Methanogenic Sediments Research Articles

Bacterial contribution to sedimentary organic matter; a comparative study of lipid moieties in bacteria and Recent sediments

A systematic study of the lipid composition of thirteen bacterial species and three Recent sediments (methanogenic sediment, cyanobacterial mat and evaporative gypsum crust) was undertaken in an attempt to recognize bacterial organic matter in sediments. A sequential method, which distinguishes between three different modes of occurrence of lipid moieties (free, OH −- and H +-labile), was applied. The acid-labile fractions are discussed. The three main groups of bacteria, archaebacteria, gram-positive eubacteria and gram-negative eubacteria, are easily distinguished. Methanogenic and extremely halophilic archaebacteria are characterized by the presence of diphytanyl glyceryl ether and the absence of fatty acids. The gram-positive eubacteria contain primarily iso- and anteiso-branched fatty acids whereas the gram-negative bacteria and sediments are dominated by β- and α-hydroxy fatty acids. A wide variety of H +-labile hydroxy fatty acids was observed which included several, as yet unknown, structures. β-Hydroxy fatty acids in this H +-labile mode of occurrence are exclusively present in bacteria. Their distribution patterns in sediments are considered “fingerprints” of past and present bacterial populations. The specific differences in β -hydroxy fatty acid compositions observed in the different bacteria and the three sediments investigated, suggest that amide-linked β-hydroxy fatty acid patterns are useful as markers of bacterial populations and therefore of environmental conditions.

Reductive Dehalogenations of Halobenzoates by Anaerobic Lake Sediment Microorganisms

Methane-producing freshwater lake sediment was found to dehalogenate chloro-, bromo-, and iodobenzoates by a reductive reaction in which the halogen was replaced by a hydrogen atom. The identity of the dehalogenated products was confirmed by mass spectrometry, nuclear magnetic resonance, or cochromatography. Removal of the halogens to produce benzoate was necessary before mineralization to CH(4) + CO(2) could occur. The dehalogenation occurred after a lag period which lasted from 1 week to more than 6 months, depending on the chemical. Dehalogenation was not observed in the absence of CH(4) production, and it was inhibited by the addition of 20% O(2). Once sediment was acclimated to halobenzoate dehalogenation, new additions of the halobenzoate were degraded without lag. Acclimation was observed regardless of whether the parent substrates were eventually mineralized to CH(4) + CO(2). Sediment acclimated to bromo- and chlorobenzoate degradation generally metabolized bromo- and chlorobenzoates, but sediment acclimated to iodobenzoate degradation only metabolized iodobenzoate. Prior acclimation of sediment to benzoate decomposition did not alter the pattern of dehalogenation, and sediment acclimated to dehalogenation was not concurrently acclimated to benzoate degradation. The presence of this apparent specificity, the lag period, and subsequent acclimation, together with our findings of the absence of dehalogenation in sterile sediments and by sediments previously incubated at >/=39 degrees C, suggests that this reaction was biologically catalyzed. Apparently, a pathway for the reductive dehalogenation of aryl halides is present in anaerobic microorganisms of this methanogenic sediment.

1668. 2,2-Dichloropropionic acid residues in asparagus: Archer, T. E., Crosby, D. G. & Carlton, A. B. (1967). 2,2-Dichloropropionic acid residues in white asparagus. J. Fd Sci.32, 599

Estuarine sediments are the repository for a wide range of contaminants. Anthropogenic impacts and variations in the belowground biomass of salt marsh plants potentially select for different sediment microbial communities with different functional capabilities, including the ability to biotransform anthropogenic contaminants. There are large differences in both root morphology and the amount of fine root biomass of Spartina alterniflora and Phragmites australis; Spartina is the species commonly used to replace Phragmites in northeastern US salt marsh restoration projects. Our study compared the effect of these two macrophyte species on sediment microbial communities responsible for the biotransformation of the halogenated flame retardant tetrabromobisphenol A (TBBPA). Sediments were obtained from contaminated and uncontaminated salt marsh field sites in New Jersey. Anaerobic methanogenic sediment microcosms were established and incubated for up to 130 days. TBBPA was reductively dehalogenated resulting in the transient formation of two intermediates, identified as tribromobisphenol A and dibromobisphenol A, and the formation and accumulation of bisphenol A (BPA) as the end product. Spartina sediments from both sites were found to dehalogenate TBBPA more rapidly than the Phragmites or unvegetated sediments, resulting in greater production of BPA. Microbial community diversity as measured by in situ sediment phospholipid fatty acid (PLFA) composition prior to TBBPA exposure, was found to be higher in the uncontaminated sediments; differences in microbial PLFA diversity were not seen in contaminated sediments associated with either the different plant species or unvegetated sediment. The results of this study demonstrate that these two plant species affected sediment microbial community function with respect to dehalogenation capabilities, even though the disturbed and undisturbed sediments varied in microbial community composition.