Biomedical subjects

J M Santini

Publications and source records attributed to J M Santini.

15 recordsLinked to original sources

PubMed2004

arrA is a reliable marker for As(V) respiration.

Arsenate [As(V)]-respiring bacteria affect the speciation and mobilization of arsenic in the environment. This can lead to arsenic contamination of drinking water supplies and deleterious consequences for human health. Using molecular genetics, we show that the functional gene for As(V) respiration, arrA, is highly conserved; that it is required for As(V) reduction to arsenite when arsenic is sorbed onto iron minerals; and that it can be used to identify the presence and activity of As(V)-respiring bacteria in arsenic-contaminated iron-rich sediments. The expression of arrA thus can be used to monitor sites in which As(V)-respiring bacteria may be controlling arsenic geochemistry.

Archaea↗

PubMed2000

Two new arsenate/sulfate-reducing bacteria: mechanisms of arsenate reduction.

Two sulfate-reducing bacteria, which also reduce arsenate, were isolated; both organisms oxidized lactate incompletely to acetate. When using lactate as the electron donor, one of these organisms, Desulfomicrobium strain Ben-RB, rapidly reduced (doubling time = 8 h) 5.1 mM arsenate at the same time it reduced sulfate (9.6 mM). Sulfate reduction was not inhibited by the presence of arsenate. Arsenate could act as the terminal electron acceptor in minimal medium (doubling time = 9 h) in the absence of sulfate. Arsenate was reduced by a membrane-bound enzyme that is either a c-type cytochrome or is associated with such a cytochrome; benzyl-viologen-dependent arsenate reductase activity was greater in cells grown with arsenate/sulfate than in cells grown with sulfate only. The second organism, Desulfovibrio strain Ben-RA, also grew (doubling time = 8 h) while reducing arsenate (3.1 mM) and sulfate (8.3 mM) concomitantly. No evidence was found, however, that this organism is able to grow using arsenate as the terminal electron acceptor. Instead, it appears that arsenate reduction by the Desulfovibrio strain Ben-RA is catalyzed by an arsenate reductase that is encoded by a chromosomally-borne gene shown to be homologous to the arsC gene of the Escherichia coli plasmid, R773 ars system.

Adenosine Triphosphatases↗

PubMed2000

A new chemolithoautotrophic arsenite-oxidizing bacterium isolated from a gold mine: phylogenetic, physiological, and preliminary biochemical studies.

A previously unknown chemolithoautotrophic arsenite-oxidizing bacterium has been isolated from a gold mine in the Northern Territory of Australia. The organism, designated NT-26, was found to be a gram-negative motile rod with two subterminal flagella. In a minimal medium containing only arsenite as the electron donor (5 mM), oxygen as the electron acceptor, and carbon dioxide-bicarbonate as the carbon source, the doubling time for chemolithoautotrophic growth was 7.6 h. Arsenite oxidation was found to be catalyzed by a periplasmic arsenite oxidase (optimum pH, 5.5). Based upon 16S rDNA phylogenetic sequence analysis, NT-26 belongs to the Agrobacterium/Rhizobium branch of the alpha-Proteobacteria and may represent a new species. This recently discovered organism is the most rapidly growing chemolithoautotrophic arsenite oxidizer known.

Alphaproteobacteria↗

PubMed1998

Both the fipA gene of pKM101 and the pifC gene of F inhibit conjugal transfer of RP1 by an effect on traG.

The mechanisms by which gene products inhibit the conjugal transfer of IncP plasmids (e.g., RP1) have been little studied. We have isolated and characterized one such gene, fipA (624 nucleotides), from the SmaI (14.8 kb)-AatII (15.6 kb) region of pKM101(IncN). This gene, which is also conserved in other IncN plasmids, is transcribed in an anticlockwise direction, probably as part of a transfer operon that includes traHI. The FipA protein (24 kDa) appears to be cytoplasmic and, when expressed from a multicopy plasmid, retards the growth of Escherichia coli WP2. The mode of action of fipA was compared with that of the apparently unrelated pifC gene from F(IncFI). Both genes inhibit the transfer of IncPalpha and IncPbeta plasmids but to different degrees. They also inhibit the mobilization of RSF1010 (which requires the RP1 pilus genes and traG) but not of CloDF13 (which encodes a traG homolog). Evidence that traG was the specific target of inhibition was obtained in an artificial system in which cloned traG was used to enhance RSF1010 mobilization via the N pilus system. Such enhancement did not occur in the presence of fipA or pifC. The availability of an in vivo assay of PifC enabled us to show that F pif operon expression increased in cells carrying F'lac and traG, but only if the traG coding sequence was intact. This finding suggested that conjugal inhibition of RP1 was most likely due to a PifC-TraG protein interaction. On phenotypic grounds inhibition of traG by fipA is also likely to occur posttranscriptionally. Whether or not the selection of traG as the inhibition target is an evolutionary tactic to limit the spread of P plasmids, we anticipate that fipA and pifC will prove useful in further investigation of the conjugal roles of traG and its homologs.

Bacterial Proteins↗

PubMed1996

A novel myb-related gene from Arabidopsis thaliana.

A novel myb-like gene (Atmyb5) has been isolated from a genomic library of Arabidopsis thaliana. The gene contains a single intron in the region coding for the Myb domains. The Myb domains are highly homologous to other animal and plant Myb proteins. Arabidopsis plants transgenic for a chimeric Atmyb5 promoter/GUS gene expressed the enzyme in a developmentally controlled and tissue specific manner. The GUS activity was detected in developing leaf trichomes, stipules, epidermal cells on the margins of young rosette and cauline leaves, and in immature seeds. Atmyb5 mRNA appears between fertilization and the 16 cell stage of embryo development and persists beyond the heart stage.

Amino Acid Sequence↗

PubMed1985