Removal of surfactant solubilized polycyclic aromatic hydrocarbons by Phanerochaete chrysosporium in a rotating biological contactor reactor

White rot fungi can oxidize surfactant solubilized polycyclic aromatic hydrocarbons (PAH). The objective of this study was to evaluate the performance of immobilized white rot fungus, Phanerochaete chrysosporium, to remove surfactant Tween 80 solubilized PAH i.e. phenanthrene, pyrene and benzo(alpha)pyrene in a rotating biological contactor (RBC) reactor. Results indicated that the immobilized P. chrysosporium in the RBC reactor system in continuous operation could effectively remove the three tested PAH at specific hydraulic loading rates and concentrations tested for each individual PAH. Batch operation of RBC reactor showed that the immobilized P. chrysosporium was stable and effective for the eight successive batch treatments of PAH in solution medium i.e. PAH removal was greater than 90% after 60 h, although only low levels of ligninolytic enzyme activity were detected. The removal of phenanthrene and pyrene in solution medium has been found to be a first order reaction in batch operation. A mass balance calculation indicated that biological oxidation was the main factor for removal of benzo(alpha)pyrene i.e. 95.7% in the RBC reactor. However, for phenanthrene and pyrene, both biological oxidation (i.e. 49 and 56%, respectively) and RBC disc foam adsorption (i.e. 44 and 34%, respectively) made a significant contribution to the removal of PAH.     

Whole cell‐catalyzed transesterification of waste vegetable oil

Enzymatic transesterification of waste cooking oil, comprising fats, oil and grease (FOG), to produce fatty acid methyl esters (FAME) i.e. biodiesel, was investigated using a novel strain of the fungus Aspergillus niger, immobilized as a whole‐cell biocatalyst. Response surface methodology (RSM), with a five‐level‐three‐factor central composite rotatable design, was used to optimize the reaction and analyze the relationship of reaction variables and their coinfluent on the response i.e. FAME yield. Independent variables that affect the transesterification reaction include temperature, feedstock water content and enzyme amount. Using RSM, a second‐order polynomial equation was derived for FAME yield using multiple regression analysis. The second‐order polynomial regression model was highly significant (P<0.001) in predicting the actual relationship between the response and the variables, where a linear relationship was apparent between observed and predicted values (R²=0.9651). In addition, the predicted determination coefficient q² i.e. 0.7723, also proved that the model has a high predictive ability. The validation experiments, under optimized conditions, showed that the predicted value of maximum FAME yield (i.e. 91.3%) was in close agreement with the experimental value (i.e. 91.8%).     

Population genetics of Plasmodium resistance genes in Anopheles gambiae: no evidence for strong selection

Anopheles mosquitoes are the primary vectors for malaria in Africa, transmitting the disease to more than 100 million people annually. Recent functional studies have revealed mosquito genes that are crucial for Plasmodium development, but there is presently little understanding of which genes mediate vector competence in the wild, or evolve in response to parasite-mediated selection. Here, we use population genetic approaches to study the strength and mode of natural selection on a suite of mosquito immune system genes, CTL4, CTLMA2, LRIM1, and APL2 (LRRD7), which have been shown to affect Plasmodium development in functional studies. We sampled these genes from two African populations of An. gambiae s.s., along with several closely related species, and conclude that there is no evidence for either strong directional or balancing selection on these genes. We highlight a number of challenges that need to be met in order to apply population genetic tests for selection in Anopheles mosquitoes; in particular the dearth of suitable outgroup species and the potential difficulties that arise when working within a closely-related species complex.     

The recent spread of a vertically transmitted virus through populations of Drosophila melanogaster

The sigma virus is a vertically transmitted pathogen that commonly infects natural populations of Drosophila melanogaster. This virus is the only known host-specific pathogen of D. melanogaster, and so offers a unique opportunity to study the genetics of Drosophila-viral interactions in a natural system. To elucidate the population genetic processes that operate in sigma virus populations, we collected D. melanogaster from 10 populations across three continents. We found that the sigma virus had a prevalence of 0-15% in these populations. Compared to other RNA viruses, we found that levels of viral genetic diversity are very low across Europe and North America. Based on laboratory measurements of the viral substitution rate, we estimate that most European and North American viral isolates shared a common ancestor approximately 200 years ago. We suggest two explanations for this: the first is that D. melanogaster has recently acquired the sigma virus; the second is that a single viral type has recently swept through D. melanogaster populations. Furthermore, in contrast to Drosophila populations, we find that the sigma viral populations are highly structured. This is surprising for a vertically transmitted pathogen that has a similar migration rate to its host. We suggest that the low structure in the viral populations can be explained by the smaller effective population size of the virus.     

Hybridization and pre-zygotic reproductive barriers in Plasmodium

Sexual reproduction is an obligate step in the life cycle of many parasites, including the causative agents of malaria (Plasmodium). Mixed-species infections are common in nature and consequently, interactions between heterospecific gametes occur. Given the importance of managing gene flow across parasite populations, remarkably little is understood about how reproductive isolation between species is maintained. We use the rodent malaria parasites P. berghei and P. yoelii to investigate the ecology of mixed-species mating groups, identify proteins involved in pre-zygotic barriers, and examine their evolution. Specifically, we show that (i) hybridization occurs, but at low frequency; (ii) hybridization reaches high levels when female gametes lack the surface proteins P230 or P48/45, demonstrating that these proteins are key for pre-zygotic reproductive isolation; (iii) asymmetric reproductive interference occurs, where the fertility of P. berghei gametes is reduced in the presence of P. yoelii and (iv) as expected for gamete recognition proteins, strong positive selection acts on a region of P230 and P47 (P48/45 paralogue). P230 and P48/45 are leading candidates for interventions to block malaria transmission. Our results suggest that depending on the viability of hybrids, applying such interventions to populations where mixed-species infections occur could either facilitate or hinder malaria control.     

Biodegradation of phenanthrene by the indigenous microbial biomass in a zinc amended soil

AIMS: To study the effect of zinc on the biodegradation of phenanthrene by the microbial biomass in soil. METHODS AND RESULTS: Uncontaminated soil was amended with zinc and phenanthrene as single or co-contaminants, and microbial metabolic activity was measured using an intracellular dehydrogenase enzyme bioassay over 37 days. Contaminants were amended at optimum, action and double the action level specified in 'The New Dutch List' (Ministry of Housing, Spatial Planning and Environment, the Netherlands, 2000). Microbial activity in soils with zinc or phenanthrene alone indicated the presence of tolerant, albeit inhibited soil micro-organisms. A zinc concentration at the optimum level of 140 mg kg(-1) in the co-contaminated soil (phenanthrene at 40 mg kg(-1)) resulted in marginal stimulation of the rate of phenanthrene biodegradation. However, Zn2+ concentrations at the action and double the action level of zinc (720 and 1440 mg kg(-1)) inhibited phenanthrene degradation. CONCLUSIONS: Biodegradation of phenanthrene in soils co-contaminated with zinc at concentrations above the action value is impeded. SIGNIFICANCE AND IMPACT OF THE STUDY: Bioremediation efforts to remove polycyclic aromatic hydrocarbon in zinc co-contaminated soils are likely to be constrained.     

Determination and occurrence of polybrominated diphenyl ethers in maternal adipose tissue from inhabitants of Singapore

Polybrominated diphenyl ethers (PBDEs), as a specific group of brominated flame retardants (BFR), are used in a variety of consumer products including electronics and household furnishings. In recent years, a marked increase in the levels of PBDEs in human biological tissues and fluids, especially breast milk, has been reported in several countries. However, few data are available from countries in the Asia-pacific region, including Singapore. This study presents a validated method procedure and the first available data of the concentrations of PBDE congeners: PBDE-47 (2,2,4,4-Tetrabromodiphenyl ether), PBDE-99 (2,2',4,4',5-Pentabromodiphenyl ether), PBDE-100 (2,2',4,4',6-Pentabromodiphenyl ether), PBDE-153 (2,2',4,4',5,5'-Hexabromodiphenyl ether), PBDE-154 (2,2',4,4',5,6'-Hexabromodiphenyl ether) in maternal adipose tissue collected from inhabitants of Singapore. Microwave-assisted extraction (MAE) of PBDEs spiked adipose tissues coupled with GC-MS analysis achieved comparable recoveries to a conventional Soxhlet Extraction (SE) procedure of between 70 and 130%. MAE also yielded comparable precision data (variance less than 13%) relative to the SE procedure. Spiked Carbon-13 PBDE congeners were also used as surrogates for MAE quality assurance and confirmed the efficiency of the procedure. PBDE congeners were detected in all of 16 maternal adipose tissues collected in Singapore, where levels were comparable to available data from Belgium.     

Ammonia removal from prawn aquaculture water using immobilized nitrifying bacteria

Intensive prawn aquaculture in tropical regions is associated with high concentrations of total ammoniacal nitrogen (TAN) as a result of high rates of prawn excretion and feed loading. Excessive TAN can adversely effect productivity and result in adverse impacts on coastal waters. Cultures of indigenous nitrifying bacteria were enriched from intensive prawn aquaculture pond water using continuous and batch enrichment techniques. Cultures were capable of TAN removal over a wide range of initial TAN concentrations - up to 200 mg/l. Cultures were immobilized onto porous clay pellets to enhance cell density and applied to culture medium and TAN-augmented pond water under aerobic conditions to determine TAN removal proficiency. Immobilized cultures were able to achieve a high TAN removal proficiency in pond water--even at a low density of 0.1 pellet per liter. A concentration of less than 0.5 mg TAN/l could be maintained under a fed-batch condition of 3.2 mg TAN/l per day, after an initial 2-day lag phase. A simplified and effective culture enrichment process was developed for culture immobilization onto pellets using TAN-augmented pond water. Overall, pellet immobilization of indigenous nitrifying bacteria represents a potentially effective TAN control system for prawn aquaculture in low-cost, but intensive tropical prawn farms.     

Directed evolution of aniline dioxygenase for enhanced bioremediation of aromatic amines

The objective of this study was to enhance the activity of aniline dioxygenase (AtdA), a multi-component Rieske non-heme iron dioxygenase enzyme isolated from Acinetobacter sp. strain YAA, so as to create an enhanced biocatalyst for the bioremediation of aromatic amines. Previously, the mutation V205A was found to widen the substrate specificity of AtdA to accept 2-isopropylaniline (2IPA) for which the wild-type enzyme has no activity (Ang EL, Obbard JP, Zhao HM, FEBS J, 274:928–939, 2007). Using mutant V205A as the parent and applying one round of saturation mutagenesis followed by a round of random mutagenesis, the activity of the final mutant, 3-R21, was increased by 8.9-, 98.0-, and 2.0-fold for aniline, 2,4-dimethylaniline (24DMA), and 2-isopropylaniline (2IPA), respectively, over the mutant V205A. In particular, the activity of the mutant 3-R21 for 24DMA, which is a carcinogenic aromatic amine pollutant, was increased by 3.5-fold over the wild-type AtdA, while the AN activity was restored to the wild-type level, thus yielding a mutant aniline dioxygenase with enhanced activity and capable of hydroxylating a wider range of aromatic amines than the wild type. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.