Metabolism of aromatic aldehydes as cosubstrates by the acetogen Clostridium formicoaceticum

When the acetogen Clostridium formicoaceticum was cultivated on mixtures of aromatic compounds (e.g., 4-hydroxybenzaldehyde plus vanillate), the oxidation of aromatic aldehyde groups occurred more rapidly than did O-demethylation. Likewise, when fructose and 4-hydroxybenzaldehyde were simultaneously provided as growth substrates, fructose was utilized only after the aromatic aldehyde group was oxidized to the carboxyl level. Aromatic aldehyde oxidoreductase activity was constitutive (activities approximated 0.8 U mg^–1), and when pulses of 4-hydroxybenzaldehyde were added during fructose-dependent growth, the rate at which fructose was utilized decreased until 4-hydroxybenzaldehyde was consumed. Although 4-hydroxybenzaldehyde inhibited the capacity of cells to metabolize fructose, lactate or gluconate were consumed simultaneously with 4-hydroxybenzaldehyde, and lactate or aromatic compounds lacking an aldehyde group were utilized concomitantly with fructose. These results demonstrate that (1) aromatic aldehydes can be utilized as cosubstrates and have negative effects on the homoacetogenic utilization of fructose by C. formicoaceticum, and (2) the consumption of certain substrates by this acetogen is not subject to catabolite repression by fructose. Received: 14 May 1998 / Accepted: 7 August 1998     

Evidence for Involvement of Gut-Associated Denitrifying Bacteria in Emission of Nitrous Oxide (N2O) by Earthworms Obtained from Garden and Forest Soils

Earthworms (Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion lacteum) obtained from nitrous oxide (N₂O)-emitting garden soils emitted 0.14 to 0.87 nmol of N₂O h⁻¹ g (fresh weight)⁻¹ under in vivo conditions. L. rubellus obtained from N₂O-emitting forest soil also emitted N₂O, which confirmed previous observations (G. R. Karsten and H. L. Drake, Appl. Environ. Microbiol. 63:1878–1882, 1997). In contrast, commercially obtained Lumbricus terrestris did not emit N₂O; however, such worms emitted N₂O when they were fed (i.e., preincubated in) garden soils. A. caliginosa, L. rubellus, and O. lacteum substantially increased the rates of N₂O emission of garden soil columns and microcosms. Extrapolation of the data to in situ conditions indicated that N₂O emission by earthworms accounted for approximately 33% of the N₂O emitted by garden soils. In vivo emission of N₂O by earthworms obtained from both garden and forest soils was greatly stimulated when worms were moistened with sterile solutions of nitrate or nitrite; in contrast, ammonium did not stimulate in vivo emission of N₂O. In the presence of nitrate, acetylene increased the N₂O emission rates of earthworms; in contrast, in the presence of nitrite, acetylene had little or no effect on emission of N₂O. In vivo emission of N₂O decreased by 80% when earthworms were preincubated in soil supplemented with streptomycin and tetracycline. On a fresh weight basis, the rates of N₂O emission of dissected earthworm gut sections were substantially higher than the rates of N₂O emission of dissected worms lacking gut sections, indicating that N₂O production occurred in the gut rather than on the worm surface. In contrast to living earthworms and gut sections that produced N₂O under oxic conditions (i.e., in the presence of air), fresh casts (feces) from N₂O-emitting earthworms produced N₂O only under anoxic conditions. Collectively, these results indicate that gut-associated denitrifying bacteria are responsible for the in vivo emission of N₂O by earthworms and contribute to the N₂O that is emitted from certain terrestrial ecosystems.     

The FTD‐like syndrome causing TREM2 T66M mutation impairs microglia function,brain perfusion,and glucose metabolism

Genetic variants in the triggering receptor expressed on myeloid cells 2 (TREM2) increase the risk for several neurodegenerative diseases including Alzheimer's disease and frontotemporal dementia (FTD). Homozygous TREM2 missense mutations, such as p.T66M, lead to the FTD‐like syndrome, but how they cause pathology is unknown. Using CRISPR/Cas9 genome editing, we generated a knock‐in mouse model for the disease‐associated Trem2 p.T66M mutation. Consistent with a loss‐of‐function mutation, we observe an intracellular accumulation of immature mutant Trem2 and reduced generation of soluble Trem2 similar to patients with the homozygous p.T66M mutation. Trem2 p.T66M knock‐in mice show delayed resolution of inflammation upon in vivo lipopolysaccharide stimulation and cultured macrophages display significantly reduced phagocytic activity. Immunohistochemistry together with in vivo TSPO small animal positron emission tomography (μPET) demonstrates an age‐dependent reduction in microglial activity. Surprisingly, perfusion magnetic resonance imaging and FDG‐μPET imaging reveal a significant reduction in cerebral blood flow and brain glucose metabolism. Thus, we demonstrate that a TREM2 loss‐of‐function mutation causes brain‐wide metabolic alterations pointing toward a possible function of microglia in regulating brain glucose metabolism.     

Axon growth and guidance genes identify T-dependent germinal centre B cells

Selection of B cells subjected to hypermutation in germinal centres (GC) during T cell-dependent (TD) antibody responses yields memory cells and long-lived plasma cells that produce high affinity antibodies biased to foreign antigens rather than self-antigens. GC also form in T-independent (TI) responses to polysaccharide antigens but failed selection results in GC involution and memory cells are not generated. To date there are no markers that allow phenotypic distinction of T-dependent and TI germinal centre B cells. We compared the global gene expression of GC B cells purified from mice immunized with either TD or TI antigens and identified eighty genes that are differentially expressed in TD GC. Significantly, the largest cluster comprises genes involved in growth and guidance of neuron axons such as Plexin B2, Basp1, Nelf, Shh, Sc4mol and Sult4alpha. This is consistent with formation of long neurite (axon and dendrite)-like structures by mouse and human GC B cells, which may facilitate T:B cell interactions within GC, affinity maturation and B cell memory formation. Expression of BASP1 and PLEXIN B2 protein is very low or undetectable in resting and TI GC B cells, but markedly upregulated in GC B cells induced in the presence of T cell help. Finally we show some of the axon growth genes upregulated in TD-GC B cells including Basp1, Shh, Sult4alpha, Sc4mol are also preferentially expressed in post-GC B cell neoplasms.     

Intra‐clutch pattern of albumen δ13C and δ15N in yellow‐legged gulls Larus michahellis: female dietary shift or resource allocation strategy?

Energy or nutritional constraints associated to female dietary shifts during the clutch production period may play a role in generating intra‐clutch egg size variation in yellow‐legged gulls Larus michahellis. To explore this possibility, we determined albumen δ¹³C and δ¹⁵N values in three‐egg clutches (modal clutch size) from three different breeding episodes: Ebro Delta 2004 and 2006, and Columbretes Islands 2004. Rather than a shift in females’ diet, consistent intra‐clutch patterns of variation in egg size and albumen isotopic values (particularly in the case of albumen δ¹³C, which values held constant throughout the laying sequence) pointed to an intrinsic mechanism as the most feasible cause for the relatively smaller size of third/last‐laid eggs. However, diet “quality” for breeding females seemed to affect intra‐clutch egg size variation. In particular, a deficit of specific nutrients for egg formation associated to refuse scraps exploitation (as suggested by depleted albumen isotopic values) likely resulted in the more apparent intra‐clutch egg size profile for the Ebro Delta 2004. In the absence of dietary shifts, the observation of consistently higher δ¹⁵N values for third‐albumens suggested a greater contribution of endogenous resources to their synthesis, as conversion of stored reserves into egg proteins results in greater isotopic fractionation, thereby yielding enriched isotopic signatures (particularly for δ¹⁵N that shows greater isotopic fractionation with respect to that commonly assumed for δ¹³C). We point to reabsorbed material derived from the hormonally‐mediated regression of the female reproductive system (which is likely the intrinsic mechanisms resulting in the intra‐clutch pattern of egg size variation: the hormonal hypothesis) as the most feasible endogenous source of nutrients for the synthesis of last‐laid eggs, as optimize reproductive investment and maximize female fitness.     

A new assembly pathway for the cytokinetic Z ring from a dynamic helical structure in vegetatively growing cells of Bacillus subtilis

The earliest event in bacterial cell division is the formation of a Z ring, composed of the tubulin-like FtsZ protein, at the division site at midcell. This ring then recruits several other division proteins and together they drive the formation of a division septum between two replicated chromosomes. Here we show that, in addition to forming a cytokinetic ring, FtsZ localizes in a helical-like pattern in vegetatively growing cells of Bacillus subtilis. FtsZ moves rapidly within this helix-like structure. Examination of FtsZ localization in individual live cells undergoing a single cell cycle suggests a new assembly mechanism for Z ring formation that involves a cell cycle-mediated multistep remodelling of FtsZ polymers. Our observations suggest that initially FtsZ localizes in a helical pattern, with movement of FtsZ within this structure occurring along the entire length of the cell. Next, movement of FtsZ in a helical-like pattern is restricted to a central region of the cell. Finally the FtsZ ring forms precisely at midcell. We further show that another division protein, FtsA, shown to interact with FtsZ prior to Z ring formation in B. subtilis, also localizes to similar helical patterns in vegetatively growing cells.     

Leukotoxic Activity of Aggregatibacter actinomycetemcomitans and Periodontal Attachment Loss

Aggregatibacter actinomycetemcomitans is a Gram-negative periodontitis-associated bacterium that expresses a toxin that selectively affects leukocytes. This leukotoxin is encoded by an operon belonging to the core genome of this bacterial species. Variations in the expression of the leukotoxin have been reported, and a well-characterized specific clonal type (JP2) of this bacterium with enhanced leukotoxin expression has been isolated. In particular, the presence of the JP2 genotype significantly increases the risk for the progression of periodontal attachment loss (AL). Based on these findings we hypothesized that variations in the leukotoxicity are linked to disease progression in infected individuals. In the present study, the leukotoxicity of 239 clinical isolates of A. actinomycetemcomitans was analysed with different bioassays, and the genetic peculiarities of the isolates were related to their leukotoxicity based on examination with molecular techniques. The periodontal status of the individuals sampled for the presence of A. actinomycetemcomitans was examined longitudinally, and the importance of the observed variations in leukotoxicity was evaluated in relation to disease progression. Our data show that high leukotoxicity correlates with an enhanced risk for the progression of AL. The JP2 genotype isolates were all highly leukotoxic, while the isolates with an intact leukotoxin promoter (non-JP2 genotypes) showed substantial variation in leukotoxicity. Genetic characterization of the non-JP2 genotype isolates indicated the presence of highly leukotoxic genotypes of serotype b with similarities to the JP2 genotype. Based on these results, we conclude that A. actinomycetemcomitans harbours other highly virulent genotypes besides the previously described JP2 genotype. In addition, the results from the present study further highlight the importance of the leukotoxin as a key virulence factor in aggressive forms of periodontitis.     

Enrofloxacin and Macrolides Alone or in Combination with Rifampicin as Antimicrobial Treatment in a Bovine Model of Acute Chlamydia psittaci Infection

Chlamydia psittaci is a zoonotic bacterium with a wide host range that can cause respiratory disease in humans and cattle. In the present study, effects of treatment with macrolides and quinolones applied alone or in combination with rifampicin were tested in a previously established bovine model of respiratory C. psittaci infection. Fifty animals were inoculated intrabronchially at the age of 6–8 weeks. Seven served as untreated controls, the others were assigned to seven treatment groups: (i) rifampicin, (ii) enrofloxacin, (iii) enrofloxacin + rifampicin, (iv) azithromycin, (v) azithromycin + rifampicin, (vi) erythromycin, and (vii) erythromycin + rifampicin. Treatment started 30 hours after inoculation and continued until 14 days after inoculation (dpi), when all animals were necropsied. The infection was successful in all animals and sufficient antibiotic levels were detected in blood plasma and tissue of the treated animals. Reisolation of the pathogen was achieved more often from untreated animals than from other groups. Nevertheless, pathogen detection by PCR was possible to the same extent in all animals and there were no significant differences between treated and untreated animals in terms of local (i.e. cell count and differentiation of BALF-cells) and systemic inflammation (i.e. white blood cells and concentration of acute phase protein LBP), clinical signs, and pathological findings at necropsy. Regardless of the reduced reisolation rate in treated animals, the treatment of experimentally induced respiratory C. psittaci infection with enrofloxacin, azithromycin or erythromycin alone or in combination with rifampicin was without obvious benefit for the host, since no significant differences in clinical and pathological findings or inflammatory parameters were detected and all animals recovered clinically within two weeks.     

A new genus of Nippostrongylinae (Nematoda: Heligmonellidae) from the water rat Scapteromys aquaticus (Sigmodontinae) in Argentina

A new genus of Nippostrongylinae, Malvinema n. gen., with 3 coparasitic species M. frederici n. sp., M. carolinae n. sp., and M. victoriae n. sp. from the intestine of the water rat, Scapteromys aquaticus Thomas (Rodentia: Muridae), from the northeast of Buenos Aires Province, Argentina, is proposed in this study. The new genus shows similarities to 2 Neotropical Nippostrongylinae: Carolinensis (Travassos, 1937) by some characters of the synlophe and Stilestrongylus Freitas, Lent and Almeida, 1937, by the pattern of the caudal bursa. It is characterized by a synlophe with triple or quadruple gradient of size of the ridges, lateromedian, decreasing from the largest left and right ridges. The gradient situated in the right ventral quadrant is always present. The caudal bursa shows a pattern of type 1-4. Malvinema frederici possesses a synlophe with 17 ridges and an axis of orientation inclined at 45 degrees from the sagittal axis; M. carolinae possesses a synlophe with 22-24 ridges and an axis of orientation almost merged with the sagittal axis. Both species have a caudal bursa with the right lobe enlarged transversally. Malvinema victoriae possesses a synlophe with 22-24 ridges, an axis of orientation inclined at 45 degrees from the sagittal axis, and a caudal bursa with the right lobe enlarged vertically.