Description: The betaproteobacteria " Aromatoleum aromaticum " pCyN1 and " Thauera " sp. strain pCyN2 anaerobically degrade the plant-derived aromatic hydrocarbon p -cymene (4-isopropyltoluene) under nitrate-reducing conditions. Metabolite analysis of p -cymene-adapted " A. aromaticum " pCyN1 cells demonstrated the specific formation of 4-isopropylbenzyl alcohol and 4-isopropylbenzaldehyde, whereas with " Thauera " sp. pCyN2, exclusively 4-isopropylbenzylsuccinate and tentatively identified (4-isopropylphenyl)itaconate were observed. 4-Isopropylbenzoate in contrast was detected with both strains. Proteogenomic investigation of p -cymene- versus succinate-adapted cells of the two strains revealed distinct protein profiles agreeing with the different metabolites formed from p -cymene. " A. aromaticum " pCyN1 specifically produced (i) a putative p -cymene dehydrogenase (CmdABC) expected to hydroxylate the benzylic methyl group of p -cymene, (ii) two dehydrogenases putatively oxidizing 4-isopropylbenzyl alcohol (Iod) and 4-isopropylbenzaldehyde (Iad), and (iii) the putative 4-isopropylbenzoate-coenzyme A (CoA) ligase (Ibl). The p -cymene-specific protein profile of " Thauera " sp. pCyN2, on the other hand, encompassed proteins homologous to subunits of toluene-activating benzylsuccinate synthase (termed [4-isopropylbenzyl]succinate synthase IbsABCDEF; identified subunits, IbsAE) and protein homologs of the benzylsuccinate β-oxidation (Bbs) pathway (termed BisABCDEFGH; all identified except for BisEF). This study reveals that two related denitrifying bacteria employ fundamentally different peripheral degradation routes for one and the same substrate, p -cymene, with the two pathways apparently converging at the level of 4-isopropylbenzoyl-CoA.

Description: d13C values of aquatic macrophytes are usually in the range of C3 plants, however limited CO2 availability due to high pH or alkalinity or due to high respiration at dense plant stands, can lead to HCO3- assimilation and hence to a shift towards more positive d13C values. Epicuticular leaf waxes of plants contain n-alkanes and different n-alkane patterns have been assigned to different sources of organic matter. Long- and mid-chain n-alkanes (C23 -C31) with a strong odd-over-even predominance are usually interpreted to be of terrestrial origin while mid-chain n-alkanes (C20 -C26) with no or weak odd-over-even predominance were assigned to aquatic macrophytes.Recent sediments of 50 Tibetan lakes were analysed for amounts of n-alkanes, bulk organic d13C and compound-specific d13C values of n-alkanes. Furthermore, bulk d13C of the dominant aquatic macrophyte species Potamogeton pectinatus (L) was measured. Sediments could be separated into three groups by hierarchical cluster analysis according to their n-alkane patterns. Some samples show a remarkable terrestrial influence (type I) while others were obviously dominated primarily by aquatic macrophytes (type II). Type III sediments are similar to type II, but contain also a strong terrestrial component (high relative amounts of C29, C31 and C33 n-alkanes). Short-chain n-alkanes of algal origin are scarce in most of the lake sediments.d13C values of Potamogeton bulk biomass and of bulk organic matter range from -6.0 to -21.4 and -18.4 to -28.1, respectively. d13C values of long-chain n-alkanes show relatively little variations between -29 and -34. However, in some samples a shift towards more positive values, up to -21, is visible in mid-chain n-alkanes. Generally, odd-numbered n-alkanes are more enriched in 13C than even-numbered ones. In our sample set, pHs of the lake waters are varying from 7.1 to 10.5. Comparing bulk d13C values of sediments and plants with pHs, a trend to more positive values at high pHs is visible. The correlation between d13C of Potamogeton biomass and of mid-chain n-alkanes is weak in all samples, but rather good in type II sediments (R2: 0.35 - 0.72). There is also a good correlation between bulk d13C values of sediments and plant organic matter (R2 = 0.71). We conclude, that limited carbon availability at high pHs can be one explanation for a positive shift of d13C values of mid-chain n-alkanes in macrophyte dominated lakes.

Description: Since the Tibetan Plateau has an essential influence on atmospheric circulations, it is important for our understanding of the dynamics of global changes and therefore interesting for paleoecological research (Lehmkuhl and Owen, 2005). Sedimentary organic matter is an excellent recorder of environmental conditions. Different n-alkane patterns have been assigned to different sources of organic matter. δ13C of aquatic macrophytes is usually in the range of C3 plants, however limited CO2 availability due to high pH or alkalinity or due to high respiration at dense plant stands, can lead to HCO3- assimilation and hence to a shift towards more positive δ13C values (Allen and Spence, 1981). To test correlations between environmental and sedimentary organic matter parameters, recent sediments of 50 Tibetan lakes (1500 5300 m a.s.l) were analysed for amounts of n-alkanes, bulk organic δ13C and compound-specific δ13C values of n-alkanes. Furthermore, bulk δ13C of the dominant aquatic macrophyte species Potamogeton pectinatus (L) was measured. The sediments can be separated into three groups by hierarchical cluster analysis according to their n-alkane patterns. Some samples show a remarkable terrestrial influence of long-and mid-chain n-alkanes with a strong odd-over-even predominance (type I) while others are dominated primarily by mid-chain n-alkanes derived from aquatic macrophytes with no odd-over even predominance (type II). Type III sediments are similar to type II, but contain also a strong terrestrial component (high relative amounts of C29, C31 and C33 n-alkanes). Short-chain n-alkanes of algal origin are scarce in most of the lake sediments (Figure 1). δ13C values of Potamogeton bulk biomass and of bulk organic matter range from -6.0 to -21.4 and -18.4 to -28.1, respectively. δ13C values of long-chain n-alkanes (C29-C31) show relatively little variations between -29 and -34. However, in some samples a shift towards more positive values, up to -21, is visible in mid-chain n-alkanes. Generally, odd-numbered n-alkanes are more enriched in 13C than even-numbered ones (Figure 1). In our lake sample set, pHs of the lake waters are varying from 7.1 to 10.5. Comparing bulk δ13C values of sediments and plants with pHs, a trend to more positive values at high pHs is visible. The correlation between δ13C of Potamogeton biomass and of mid-chain n-alkanes (C20-C26) is weak in all samples, but rather good in type II sediments (R2: 0.35 - 0.72). There is also a good correlation between bulk δ13C values of sediments and plant organic matter (R2 = 0.71). We conclude that limited CO2 availability at high pHs can be one explanation for a positive shift of δ13C values of mid-chain n-alkanes in macrophyte dominated lakes, a fact which can be applied for the interpretation of δ13C values of n-alkanes in sediment cores.

Description: Organic geochemical proxy data from surface sediment samples and a sediment core from Lake Donggi Cona were used to infer environmental changes on the northeastern Tibetan Plateau spanning the last 18.4 kyr. Long-chain n-alkanes dominate the aliphatic hydrocarbon fraction of the sediment extract from most surface sediment samples and the sediment core. Unsaturated mid-chain n-alkanes (nC23:1 and nC25:1) have high abundances in some samples, especially in core samples from the late glacial and early Holocene. TOC contents, organic biomarker and non-pollen-palynomorph concentrations and results from organic petrologic analysis on selected samples suggest three major episodes in the history of Lake Donggi Cona. Before ca. 12.6 cal ka BP samples contain low amounts of organic matter due to cold and arid conditions during the late glacial. After 12.6 cal ka BP, relatively high contents of TOC and concentrations of Botryococcus fossils, as well as enhanced concentrations of mid-chain n-alkanes and n-alkenes suggest a higher primary and macrophyte productivity than at present. This is supported by high contents of palynomorphs derived from higher plants and algae and was possibly triggered by a decrease of salinity and amelioration of climate during the early Holocene. Since 6.8 cal ka BP Lake Donggi Cona has been an oligotrophic freshwater lake. Proxy data suggest that variations in insolation drive ecological changes in the lake, with increased aquatic productivity during the early Holocene summer insolation maximum. Short-term drops of TOC contents or biomarker concentrations (at 9.9 cal ka BP, after 8.0 and between 3.5 and 1.7 cal ka BP) can possibly be related to relatively cool and dry episodes reported from other sites on the north-eastern Tibetan Plateau, which are hypothesized to occur in phase with Northern Hemisphere cooling events.