Young-Sook Oh

Effects of Nutrients on Crude Oil Biodegradation in the Upper Intertidal Zone

To enhance biodegradation, nutrients in the form of slow-release fertilizer (SRF) were applied to oil-contaminated microcosms (3%, v/v) which simulated intertidal environmental systems. Although nutrient concentrations in the interstitial water were not proportional to those in amended SRF, microbial activity, growth of oil-degrading microorganisms, and oil-degradation rate were closely related to the concentration of nutrients in the interstitial water. Adding nutrients at higher dose (microcosm I, 144.4 mg C/kg sand/day, versus microcosm II, 8.5 mg C/kg sand/day) had a positive effect on oil degradation rate, which was especially obvious during the early phase of treatment. Use of pristane, phytane, and nor-hopane as biomarkers enabled the detection of significant treatment differences in hydrocarbon biodegradation, which were not reliable enough when the data were normalized to sand mass.

Simultaneous removal of benzene, toluene and xylenes mixture by a constructed microbial consortium during biofiltration

A bacterial consortium with complementary metabolic capabilities was formulated and specific removal rates were 0.14, 0.35, 0.04, and 0.39 h−1 for benzene, toluene, o-xylene, and m,p-xylene, respectively. When immobilized on a porous peat moss biofilter, removal of all five (= BTX) components was observed with rates of 1.8–15.4 g m−3 filter bed h−1. Elimination capacities with respect to the inlet gas concentrations of BTX and airflow rates showed diffusive regimes in the tested concentration range of (0.1–5.3 g m−3) and airflow (0.55–1.82 m3 m−2 h−1) except for o-xylene which reached its critical gas concentration at 0.3 g m−3.

Inhibitory effects of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) on acyl-homoserine lactone-mediated virulence factor production and biofilm formation in Pseudomonas aeruginosa PAO1

Abstract4-Hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF), a non-halogenated furanone found in a variety of fruits, has been shown to have antimicrobial activity. However, few studies have focused on its inhibitory effect on bacterial quorum sensing (QS) at levels below the non-inhibitory concentration. In this study, 0.1 μM HDMF decreased the production of QS signal molecules and inhibited QS-controlled biofilm formation by Pseudomonas aeruginosa PAO1 without causing growth inhibition. In the presence of 0.1 and 1.0 μM HDMF, biofilm production by PAO1 was reduced by 27.8 and 42.6%, respectively, compared to that by untreated control cells. HDMF (1.0 μM) also significantly affected virulence factor expression (regulated by the las, rhl, and pqs system), resulting in a significant reduction in the production of LasA protease (53.8%), rhamnolipid (40.9%), and pyocyanin (51.4%). This HDMF-dependent inhibition of virulence factor expression was overcome by increasing the levels of two QS signal molecules of P. aeruginosa, N-(3-oxo-dodecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone, suggesting reversible competitive inhibition between HDMF and these molecules. The results of this study indicate that HDMF has great potential as an inhibitor of QS, and that it may be of value as a therapeutic agent and in biofilm control, without increasing selective pressure for resistance development.

Arsenite oxidation by a facultative chemolithotrophic bacterium SDB1 isolated from mine tailing

An arsenite (As[III])-oxidizing bacterium, SDB1, was isolated from mine tailing collected from the Sangdong mine area in Korea and showed chemolithotrophic growth on As[III] and CO2 as the respective electron and carbon sources. SDB1 is Gram-negative, rod-shaped, and belongs to the Sinorhizobium-Ensifer branch of α-Proteobacteria. Growth and As[III] oxidation was enhanced significantly by the presence of yeast extract (0.005%) in minimal salt medium containing 5 mM As[III]; decreasing the doubling time from 9.8 to 2.1 h and increasing the As [III] oxidation rate from 0.014 to 0.349 pmol As [III] oxidized cell−1 h−1. As[III] oxidation nearly stopped at pH around 4 and should be performed at pH 7∼8 to be most effective. SDB1 was immobilized in calcium-alginate beads and the oxidation capacity was investigated. Specific As[III] oxidation rates obtained with SDB1 (10.1−33.7 mM As[III] oxidized g−1 dry cell h−1) were 10∼16-times higher than those reported previously with a heterotrophic bacterial strain (Simeonova et al., 2005). The stability and reusability of immobilized SDB1 strongly suggested that the immobilized SDB1 cell System can make the As[III] oxidation process technically and economically feasible in practical applications.

Monitoring nutrient impact on bacterial community composition during bioremediation of anoxic PAH-contaminated sediment

Marine harbor sediments are frequently polluted with significant amount of polycyclic aromatic hydrocarbons (PAHs) some of which are naturally toxic, recalcitrant, mutagenic, and carcinogenic. To stimulate biodegradation of PAHs in PAH-contaminated sediments collected from near Gwangyang Bay, Korea, lactate was chosen as a supplementary carbonaceous substrate. Sediment packed into 600 ml air-tight jar was either under no treatment condition or lactate amended condition (1%, w/v). Microbial community composition was monitored by bacteria-specific and archaea-specific PCR-terminal restriction fragment length polymorphism (T-RFLP), in addition to measuring the residual PAH concentration. Results showed that lactate amendment enhanced biodegradation rate of PAHs in the sediment by 4 to 8 times, and caused a significant shift in archaebacterial community in terms of structure and diversity with time. Phylogenetic analysis of 23 archaeal clones with distinctive RFLP patterns among 288 archaeal clones indicated that majority of the archaeal members were closest to unculturable environmental rDNA clones from hydrocarbon-contaminated and/or methanogenesis-bearing sediments. Lactate amendment led to the enrichment of some clones that were most closely related to PAH-degrading Methanosarcina species. These results suggest a possible contribution of methanogenic community to PAH degradation and give us more insights on how to effectively remediate PAH-contaminated sediments.

Two-step pilot-scale biofilter system for the abatement of food waste composting emission

A pilot-scale two-step biofilter system was evaluated in treating food waste composting emission for 220 days. Wood chips were packed at the bottom section while mixture of rock wool and earthworm compost (6% w/v) was packed at the top section. Inlet ammonia concentration was found to be dominant and intermittent. The overall ammonia removal of over 98% was achieved, 70% of which was removed in the wood chip section. The highest ammonia elimination capacity was determined to be 39.43 g-NH3/m3/h at 99.5% removal efficiency. From biodegradation kinetic analysis, the maximum removal rate, V m, of the wood chip section was determined to be 200 g-NH3/m3/h and the saturation constant, K s, 180 mg/m3. For the rock wool-earthworm cast mixture section, the V m was 87 g-NH3/m3/h and K s was 87 mg/m3. Complete removal of hydrogen sulfide and most trace compounds were achieved by the biofilter. Highest hydrogen sulfide elimination rate was 0.22 g-H2S/m3/h. The biofilter was optimized from 24 to 16 s EBRT with resulting low average pressure drops of 16 and 29 mm H2O/m, respectively.

Dynamic Behavior of Compost Biofilters During Periods of Starvation and Fluctuating Hydrogen Sulfide Loadings

Abstract To understand transient-state performance of biofilters and the phenomena occurring during changes and interruptions in their operating conditions, dynamic behavior of biofilters exposed to shock loadings of contaminant (H2S) and periods of starvation has been investigated. The initial startup and the response of the biofilters to step changes in the H2S concentration and air-loading rate were also presented and discussed. Biofilters responded very effectively to H2S concentration spikes at H2S mass loading rates of 19.8–48.0 g/m3h by rapidly recovering their original removal rates within 1.2–20.2 min. The recovery time after each spike showed a positive correlation to the total amount of H2S loadings during the spike. Biofilters showed capabilities of withstanding 11–28 days of starvations and recovered their full performances after the starvations without any evident lag period.