Preferential expression of IgG2b in nose draining cervical lymph nodes and its putative role in mucosal tolerance induction.

Induction of intranasal tolerance prevents the body from eliciting unwanted immune responses against harmless antigens that enter the body through the nasal mucosa. To study the intrinsic capacities of the cervical, nose draining lymph nodes (CLN), which are essential for tolerance induction, genes that are differentially expressed in CLN and not in peripheral lymph nodes (PLN) were characterized. The gene that is predominantly overexpressed in CLN codes for IgG2b. This is confirmed by a higher percentage of IgG2b+ B220+ cells in CLN compared with any PLN. However, this predominance of IgG2b-positive B cells in the CLN is not specific for the lymph node itself but rather determined by the region drained by lymph nodes at the cervical site, as transplanted PLN at these locations show a comparable predominance. It was demonstrated that IgG2b, when compared with IgG1, led to differential activation of dendritic cells (DC) through Fc receptor signalling. The results point to a unique local combination of cells and factors in the nose draining CLN leading to highly specialized immune reactivity. The results point out that predominance of a distinct IgG isotype in a lymphoid environment may lead to highly specialized immune reactivity.

Fused nucleoids resegregate faster than cell elongation in Escherichia coli pbpB(Ts) filaments after release from chloramphenicol inhibition.

The course of nucleoid movement during and upon release from protein synthesis inhibition by chloramphenicol in filaments of Escherichia coli pbpB(Ts) was analysed. Cells were grown at 42 degrees C in glucose minimal medium for two mass doublings and were treated with chloramphenicol to generate fusion (coalescence) of the nucleoids. Upon release from protein synthesis inhibition, the large distance between the border of the fused nucleoids and the cell poles immediately decreased, before full recovery of the rates of mass growth and length increase at 30 degrees C. This indicates that nucleoids can reoccupy the DNA-free cell ends independently of cell elongation. During filamentation at 42 degrees C, the pbpB cells established initial constrictions at midcell and at one-quarter and three-quarter positions. Nevertheless, divisions only started 75 min after chloramphenicol removal at 30 degrees C, when most nucleoids had moved back into the vacated cell ends. No 'guillotine-like' constrictions at the site of the nucleoids occurred. This suggests that segregating nucleoids postpone division recovery at previously established sites. The results are discussed in the light of a working model for transcription/translation-mediated chromosome segregation and nucleoid occlusion of cell division.

Chloramphenicol causes fusion of separated nucleoids in Escherichia coli K-12 cells and filaments.

Chloramphenicol is frequently used for better visualization of the Escherichia coli nucleoid. Here, we show that chloramphenicol causes not only rounding off of the nucleoid but also fusion of as many as four separated nucleoids. Nucleoid fusion occurred in fast-growing cells and in filaments obtained by dicF antisense RNA induction or in ftsZ84(Ts) and pbpB(Ts) mutants. Thus, treatment with chloramphenicol erroneously suggests that DNA segregation is inhibited.

Nucleoid partitioning in Escherichia coli during steady-state growth and upon recovery from chloramphenicol treatment.

To distinguish between a gradual or an abrupt movement of the Escherichia coli nucleoid during partitioning we determined the distances between nucleoid borders and cell poles. Measurements were performed on fixed but hydrated cells and on living cells growing in steady state. The distance between nucleoid outer border and cell pole remained constant in cells with either one or two nucleoids. Thus the nucleoid outer borders moved gradually during the partition process. To study partitioning during recovery from protein-synthesis inhibition cells were treated with chloramphenicol. After growth resumption, cells and nucleoids first elongated before partitioning occurred. Again, no indication of a rapid displacement of the nucleoid to one-quarter and three-quarter positions in the cell was observed.

Novel degradative pathway of 4-nitrobenzoate in Comamonas acidovorans NBA-10.

A Comamonas acidovorans strain, designated NBA-10, was isolated on 4-nitrobenzoate as sole carbon and energy source. When grown on 4-nitrobenzoate, it was simultaneously adapted to 4-nitrosobenzoate and 4-hydroxylaminobenzoate but not to 4-hydroxybenzoate or 4-aminobenzoate. In cell extracts with NADPH present, 4-nitrobenzoate was degraded to 4-hydroxylaminobenzoate and 3,4-dihydroxybenzoate. Partial purification of the 4-nitrobenzoate reductase revealed that 4-nitrobenzoate is degraded via 4-nitrosobenzoate to 4-hydroxylamino-benzoate. The substrate specificity of the enzyme was narrow and NADPH was 15 times more effective as a cofactor than NADH. The results provide evidence for a novel pathway for aerobic degradation of 4-nitrobenzoate, since neither 4-hydroxybenzoate nor 4-aminobenzoate were involved in the degradative pathway.

The third subunit of desulfoviridin-type dissimilatory sulfite reductases.

In addition to the 50-kDa (alpha) and 40-kDa (beta) subunits, an 11-kDa polypeptide has been discovered in highly purified Desulfovibrio vulgaris (Hildenborough) dissimilatory sulfite reductase. This is in contrast with the hitherto generally accepted alpha 2 beta 2 tetrameric subunit composition. Purification, high-ionic-strength gel-filtration, native electrophoresis and isoelectric focussing do not result in dissociation of the 11-kDa polypeptide from the complex. Densitometric scanning of SDS gels and denaturing gel-filtration indicate a stoichiometric occurrence. A similar 11-kDa polypeptide is present in the desulfoviridin of D. vulgaris oxamicus (Monticello), D. gigas and D. desulfuricans ATCC 27774. We attribute an alpha 2 beta 2 gamma 2 subunit structure to desulfoviridin-type sulfite reductases. N-terminal sequences of the alpha, beta and gamma subunits are reported.