| Küsel, K; Wagner, C; Drake, HL: Enumeration and metabolic product profiles of the anaerobic microflora in the mineral soil and litter of a beech forest, FEMS Microbiology Ecology, 29, 91-103 (1999) | |
| Abstract: Although anaerobic microorganisms can be isolated from well-drained soils, the qualitative and quantitative composition of the anaerobic populations potentially involved in the turnover of carbon in oxic soils is poorly resolved. In the present study, most probable number (MPN) estimates demonstrated that the number of anaerobes that were cultured from both forest (beech) mineral soil and litter approximated 107 to 108 (g dry wt. soil or litter)-1, a value that also approximated the number of acetate-producing anaerobes. When a complex mixture of substrates was provided, the substrate-product profiles of the MPN series indicated that the substrates that yielded the highest numbers of microbes were: yeast extract > sugars > H2 > organic acids and alcohols > methoxylated aromatic compounds. Except for acetate, this sequence also reflected the temporal consumption of these substrates in the MPN series. The cultured anaerobic population was dominated by members of the Enterobacteriaceae and other facultative anaerobes; the facultative microorganisms appeared to determine the initial anaerobic activities of both forest soil and litter. Compared to mineral soil, litter contained more sugar-consuming anaerobes but lower numbers of butyrate-forming anaerobes. H2, ethanol, butanediol, and aromatic methoxyl groups were utilized by acetogenic bacteria. H2-utilizing acetogens were a dominant group of obligate anaerobes, attesting to the ability of acetogens to survive transient or sustained periods of aeration in habitats such as leaf litter. The numbers of cultured methanogens were negligible. Together with previous findings, these results (i) demonstrate that the formation of acetate in soils is dependent on the combined activity of facultative and obligately anaerobic microorganisms, and (ii) emphasize the potential importance of acetate as an intermediate during the turnover of carbon in habitats subject to steep oxygen gradients. |
