TABLE 1.

Carbon fixed into bacterial biomass during experiment 2^a

Treatment	μM 13C incorporated
Arsenate + sulfide	200 ± 2
Arsenate alone	50 ± 4
Sulfide alone	68 ± 3
Filtered arsenate + sulfide	5 ± 0.5
No added electron acceptors or donors	46 ± 4
Blank	15

^aThe amount of carbon fixed after 11 days of incubation (∼5 mM of arsenate reduced) was measured by incorporation of ¹³C supplied as bicarbonate. The values are means ± standard errors; n = 2.