Optimizing biodegradation of phenanthrene dissolved in nonaqueous-phase liquids

 A study was conducted to optimize the biodegradation in soil slurries of phenanthrene initially dissolved in nonaqueous-phase liquids (NAPLs). The slow rate of degradation of phenanthrene in dibutyl phthalate was increased by addition of phenanthrene-degrading microorganisms to soil slurries containing the NAPL. The rate was further increased and the acclimation phase was shortened if the inoculum was grown in a medium containing the hydrocarbon and the phthalate before addition to the slurries. Composition of the growth medium only shortened the acclimation but had no effect on the rate. Vigorous agitation increased the rate and extent of mineralization of phenanthrene in dibutyl phthalate. The effect of temperature was affected by the presence and identity of the inoculum. Rapid and extensive mineralization of phenanthrene initially present in hexadecane and diesel oil were attained by use of intense agitation of the NAPL/soil slurry and inoculation with microorganisms grown in the presence of the NAPLs, but the influence of these variables was less with other NAPLs. Vigorous agitation and addition of an inoculum 24 h after introduction of a nonionic surfactant enhanced biodegradation of phenanthrene initially in 150 Bright stock oil and dibutyl phthalate. The results suggest improved means for the bioremediation of sites contaminated with NAPLs. Received: 17 May 1995/Received revision: 1 August 1995/Accepted: 22 August 1995     

Roles of bacterial attachment and spontaneous partitioning in the biodegradation of naphthalene initially present in nonaqueous-phase liquids.

The mineralization by an Arthrobacter sp. of naphthalene initially dissolved in di(2-ethylhexyl)phthalate exhibited a slow phase followed by a rapid phase. Triton X-100, which inhibited cell attachment, prevented the onset of the second phase. Triton X-100 increased the extent of mineralization of naphthalene initially present in 2,2,4,4,6,8,8-heptamethylnonane. Cells attached to the interface mineralized the aromatic hydrocarbon at a rate four times higher than the rate of partitioning in the absence of microorganisms, but this microbial activity was markedly reduced by Triton X-100. We suggest that utilization of naphthalene originally present in nonaqueous-phase liquids may involve a partitioning-limited initial stage carried out by bacteria freely suspended in the aqueous phase and a subsequent, more rapid stage effected by bacteria present directly at the nonaqueous-liquid-water interface.     

Using volatile organic compounds to enhance atrazine biodegradation in a biobed system

The effect of the terpenes α-pinene, eucalyptol, and limonene, individually and as mixtures, on atrazine (ATZ) biodegradation and on biological activity in a biobed biomixture was evaluated. Additionally, terpenes emitted from the biomixture were captured using solid-phase microextraction. Terpenes added individually at relatively low concentrations (50 μg kg^?1) significantly enhanced ATZ degradation and biological activity during the first incubation days. No significant effect on ATZ degradation was found from adding the terpene mixture, and, interestingly, an inhibitory effect on phenoloxidase activity was found during the first 20 days of incubation when mixed terpenes were present at 100 μg kg^?1. Capturing terpenes demonstrated that during the first hour of incubation a significant fraction of the terpenes was volatilized. These results are the first to demonstrate the feasibility of using terpenes to enhance the degradation of a pesticide. However, successive applications of terpenes or the addition of materials that slowly release terpenes could sustain the ATZ degradation enhancement.     

Use of continuous-flow UV-induced mutation technique to enhance chlorinated organic biodegradation

Summary In this study, a continuous-flow UV-induced mutation (CUM) device and the CUM device coupled to a selector (CUMS) reactor were fabricated and tested for their ability to enhance the probability of obtaining populations capable of chlorinated organic biodegradation. A mixed culture of bacteria were used as the starting strain for both the CUM and CUMS processes. Populations were obtained from the CUM and CUMS systems capable of 4-chlorobenzoic acid, 2,4-dichlorobenzoic acid and chlorendic acid biodegradation. Non-UV irradiated population served as controls for the experiments and did not demonstrate chlorinated organic biodegradation over the test duration.     

Repeated application of carvone-induced bacteria to enhance biodegradation of polychlorinated biphenyls in soil

Carvone, the principal component of spearmint oil, induces biodegradation of polychlorinated biphenyls (PCB) by Arthrobacter sp. strain B1B. This study investigated the effectiveness of the repeated application of carvone-induced bacteria for bioremediation of Aroclor-1242-contaminated soil. Control treatments compared a single inoculation of carvone-induced cells, repeated applications of noninduced cells, and repeated applications of cell-free carvone/fructose medium. The results showed that repeated application of carvone-induced bacteria was the most effective treatment for mineralizing PCB, resulting in 27 ± 6% degradation of Aroclor 1242 after 9 weeks; whereas a single application of cells resulted in no significant degradation. Addition of cell-free, carvone/fructose medium resulted in 10% degradation of PCB, which suggests that this treatment stimulated biodegradation of PCB by the indigenous microflora. The di- and trichlorobiphenyls were the most readily degraded congeners. More highly chlorinated congeners, which had been previously shown to be degraded in liquid culture, were not substantially degraded in soil, indicating that low bioavailability may have limited their degradation. With the development of new technology, which permits automated in situ fermentation and delivery of degrader microorganisms, the repeated application of carvone-induced bacteria may facilitate bioremediation of PCB-contaminated soils. Received: 7 January 1998 / Received revision: 18 June 1998 / Accepted: 27 June 1998     

The biodegradation of surfactants in the environment

The possible contamination of the environment by surfactants arising from the widespread use of detergent formulations has been reviewed. Two of the major surfactants in current use are the linear alkylbenzene sulphonates (LAS) and the alkyl phenol ethoxylates (APE). These pass into the sewage treatment plants where they are partially aerobically degraded and partially adsorbed to sewage sludge that is applied to land. The biodegradation of these and a range of other surfactants both in wastewater treatment plants and after discharge into natural waters and application to land resulting in sewage sludge amended soils has been considered. Although the application of sewage sludge to soil can result in surfactant levels generally in a range 0 to 3 mg kg(-1), in the aerobic soil environment a surfactant can undergo further degradation so that the risk to the biota in soil is very small, with margins of safety that are often at least 100. In the case of APE, while the surfactants themselves show little toxicity their breakdown products, principally nonyl and octyl phenols adsorb readily to suspended solids and are known to exhibit oestrogen-like properties, possibly linked to a decreasing male sperm count and carcinogenic effects. While there is little serious risk to the environment from commonly used anionic surfactants, cationic surfactants are known to be much more toxic and at present there is a lack of data on the degradation of cationics and their fate in the environment.     

Use of a sequencing batch reactor to study the biodegradation of 4-chlorophenol in soil

Summary A sequencing batch reactor (SBR) was used to study the biodegradation of 4-chlorophenol (4CP) in a soil slurry. The SBR system was controlled by measuring the carbon dioxide evolution rate (CER) in the gas phase. The biodegradation rate was increased from 3.2 to 67 mg 4CP/l·h after 13 cycles.     

Effects of dissolved organic carbon and second substrates on the biodegradation of organic compounds at low concentrations

Pseudomonas acidovorans and Pseudomonas sp. strain ANL but not Salmonella typhimurium grew in an inorganic salts solution. The growth of P. acidovorans in this solution was not enhanced by the addition of 2.0 micrograms of phenol per liter, but the phenol was mineralized. Mineralization of 2.0 micrograms of phenol per liter by P. acidovorans was delayed 16 h by 70 micrograms of acetate per liter, and the delay was lengthened by increasing acetate concentrations, whereas phenol and acetate were utilized simultaneously at concentrations of 2.0 and 13 micrograms/liter, respectively. Growth of Pseudomonas sp. in the inorganic salts solution was not affected by the addition of 3.0 micrograms each of glucose and aniline per liter, nor was mineralization of the two compounds detected during the initial period of growth. However, mineralization of both substrates by this organism occurred simultaneously during the latter phases of growth and after growth had ended at the expense of the uncharacterized dissolved organic compounds in the salts solution. In contrast, when Pseudomonas sp. was grown in the salts solution supplemented with 300 micrograms each of glucose and aniline, the sugar was mineralized first, and aniline was mineralized only after much of the glucose carbon was converted to CO2. S. typhimurium failed to multiply in the salts solution with 1.0 micrograms of glucose per liter. It grew slightly but mineralized little of the sugar at 5.0 micrograms/liter, but its population density rose at 10 micrograms of glucose per liter or higher. The hexose could be mineralized at 0.5 micrograms/liter, however, if the solution contained 5.0 mg of arabinose per liter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Versatility of soil column experiments to study biodegradation of halogenated compounds under environmental conditions

Soil column experiments were performed to obtain insight in the different biological and physico-chemical processes affecting biodegradation of halogenated compounds under natural conditions in a water infiltration site. Lower chlorinated aromatic compounds could be degraded under aerobic conditions, whereas highly chlorinated compounds and chlorinated aliphatic compounds were mainly transformed under anaerobic conditions. Microorganisms which derive energy from reductive dechlorination were enriched and characterized. It was found that microbes could adapt to using chlorinated benzenes by evolution of new enzyme specificities and by exchange of genetic material. For halogenated pollutants, which are generally hydrophobic, sorption processes control the concentration available for biodegradation. The effects of very low concentrations of halogenated compounds on their biodegradability are described. The use of isolated bacterial strains to enhance biodegradation was evaluated with respect to their temperature-related activity and to their adhesion properties.Abbreviations 3-CB 3-chlorobenzoate - DCB dichlorobenzene - HCH hexachlorocyclohexane - IS insertion sequence - PER tetrachloroethylene - S_min minimal substrate concentration for growth - TCB trichlorobenzene - TRI trichloroethylene - filtration coefficient     

Effects of dissolved organic carbon and second substrates on the biodegradation of organic compounds at low concentrations.

Pseudomonas acidovorans and Pseudomonas sp. strain ANL but not Salmonella typhimurium grew in an inorganic salts solution. The growth of P. acidovorans in this solution was not enhanced by the addition of 2.0 micrograms of phenol per liter, but the phenol was mineralized. Mineralization of 2.0 micrograms of phenol per liter by P. acidovorans was delayed 16 h by 70 micrograms of acetate per liter, and the delay was lengthened by increasing acetate concentrations, whereas phenol and acetate were utilized simultaneously at concentrations of 2.0 and 13 micrograms/liter, respectively. Growth of Pseudomonas sp. in the inorganic salts solution was not affected by the addition of 3.0 micrograms each of glucose and aniline per liter, nor was mineralization of the two compounds detected during the initial period of growth. However, mineralization of both substrates by this organism occurred simultaneously during the latter phases of growth and after growth had ended at the expense of the uncharacterized dissolved organic compounds in the salts solution. In contrast, when Pseudomonas sp. was grown in the salts solution supplemented with 300 micrograms each of glucose and aniline, the sugar was mineralized first, and aniline was mineralized only after much of the glucose carbon was converted to CO2. S. typhimurium failed to multiply in the salts solution with 1.0 micrograms of glucose per liter. It grew slightly but mineralized little of the sugar at 5.0 micrograms/liter, but its population density rose at 10 micrograms of glucose per liter or higher. The hexose could be mineralized at 0.5 micrograms/liter, however, if the solution contained 5.0 mg of arabinose per liter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reasons for possible failure of inoculation to enhance biodegradation

Pseudomonas strains capable of mineralizing 2,4-dichlorophenol (DCP) and p-nitrophenol (PNP) in culture media were isolated from soil. One DCP-metabolizing strain mineralized 1.0 and 10 micrograms of DCP but not 2.0 to 300 ng/ml in culture. When added to lake water containing 10 micrograms of DCP per ml, the bacterium did not mineralize the compound, and only after 6 days did it cause the degradation of 1.0 microgram of DCP per ml. The organism did not grow or metabolize DCP when inoculated into sterile lake water, but it multiplied in sterile lake water amended with glucose or with DCP and supplemental nutrients. Its population density declined and DCP was not mineralized when the pseudomonad was added to nonsterile sewage, but the bacterium grew in sterile DCP-amended sewage, although not causing appreciable mineralization of the test compound. Addition of the bacterium to nonsterile soil did not result in the mineralization of 10 micrograms of DCP per g, although mineralization was evident if the inoculum was added to sterile soil. A second DCP-utilizing pseudomonad failed to mineralize DCP when added to the surface of sterile soil, although activity was evident if the inoculum was mixed with the soil. A pseudomonad able to mineralize 5.0 micrograms of PNP per ml in culture did not mineralize the compound in sterile or nonsterile lake water. The bacterium destroyed PNP in sterile sewage and enhanced PNP mineralization in nonsterile sewage. When added to the surface of sterile soil, the bacterium mineralized little of the PNP present at 5.0 micrograms/g, but it was active if mixed well with the sterile soil.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of biomass adaptation to biodegradation of dissolved organic carbon in water

In the present study the time of adaptation of fixed biomass for biodegradation of natural organic matter was investigated. The experiments were done in columns that are usually used for rapid determination of biodegradable dissolved organic carbon (BDOC). The biomass was adapted to samples with different concentrations of organic substances before measurements by pumping water to be investigated through the columns for several days. The time of adaptation was dependent on the initial concentration of the organic matter in the water sample. The adaptation time increased from 6 to 24 h with increase of concentration of acetate solution from 2 to 10 mg/l, thus adaptation rate decreased simultaneously from 0.28 to 0.11 min⁻¹. In natural water samples with the initial concentration in the range from 4.61–10.82 mg/l of dissolved organic carbon (DOC) the maximal adaptation time was less than 24 h. During the adaptation period the increase in reproducibility and decrease in the standard deviation was observed. The study showed that adaptation of column to the different concentration of organic matter in water sample is necessary in order to decrease the bias in BDOC measurements when using columns tests.     

Reasons for possible failure of inoculation to enhance biodegradation.

Pseudomonas strains capable of mineralizing 2,4-dichlorophenol (DCP) and p-nitrophenol (PNP) in culture media were isolated from soil. One DCP-metabolizing strain mineralized 1.0 and 10 micrograms of DCP but not 2.0 to 300 ng/ml in culture. When added to lake water containing 10 micrograms of DCP per ml, the bacterium did not mineralize the compound, and only after 6 days did it cause the degradation of 1.0 microgram of DCP per ml. The organism did not grow or metabolize DCP when inoculated into sterile lake water, but it multiplied in sterile lake water amended with glucose or with DCP and supplemental nutrients. Its population density declined and DCP was not mineralized when the pseudomonad was added to nonsterile sewage, but the bacterium grew in sterile DCP-amended sewage, although not causing appreciable mineralization of the test compound. Addition of the bacterium to nonsterile soil did not result in the mineralization of 10 micrograms of DCP per g, although mineralization was evident if the inoculum was added to sterile soil. A second DCP-utilizing pseudomonad failed to mineralize DCP when added to the surface of sterile soil, although activity was evident if the inoculum was mixed with the soil. A pseudomonad able to mineralize 5.0 micrograms of PNP per ml in culture did not mineralize the compound in sterile or nonsterile lake water. The bacterium destroyed PNP in sterile sewage and enhanced PNP mineralization in nonsterile sewage. When added to the surface of sterile soil, the bacterium mineralized little of the PNP present at 5.0 micrograms/g, but it was active if mixed well with the sterile soil.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of nonionic surfactants on naphthalene dissolution and biodegradation

The effect of six nonionic surfactants, Igepal CA-720, Tergitol NPX, Triton X-100, PLE4, PLE10, and PLE23, on the dissolution rate of solid naphthalene was studied in stirred batch reactors. Results showed increased mass-transfer rates with increased surfactant concentrations up to 10 kg m-3. Dissolution experiments were adequatly described by a mechanistic mass-transfer model. Partitioning of naphthalene into the micelles and the diffusion coefficients of the micelles affected the dissolution rate most significantly. Combined dissolution and biodegradation experiments with Triton X-100 or PLE10 with naphthalene showed that the biomass-formation rate of Pseudomonas 8909N (DSM No. 11634) increased concomitantly with the mass-transfer rate under naphthalene-dissolution limited conditions up to surfactant concentrations of 6 kg m-3.     

Exploiting nonionic surfactants to enhance fatty alcohol production in Rhodosporidium toruloides

Fatty alcohols (FOHs) are important feedstocks in the chemical industry to produce detergents, cosmetics, and lubricants. Microbial production of FOHs has become an attractive alternative to production in plants and animals due to growing energy demands and environmental concerns. However, inhibition of cell growth caused by intracellular FOH accumulation is one major issue that limits FOH titers in microbial hosts. In addition, identification of FOH-specific exporters remains a challenge and previous studies towards this end are limited. To alleviate the toxicity issue, we exploited nonionic surfactants to promote the export of FOHs in Rhodosporidium toruloides, an oleaginous yeast that is considered an attractive next-generation host for the production of fatty acid-derived chemicals. Our results showed FOH export efficiency was dramatically improved and the growth inhibition was alleviated in the presence of small amounts of tergitol and other surfactants. As a result, FOH titers increase by 4.3-fold at bench scale to 352.6 mg/L. With further process optimization in a 2-L bioreactor, the titer was further increased to 1.6 g/L. The method we show here can potentially be applied to other microbial hosts and may facilitate the commercialization of microbial FOH production.     

Involvement of fungi and bacteria in enhanced and nonenhanced biodegradation of carbendazim and other benzimidazole compounds in soil

The relationship between chemical structure and the enhancement of microbial degradation of three benzimidazole compounds in soil was determined. Preapplication of methyl benzimidazole-2-ylcarbamate (carbendazim or MBC), 2-aminobenzimidazole (2AB), and benzimidazole enhanced their degradation upon repeated application (self-enhanced degradation). MBC and 2AB cross-enhanced the degradation of each of these two compounds, whereas benzimidazole did not enhance the degradation of MBC. Thiabendazole (TBZ) did not enhance its own degradation or cross-enhance the degradation of MBC. No increase in the number of MBC-degrading fungi or in the capacity of soilborne fungi to degrade MBC was detected in soil exhibiting enhanced MBC degradation (MBC-history). A sharp increase in esterolytic activity in the microsomal fraction of Alternaria alternata capable of degrading MBC in culture was induced by the presence of MBC in the growth medium. 2AB was the main metabolite of MBC that accumulated in A. alternata cultures and in cell-free preparations. MBC was degraded much faster by mixed bacterial cultures that originated from MBC-history soil than in cultures from MBC-nonhistory soil. Fluctuations in the MBC degrading capacity of mixed bacterial cultures occurred during repeated subculturing of the mixed culture. Inoculation of nonhistory soil with mixed bacterial cultures resulted in enhanced MBC degradation, whereas inoculation with A. alternata did not enhance MBC degradation. It is suggested that while fungi contribute to MBC dissipation in soil, bacteria have a greater role in enhanced biodegradation of MBC in soil.     

表面活性剂的增溶作用及在土壤中的行为

表面活性剂胶束的存在是导致难溶有机化合物(HOCs)溶解度增加的主要原因,表面活性剂对土壤的影响很大,即使很低浓度的表面活性剂也会明显改变土壤的物理、化学和生物性质,其中表面活性剂的吸附过程起了主要作用,另外,表面活性剂的类型、结构和浓度以及所处环境条件和微生物种类都对土壤中植物、微生物生长和其本身的生物降解和去除有影响,这些都将导致土壤中原有污染物迁移转化的改变,应该引起人们的日益重视。