Shiu-Mei Liu

Reductive dechlorination of chlorophenols and pentachlorophenol in anoxic estuarine sediments

The fates of three isomers of chlorophenol (CP), three isomers of dichlorophenol (DCP), and pentachlorophenol (PCP) were investigated in anoxic estuarine sediment slurries. The relative dechlorination rates of the three isomers of CP were 2-CP > 3-CP > 4-CP. All three isomers of CP were dechlorinated to phenol. The relative dechlorination rates of the three isomers of DCP were 2,5-DCP > 3,4-DCP > 3,5-DCP. All these isomers were dechlorinated to 3-CP. PCP was transformed through sequential dechlorination and the relative order of product formation was (i) 2,3,4,5-tetrachlorophenol (TeCP), (ii) 3,4,5-trichlorophenol (TCP) and (iii) 3,5-dichlorophenol (DCP). 3,4-DCP was also observed. The rates of PCP dechlorination were greatest in 3,4-DCP-adapted and 2-CP-adapted sediment slurries. The PCP-adapted sediment cultures were inhibited by the addition of molybdate, or molybdate plus sulfate, but not inhibited by the addition of sulfate or bromoethanesulfonic acid (BESA). Sulfate consumption by the cultures corresponded to the stoichiometric values expected for reductive dechlorination of PCP to DCP (PCP:SO4−2 = 1:1.5). The addition of metabolizable carbon sources to sediment slurries partially repressed PCP dechlorination.

Toxicity and anaerobic biodegradability of pyridine and its derivatives under sulfidogenic conditions

Attempts were made to correlate the chemical structure of pyridine and 15 pyridine derivatives with both their biodegradability by estuarine sediment microorganisms under anaerobic conditions and also with their toxicity to the marine bacterium Vibrio fischeri Beijerinck 1889 by using the Microtox bacterial assay. Among monosubstituted pyridines, comparisons of different substituents at positions C-2, C-3, or C-4 atom of the pyridine ring showed that isomers of carboxylpyridine (COOHPYR), hydroxypyridine (OHPYR), and cyanopyridine (CNPYR) were more susceptible to biotransformation than isomers of chloropyridine (ClPYR) and methylpyridine (CH3PYR) in anoxic estuarine sediment slurries under sulfidogenic conditions. Isomers with the functional group at the C-2 or C-3 atom of the pyridine ring were biotransformed faster than those with the same functional group at C-4. The only exception was 4-ClPYR, which was biotransformed within 130 days, while 2- and 3-ClPYR continued to persist in the anoxic sediment slurries. Median effect concentrations (EC50) of pyridine and pyridine derivatives were in the range of 0.027 to 49.1 mmol/L. Pyridine derivatives with -CN and -OH functional groups tended to be less toxic, while pyridine derivatives with -CH3, -Cl, and -COOH functional groups tended to be more toxic. Isomers with the substituent at C-2 were less toxic than the C-3 or C-4 isomers. There was no clear correlation between the pseudo-first-order rate constants for the microbial transformation of pyridine and its derivatives and their toxicity to the marine bacterium.

CO2–H2-dependent anaerobic biotransformation of phthalic acid isomers in sediment slurries

This paper investigates the anaerobic biotransformation of three isomers of phthalic acid and benzoic acid in sediment slurries under four different atmospheres [N(2), N(2)/H(2) (19:1, v/v), CO(2), and CO(2)/H(2) (4:1, v/v)]. Significant differences were observed in lag periods and biotransformation rates among the phthalic acid isomers and under the different atmospheres. In most cases, the relative biotransformation rates of the three isomers of phthalic acid were ortho-phthalic acid>isophthalic acid>terephthalic acid. Benzoate was transformed faster than any isomer of phthalic acid. Since biotransformation of phthalic acid isomers in sediment slurries was enhanced by high initial levels of H(2) and CO(2) in the headspace, we propose a pathway for phthalic acid biodegradation in which the initial transformation to benzoate is CO(2)-H(2) dependent. Acetogenic bacteria were investigated for their possible involvement in this transformation reaction, but when MPN counts were used to compare the growth dynamics of acetogenic bacteria with the time course of the terephthalic acid transformation under N(2)/H(2) (19:1, v/v) and CO(2)/H(2) (4:1, v/v) atmospheres, the results were inconclusive.

Anaerobic biotransformation of pyridine in estuarine sediments

Abstract The potential for biotransformation of pyridine in sediments from the Tsengwen River was examined. Along the river, from a freshwater (0.0% salinity) to an oceanic (3.7% salinity) environment, sediment was collected from five sampling stations. Sediment slurries were incubated in an anaerobic mineral salts medium that was amended with sulfate or sulfate plus Fe(OH)3 or MnO2. In sulfate amended sediment slurries, pyridine was removed only in the sediment slurries collected from the oceanic site. Amendment of amorphous Fe(OH)3 or MnO2 in addition to sulfate greatly facilitated the onset of pyridine removal in the sediment slurries collected from the freshwater site but not in the sediment slurries collected from the more saline sites. Addition of BESA or molybdate into Fe(OH)3 amended sediment slurries sometimes enhanced pyridine removal and sometimes inhibited pyridine removal. In MnO2 amended sediment slurries, addition of BESA enhanced pyridine removal, while addition of molybdate inhibited pyridine removal.

Biodegradation of anthraquinone dyes by Shewanella sp. NTOU1 under anaerobic conditions

Shewanella sp. NTOU1 was able to decolorize a range of anthraquinone dyes [Reactive Blue 4 (RB4), Reactive Blue 19 (RB19), Mordant Red 11 (MR11), Disperse Red 15 (DR15), and Disperse Blue 3 (DB3)] under anaerobic conditions. By supplementing the medium with formate and ferric citrate as the electron donor and acceptor, respectively and cultivating it under the optimum pH (8-9) and temperature (45 degrees C), this strain could decolorize these dyes (1,000 mg/L) at the initial color removal rates of 15-126 mg/L/h and the rates among them were RB19 > RB4 > DB3 > DR15 > MR11. The extent of color removal was in the range of 90-98% for RB19, 86-96% for RB4, 39-41% for MR11, 69-82% for DR15, and 89-91% for DB3. Based on the decolorization products detected by means of GC/MS analyses, probable pathways for the decolorization of these dyes by this strain were proposed.

Biotransformation of p-toluic acid in anoxic estuarine sediments under a CO2 or N2/H2 atmosphere

The composition of the headspace gas affected the growth dynamics of microbial populations and the biotransformation pattern of p-toluic acid in anoxic estuarine sediments. Under CO2 atmosphere, p-toluic acid was transformed by the sediment microorganisms without a lag period, while under N2/H2 atmosphere, p-toluic acid was transformed after a lag period of 55 days. Under the N2/H2 atmosphere, the methanogen population, following a rapid increase of almost two orders of magnitude, remained at a high level until just before the onset of biotransformation. We hypothesize that during the lag period, the hydrogenotrophic methanogens were removing the H2, a step which is essential before the reaction can be exergonic. Acetogenic bacteria did not initiate decarboxylation as the first step of biotransformation under either atmosphere. Neither the methanogens nor the acetogenic bacteria appeared to be directly involved in the biotransformation of p-toluic acid under either atmosphere. Under the CO2 atmosphere, biotransformation of p-toluic acid involved sulfate-reducing bacteria, while under N2/H2, both sulfate-reducing bacteria and other eubacteria were involved.