Microbial populations and activity in two soils of Tanzania as influenced by mercury

Summary The influence of mercury on microbial populations and activity of two soils from Tanzania was studied. Aretan (2-methoxyethylmercury chloride) slightly affected the microbial population of the Morogoro (Oxisol) soil, which was 10⁷ c.f.u./g in control soil and 10⁶ c.f.u./g in the presence of 2000 mg Hg/kg soil. Mercuric chloride at >8 mg Hg/kg soil increased the population slightly, with a sharp decrease at >100 mg Hg/kg soil, dropping ultimately to 10³ c.f.u./g at 2000 mg Hg/kg soil. In the Arusha (Andept) soil, the microbial response to the two mercury compounds was the opposite of that for the Morogoro soil. Aretan sharply reduced the nitrogenase activity of aerobically incubated Morogoro soils at Hg levels >24 mg/kg, resulting in very low activity at >50 mg Hg/kg soil. Mercuric chloride increased the activity, which showed a peak at 24 mg Hg/kg soils, followed by a sharp drop at 30 mg Hg/kg and remained low thereafter. In the Arusha soil, the activity was reduced gradually by both Aretan and HgCl₂. The response of the activity under anaerobic incubation in the Morogoro soil was the opposite of that under aerobic incubation, in that it was Aretan which at first increased the activity. In the Arusha soil the activity under anaerobic incubation decreased gradually over the entire range of added Hg. Nitrification was decreased by HgCl₂ atlevels of <2 and <10 mg Hg/kg soil in the Arusha and Morogoro soils, respectively. The tolerance to Hg by microorganisms in this study was in the order: total population > nitrogen fixers > nitrifiers. This may be explained in terms of species diversity of the microorganisms, which may be expected to follow the same sequence.

---

Population et activités microbiennes dans deux sols de Tanzanie sous l'influence du mercure

Résumé On étudie l'influence du mercure sur les populations et les activités microbiennes de deux sols en provenance de Tanzanie. L'Aretan (chlorure de 2-méthoxyéthylmercure) n'affecte que faiblement la population microbienne du sol de Morogoro (oxisol), qui compte 10⁷ individus par g dans le sol témoin et 10⁶ individus en présence de 2000 mg de mercure par kg de sol. Le chlorure mercurique, à une dose supérieure à 8 mg de mercure par kg de sol, augmente quelque peu la population. Celle-ci décroît brutalement au delà de 100 mg de mercure par kg de sol, pour tomber finalement à 10³ individus par g à 2000 mg de mercure par kg de sol. Dans le sol d'Arusha (Andept), la réponse microbienne aux deux composés mercuriels est l'inverse de celle obtenue avec le sol de Morogoro. L'Aretan réduit fortement l'activité de la nitrogénase de sols de Morogoro incubés en aérobiose à des teneurs en mercure au delà de 24 mg par kg. L'activité devient très faible au delà de 50 mg de mercure par kg de sol. Le chlorure mercurique augmente cette activité, avec un pic de 24 mg de mercure par kg de sol, suivi d'une chute sévère à 30 mg de mercure par kg. L'activité demeure faible aux doses plus fortes. Dans le sol d'Arusha, l'activité est réduite progressivement tant par l'Aretan que par HgCl₂. La réponse de l'activité en incubation anaérobie dans le sol de Morogoro est l'inverse de celle en incubation aérobie en ceci que c'est l'Aretan, cette fois-ci, qui augmente d'abord l'activité. Dans le sol d'Arusha, l'activité en incubation anaérobie décroît progressivement sur l'échelle entière des concentrations d'ajout de mercure. La nitrification est réduite par HgCl₂ à des seuils au dessous de 2 et 10 mg de mercure par kg de sol, respectivement pour les sols d'Arusha et de Morogoro. La tolérance des microorganismes au mercure dans cette étude est dans l'ordre: population totale > fixateurs d'azote > nitrificateurs. Ceci peut être expliqué en termes de diversité des espèces de microorganismes qui suit vraisemblablement la même séquence.

     

Identical subcellular distribution of palmitoyl-CoA and arachidonoyl-CoA synthetase activities in human blood platelets.

Fractionation of human blood platelets showed that palmitoyl-CoA synthetase and arachidonoyl-CoA synthetase activities had an identical distribution among subcellular fractions. The activity was highest with arachidonic acid as substrate in all fractions, with an enzyme activity of 50 nmol/min per mg of protein, in a 'dense-tubular-system'-enriched fraction. The ratio activities with arachidonate and palmitate as substrates was about 1.5 in all fractions. Heat inactivation did not distinguish between arachidonoyl-CoA synthetase and a palmitoyl-CoA synthetase. On the other hand, heat inactivation indicated two pools of long-chain acyl-CoA synthetases: one in a mitochondria- and one in the dense-tubular-system-enriched fraction.     

Energetic costs of the winter arboreal microclimate: The gray squirrel in a tree

Heated taxidermic mounts of the gray squirrel were used to analyze the thermal environment of a small arboreal endotherm. Changes in the standard operative temperature (T _es) calculated from the temperatures of heated and unheated mounts agreed well with the power consumption (M–E) of mounts on the ground and on the wind-ward side of a 48-cm diameter tree trunk. As wind speed (u) rose and sky solar radiation (Q _r) decreased, the windward side of the tree trunk became an increasingly more stressful thermal environment than the leeward side of the trunk or the ground, producingM–E differences of more than 30%. Although theM–E of a ground mount and a limb mount 4 m in the air are dependent onQ _ras well asu, the ratio of the two value ofM–E is independent ofQ _r, poorly predicted byu and well predicted byu ^1/2.     

Purification and partial characterization of a major outer-membrane protein of Fusobacterium nucleatum

The major outer-membrane proteins of 40-41 kDa were identified by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) in Fusobacterium nucleatum strains ATCC 10953, ATCC 25586, F3, F6 and Fev1. The proteins were purified by preparative gel electrophoresis. Their behaviour in gel filtration and gel electrophoresis, their sensitivity to proteolytic enzymes, and their amino acid composition were investigated. The purified proteins were partly sequenced from the N-terminal end. A 36.5 kDa portion was protected against extrinsic proteolytic (trypsin, chymotrypsin or pronase) digestion of whole cells. This polypeptide was isolated and partially sequenced from the N-terminal end. From these data and data from extrinsic iodination it was concluded that the N-terminal end of the protein is probably exposed on the surface of the cell. A database search revealed amino acid sequence similarity in an Ala-Pro-rich region of outer-membrane protein A (OmpA) in other Gram-negative bacteria.     

Detoxification of ochratoxin A,a food contaminant: Prevention of growth of Aspergillus ochraceus and its production of ochratoxin A

The toxicity of ochratoxin A (OTA), a mycotoxin produced by fungi ofAspergillus orPenicillium genera is now well documented. Its nephrotoxicity, immunosuppression, teratogenicity, and carcinogenicity have been widely studied. Physical and biochemical methods have been studied to prevent these toxinogenicAspergillus andPenicillium from producing OTA, and/or to destroy the mycotoxin when already produced in a liquid or a solid medium. Repeated freezing at ? 20?C and thawing at + 26?C aleatory reduce OTA production in a liquid medium. Exposure to UV B for different periods of time is efficient in preventing OTA production in a liquid medium. Gamma-irradiation from 2 to 5 kGy gives good results in preventing the production of OTA or destroying it when already produced. Carboxypeptidase is very efficient at 5 units/50 ml in a liquid medium for cleaving the OTA already produced.     

The application of the “Lojda” method for intestinal lactase in intestinal biopsies from jaundiced newborn infants

Summary A new use of the histochemical method for intestinal lactase activity is described. Peroral intestinal biopsies from newborn light-treated infants with diarrhoea were investigated for brush-border lactase. The lactase activity found in these infants by the histochemical method correlated well with the infants ability to hydrolyze lactose judged by lactose tolerance test.     

The importance of denitrification for N2O emissions from an N-saturated forest in SW China: results from in situ 15N labeling experiments

Long-term elevated atmogenic deposition (~5 g m^?2 year^?1) of reactive nitrogen (N) causes N saturation in forests of subtropical China which may lead to high nitrous oxide (N₂O) emissions. Recently, we found high N₂O emission rates (up to 1,730 μg N₂O–N m^?2 h^?1) during summer on well-drained acidic acrisols (pH = 4.0) along a hill slope in the forested Tieshanping catchment, Chongqing, southwest China. Here, we present results from an in situ ¹⁵N–NO₃ ^? labeling experiment to assess the contribution of nitrification and denitrification to N₂O emissions in these soils. Two loads of 99 at.% K¹⁵NO₃ (equivalent to 0.2 and 1.0 g N m^?2) were applied as a single dose to replicated plots at two positions along the hill slope (at top and bottom, respectively) during monsoonal summer. During a 6-day period after label application, we found that 71–100 % of the emitted N₂O was derived from the labeled NO₃ ^? pool irrespective of slope position. Based on this, we assume that denitrification is the dominant process of N₂O formation in these forest soils. Within 6 days after label addition, the fraction of the added ¹⁵N–NO₃ ^? emitted as ¹⁵N–N₂O was highest at the low-N addition plots (0.2 g N m^?2), amounting to 1.3 % at the top position of the hill slope and to 3.2 % at the bottom position, respectively. Our data illustrate the large potential of acid forest soils in subtropical China to form N₂O from excess NO₃ ^? most likely through denitrification.     

The role of fish-poultry integration on fish growth performance,yields and economic benefits among smallholder farmers in sub-Saharan Africa,Tanzania

Aquaculture practices from sub-Saharan Africa are characterised by low production, owing to improper technology. Production can be increased through integrating fish farming with other existing on-farm activities, particularly livestock husbandry. We assessed the role of fish-poultry integration on all male Nile tilapia, Oreochromis niloticus growth performance, yields and economic benefits among smallholder farmers in sub-Saharan Africa, Tanzania. The study also compared phytoplankton species composition, abundance and biomass between the fish-poultry integration and non-integrated system. After 180 days of the experiment, all male O. niloticus cultured under fish-poultry integration exhibited significantly higher growth rates than those in the non-integrated system (p < 0.05). Gross fish yield (GFY), net fish yield (NFY) and net annual yields (NAY) obtained from fish-poultry integration were significantly higher than those from non-integrated system (p < 0.05). Partial enterprise budget analysis revealed that fish-poultry integration was more profitable than the non-integrated system. Moreover, fish-poultry integrated system produced significantly higher phytoplankton abundance and biomass than those from the non-integrated system. Results demonstrate that rural smallholder farmers can achieve higher growth rate, farm net yields and income by integrating all male O. niloticus with other on-farm activities than practising a stand-alone fish culture system.