Reduction of Cr(VI) by a Consortium of Sulfate-Reducing Bacteria (SRB III)

A consortium of bacteria with tolerance to high concentrations of Cr(VI) (up to 2,500 ppm) and other toxic heavy metals has been obtained from metal-refinishing wastewaters in Chengdu, People's Republic of China. This consortium consists of a range of gram-positive and gram-negative rods and has the capacity to reduce Cr(VI) to Cr(III) as amorphous precipitates which are associated with the bacterial surfaces. An endospore-producing, gram-positive rod and a gram-negative rod accumulate the most metallic precipitates, and, over time, 80 to 95% of Cr can be removed from concentrations ranging from 50 to 2,000 ppm (0.96 to 38.45 mM). Kinetic studies revealed a first-order constant for Cr removal of 0.1518 h^-1 for an initial concentration of 1,000 ppm (19.3 mM), and the sorption isothermal data could be interpreted by the Freundlich relationship. The sorption was not entirely due to a passive interaction with reactive sites on the bacterial surfaces since gamma-irradiated, killed cells could not immobilize as much metal. When U or Zn was added with the Cr, it was also removed and could even increase the total amount of Cr immobilized. The consortium was tolerant to small amounts of oxygen in the headspace of tubes, but active growth of the bacteria was a requirement for Cr immobilization through Cr(VI) reduction, resulting in the lowering of E_h. Our data suggest that the reduction was via H₂S. This consortium has been named SRB III, and it may be useful for the bioremediation of fluid metal-refining wastes.     

Feeding behaviour of Cerastoderma edule in a turbid environment: physiological adaptations and derived benefit

Resuspension of bottom sediments by wind andtide-driven currents often occur in shallow waters,coastal embayments and estuaries. These processes maylead to dramatic variations in the concentration andorganic richness of suspended particle assemblages.Since resuspended matter is mainly inorganic,decreasing organic contents are usually associatedwith higher seston loads.Under this environmental context the feeding behaviourof bivalves shows a wide degree of plasticity, whichhas been interpreted as having high adaptive value. Inorder to evaluate benefits derived from thisbehaviour, we have used functional relationshipsobtained in previous studies, relating feedingparameters to characteristics of suspended food, topredict the effect that different feeding responseswould have exerted. In cockles, main processesdetermining energy acquisition are feeding rates andpreingestive food selection. Thus, the procedurefollowed in the present work consisted of simulatingrates of food absorption under alternative feedingbehaviours characterised by: (a) no preferentialingestion of filtered organic matter and (b) maintenance ofconstant clearance rates. In theabsence of selection of organic matter at thepreingestive level, ingestion rate of organics (OIR)would decline with increasing seston loads to 30% ofvalues predicted by functions fitted to experimentaldata; difference in absorption rate (AR) would be evengreater, falling to 10%, due to the strong effectthat the organic content of ingested matter exerts onabsorption efficiency. On the other hand, had theclearance rate (CR) kept constant despite theincreasing seston load, OIR and AR would have fallento values respectively 30% and 49% lower than actualvalues.From these results it is concluded that the ability ofsorting particles before ingestion and the capabilityof adjusting clearance rate are key elements in thefeeding behaviour that enable cockles to be welladapted to cope with changes in the water columncaused by resuspension events.     

Theoretical basis for the interpretation of surface permeability data by a transient method

Surface permeability data are frequently required when the system under study consists of a multiple zone membrane. Rotunno et al. (1970) developed a transient method to determine surface permeabilities in which the solute from one compartment is fully absorbed by the membrane without being transferred to the other. The theoretical analysis of the various possible situations is presented here to show that: (1) a linear plot of uptake vs. contact time can be expected for the most simple case (quasi-steady state in the external zone) even in the presence of considerable boundary layer resistance, and (2) a linear display of experimental data is not exclusive for that case, but it can also occur in the more complex situation of a composite resistance of a semi-infinite medium plus boundary layer. On this basis, different alternatives to interpret the data are suggested, according to the physical situation and the equations developed for each case.     

Immunohistochemistry in the evaluation of neovascularization in tumor xenografts

Angiogenesis, or neovascularization, is known to play an important role in the neoplastic progression leading to metastasis. CD31 or Factor VIII-related antigen (F VIII RAg) immunohistochemistry is widely used in experimental studies for quantifying tumor neovascularization in immunocompromised animal models implanted with transformed human cell lines. Quantification, however, can be affected by variations in the methodology used to measure vascularization including antibody selection, antigen retrieval (AR) pretreatment, and evaluation techniques. To examine this further, we investigated the microvessel density (MVD) and the intensity of microvascular staining among five different human tumor xenografts and a mouse syngeneic tumor using anti-CD31 and F VIII RAg immunohistochemical staining. Different AR methods also were evaluated. Maximal retrieval of CD31 was achieved using 0.5 M Tris (pH 10) buffer, while maximum retrieval of F VIII RAg was achieved using 0.05% pepsin treatment of tissue sections. For each optimized retrieval condition, anti-CD31 highlighted small vessels better than F VIII RAg. Furthermore, the MVD of CD31 was significantly greater than that of F VIII RAg decorated vessels (p<0.001). The choice of antibody and AR method has a significant affect on immunohistochemical findings when studying angiogenesis. One also must use caution when comparing studies in the literature that use different techniques and reagents.     

Impact of the Phoretic Phase on Reproduction and Damage Caused by Varroa destructor (Anderson and Trueman) to Its Host,the European Honey Bee (Apis mellifera L.)

Varroa destructor is a parasitic mite of the honeybee that causes thousands of colony losses worldwide. The parasite cycle is composed of a phoretic and a reproductive phase. During the former, mites stay on adult bees, mostly on nurses, to feed on hemolymph. During the latter, the parasites enter brood cells and reproduce. We investigated if the type of bees on which Varroa stays during the phoretic phase and if the duration of this stay influenced the reproductive success of the parasite and the damage caused to bees. For that purpose, we used an in vitro rearing method developed in our laboratory to assess egg laying rate and the presence and number of fully molted daughters. The expression level of two Varroa vitellogenin genes (VdVg1 and VdVg2), known to vary throughout reproduction, was also quantified. Results showed that the status of the bees or time spent during the phoretic phase impacts neither reproduction parameters nor the Varroa vitellogenin genes levels of expression. However, we correlated these parameters to the gene expression and demonstrated that daughters expressed the vitellogenin genes at lower levels than their mother. Regarding the damage to bees, the data indicated that a longer stay on adult bees during the phoretic phase resulted in more frequent physical deformity in newborn bees. We showed that those mites carry more viral loads of the Deformed Wing Virus and hence trigger more frequently overt infections. This study provides new perspectives towards a better understanding of the Varroa-honeybee interactions.     

Monooxygenases involved in GA12 and GA14 synthesis in Gibberella fujikuroi

A microsomal preparation from mycelia of the gibberellin (GA)-producing fungus Gibberella fujikuroi catalyzed the first two steps in the conversion of the biosynthetic intermediate GA12-aldehyde to gibberellic acid (GA3). [14C]GA12-Aldehyde was converted to radiolabelled GA14, the major product, together with smaller amounts of non-hydroxylated GA12. The microsomal activities required reduced pyridine nucleotides and molecular oxygen. However, GA12 and GA14 synthesis differed markedly in the preferred electron source. Formation of GA12 required NADH or NADPH, while GA14 synthesis from GA12-aldehyde occurred only with NADPH. Marked differences were also found in the activating effect of FAD. When NADPH was the reductant, the rate of GA14 synthesis was enhanced 3.5 times by 5 microM FAD while this flavin nucleotide did not alter the synthesis of GA12. In contrast, GA12 synthesis was activated 3.8 times by 50 microM FAD in the presence of NADH. Both activities were inhibited by carbon monoxide and cytochrome c. These properties suggest that the 3beta-hydroxylation of GA12-aldehyde and further oxidation of carbon 7 are catalyzed by cytochrome P-450 monooxygenases in Gibberella fujikuroi.