Biomethylation of Arsenic in Contaminated Soils - Environmental Contamination: Health Risks and Ecological Restoration - page 246

anaerobic. environments. that. have. been. shown. to. volatilize. As. includes.
Desulfovibrio vulgaris .(McBride.and. Wolfe. 1971),. Methanobacterium thermoau-
totrophicum .(Cullen.et.al..1989),. Methanobacterium formicicum .(Michalke.et.al..
2000),. Methanosarcina barkeri .(Michalke.et.al..2000),.and. Serratia marinorubra .
(marine.facultative.anaerobe).(Vidal.and.Vidal.1980)..Some.of.those.identi-
ied.as.As.volatilizers.are.sulfur.reducers.(e.g.,. Methanobacterium formicicum ).
(Bright.et.al..1994,.Michalke.et.al..2000).
Meyer. et.al.. (2007).isolated.a. strict. anaerobe.Gram-positive.strain.(ASI-1).
from. a. soil. with. low. levels. of. As. contamination. that. under. anaerobic. and.
pure.culture.conditions.produced.volatile.compounds.as.methylated.As.spe-
cies.and.arsine.(Table.12.2)..It.showed.high.similarity.to. Clostridium glycoli-
cum .(based.on.16S.rDNA.sequencing).but.interestingly.this.known.species.
did.not.produce.any.detectable.levels.volatile.As..From.luorescence. in situ .
hybridization,.it.was.estimated.that.strain.ASI-1.was.2%.of.the.total.microbial.
lora.of.this.soil..From.this.the.authors.suggested.that.this.strain.represented.
a. dominant. member. of. the. metal(loid). volatilizing. population. in. this. soil..
Additionally. they. showed. ASI-1. grows. fermentatively. in. presence. of. yeast.
extract.(1%).and.uses.the.organic.compounds.glucose,.maltose,.sucrose,.man-
nose.ribose,.sorbitol,.glycerol,.and.starch..Besides.the.fact.that.this.research.
was.on.an.anaerobe,.it.is.illustrative.of.the.type.of.work.that.should.be.done.
on. a. wider. range. of. soils. and. under. anaerobic. conditions. to. manage. soils.
for.natural. attenuation. of. As-contaminated. soils..This. approach.shows.the.
potential.to.develop.such.systems.based.on.the.knowledge.of.the.organisms.
and. their. physiological. requirements,. to. develop. targeted. substrates. and.
optimal.conditions.to.promote.As.volatilization.
An.interesting.observation.is.that.bacteria.adapted.for.biomethylation.of.
As.or.resistance.to.As,.apparently.can.grow.better.in.the.presence.of.As.than.
without.As.up.to.some.As.threshold.level..This.was.shown.by.Honshopp.et.al..
(1996).who.compared.uptake.of.As.by.two.soil.bacteria.(one.that.methylates.
As.and.the.other.exhibited.As.resistance).and.found.growth.rates.increased.
up. to. 200.μg/mL. in. the. growth. medium.. As. expected. Flavobacterium-
Cytophaga . sp.. which. exhibits. biomethylation. accumulated. signiicantly. less.
As.in.its.biomass.than.the.As.resistant.species.
Fungi
Fungi.were.the.irst.microorganisms.to.be.associated.with. As.volatiliza-
tion.. Although. there. were. earlier. reports. of. fungal. involvement. in. As.
volatilization,.it.was.not.until.Gosio.in.the.late.1800s.did.systematic.stud-
ies. that. unraveled. the. mystery. of. As. poisoning. and. found. fungi. were.
conclusively. implicated. in. this. phenomena.. He. showed. the. poisonings.
were. As. gas. released. from. wallpaper. that. contained. arsenical. pigments.
for. coloring. purposes. (Agrifoglio. 1954).. Speciically. he. determined. that.
Penicillium brevicaule . (now. called. Scopulariopsis brevicaulis . (Sacc.). could.
form. an. arsenical. gas. that. killed. rats. (Gasio. 1892,. 1893).. He. implicated.