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B R Byers

Publications and source records attributed to B R Byers.

At least 19 recordsLinked to original sources
PubMed2001

Small recirculating filters for nitrogen reduction.

Concerned about the negative impacts of nitrogen loading from septic systems on the Chesapeake Bay watershed, Maryland's Anne Arundel County Health Department has pioneered the use of small recirculating sand filters to reduce nitrogen in effluent from residential septic systems. Recirculating sand filters can reduce the total nitrogen in septic-tank effluent by up to 70 percent. Years of experience and the county's participation in the National Onsite Demonstration Project have led to modifications that make the filters more acceptable to homeowners. Use of alternative media, changes in flow patterns, and homeowner education have increased acceptance by homeowners.

Adsorption↗
PubMed1998

Exochelin genes in Mycobacterium smegmatis: identification of an ABC transporter and two non-ribosomal peptide synthetase genes.

Many strains of mycobacteria produce two ferric chelating substances that are termed exochelin (an excreted product) and mycobactin (a cell-associated product). These agents may function as iron acquisition siderophores. To examine the genetics of the iron acquisition system in mycobacteria, ultraviolet (UV) and transposon (Tn611) mutagenesis techniques were used to generate exochelin-deficient mutants of Mycobacterium smegmatis strains ATCC 607 and LR222 respectively. Mutants were identified on CAS siderophore detection agar plates. Comparisons of the amounts of CAS-reactive material excreted by the possible mutant strains with that of the wild-type strains verified that seven UV mutant strains and two confirmed transposition mutant strains were deficient in exochelin production. Cell-associated mycobactin production in the mutants appeared to be normal. From the two transposon mutants, the mutated gene regions were cloned and identified by colony hybridization with an IS6100 probe, and the DNA regions flanking the transposon insertion sites were then used as probes to clone the wild-type loci from M. smegmatis LR222 genomic DNA. Complementation assays showed that an 8 kb PstI fragment and a 4.8 kb PstI/SacI subclone of this fragment complemented one transposon mutant (LUN2) and one UV mutant (R92). A 10.1 kb SacI fragment restored exochelin production to the other transposon mutant (LUN1). The nucleotide sequence of the 15.3 kb DNA region that spanned the two transposon insertion sites overlapped the 5' region of the previously reported exochelin biosynthetic gene fxbA and contained three open reading frames that were transcribed in the opposite orientation to fxbA. The corresponding genes were designated exiT, fxbB and fxbC. The deduced amino acid sequence of ExiT suggested that it was a member of the ABC transporter superfamily, while FxbB and FxbC displayed significant homology with many enzymes (including pristinamycin I synthetase) that catalyse non-ribosomal peptide synthesis. We propose that the peptide backbone of the siderophore exochelin is synthesized in part by enzymes resembling non-ribosomal peptide synthetases and that the ABC transporter ExiT is responsible for exochelin excretion.

ATP-Binding Cassette Transporters↗
PubMed1997

Enhanced hydrogen peroxide sensitivity and altered stress protein expression in iron-starved Mycobacterium smegmatis.

Mycobactericum smegmatis ATCC 607 became iron starved and did not reach maximum population density when grown at an iron concentration of 0.1 microM, or less. Iron deficient cells were more susceptible than iron replete cells to H2O2 killing; 9 mM H2O2 killed about 80% of the population of cultures grown at 0.05 microM iron, while about 25 mM H2O2 was required for similar killing of cultures grown at 1 or 20 microM iron. In response to H2O2, iron sufficient cells produced major oxidative stress proteins of molecular masses of 90, 75, 65, 62, and 43 kDa (the 75 and 65 kDa proteins were identified as DnaK and GroEL homologs, respectively). Iron deficient M. smegmatis did not upregulate the DnaK and GroEL proteins when stressed with H2O2. Both iron deficient and iron sufficient M. smegmatis produced (at 48 degrees C) major heat shock proteins of molecular masses of 90, 75 (DnaK), 65 (GroEL), 62, 43, and 16 kDa. The stress protein response induced by 2 M ethanol challenge was similar to the heat shock response except that ethanol induced a unique 55 kDa protein and the 16 kDa heat shock protein was not apparent. Induction of ethanol stress proteins was identical in high iron and low iron cells. All of the stress agents induced expression of a 62 kDa protein which may also be induced by iron insufficiency. The heat and ethanol shock responses of M. smegmatis were unchanged by iron deficiency; therefore, the absence of DnaK and GroEL from the response of iron starved M. smegmatis to H2O2 may be due to a specific defect (or alteration) of the oxidative stress response during iron starvation.

Amino Acid Sequence↗
PubMed1994

Diversity of siderophore genes encoding biosynthesis of 2,3-dihydroxybenzoic acid in Aeromonas spp.

Most species of the genus Aeromonas produce the siderophore amonabactin, although two species produce enterobactin, the siderophore of many enteric bacteria. Both siderophores contain 2,3-dihydroxybenzoic acid (2,3-DHB). Siderophore genes (designated aebC, -E, -B and -A, for aeromonad enterobactin biosynthesis) that complemented mutations in the enterobactin genes of the Escherichia coli 2,3-DHB operon, entCEBA(P15), were cloned from an enterobactin-producing isolate of the Aeromonas spp. Mapping of the aeromonad genes suggested a gene order of aebCEBA, identical to that of the E. coli 2,3-DHB operon. Gene probes for the aeromonad aebCE genes and for amoA (the entC-equivalent gene previously cloned from an amonabactin-producing Aeromonas spp.) did not cross-hybridize. Gene probes for the E. coli 2,3-DHB genes entCEBA did not hybridize with Aeromonas spp. DNA. Therefore, in the genus Aeromonas, 2,3-DHB synthesis is encoded by two distinct gene groups; one (amo) is present in the amonabactin-producers, while the other (aeb) occurs in the enterobactin-producers. Each of these systems differs from (but is functionally related to) the E. coli 2,3-DHB operon. These genes may have diverged from an ancestral group of 2,3-DHB genes.

Aeromonas↗
PubMed1992

Novel heme-binding component in the serum of the channel catfish (Ictalurus punctatus).

The serum of the channel catfish (Ictalurus punctatus) was examined for heme- and hemoglobin-binding proteins. Electrophoretic mobility retardation assays failed to detect a hemoglobin-binding material similar to mammalian haptoglobin; however, a heme-binding component (not previously described) was identified in catfish serum. The heme-binding component was purified by gel filtration chromatography; electrophoretic analyses suggested it to be composed of two polypeptide subunits of molecular masses about 115 and 98 kDa. This composition is inconsistent with hemopexin, the known heme-binding serum protein of mammals. Although it was not fully saturated with heme, the catfish component contained detectable heme in normal sera. When complexed by the binding material, heme was used as an iron source by isolates of the bacterial Gram-negative genus Aeromonas; the capacity of other bacteria to use the complex was not tested. The physiological function of the catfish heme-binding serum protein is presently not clear.

Animals↗
PubMed1992

Siderophore production and DNA hybridization groups of Aeromonas spp.

A correlation between the genospecies (DNA-DNA hybridization group) and the type of siderophore produced by 118 isolates of the genus Aeromonas was established. Organisms in hybridization groups 1 through 5 (including 5A, 5B, and 5AB) and group 12 predominantly produced the siderophore amonabactin, while an enterobactinlike siderophore was prevalent in groups 8/10 and 9. The siderophore produced by strains in group 6 may be an as-yet-unidentified nonphenolate, nonhydroxamate compound, and group 7 isolates synthesized no siderophores. Determination of the indigeneous siderophore (or the absence of one) produced by an isolate of the genus Aeromonas may assist in identification of the organism's genetic species and may suggest the presence of certain virulence properties.

Aeromonas↗
PubMed1991

Iron acquisition and virulence in the motile aeromonads: siderophore-dependent and -independent systems.

During an infection, a microbial pathogen must acquire all of its iron from the host. Aeromonas isolated producing the siderophore amonabactin obtain iron either from host Fe-transferrin (siderophore dependent) or from host heme-containing molecules (siderophore independent). Isolates producing the siderophore enterobactin do not utilize Fe-transferrin in serum and probably rely exclusively on host heme iron.

Aeromonas↗
PubMed1991

Acquisition of iron from host sources by mesophilic Aeromonas species.

The mesophilic Aeromonas species are opportunistic pathogens that produce either of the siderophores amonabactin or enterobactin. Acquisition of iron for growth from Fe-transferrin in serum was dependent on the siderophore amonabactin; 50 of 54 amonabactin-producing isolates grew in heat-inactivated serum, whereas none of 30 enterobactin-producing strains were able to grow. Most isolates (regardless of siderophore produced) used haem as a sole source of iron for growth; all of 33 isolates grew with either haematin or haemoglobin and 30 of these used haemoglobin when complexed to human haptoglobin. Mutants unable to synthesize a siderophore used iron from haem, suggesting that this capacity was unrelated to siderophore production. Some members of the mesophilic Aeromonas species have evolved both siderophore-dependent and -independent mechanisms for acquisition of iron from a host.

Aeromonas↗
PubMed1991

Cloning, mutagenesis, and nucleotide sequence of a siderophore biosynthetic gene (amoA) from Aeromonas hydrophila.

Many isolates of the Aeromonas species produce amonabactin, a phenolate siderophore containing 2,3-dihydroxybenzoic acid (2,3-DHB). An amonabactin biosynthetic gene (amoA) was identified (in a Sau3A1 gene library of Aeromonas hydrophila 495A2 chromosomal DNA) by its complementation of the requirement of Escherichia coli SAB11 for exogenous 2,3-DHB to support siderophore (enterobactin) synthesis. The gene amoA was subcloned as a SalI-HindIII 3.4-kb DNA fragment into pSUP202, and the complete nucleotide sequence of amoA was determined. A putative iron-regulatory sequence resembling the Fur repressor protein-binding site overlapped a possible promoter region. A translational reading frame, beginning with valine and encoding 396 amino acids, was open for 1,188 bp. The C-terminal portion of the deduced amino acid sequence showed 58% identity and 79% similarity with the E. coli EntC protein (isochorismate synthetase), the first enzyme in the E. coli 2,3-DHB biosynthetic pathway, suggesting that amoA probably encodes a step in 2,3-DHB biosynthesis and is the A. hydrophila equivalent of the E. coli entC gene. An isogenic amonabactin-negative mutant, A. hydrophila SB22, was isolated after marker exchange mutagenesis with Tn5-inactivated amoA (amoA::Tn5). The mutant excreted neither 2,3-DHB nor amonabactin, was more sensitive than the wild-type to growth inhibition by iron restriction, and used amonabactin to overcome iron starvation.

Aeromonas↗
PubMed1989

Physiological control of amonabactin biosynthesis in Aeromonas hydrophila.

Amonabactin is a siderophore from Aeromonas hydrophila which is produced in two biologically active forms composed of the phenolate 2,3-dihydroxybenzoic acid (DHB), lysine, glycine, and either trytophan (amonabactin T) or phenylalanine (amonabactin P). Amonabactin biosynthetic mutants (generated by chemical mutagenesis) that either produced no amonabactin or overproduced the siderophore were isolated and identified on chrome azurol S siderophore detection agar. Amonabactin-negative mutants were of two categories. One type produced no phenolates and used exogenous DHB to synthesize amonabactin (both forms) while the other type excreted DHB but not amonabactin. This suggests an amonabactin biosynthetic pathway composed of two segments, one producing DHB and the other assembling amonabactin from DHB and the amino acids. Overproduction mutants used amonabactin poorly or not at all, indicating that they contained lesions in amonabactin utilization. Adding the analog D-tryptophan to wild-type A. hydrophila cultures reduced synthesis of both amonabactin T and amonabactin P and lengthened the lag phase in iron restricted medium. The tryptophan and phenylalanine forms of amonabactin may be synthesized by a single assembly pathway that contains a novel enzyme (sensitive to D-tryptophan) which inserts either tryptophan or phenylalanine into amonabactin.

Aeromonas↗
PubMed1989

Amonabactin, a novel tryptophan- or phenylalanine-containing phenolate siderophore in Aeromonas hydrophila.

Aeromonas hydrophila 495A2 excreted two forms of amonabactin, a new phenolate siderophore composed of 2,3-dihydroxybenzoic acid, lysine, glycine, and either tryptophan (amonabactin T) or phenylalanine (amonabactin P). Supplementing cultures with L-tryptophan (0.3 mM) caused exclusive synthesis of amonabactin T, whereas supplements of L-phenylalanine (0.3 to 30 mM) gave predominant production of amonabactin P. The two forms of amonabactin were separately purified by a combination of production and polyamide column chromatographic methods. Both forms were biologically active, stimulating growth in iron-deficient medium of an amonabactin-negative mutant. Of 43 additional siderophore-producing isolates of the Aeromonas species that were tested, 76% (19 of 25) of the A. hydrophila isolates were amonabactin positive, whereas only 19% (3 of 16) of the A. sobria isolates and all (3 of 3) of the A. caviae isolates produced amonabactin, suggesting a predominant synthesis of amonabactin in certain Aeromonas species.

Aeromonas↗
PubMed1986

A Streptococcus mutans superoxide dismutase that is active with either manganese or iron as a cofactor.

The superoxide dismutase produced by Streptococcus mutans OMZ176 during aerobic growth in a chemically defined medium (modified FMC) that was treated with Chelex 100 (to lower trace metal contamination) and supplemented with high purity manganese was purified (162-fold) by heat treatment, ammonium sulfate precipitation, and chromatofocusing chromatography. The superoxide dismutase produced during aerobic growth in the same medium, but without manganese and supplemented with high purity iron, was similarly purified (220-fold). The molecular masses of each holoenzyme were approximately 43,000 with a subunit mass of 20,700, indicating that the enzymes were dimers of two equally sized subunits. The superoxide dismutase from manganese-grown cells was a manganese enzyme (MnSOD) containing 1.2 atoms of manganese and 0.25 atoms of iron/subunit. The superoxide dismutase from iron-grown cells was an iron enzyme (FeSOD) containing 0.07 atoms of manganese and 0.78 atoms of iron/subunit. The amino acid compositions of the MnSOD and the FeSOD were virtually identical, and their amino-terminal sequences were identical through the first 22 amino acids. Dialysis of the FeSOD with o-phenanthroline and sodium ascorbate generated aposuperoxide dismutase with 94% loss of activity; subsequent dialysis of apoenzyme with either manganese sulfate or ferrous sulfate reconstituted activity (recoveries of 37 and 30%, respectively). Electrophoretic determination of cytoplasmic radioiron distribution indicated that (during aerobic growth) manganese prevented insertion of iron into superoxide dismutase, although the iron levels of at least two other cytoplasmic fractions were not altered by manganese. Therefore, S. mutans used the same aposuperoxide dismutase to form either FeSOD or MnSOD, depending upon which metal was available in the culture medium. Such "cambialistic" enzymes (those capable of making a cofactor substitution) may represent a previously unrecognized family of superoxide dismutases.

Aerobiosis↗
PubMed1986

Calcium modulation of growth of Streptococcus mutans.

The steady-state growth yield of Streptococcus mutans (in a Teflon chemostat using a chemically defined medium that was treated to lower trace metal contamination and supplemented with high-purity trace metals) was doubled by addition of 0.63 microM calcium. Subsequent increases in calcium concentration to 1.3 microM and 2.5 microM lowered steady-state growth yield below the level with no added calcium, suggesting that calcium has dose-dependent stimulatory and inhibitory effects on S. mutans.

Calcium↗
PubMed1986

Enhanced toxicity of copper for Streptococcus mutans under anaerobic conditions.

Copper inhibition of 11 strains (serotypes a through g) of Streptococcus mutans was increased by anaerobic incubation. Anaerobic toxicity was reversed by cuprous, but not by cupric, chelators. Susceptibility to aerobic copper inhibition was related to serotype; serotypes c, e, and f (biotype I) were most sensitive.

Anaerobiosis↗
PubMed1986

Ferrous iron transport in Streptococcus mutans.

Radioiron uptake from 59FeCl3 by Streptococcus mutans OMZ176 was increased by anaerobiosis, sodium ascorbate, and phenazine methosulfate (PMS), although there was a 10-min lag before PMS stimulation was evident. The reductant ascorbate may have provided ferrous iron. The PMS was reduced by the cells, and the reduced PMS then may have generated ferrous iron for transport; reduced PMS also may have depleted dissolved oxygen. We conclude that S. mutans transports only ferrous iron, utilizing reductants furnished by glucose metabolism to reduce iron prior to its uptake.

Anaerobiosis↗
PubMed1984

Enhancement of copper toxicity by siderophores in Bacillus megaterium.

Chelation of copper by siderophores enhanced the toxicity of copper for Bacillus megaterium. Although this antibacterial activity appeared to be rapidly bactericidal, it could be partly reversed by addition of deferrisiderophore , or of ferrisiderophore at high concentration, immediately after exposure of cells to the cupric-siderophore complex.

Bacillus megaterium↗
PubMed1984

Oxygen toxicity in Streptococcus mutans: manganese, iron, and superoxide dismutase.

When cultured anaerobically in a chemically defined medium that was treated with Chelex-100 to lower its trace metal content, Streptococcus mutans OMZ176 had no apparent requirement for manganese or iron. Manganese or iron was necessary for aerobic cultivation in deep static cultures. During continuous aerobic cultivation in a stirred chemostat, iron did not support the growth rate achieved with manganese. Since the dissolved oxygen level in the chemostat cultures was higher than the final level in the static cultures, manganese may be required for growth at elevated oxygen levels. In medium supplemented with manganese, cells grown anaerobically contained a low level of superoxide dismutase (SOD) activity; aerobic cultivation increased SOD activity at least threefold. In iron-supplemented medium, cells grown anaerobically also had low SOD activity; aerobic incubation resulted in little increase in SOD activity. Polyacrylamide gel electrophoresis of the cell extracts revealed a major band and a minor band of SOD activity in the cells grown with manganese; however, cells grown with iron contained a single band of SOD activity with an Rf value similar to that of the major band found in cells grown with manganese. None of the SOD activity bands were abolished by the inclusion of 2 mM hydrogen peroxide in the SOD activity strain. S. mutans may not produce a separate iron-containing SOD but may insert either iron or manganese into an apo-SOD protein. Alternatively, iron may function in another activity (not SOD) that augments the defense against oxygen toxicity at low SOD levels.

Anaerobiosis↗