Microbial degradation of quinoline: Kinetic studies with Comamonas acidovorans DSM 6426

The microbial degradation of quinoline by Comamonas acidovorans was studied in a laboratory scale stirred tank reactor. In continuous culture experiments using quinoline as a sole source of carbon and nitrogen, it was shown by means of mass balances that quinoline was converted completely to biomass, carbon dioxide, and ammonia. Degradation rates up to 0.7 g/L h were obtained. Measured yield coefficients Y(x/s) for quinoline were about 0.7 g/g, which is in agreement with the theoretical value for complete mineralization. Kinetic constants based on Haldane substrate inhibition were evaluated. The values were mu(max) = 0.48 h(-1), K(i) = 69 mg/L, and K(s) < 1.45 mg/L. (c) 1993 John Wiley & Sons, Inc.     

Nutrient-split feeding strategy for dialysis cultivation of Escherichia coli

Reduction in nutrient loss during dialysis cultivation of Escherichia coli on a glycerol medium was investigated. A dialysis reactor with an inner fermentation and an outer dialysis chamber was used. Aerobic condition was maintained by limiting the glycerol feed rate to an optimum value which was estimated from the oxygen requirements for glycerol oxidation and oxygen transfer capacity of the reactor. High reduction in nutrient loss was achieved by using water as the dialyzing fluid. However, osmotic movement of water from the dialysis to the fermentation chamber was observed, and the final cell concentration was low. With a nutrient-split feeding strategy (feeding glycerol directly to the fermentation chamber and dialyzing with salt solution), glycerol loss was small, there was no osmotic flux of water to the fermentation chamber, and the cell concentration was high. Both glycerol and salt loss could be avoided, and a cell concentration of 170 g/L was obtained when the dialysis process was substituted by addition of XAD adsorbents to the dialysis chamber. Application of this nutrient-split feeding strategy to cell cultivation in a stirred tank reactor, coupled with dialysis in external dialyzer modules, resulted in low cell concentrations. (c) 1993 Wiley & Sons, Inc.     

On choice of substrate and habitat in bdelzoid rotifers

Information on the distributions of 77 bdelloid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Only two species were reported from plankton, both in low frequency. An artificial substrate, white cotton, was utilized only by few bdelloids, mainly by species with eyes. Only one species occurred at higher frequency on the saprobic substrate Sphaerotilus. Most bdelloids prefer environments rich in oxygen, but some species may be found in soft-bottom sediments. Several species dwell preferentially in diverse habitats of bogs. Some bdelloids have an exceptionally broad ecological range, but even for these is it possible to distinguish a pattern of preference and avoidance.     

On the ecology of Dicranophoridae (Rotifera)

Information on the distribution of 59 dicranophorid rotifers from diverse habitats in south and central Sweden was analyzed to reveal their relationships to their substrate. They were mainly frequenting macrophytic vegetation. Even some species which have previously been regarded as psammobionts were mostly or only found on periphytic substrates. Like other raptorial predators, dicranophorids have a very broad ecological range.     

Evidence for the presence of a receptor for the cytolethal distending toxin (CLDT) of Campylobacter jejuni on CHO and HeLa cell membranes and development of a receptor-based enzyme-linked immunosorbent assay for detection of CLDT

Abstract Using ligand blotting, it was found that partially purified cytolethal distending toxin prepared from and enterotoxigenic strain of Campylobacter jejuni , bound to two peptides of molecular masses of approximately 59 kDa and 45 kDa and to a single peptide of 59 kDa in protein blots prepared from HeLa and CHO cell membranes, respectively. In contrast, labile toxin of Escherichia coli and cholera toxin bound to a single peptide of the same molecular mass (15 kDa) on protein blots prepared from both CHO and HeLa cell crude membranes resolved by gel electrophoresis. This banding pattern was identical using SDS-solubilized membrane, with or without heat treatment, but no band was obtained when reduced (treatment with 2-mercaptoethanol) samples were used for the gel electrophoresis. The differences between receptors of cytolethal distending toxin and cholera toxin/labile toxin were exploited to develop a receptor-based enzyme-linked immunosorbent assay for detection of cytolethal distending toxin which involved the consecutive addition of either solubilized CHO or HeLa membranes, antigen and antibody. This enzyme-linked immunosorbent assay consistently detected crude cytolethal distending toxin diluted up to 16-fold. The receptor-based enzyme-linked immunosorbent assay for detection of cytolethal distending toxin developed in this study is a suitable alternative assay which can be performed easily in laboratories with minimal facilities and, more importantly, the results are available within a few hours as compared to times of up to 5 days in the conventional tissue culture detection of cytolethal distending toxin.     

Suppressive Effect of Liposomes Containing DNA Coding for Diphtheria Toxin A-Chain on Cells Transformed with Bovine Leukemia Virus

A recombinant plasmid which contained a gene for diphtheria toxin A-chain (DT-A) under the control of the long terminal repeat (LTR) of bovine leukemia virus (BLV) (BLV-LTR) was constructed to test a novel application of liposomes as antiviral agents. The promoter activity of BLV-LTR was estimated by the chloramphenicol acetyltransferase (CAT) assay using a plasmid which contains the coding sequence of CAT under the control of BLV-LTR (pBLVCAT). When BLV-infected cells were transfected with pBLVCAT, CAT activity was detected. BLV-uninfected cell lines, however, showed no detectable CAT activity. The plasmid DNA entrapped in liposomes was added to BLV-infected cells in culture. Syncytium formation induced by BLV-infected cells was effectively suppressed by the liposomes containing the gene for DT-A under the control of BLV-LTR. Conversely, liposomes containing the gene for DT-A without a promoter showed no such effect. DT-A gene-containing liposomes with BLV-LTR did not affect formation of syncytium induced by bovine immunodeficiency virus. These observations indicate that BLV-infected cells were readily targeted on the level of gene expression. This strategy could be applied to the treatment of BLV-induced B-cell proliferation of cattle, and further to other viral/neoplastic diseases where specific gene expression is exerted.     

Cloning and Sequencing of Two New Verotoxin 2 Variant Genes of Escherichia coli Isolated from Cases of Human and Bovine Diarrhea

We cloned and sequenced two new Verotoxin 2 (VT2) variant genes: one from an Escherichia coli strain from a case of bovine diarrhea and the other from an E. coli strain from a patient with diarrhea. The nucleotide and amino acid sequences of these two genes were highly homologous with, but distinct from those of the VT2, VT2vha, VT2vhb, SLT-IIv (VT2vp1) and SLT-IIva (VT2vp2) genes. Their nucleotide sequences were much more closely homologous to that of VT2vh than to that of VT2vp. Search for these two new genes in other Verocytotoxin-producing E. coli strains resulted in the isolation of 2 strains carrying one of the new VT2 variant genes, one strain from Tokyo and the other from Canada.     

Structural insights into thermostable direct hemolysin of Vibrio parahaemolyticus using single-particle cryo-EM

Thermostable direct hemolysin (TDH) is a ~19 kDa, hemolytic pore-forming toxin from the gram-negative marine bacterium Vibrio parahaemolyticus, one of the causative agents of seafood-borne acute gastroenteritis and septicemia. Previous studies have established that TDH exists as a tetrameric assembly in physiological state; however, there is limited knowledge regarding the molecular arrangement of its disordered N-terminal region (NTR)—the absence of which has been shown to compromise TDH's hemolytic and cytotoxic abilities. In our current study, we have employed single-particle cryo-electron microscopy to resolve the solution-state structures of wild-type TDH and a TDH construct with deletion of the NTR (NTD), in order to investigate structural aspects of NTR on the overall tetrameric architecture. We observed that both TDH and NTD electron density maps, resolved at global resolutions of 4.5 and 4.2 Å, respectively, showed good correlation in their respective oligomeric architecture. Additionally, we were able to locate extra densities near the pore opening of TDH which might correspond to the disordered NTR. Surprisingly, under cryogenic conditions, we were also able to observe novel supramolecular assemblies of TDH tetramers, which we were able to resolve to 4.3 Å. We further investigated the tetrameric and inter-tetrameric interaction interfaces to elaborate upon the key residues involved in both TDH tetramers and TDH super assemblies. Our current structural study will aid in understanding the mechanistic aspects of this pore-forming toxin and the role of its disordered NTR in membrane interaction.