Continuous Production of Biogenic Magnetite Nanoparticles by the Marine Bacterium Magnetovibrio blakemorei Strain MV-1T with a Nitrous Oxide Injection Strategy

Magnetotactic bacteria (MTB) produce magnetosomes, which are membrane-embedded magnetic nanoparticles. Despite their technological applicability, the production of magnetite magnetosomes depends on the cultivation of MTB, which results in low yields. Thus, strategies for the large-scale cultivation of MTB need to be improved. Here, we describe a new approach for bioreactor cultivation of Magnetovibrio blakemorei strain MV-1^T. Firstly, a fed-batch with a supplementation of iron source and N₂O injection in 24-h pulses was established. After 120 h of cultivation, the production of magnetite reached 24.5 mg∙L⁻¹. The maximum productivity (16.8 mg∙L⁻¹∙day⁻¹) was reached between 48 and 72 h. However, the productivity and mean number of magnetosomes per cell decreased after 72 h. Therefore, continuous culture in the chemostat was established. In the continuous process, magnetite production and productivity were 27.1 mg∙L⁻¹ and 22.7 mg∙L⁻¹∙day⁻¹, respectively, at 120 h. This new approach prevented a decrease in magnetite production in comparison to the fed-batch strategy.     

Attempted transmission of Ehrlichia risticii by field-captured Dermacentor variabilis (Acari: Ixodidae)

The capability of field-collected American dog ticks, Dermacentor variabilis, to infect horses with Ehrlichia risticii, causative agent of Potomac horse fever (PHF), was examined by allowing adult ticks collected from horse farms with a history of PHF to feed on susceptible horses. More than 500 male and female ticks attached and fed on 3 test horses; however, no clinical or serologic evidence of PHF was observed in treated or control horses. All horses were challenge exposed with E risticii-infective blood by inoculation at 60 to 65 days after ticks fed, and all developed clinical PHF with subsequent seroconversion. The data, therefore, indicated that adult D variabilis, a common parasite of horses on Maryland premises where PHF is enzootic, may not serve as a vector of E risticii.     

Regulation of urease production in soil by microbial assimilation of nitrogen

Summary Studies of the effects of different forms of N on urease production in soils amended with organic C showed that although microbial activity, as measured by CO₂ production, was stimulated by the addition of NH₄ ⁺ or NO₃ ^- to C-amended soils (200 mol glucose-C g^–1 soil), urease production was repressed by these forms of N. The addition of L-methionine sulfoximine, an inhibitor of inorganic N assimilation by microorganisms, relieved the NH₄ ⁺ and NO₃ ^- repression of urease production in C-amended soil. The addition of sodium chlorate, an inhibitor of NO₃ ^- reduction to NH₄ ⁺ by microorganisms, relieved the NO₃ ^- repression of urease production, but did not eliminate the repression associated with NH₄ ⁺. These observations indicate that microbial production of urease in C-amended soils is not directly repressed by NH₄ ⁺ or NO₃ ^-, but by products formed by microbial assimilation of these forms of N. This conclusion is supported by our finding that the biologically active L-isomers of alanine, arginine, asparagine, aspartate, and glutamine, repressed urease production in C-amended soil, whereas the D-isomers of these amino acids had little or no influence on urease production. This work suggests that urease synthesis by soil microorganisms is controlled by the global N regulon.     

Effects of hexavalent chromium on development of crabs,Rhithropanopeus harrisii and Callinectes sapidus

Survival of Rhithropanopeus harrisii larvae from hatching to first crab stage occurred in Na₂CrO₄ concentrations from 1.1 to 29.1 ppm. Estimated LC50 for complete zoeal development was 17.8 ppm Na₂CrO₄ and it was 13.7 ppm for development to first crab stage. A concentration of 1.1 ppm Na₂CrO₄ was nontoxic, while Na₂CrO₄ concentrations of 7.2 and 14.5 ppm were sublethal and concentrations of 29.1 to 58.1 ppm were acutely toxic. Low concentrations of Na₂Cr0₄ caused an increase in swimming speed and high concentrations caused a decline. Survival of Callinectes sapidus larvae occurred in Na₂CrO₄ concentrations from 1.1 to 4.7 ppm. The LC50 for complete zoeal development was estimated to be 2.9 ppm Na₂CrO₄ and the LC50 for development to first crab stage was estimated to be 1.0 ppm Na₂CrO₄ The total Cr in sodium chromate is 32% by weight (Tacey,1981), hence, the total Cr concentrations tested were 32% of the Cr salts given above. Statistical analyses of the data on survival, duration and mortality of larvae are presented.     

Effect of bulk density and soil water tension on denitrification in the rhizosphere of spring wheat (Triticum vulgare

Summary Pot experiments were carried out to study the influence of bulk density (D _b), soil water tension (pF) and presence of plants (spring wheat) on denitrification in a low-humus B_t-horizon of a udalf. Pots of only 5-cm depth were found to be most suitable for the experiments when using the acetylene inhibition method. Almost homogeneous soil compaction between 1.1 and 1.6g soil cm^–3 was achieved by a Proctor tamper. Water tensions were adjusted by means of ceramic plates on which negative pressure was applied. No denitrification was detected in unplanted pots. With planted pots and increasing bulk density denitrification increased more in pots with 14-day-old plants than in pots with 7-day-old plants. With 14-day-old plants N₂O emission pot^–1 increased steadily from 2 mol at D _b 1.1 to 8 mol at D _b 1.6, when soil moisture was adjusted to pF 1.5, although root growth was impaired by higher bulk density. From an experiment with different bulk densities and water tensions it could be deduced that the air-filled porosity ultimately determined the rate of denitrification. When low water tension was applied for a longer period, water tension had an overriding effect on total denitrification. Denitrification intensity, however, i.e. the amount of N₂O g^–1 root fresh weight, was highest when low water tension was accompanied by high bulk density. The results suggest that the increase in denitrification intensity at oxygen stress is partly due to higher root exudation.     

Epidemiology of porcine non-specific colitis on Scottish farms

The objective of this study was to investigate epidemiological risk factors for porcine non-specific colitis (NSC). Forty-seven Scottish pig farms, with and without a clinical history of diarrhoea during the growing period (15-40 kg), were selected. The study included farm visits, clinical inspection of pigs, completion of farm management questionnaires, pathological tests into the cause of the diarrhoea and analysis of the non-starch polysaccharide (NSP) content of feeds. The results from 17 farms designated as NSC and 10 control farms suggest dietary associations with NSC. Farms with NSC fed diets with significantly higher levels of NSPs, especially containing the sugars glucose, arabinose and xylose. Few management factors were identified, although the high prevalence of infectious colitis reduced the power of the study.     

The role of humic acid on sulfate retention and release in a podzol

Sequential leaching experiments were performed to evaluate the effects of humic acid (HA) and pH on SO₄ retention and release in a Swedish podzolic B-horizon. Results showed that the presence of HA reduced SO₄ retention and that HA was released when SO₄ was retained. Increasing HA concentration increased the rate of SO₄ release. The ability of HA to compete with SO₄ increased with pH. More than 40% of total sorbed SO₄ was irreversibly retained.