ena-STUDY-INRS - IAF-13-09-2013-16:42:39:833-11
Development of molecular tools to detect and quantify atmospheric CO-oxidizing bacteria and identification of environmental factors regulating their distribution and activity.
Soil bacteria scavenging carbon monoxide (CO) are responsible for the biological sink of atmospheric CO. These bacteria exert a significant influence on atmospheric photochemical processes, because the soil uptake of CO mitigates an important fraction of the global emissions of CO from natural and anthropogenic sources. Mitigation of these emissions is of critical importance since CO indirectly regulates the atmospheric lifetime of methane - the second most powerful greenhouse gas. Studies of microbial CO metabolism unveiled the occurrence of two functional groups of CO-oxidizing bacteria: the “carboxydotroph”, bacteria capable of using CO as the sole source of carbon and energy, and “carboxydovore” bacteria unable to grow chemoautotrophically with CO. So far, only few carboxydovore bacteria were shown to oxidize atmospheric CO. The CO-dehydrogenase (CODH) is the enzyme catalyzing the CO oxidation reaction in bacteria. The enzyme is a dimer of heterotrimers encoded by the genes coxS, coxM and coxL. CoxL is the large subunit of the CODH. Phylogenetic analyzes revealed that coxL gene sequences encompass two main clusters: BMS and OMP but the version conferring a high affinity for CO and the ability to scavenge atmospheric CO is unknown. The objective of this investigation was to relate the diversity of coxL gene sequences with CO soil uptake activity and soil physicochemical properties. For this purpose, we collected soil samples in three neighbouring sites encompassing different land-use types: an undisturbed deciduous forest, a maize field and a larch monoculture. We analyzed (i) coxL diversity in the three environments, using a new coxL PCR detection assay targeting both OMP and BMS groups, (ii) CO oxidation activity using a gas chromatography assay and, (iii) soil physicochemical properties. Our results demonstrate that land-use change exerts a significant impact on coxL diversity as well as CO oxidation activity, with significant loss of the potential CO soil uptake activity following the conversion of native forest to maize or larch plantation. Most of the coxL gene sequences retrieved from the soil samples were not affiliated to sequences derived from microbial genome databases, impairing a taxonomic identification of the potential CO-oxidizing bacteria detected in soil. Canonical ordination analysis allowed us to identify coxL sequences belonging to potential high affinity CO-oxidizing bacteria, in addition to recognise environmental factors influencing their distribution and CO soil uptake activity. Work is currently in progress to isolate, assess the abundance and the CO uptake activity of these microorganisms in soil. Taken together, these results will be implemented into molecular models aimed at predicting CO uptake activity in soil. These models will be utilized to predict the response of the biological sink of CO to global change, while determining how land management practices could protect this important ecosystem service.
Soil bacteria scavenging carbon monoxide (CO) are responsible for the biological sink of atmospheric CO. These bacteria exert a significant influence on atmospheric photochemical processes, because the soil uptake of CO mitigates an important fraction of the global emissions of CO from natural and anthropogenic sources. Mitigation of these emissions is of critical importance since CO indirectly regulates the atmospheric lifetime of methane - the second most powerful greenhouse gas. Studies of microbial CO metabolism unveiled the occurrence of two functional groups of CO-oxidizing bacteria: the “carboxydotroph”, bacteria capable of using CO as the sole source of carbon and energy, and “carboxydovore” bacteria unable to grow chemoautotrophically with CO. So far, only few carboxydovore bacteria were shown to oxidize atmospheric CO. The CO-dehydrogenase (CODH) is the enzyme catalyzing the CO oxidation reaction in bacteria. The enzyme is a dimer of heterotrimers encoded by the genes coxS, coxM and coxL. CoxL is the large subunit of the CODH. Phylogenetic analyzes revealed that coxL gene sequences encompass two main clusters: BMS and OMP but the version conferring a high affinity for CO and the ability to scavenge atmospheric CO is unknown. The objective of this investigation was to relate the diversity of coxL gene sequences with CO soil uptake activity and soil physicochemical properties. For this purpose, we collected soil samples in three neighbouring sites encompassing different land-use types: an undisturbed deciduous forest, a maize field and a larch monoculture. We analyzed (i) coxL diversity in the three environments, using a new coxL PCR detection assay targeting both OMP and BMS groups, (ii) CO oxidation activity using a gas chromatography assay and, (iii) soil physicochemical properties. Our results demonstrate that land-use change exerts a significant impact on coxL diversity as well as CO oxidation activity, with significant loss of the potential CO soil uptake activity following the conversion of native forest to maize or larch plantation. Most of the coxL gene sequences retrieved from the soil samples were not affiliated to sequences derived from microbial genome databases, impairing a taxonomic identification of the potential CO-oxidizing bacteria detected in soil. Canonical ordination analysis allowed us to identify coxL sequences belonging to potential high affinity CO-oxidizing bacteria, in addition to recognise environmental factors influencing their distribution and CO soil uptake activity. Work is currently in progress to isolate, assess the abundance and the CO uptake activity of these microorganisms in soil. Taken together, these results will be implemented into molecular models aimed at predicting CO uptake activity in soil. These models will be utilized to predict the response of the biological sink of CO to global change, while determining how land management practices could protect this important ecosystem service.