Hongqi Wang

Uptake modes of octadecane by Pseudomonas sp. DG17 and synthesis of biosurfactant

Aims:  In order to gain more insight into the uptake modes of octadecane by bacteria.

Uptake and trans-membrane transport of petroleum hydrocarbons by microorganisms

Petroleum-based products are a primary energy source in the industry and daily life. During the exploration, processing, transport and storage of petroleum and petroleum products, water or soil pollution occurs regularly. Biodegradation of the hydrocarbon pollutants by indigenous microorganisms is one of the primary mechanisms of removal of petroleum compounds from the environment. However, the physical contact between microorganisms and hydrophobic hydrocarbons limits the biodegradation rate. This paper presents an updated review of the petroleum hydrocarbon uptake and transport across the outer membrane of microorganisms with the help of outer membrane proteins.

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils. Bidens maximowicziana is a new Pb hyperaccumulator, which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb. The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues. The Pb distribution order in the B. maximowicziana was: leaf > stem > root. The effect of amendments on phytoremediation was also studied. The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application. Compared with CK (control check), EDTA application promoted translocation of Pb to overground parts of the plant. The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg. This research demonstrated that B. maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil, especially, combination with EDTA.

Isolation and characterization of gasoline-degrading bacteria from gas station leaking-contaminated soils

The effects of culture conditions in vitro and biosurfactant detection were studied on bacterial strains capable of degrading gasoline from contaminated soils near gas station. The main results were summarized as follows. Three bacteria (strains Q 10, Q14 and Q18) that were considered as efficiently degrading strains were isolated and identified as Pseudomonas sp., Flavobacterium sp. and Rhodococcus sp., respectively. The optimal growth conditions of three bacteria including pH, temperature and the concentration of gasoline were similar. The reduction in surface tension was observed with all the three bacteria, indicating the production of biosurfactant compounds. The value of surface tension reduced by the three strains Q10, Q14 and Q18 was 32.6 mN x m, 12.4 mNx m and 21.9 mN x m, respectively. Strain Q10 could be considered as a potential biosurfactant producer. Gasoline, diesel oil, benzene, toluene, ethylbenzene and xylene (BTEX) could easily be degraded by the three isolates. The consortium was more effective than the individual cultures in degrading added gasoline, diesel oil, and BTEX. These results indicate that these strains have great potential for in situ remediation of soils contaminated by gas station leaking.

Trans-membrane transport of fluoranthene by Rhodococcus sp. BAP-1 and optimization of uptake process

The mechanism of transport of (14)C-fluoranthene by Rhodococcus sp. BAP-1, a Gram-positive bacterium isolated from crude oil-polluted soil, was examined. Our finding demonstrated that the mechanism for fluoranthene travel across the cell membrane in Rhodococcus sp. BAP-1 requires energy. Meanwhile, the transport of fluoranthene involves concurrent catabolism of (14)C, that leading to the generation of significant amount of (14)CO2. Combined with trans-membrane transport dynamic and response surface methodology, a significant influence of temperature, pH and salinity on cellular uptake rate was screened by Plackett-Burman design. Then, Box-Behnken design was employed to optimize and enhanced the trans-membrane transport process. The results predicted by Box-Behnken design indicated that the maximum cellular uptake rate of fluoranthene could be achieve to 0.308μmolmin(-1)mg(-1)·protein (observed) and 0.304μmolmin(-1)mg(-1)·protein (predicted) when the initial temperature, pH and salinity were set at 20°C, 9% and 1%, respectively.

Effect of Surfactant SDS, Tween 80, Triton X-100 and Rhamnolipid on Biodegradation of Hydrophobic Organic Pollutants

The effects of synthetic surfactants SDS, Tween 80, Triton X-100 on bacteria Flauobacteriurn sp. Q14 capable of degrading gasoline were studied. Biosurfactant rhamnolipid was used to analyze the effect on the biodegradation of n-hexadecane and the cell surface hydrophobicity for Bacillus sp. DQ02. The results showed that all the three chemical surfactants could delay the logarithmic phase of Flauobacteriurn sp. Q14. The anionic surfactant SDS did not significantly increase the degradation rate of diesel both at day 2 and 4. The maximum degradation value was 42.2% and 44.5% at 100 mg/L in the presence of Triton X-100 and Tween 80, respectively. The removal efficiency declined with the increase of concentration of surfactants over 100 mg/L. At day 4, the maximum degradation value reached 44.7% and 46.3% at 200 mg/L. The degradation of n-hexadecane by Bacillus sp.DQ02 was increased 11.6% within 48 h in the presence of the rhamnolipid than that of in the absence of the rhamnolipid. The growth of the strain and BATH (bacterial adherence to hydrocarbon) increased with obviously in the presence of the rhamnolipid. And the BATH reached 44% in the presence of rhamnolipid. Moreover, the interfacial tension decreased almost half with the addition of rhamnolipid.

Trans-membrane transport of n -octadecane by Pseudomonas sp. DG17

The trans-membrane transport of hydrocarbons is an important and complex aspect of the process of biodegradation of hydrocarbons by microorganisms. The mechanism of transport of 14C n-octadecane by Pseudomonas sp. DG17, an alkane-degrading bacterium, was studied by the addition of ATP inhibitors and different substrate concentrations. When the concentration of n-octadecane was higher than 4.54 μmol/L, the transport of 14C n-octadecane was driven by a facilitated passive mechanism following the intra/extra substrate concentration gradient. However, when the cells were grown with a low concentration of the substrate, the cellular accumulation of n-octadecane, an energy-dependent process, was dramatically decreased by the presence of ATP inhibitors, and n-octadecane accumulation continually increased against its concentration gradient. Furthermore, the presence of non-labeled alkanes blocked 14C n-octadecane transport only in the induced cells, and the trans-membrane transport of n-octadecane was specific with an apparent dissociation constant Kt of 11.27 μmol/L and Vmax of 0.96 μmol/min/mg protein. The results indicated that the trans-membrane transport of n-octadecane by Pseudomonas sp. DG17 was related to the substrate concentration and ATP.

Selective pseudosolubilization capability of Pseudomonas sp. DG17 on n-alkanes and uptake mechanisms analysis

Pseudosolubilized ability of Pseudomonas sp. DG17 on n-alkanes, role of biosurfactants in n-octadecane uptake and trans-membrane transport mechanism of n-octadecane were studied by analyzing amount of pseudosolubilized oil components in water phase, and the fraction of radiolabeled 14C n-octadecane in the broth and cell pellet. GC-MS results showed that pseudosolubilized oil components were mainly C12 to C28 of n-alkanes. In n-octadecane broth, pseudosolubilized n-octadecane could be accumulated as long as pseudosolubilized rate was faster than mineralization rate of substrate, and the maximum concentration of pseudosolubilized n-octadecane achieved to 45.37 mg·L−1. All of these results showed that Pseudomonas sp. DG17 mainly utilized alkanes by directly contacting with pseudosolubilized small oil droplets in the water phase. Analysis of 14C amount in cell pellet revealed that an energy-dependent system mainly controlled the trans-membrane transport of n-octadecane.

Factors influencing the trans-membrane transport of n-octadecane by Pseudomonas sp. DG17

In soil bioremediation techniques, the trans-membrane transport of hydrocarbons across the cell membrane is a new and complex point of understanding the process of hydrocarbons biodegradation. In this study, the effect of different environmental factors, including substrate concentration, bacterial inoculums, pH, salinity, substrate analogues and nutrients, on the transport of [14C]n-octadecane by Pseudomonas sp. DG17 was investigated. The results showed that cellular [14C]n-octadecane levels increased along with the increase in the substrate concentration. However, the trans-membrane transport of [14C]n-octadecane was a saturable process in the case of equal amounts of inoculum (biomass). The highest concentration of accumulated [14C]n-octadecane was 0.51 μmol mg−1 ± 0.028 μmol mg−1 after incubation for 20 min. Meanwhile, the cellular n-octadecane concentration decreased along with the biomass increase, and reached a stable level. Acidic/alkaline conditions, high salinity, and supplement of substrate analogues could inhibit the transport of [14C]n-octadecane by Pseudomonas sp. DG17, whereas nitrogen or phosphorus deficiency did not influence this transport. The results suggested that trans-membrane transport of octadecane depends on both the substrate concentration and the microorganism biomass, and extreme environmental conditions could influence the biodegradation ability of microorganisms through inhibiting the transport of extracellular octadecane.

Immobilization of Pseudomonas sp. DG17 onto sodium alginate-attapulgite-calcium carbonate.

A strain of Pseudomonas sp. DG17, capable of degrading crude oil, was immobilized in sodium alginate–attapulgite–calcium carbonate for biodegradation of crude oil contaminated soil. In this work, proportion of independent variables, the laboratory immobilization parameters, the micromorphology and internal structure of the immobilized granule, as well as the crude oil biodegradation by sodium alginate–attapulgite–calcium carbonate immobilized cells and sodium alginate–attapulgite immobilized cells were studied to build the optimal immobilization carrier and granule-forming method. The results showed that the optimal concentrations of sodium alginate–attapulgite–calcium carbonate and calcium chloride were 2.5%–3.5%, 0.5%–1%, 3%–7% and 2%–4%, respectively. Meanwhile, the optimal bath temperature, embedding cell amount, reaction time and multiplication time were 50–60 °C, 2%, 18 h and 48 h, respectively. Moreover, biodegradation was enhanced by immobilized cells with a total petroleum hydrocarbon removal ranging from 33.56% ± 3.84% to 56.82% ± 3.26% after 20 days. The SEM results indicated that adding calcium carbonate was helpful to form internal honeycomb-like pores in the immobilized granules.