John Haddock

Anoxic bioremediation of hydrocarbons

The contamination of soils and sediments by petroleum is a matter of international concern because of the toxicity and refractory character of the aromatic components in the absence of oxygen. Gaseous oxygen can be injected into the anaerobic zone of a contaminated environment to stimulate biodegradation, but this is costly and inefficient. Other more soluble electron acceptors, such as nitrate or sulphate, can be used instead, but oxidation is slow and hydrocarbon degradation is incomplete. Here we describe how chlorite dismutation by perchlorate-reducing bacteria can be used as an alternative source of oxygen for degrading contaminants. This dismutation of chlorite into molecular oxygen and chloride is an intermediate step in the microbial reduction of perchlorate or chlorate.

Influence of Chlorine Substituents on Rates of Oxidation of Chlorinated Biphenyls by the Biphenyl Dioxygenase of Burkholderia sp. Strain LB400

ABSTRACT Biphenyl dioxygenase from Burkholderia(Pseudomonas) sp. strain LB400 catalyzes the first reaction of a pathway for the degradation of biphenyl and a broad range of chlorinated biphenyls (CBs). The effect of chlorine substituents on catalysis was determined by measuring the specific activity of the enzyme with biphenyl and 18 congeners. The catalytic oxygenase component was purified and incubated with individual CBs in the presence of electron transport proteins and cofactors that were required for enzyme activity. The rate of depletion of biphenyl from the assay mixture and the rate of formation ofcis-biphenyl 2,3-dihydrodiol, the oxidation product, were almost equal, indicating that the assay accurately measured enzyme-specific activity. Four classes of CBs were defined based on their oxidation rates. Class I contained 3-CB and 2,5-CB, which gave rates that were approximately twice that of biphenyl. Class II contained 2,5,3′,4′-CB, 2,3,2′,5′-CB, 2,3,4,5-CB, 2,3,2′,3′-CB, 2,4,5,2′,5′-CB, 2,5,3′-CB, 2,5,4′-CB, 2-CB, and 3,4,5-CB, which gave rates that ranged from 97 to 35% of the biphenyl rate. Class III contained only 2,3,4,2′,5′-CB, which gave a rate that was 4% of the biphenyl rate. Class IV contained 2,4,4′-CB, 2,4,2′,4′-CB, 3,4,5,2′-CB, 3,4,5,3′-CB, 3,5,3′,5′-CB, and 3,4,5,2′,5′-CB, which showed no detectable depletion. Rates were not significantly correlated with the aqueous solubilities of the CBs or the number of chlorine substituents on the rings. Oxidation products were detected for all class I, II, and III congeners and were identified as chlorinatedcis-dihydrodiols for classes I and II. The specificity of biphenyl dioxygenase for the CBs examined in this study was determined by the relative positions of the chlorine substituents on the aromatic rings rather than the number of chlorine substituents on the rings.

PHENOTYPIC AND PHYLOGENETIC CHARACTERIZATION OF BURKHOLDERIA (PSEUDOMONAS) SP. STRAIN LB400

The relevant phenotypic traits and phylogenetic relationships between Burkholderia (Pseudomonas) sp. strain LB400 and B. cepacia ATCC 25416T were compared to determine the degree to which these two strains might be related. Strain LB400 degrades chlorinated biphenyls and has been a model system for potential use in the bioremediation of polychlorinated biphenyls, while some strains of B. cepacia are plant and human pathogens. The fatty acid methyl ester profile, sole carbon source utilization, and biochemical tests confirmed that strain LB400 was a member of the genus Burkholderia. The 16S rRNA gene sequence showed that this strain was not as closely related to B. cepacia as previously suspected or to other known pathogens of this genus, but is closely related to B. phenazinium, B. caribensis, B. graminis, and three unnamed Burkholderia spp. not known to be pathogenic.

Polydiacetylene nanovesicles as carriers of natural phenylpropanoids for creating antimicrobial food-contact surfaces.

The ultimate goal of this study was developing antimicrobial food-contact materials based on natural phenolic compounds using nanotechnological approaches. Among the methyl-β-cyclodextrin-encapsulated phenolics tested, curcumin showed by far the highest activity toward Escherichia coli with a minimum inhibitory concentration of 0.4 mM. Curcumin was enclosed in liposome-type polydiacetylene/phosholipid nanovesicles supplemented with N-hydroxysuccinimide and glucose. The fluorescence spectrum of the nanovesicles suggested that curcumin was located in their bilayer region. Free-suspended nanovesicles tended to bind to the bacterial surface and demonstrated bactericidal activity toward Gram-negative (E. coli) and vegetative cells of Gram-positive (Bacillus cereus) bacteria reducing their counts from 5 log CFU mL(-1) to an undetectable level within 8 h. The nanovesicles were covalently bound to silanized glass. Incubation of E. coli and B. cereus with nanovesicle-coated glass resulted in a 2.5 log reduction in their counts. After optimization this approach can be used for controlling microbial growth, cross-contamination, and biofilm formation on food-contacting surfaces.

Optimization of Lime Pretreatment of Sweet Sorghum Bagasse for Enzymatic Saccharification

With recent emphasis on development of alternatives to fossil fuels, sincere attempts are being made on finding suitable lignocellulosic feedstocks for biological conversion to fuels and chemicals. Sweet Sorghum is among the most widely adaptable cereal grasses, with high drought resistance, and ability to grow on low quality soils with low inputs. It is a C4 crop with high photosynthetic efficiency and biomass yield. Our research objective is to optimize lime pretreatment of sweet sorghum bagasse for its enzymatic conversion into fermentable sugars for biofuels. Sweet sorghum biomass was ground and passed through a 35 mesh screen. Moisture content of the biomass was approximately 12%. It had 32.3% cellulose, 21.2% hemicelluloses, and 8.3% acid detergent lignin on dry matter basis. Lime pretreatment was provided in atmospheric pressure at 100oC. The lime concentration was varied from 0.05 g/g biomass to 0.2 g/g biomass; reaction time was 1 hour to 3 hours, and liquid loading was varied from 7 to 20 ml lime solution /g biomass sample. Pretreated biomass was hydrolyzed with mixture of two enzymes, Accellerase® 1500 (Cellulase) at 0.24 mL/g of SSB and Accellerase® XC (xylanase) at 0.25 ml/g of SSB, and measured for total reducing sugars by DNS (1,3-dinitrosalicylic acid) reagent.