A mutant form of the Neisseria gonorrhoeae pilus secretin protein PilQ allows increased entry of heme and antimicrobial compounds

A spontaneous point mutation in pilQ (pilQ1) resulted in phenotypic suppression of a hemoglobin (Hb) receptor mutant (hpuAB mutant), allowing gonococci to grow on Hb as the sole source of iron. PilQ, formerly designated OMP-MC, is a member of the secretin family of proteins located in the outer membrane and is required for pilus biogenesis. The pilQ1 mutant also showed decreased piliation and transformation efficiency. Insertional inactivation of pilQ1 resulted in the loss of the Hb utilization phenotype and decreased entry of free heme. Despite the ability of the pilQ1 mutant to use Hb for iron acquisition and porphyrin, there was no demonstrable binding of Hb to the cell surface. The pilQ1 mutant was more sensitive to the toxic effect of free heme in growth medium and hypersensitive to the detergent Triton X-100 and multiple antibiotics. Double mutation in pilQ1 and tonB had no effect on these phenotypes, but a double pilQ1 pilT mutant showed a reduction in Hb-dependent growth and decreased sensitivity to heme and various antimicrobial agents. Insertional inactivation of wild-type pilQ also resulted in reduced entry of heme, Triton X-100, and some antibiotics. These results show that PilQ forms a channel that allows entry of heme and certain antimicrobial compounds and that a gain-of function point mutation in pilQ results in TonB-independent, PilT-dependent increase of entry.     

Ants as Indicators of Restoration Success: Relationship with Soil Microbial Biomass in the Australian Seasonal Tropics

Ants are widely used as bioindicators in Australian land assessment and monitoring programs, particularly in relation to ecosystem restoration following mining. Little is known, however, about the relationship between ant community development and key ecological processes such as nutrient cycling. We have examined the relationship between ant species richness and soil microbial biomass at 17 sites subject to disturbance by mining in the Kakadu region of Australia's Northern Territory. The number of ant species recorded ranged from 7 at an unvegetated site undergoing restoration to 43 at a site that was undisturbed except for edge effects. Soil microbial biomass ranged from 19.3 to 134.3 μgC/g. Ant species richness was positively correlated with soil microbial biomass (r= 0.638), more so than was plant species richness (r= 0.342 for total plant species, r= 0.499 for woody species only). Our findings demonstrate a correlation between aboveground ant activity and belowground decomposition processes at disturbed sites, thereby providing support for the use of ants as indicators of restoration success following disturbance. Interestingly, when a range of undisturbed sites in the region was considered, a negative rather than positive relationship between ant richness and soil microbial biomass was found. This illustrates the importance of distinguishing between variation within a habitat due to disturbance and variation across different habitats when searching for indicators of ecological change.     

Energy-dependent changes in the gonococcal transferrin receptor

The pathogenic Neisseria spp. are capable of iron utilization from host iron-binding proteins including transferrin and lactoferrin. Transferrin iron utilization is an energy-dependent, receptor-mediated event in which two identified transferrin-binding proteins participate. One of these proteins, TbpA, is homologous to the TonB-dependent family of outer membrane receptors that are required for high-affinity uptake of vitamin B₁₂ and ferric siderophores. The 'TonB box' is a conserved domain near the amino-terminus of these proteins that has been implicated in interaction with TonB. Interaction between a periplasmic domain of TonB and the TonB box allows energy transduction to occur from the cytoplasmic membrane to the energy-dependent receptor in the outer membrane. We created a TonB box mutant of gonococcal TbpA and demonstrated that its binding and protease accessibility characteristics were indistinguishable from those of gonococcal Ton system mutants. The protease exposure of the second transferrin-binding protein, TbpB, was affected by the energization of TbpA, consistent with an interaction between these proteins. TbpB expressed by the de-energized mutants was readily accessible to protease, similar to TbpB expressed in the absence of TbpA. The de-energized mutants exhibited a marked decrease in transferrin diffusion rate, suggesting that receptor energization was necessary for ligand release. We propose a model to explain the observed Ton-dependent changes in the binding parameters and exposures of TbpA and TbpB.     

Source of carbon and hydrogen in methane produced from formate by Methanococcus thermolithotrophicus.

Methanococcus thermolithotrophicus is able to produce methane either from H2-CO2 or from formate. The route of formate entry into the methanogenic pathway was investigated by using 2H2O or [13C]formate and analysis by mass spectrometry. When cells (H2-CO2 or formate grown) were transferred to formate medium in 95% 2H water, the proportion of 2H in methane was 95%. When cells (H2-CO2 or formate grown) were transferred to media containing [13C]formate in the presence of H2-CO2 or He-CO2, the ratio of 13CH4 to 12CH4 increased over time parallel to the ratio of 13CO2 to 12CO2. The cells catalyzed a significant exchange of label between [13C]formate and 13CO2.     

Microvascular closure in malignant histiocytosis.

Two patients with malignant histiocytosis were found to have capillary occlusion by aggregates of neoplastic histiocytes, in skeletal muscle in one, and in renal glomeruli in the other. One patient had clinical evidence of similar occlusions in the arterioles and capillaries of the ocular fundi. Occlusion of small vessels by tumour cells may explain the confusion of both patients.     

Effect of substrate loading on hydrogen production during anaerobic fermentation by Clostridium thermocellum 27405

We have investigated hydrogen (H₂) production by the cellulose-degrading anaerobic bacterium, Clostridium thermocellum. In the following experiments, batch-fermentations were carried out with cellobiose at three different substrate concentrations to observe the effects of carbon-limited or carbon-excess conditions on the carbon flow, H₂-production, and synthesis of other fermentation end products, such as ethanol and organic acids. Rates of cell growth were unaffected by different substrate concentrations. H₂, carbon dioxide (CO₂), acetate, and ethanol were the main products of fermentation. Other significant end products detected were formate and lactate. In cultures where cell growth was severely limited due to low initial substrate concentrations, hydrogen yields of 1 mol H₂/mol of glucose were obtained. In the cultures where growth ceased due to carbon depletion, lactate and formate represented a small fraction of the total end products produced, which consisted mainly of H₂, CO₂, acetate, and ethanol throughout growth. In cultures with high initial substrate concentrations, cellobiose consumption was incomplete and cell growth was limited by factors other than carbon availability. H₂-production continued even in stationary phase and H₂/CO₂ ratios were consistently greater than 1 with a maximum of 1.2 at the stationary phase. A maximum specific H₂ production rate of 14.6 mmol g dry cell⁻¹ h⁻¹ was observed. As cells entered stationary phase, extracellular pyruvate production was observed in high substrate concentration cultures and lactate became a major end product.     

Continuous hydrogen production during fermentation of alpha-cellulose by the thermophillic bacterium Clostridium thermocellum

Continuous hydrogen (H2) production during fermentation of alpha-cellulose was established using the thermophillic, anaerobic bacterium Clostridium thermocellum ATCC 27405. The objectives of this work were to characterize growth of C. thermocellum, quantify H2 production and determine soluble end-product synthesis patterns during fermentation of a cellulosic substrate under continuous culture conditions. A 5 L working volume fermentor was established and growth experiments were maintained for over 3,000 h. Substrate concentrations were varied from 1 to 4 g/L and the feed was introduced with continuous nitrogen gas sparging to prevent clogging of the feed-line. The pH and temperature of the reactor were maintained at 7.0 and 600 degrees C, respectively, throughout the study. At concentrations above 4 g/L, the delivery of alpha-cellulose was impaired due to feed-line clogging and it became difficult to maintain a homogenous suspension. The highest total gas (H2 plus CO2) production rate, 56.6 mL L(-1) h(-1), was observed at a dilution rate of 0.042 h(-1) and substrate concentration of 4 g/L. Under these conditions, the H2 production rate was 5.06 mmol h(-1). Acetate and ethanol were the major soluble end-products, while lactate and formate were greatly reduced compared to production in batch cultures. Concentrations of all metabolites increased with increasing substrate concentration, with the exception of lactate. Despite a number of short-term electrical and mechanical failures during the testing period, the system recovered quickly, exhibiting substantial robustness. A carbon balance was completed to ensure that all end-products were accounted for, with final results indicating near 100% carbon recovery. This study shows that long-term, stable H2 production can be achieved during direct fermentation of an insoluble cellulosic substrate under continuous culture conditions.