Enrichment of High-Affinity CO Oxidizers in Maine Forest Soil

Abstract

Carboxydotrophic activity in forest soils was enriched by incubation in a flowthrough system with elevated concentrations of headspace CO (40 to 400 ppm). CO uptake increased substantially over time, while the apparent K m ( app K m ) for uptake remained similar to that of unenriched soils (<10 to 20 ppm). Carboxydotrophic activity was transferred to and further enriched in sterile sand and forest soil. The app K m s for secondary and tertiary enrichments remained similar to values for unenriched soils. CO uptake by enriched soil and freshly collected forest soil was inhibited at headspace CO concentrations greater than about 1%. A novel isolate, COX1, obtained from the enrichments was inhibited similarly. However, in contrast to extant carboxydotrophs, COX1 consumed CO with an app K m of about 15 ppm, a value comparable to that of fresh soils. Phylogenetic analysis based on approximately 1,200 bp of its 16S rRNA gene sequence suggested that the isolate is an ␣-proteobacterium most closely related to the genera Pseudaminobacter, Aminobacter, and Chelatobacter (98.1 to 98.3% sequence identity).Carbon monoxide (CO) regulates concentrations of hydroxyl radical (the primary oxidizing agent in the troposphere [33,39,40]) and several greenhouse gases (e.g., methane and ozone [16,27]). Due to its direct and indirect effects on atmospheric chemistry, Daniel and Solomon (19) have suggested that short-term cumulative radiative forcing due to anthropogenic CO emission may be greater than that due to nitrous oxide (see also reference 25).Although chemical oxidation in the troposphere consumes 75 to 85% of annual CO emissions (7,8,16), biological oxidation contributes significantly to CO regulation (10, 36). In particular, soils consume 7 to 25% of net global annual emissions (10,36,40,45,50). A number of studies have addressed various aspects of soil CO consumption (e.g., 2-4, 6, 12-15, 20, 28, 45), but much remains to be learned about the microorganisms involved.Certain fungi (31), algae (9), actinomycetes and streptomycetes (4, 26), ammonium oxidizers (5, 32), and methanotrophs (5, 23, 30) oxidize CO. However, apparent half-saturation constants ( app K m ) for many of these organisms (e.g., 465 to 1,110 ppm [10,11,15]) substantially exceed values measured for soils (5 to 51 ppm [e.g., references 12 and 35]), with results for a thermophilic streptomycete (88 ppm) being exceptional (26). Accordingly, Conrad et al. (15) have concluded that known CO-oxidizing bacteria (carboxydotrophs) cannot account for observed soil CO consumption. In addition, King (35) has suggested that neither methanotrophs nor ammonia oxidizers are important CO oxidizers in a Maine forest soil.Since enrichments for carboxydotrophs typically contain headspace CO concentrations of Ն10%, the populations isolated from them may represent taxa that are not representative of those that dominate activity in situ. Thus, in this study forest soil was incubated with a flow of air containing CO at 40 to 400 ppm. Sterile sand and soil inoculated with previously e...

Soil Uptake of Carbon Monoxide Emitted in the Exhaust of a Gasoline-Powered Engine

“…Similarly, subtracting the uptake rate of Soil from the uptake rate of SoilϩVeg indicated that CO uptake solely because of vegetation was 0.5 mg hr Ϫ1 per 100-ppm CO, which was identical to soil by itself. The fact that CO uptake exhibited first-order kinetics supports the work of other researchers 26 who have found that soil CO uptake followed Michaelis-Menten kinetics. That is, CO uptake is affected by CO concentration.…”

Molecular andCulture-Based Analyses of Aerobic Carbon Monoxide OxidizerDiversity†

“…I-4, p. 247, 2002), including a previously described high-affinity soil isolate (Aminobacter sp. strain COX) (14). The results significantly expand the known diversity of CO-oxidizing bacteria and provide a basis for new ecological studies.…”

“…Isolates were obtained by incubating air dried peat, rinsed macroalgae (Ulva lactuca or Ascophyllum nodosum), or soil-free roots of Phaseolus vulgaris (bean), Lupinus perennis (lupine), or Pontederia cordata (pickerelweed) in basal salts medium containing 0.01 to 0.05% yeast extract (14). All of these materials supported CO-oxidizing microbes (24, 36; King and Crosby, Abstr.…”

Physiological, Ecological, and Phylogenetic Characterization of Stappia , a Marine CO-Oxidizing Bacterial Genus

“…CO was added to the bottle headspaces (1,000 ppm), and absorbance (Abs; optical density at 600 nm [OD 600 ]) and headspace CO concentrations were monitored at suitable intervals. CO uptake rates were determined from analyses of CO concentrations over time using KaleidaGraph software (version 4.0.5; Synergy Software, Inc.) as previously described by Hardy and King (6,12). Cell biomass was estimated from absorbance using the following empirical expression after correcting for differences in absorbance at 600 and 660 nm (16): g dry weight ml Ϫ1 ϭ (364.74)(Abs600 nm) ϩ (6.7)(Abs600 nm).…”