Life at the oxic–anoxic interface: microbial activities and adaptations

Abstract

Molecular oxygen is one of the most important reactants in biogeochemical cycles. Due to its low solubility in water, the consumption of oxygen leads to the development of oxic-anoxic interfaces, which separate aerobic from anaerobic processes in virtually all environments, ranging in scale from oceanic sediments to the fecal pellets of a small soil invertebrate. Three case studies were selected to illustrate the basic situation and the specific characteristics of oxic-anoxic interfaces: sediments, the rhizosphere of aquatic plants, and the intestinal tract of insects. Each system is governed by the same general principles, but striking differences arise from, e.g., the nature of the major microbial activities and the mechanisms controlling metabolite fluxes. Also scale and dimensional differences as well as the consequences of temporal fluctuations are of fundamental importance. Recent developments in microbial ecology, which often combine traditional and modern approaches, have significantly furthered our understanding of the specific microniches and the metabolic and behavioral adaptations of microorganisms to life at the oxic-anoxic interface. New concepts help to define the targets of future studies: the spatial organization of microbial populations, their microenvironments and in situ activities, and the functional interactions within structured microbial communities.

Response of microbial community structure to natural and accelerated hydrarch successions in the boreal wetlands in northern Hokkaido, Japan

“…Change in the vegetation, especially from Sphagnum mosses to larger and taller plants, increases the supply of oxygen and organic matter to the soil (Brune et al 2000). Immediately after the oxygen and organic matter in the peat layers are consumed, reduction reactions mediated by anaerobic microbes ensue (Reddy and DeLaune 2008).…”

“…However, artificial drainage, for example, that is used for agricultural development, has accelerated the terrestrialization of wetlands worldwide (Mitsch and Gosselink 2007). In the case of both natural and accelerated terrestrialization, invading vegetation, including large plants, rather than the original vegetation introduces oxygen and organic matter into the peat layer by extending the rhizosphere (Bardgett and Shine 1999;Brune et al 2000). Variations in the covering vegetation may greatly impact microbial activity and material cycling in peat layers beneath the vegetation.…”

Microbial Community Composition and Extracellular Enzyme Activities Associated with Juncus roemerianus and Spartina alterniflora Vegetated Sediments in Louisiana Saltmarshes

“…These rhizomes can change local sediment conditions through root exudates, radial oxygen loss, and soil temperature effects [3][4][5]. Each of these factors can be important in shaping the sediment microbial community, which in turn drives vegetation development and composition through biogeochemical transformations [6].…”

Short-term effect of oxic to anoxic transition on benthic microbial activity and solute fluxes in organic-rich phytotreatment ponds

“…For example, the qualiquantitative nature of the mineralization processes within oxic and anoxic environments has been investigated, leading to a general conclusion that microbial biomass production and organic matter mineralization display lower rates under anoxic conditions, in particular, when the organic carbon bulk is mainly refractory (Kristensen et al, 1995;Sun et al, 1997;Amtoft Neubauer et al, 2004;Lomstein et al, 2006). The occurrence of steep vertical oxygen gradients and the establishment of an oxic-anoxic interface (OAI) within the sediment layers constitute a natural model for investigation of the oxic to anoxic transition (Brune et al, 2000). Studies on the structure and activity of the benthic community at the OAI have been carried out in sediment and microbial mats, where they highlighted a complex structural and functional organization of microbial groups in relation to a narrow stratification of physicochemical variables (Canfield & DesMarais, 1993;Bernard & Fenchel, 1995).…”