to enter. Also 3,4-dichlo-robenzoate and 3,5-dichlorobenzoate hindered the uptake of the growth substrate (2-chlorobenzoate and 2,5-dichlorobenzoate, respectively), but they did not enter themselves the cells. Finally, 3,5-dichlorobenzoate neither entered the 4-chlorobenzoate-grown cells nor hindered 4-chlorobenzoate uptake. The relationships between growth inhibiting effects and chlorosubstituent position on the aromatic ring of the chlorobenzoates supplied as co-substrates are discussed.