The oxalate-carbonate pathway (OCP) leads to a potential carbon sink in
terrestrial environments. This process is linked to the activity of
oxalotrophic bacteria. Although isolation and molecular
characterizations are used to study oxalotrophic bacteria, these
approaches do not give information on the active oxalotrophs present in
soil undergoing the OCP. The aim of this study was to assess the
diversity of active oxalotrophic bacteria in soil microcosms using the
Bromodeoxyuridine (BrdU) DNA labeling technique. Soil was collected near
an oxalogenic tree (Milicia excelsa). Different concentrations of
calcium oxalate (0.5%, 1%, and 4% w/w) were added to the soil
microcosms and compared with an untreated control. After 12days of
incubation, a maximal pH of 7.7 was measured for microcosms with oxalate
(initial pH 6.4). At this time point, a DGGE profile of the frc gene was
performed from BrdU-labeled soil DNA and unlabeled soil DNA.
Actinobacteria (Streptomyces- and Kribbella-like sequences),
Gammaproteobacteria and Betaproteobacteria were found as the main active
oxalotrophic bacterial groups. This study highlights the relevance of
Actinobacteria as members of the active bacterial community and the
identification of novel uncultured oxalotrophic groups (i.e. Kribbella)
active in soils.