Affiliation:
1. Departamento de Ecología, Genética y Microbiología, Área de Microbiología, Facultad de Biología, Universidad de León, 24071 León, Spain
Abstract
ABSTRACT
Corynebacterium glutamicum
is able to grow in media containing up to 12 mM arsenite and 500 mM arsenate and is one of the most arsenic-resistant microorganisms described to date. Two operons (
ars1
and
ars2
) involved in arsenate and arsenite resistance have been identified in the complete genome sequence of
Corynebacterium glutamicum
. The operons
ars1
and
ars2
are located some distance from each other in the bacterial chromosome, but they are both composed of genes encoding a regulatory protein (
arsR
), an arsenite permease (
arsB
), and an arsenate reductase (
arsC
); operon
ars1
contains an additional arsenate reductase gene (
arsC1′
) located immediately downstream from
arsC1
. Additional arsenite permease and arsenate reductase genes (
arsB3
and
arsC4
) scattered on the chromosome were also identified. The involvement of
ars
operons in arsenic resistance in
C. glutamicum
was confirmed by gene disruption experiments of the three arsenite permease genes present in its genome. Wild-type and
arsB3
insertional mutant
C. glutamicum
strains were able to grow with up to 12 mM arsenite, whereas
arsB1
and
arsB2 C. glutamicum
insertional mutants were resistant to 4 mM and 9 mM arsenite, respectively. The double
arsB1-arsB2
insertional mutant was resistant to only 0.4 mM arsenite and 10 mM arsenate. Gene amplification assays of operons
ars1
and
ars2
in
C. glutamicum
revealed that the recombinant strains containing the
ars1
operon were resistant to up to 60 mM arsenite, this being one of the highest levels of bacterial resistance to arsenite so far described, whereas recombinant strains containing operon
ars2
were resistant to only 20 mM arsenite. Northern blot and reverse transcription-PCR analysis confirmed the presence of transcripts for all the
ars
genes, the expression of
arsB3
and
arsC4
being constitutive, and the expression of
arsR1
,
arsB1
,
arsC1
,
arsC1′
,
arsR2
,
arsB2
, and
arsC2
being inducible by arsenite.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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