Effect of Phosphate on the Corrosion of Carbon Steel and on the Composition of Corrosion Products in Two-Stage Continuous Cultures of Desulfovibrio desulfuricans

A field isolate of Desulfovibrio desulfuricans was grown in defined medium in a two-stage continuous culture apparatus with different concentrations of phosphate in the feed medium. The first state (V1) was operated as a conventional chemostat (D = 0.045 h⁻¹) that was limited in energy source (lactate) or phosphate. The second stage (V2) received effluent from V1 but no additional nutrients, and contained a healthy population of transiently starved or resting cells. An increase in the concentration of phosphate in the medium fed to V1 resulted in increased corrosion rates of carbon steel in both V1 and V2. Despite the more rapid corrosion observed in growing cultures relative to that in resting cultures, corrosion products that were isolated under strictly anaerobic conditions from the two culture modes had similar bulk compositions which varied with the phosphate content of the medium. Crystalline mackinawite (Fe₉S₈), vivianite [Fe₃(PO₄)₂ · 8H₂O], and goethite [FeO(OH)] were detected in amounts which varied with the culture conditions. Chemical analyses indicated that the S in the corrosion product was almost exclusively in the form of sulfides, while the P was present both as phosphate and as unidentified components, possibly reduced P species. Some differential localization of S and P was observed in intact corrosion products. Cells from lactate-limited, but not from phosphate-limited, cultures contained intracellular granules that were enriched in P and Fe. The results are discussed in terms of several proposed mechanisms of microbiologically influenced corrosion.     

Relationship between the fine structure of native cellulose and cellulose degradability by the cellulase complexes of Trichoderma reesei and Clostridium thermocellum

The initial rate of hydrolysis of six commercially available native (type l) celluloses was determined for the crude cellulase complexes of the thermophilic anaerobic bacterium C. thermocellum and the mesophilic fungus T. reesei. These rates were then compared with certain physical features of the substrates in an attempt to determine the role of cellulose structure in its degradability. Within the substrate series tested, the Clostridium system showed a greater relative range in rate of enzymatic hydrolysis than did the Trichoderma system. Average correlation coefficients for the kinetic rates from bacterial and fungal cellulases, respectively, and the following physical parameters were obtained: relative crystallinity index (RCl) from acid hydrolysis, -0.61 and -0.85; RCl from x-ray diffraction, -0.75 and -0.89; accessibility to formylation at 4 degrees C, + 0.49 and +0.60; nonaccessibility to formylation at 65 degrees C, -0.40 and -0.73; fiber saturation point, + 0.83 and + 0.85. Kinetic and pore volume distribution data suggest that the rate-limiting components of both the bacterial and fungal cellulase systems are of similar size, approximately 43 A along one axis.     

The effects of mispair and nonpair correction in hybrid DNA on base ratios (G + C content) and total amounts of DNA

Base ratios and total DNA amounts can vary substantially between and within higher taxa and genera, and even within species. Gene conversion is one of several mechanisms that could cause such changes. For base substitutions, disparity in conversion direction is accompanied by an equivalent disparity in base ratio at the heterozygous site. Disparity in the direction of gene conversion at meiosis is common and can be extreme. For transitions (which give purine [R]/pyrimidine [Y] mispairs) and for transversions giving unlike R/R and Y/Y mispairs in hybrid DNA, this disparity could give slow but systematic changes in G + C percentage. For transversions giving like R/R and Y/Y mispairs, it could change AT/TA and CG/GC ratios. From the extent of correction direction disparity, one can deduce properties of repair enzymes, such as the ability (1) to excise preferentially the purine from one mispair and the pyrimidine from the other for two different R/Y mispairs from a single heterozygous site and (2) to excise one base preferentially from unlike R/R or Y/Y mispairs. Frame-shifts usually show strong disparity in conversion direction, with preferential cutting of the nonlooped or the looped-out strand of the nonpair in heterozygous h-DNA. The opposite directions of disparity for frame-shifts and their intragenic suppressors as Ascobolus suggest that repair enzymes have a strong, systematic bias as to which strand is cut. The conversion spectra of mutations induced with different mutagens suggest that the nonlooped strand is preferentially cut, so that base additions generally convert to mutant and deletions generally convert to wild-type forms. Especially in nonfunctional or noncoding DNA, this could cause a general increase in DNA amounts. Conversion disparity, selection, mutation, and other processes interact, affecting rates of change in base ratios and total DNA.      

Mapping of B-cell epitopes of the human hepatitis B virus X protein.

The immune response to the X protein of human hepatitis B virus (HBV) was studied by epitope mapping by using a set of MS2-HBx fusion proteins and synthetic peptides. Antibodies in sera of patients with acute and chronic HBV infection showed a multispecific immune response. Each serum contained antibodies to a different set of epitopes, which taken together cover most of the HBx sequence. Some of the epitopes were detectable only by immunoblotting with fusion proteins; others were detectable only by an enzyme-linked immunosorbent assay (ELISA) with synthetic peptides. The carboxy-terminal half of the HBx protein was preferentially recognized by antibodies from patients with chronic hepatitis and contained a short immunodominant antigenic region with at least two major nonoverlapping epitopes. Anti-HBx antibody titers as revealed by peptide ELISAs were highest and most frequent in patients with chronic hepatitis and usually low in acutely infected patients and asymptomatic carriers. The data demonstrate a remarkable qualitative and quantitative heterogeneity of the humoral HBx immune response which can be monitored by HBx-specific peptide ELISAs. Such tests may become useful diagnostic tools.     

Utilization of individual cellodextrins by three predominant ruminal cellulolytic bacteria.

Growth of the ruminal bacteria Fibrobacter succinogenes S85, Ruminococcus flavefaciens FD-1, and R. albus 7 followed Monod kinetics with respect to concentrations of individual pure cellodextrins (cellobiose, cellotriose, cellotetraose, cellopentaose, and cellohexaose). Under the conditions tested, R. flavefaciens FD-1 possesses the greatest capacity to compete for low concentrations of these cellodextrins.     

Allozymic characterization and evolutionary relationships in the BrazilianAkodon cursor species group (Rodentia-Cricetidae)

The present study involved an electrophoretic survey of 22 protein loci in 269 individuals belonging to three species of the genusAkodon, A. aff.cursor (2n=16),A. cursor (2n=14/15), andA. montensis (2n=24/25/26), collected in Eastern Brazil. The joint results of gene diversity, genetic distances, phenetic analyses, and phylogenetic trees suggested thatA. aff.cursor has recently separated fromA. cursor and that the three species have experienced a recent chromosomal divergence followed by low allozyme differentiation. These data are in agreement with their classification as sibling species.     

Fermentation of 6-Deoxyhexoses by Bacillus macerans

Under anaerobic conditions Bacillus macerans ATCC 7068 fermented 6-deoxyhexoses (l-rhamnose, l-fucose, and d-fucose) to a mixture of 1,2-propanediol (PD), acetone, H(2), CO(2), and ethanol. The final PD concentration was proportional to the amount of l-rhamnose fermented ( approximately 0.9 mol of PD per mol of rhamnose). PD was not produced from hexoses (e.g., d-glucose or l-mannose), despite active fermentation of these substrates. Relative to the fermentation of d-glucose, the fermentation of l-rhamnose was accompanied by a twofold reduction in yield of H(2), CO(2), and cell mass. Exposure of cell extracts to l-rhamnose resulted in the transient appearance of an aldehyde intermediate. Cell extracts contained a pyridine nucleotide-linked lactaldehyde reductase activity which converted synthetic d- or l-lactaldehyde to PD. The data suggest an Embden-Meyerhof pathway for 6-deoxyhexose catabolism, with the formation of lactaldehyde by a conventional aldolase cleavage reaction and subsequent reduction to PD.     

Hog cerebellar D-amino acid oxidase and its histochemical and immunofluorescent localization.

Abstract— Hog cerebellar d -amino acid oxidase (d -AAO; EC 1.4.3.3) has been purified to homogeneity. The enzyme was found to be indistinguishable from crystalline hog kidney d -AAO by a number of criteria, including electrophoresis in both cationic and anionic discontinuous buffer systems, FAD and sulfhydryl contents, and monomer molecular weights of about 40,000 as determined by SDS disc gel electrophoresis. Both preparations exhibited similar specific activities (23 μmol d -ala oxidized min^?1 mg^?1 protein), substrate specificities, and susceptibilities to competitive inhibitors. Rabbit antisera were prepared against each enzyme preparation. Double immunodiffusion revealed no antigenic differences between the two when antiserum against either preparation was used. Although a soluble protein, d -AAO activity in cerebellum is particulate. Two methods were utilized to study the histological localization of d -AAO activity in hog cerebellum: peroxidase-coupled histochemistry and immunofluorescence. The histochemical procedure seems specific for d -AAO since l -amino acids are inert and known competitive inhibitors of the purified flavoenzyme prevent staining. Rabbit antiserum prepared against purified hog cerebellar d -AAO was visualized indirectly with fluorescein-labeled goat antirabbit IgG antiserum. Control experiments with serum from unimmunized rabbits were negative. The results of both techniques were identical in three respects: (1) d -AAO was observed in many fibers emanating from cerebellar white matter; the white matter itself did not exhibit d -AAO, despite presence of the oxidase by biochemical assay; (2) intense d -AAO activity (or antigen) was found in mossy fiber rosettes (glomeruli) in the granular layer; (3) a peculiar and intense localization of d -AAO was noted at the level of, but not within, the Purkinje cell soma. The molecular layer was essentially devoid of d -AAO histochemical activity except for minimal staining near the pial surface. However, the more sensitive immunofluorescent technique revealed d -AAO containing fibers in the molecular layer running parallel to each other and perpendicular to the pial surface; the relatively large size and small number of these fibers do not suggest identification as granule cell axons. No d -AAO has been found in granule cell soma, Golgi Type-II cells, or Purkinje cell soma. These results are discussed in terms of the localization of d -AAO in mossy fibers and their terminals and in certain cell-type(s) of cerebellar origin.     

Fermentation of cellulose and cellobiose by Clostridium thermocellum in the absence of Methanobacterium thermoautotrophicum.

The fermentation of cellulose and cellobiose by Clostridium thermocellum monocultures and C. thermocellum/Methanobacterium thermoautotrophicum cocultures was studied. All cultures were grown under anaerobic conditions in batch culture at 60 degrees C. When grown on cellulose, the coculture exhibited a shorter lag before initiation and growth and celluloysis than did the monoculture. Cellulase activity appeared earlier in the coculture than in the monoculture; however, after growth had ceased, cellulase activity was greater in the monoculture. Monocultures produced primarily ethanol, acetic acid, H2 and CO2. Cocultures produced more H2 and acetic acid and less ethanol than did the monoculture. In the coculture, conversion of H2 to methane was usually complete, and most of the methane produced was derived from CO2 reduction rather than from acetate conversion. Agents of fermentation stoppage were found to be low pH and high concentrations of ethanol in the monoculture and low pH in the coculture. Fermentation of cellobiose was more rapid than that of cellulose. In cellobiose medium, the methanogen caused only slight changes in the fermentation balance of the Clostridium, and free H2 was produced.