Utilization and Transformation of Aquatic Humic Substances by Autochthonous Microorganisms

Abstract

Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.

Rapid biotic molecular transformation of fulvic acids in a karst aquifer

“…Mass balances computed from hydrogeological data showed mineralization of 50-60% of FAs in the deeper part of the shallow aquifer (Heinrichs, 1987). These data suggest that FAs contribute with increasing proportions to the deeper groundwater DOC whereas HAs, with a structure more closely related to biomolecules, probably degrade at a higher rate (Hertkorn et al, 2002a). Alternative mechanisms of removal such as sorption to the mineral soil (Feng et al, 2005) and coagulation by metal ions such as Ca 2+ ,Fe 3+ and Al 3+ (Christl and Kretzschmar, 2007) operate more effectively for HAs than FAs.…”

“…Microbial utilization and transformation of humic substances (HS) as confirmed by laboratory studies and observed in surface waters and marine environments (Bianchi et al, 1996;Krumholz et al, 1997;Lovley et al, 1999;Ogawa et al, 1999;Hertkorn et al, 2002a;Hansell et al, 2004;Qualls, 2004;Koch et al, 2005) may also occur in groundwater systems, in which microorganisms use ancient organic material trapped within shales as electron donors (Krumholz et al, 1997). In contrast to other aquatic environments, hitherto few studies have addressed molecular characterization and turnover dynamics of groundwater HS on the basis of natural samples (Leenheer et al, 2003).…”

Comparative study on humic substances isolated in thermal groundwaters from deep aquifers below 700 m

“…The interest in studying HS from shallow to deep aquifers has increased recently Buckau et al, 2000;Hertkorn et al, 2002;McIntyre et al, 2005;Einsiedl et al, 2008). Most geochemical studies of thermal waters are focused on isotope composition of the water as well as major and minor dissolved ions or trace elements (Varsányi et al, 1997;Kralj, 2004;Yalcin, 2007;Parello et al, 2008;Fekete et al, 2009).…”

Water quality in cutaway peatland lakes in Seda mire, Latvia

“…An increased level of humic substances increases bacterial abundance in humic lakes (Vrede et al, 2003). Autochthonous bacteria utilise and transform aquatic humic substances (HS), decreasing particle size and aromaticity, aliphatic carbon in HS, and increasing the nitrogen content of HS, probably due to some constituents of microbial biomass, such as proteins and amino sugars (Hertkorn et al, 2002). Reduced humic substances (HS) can be reoxidised by anaerobic bacteria, and in general microbial oxidation of HS is a ubiquitous metabolism in the environment (Coates et al, 2002).…”