Muramic acid

Abstract: Muramic acid, glucosamine, mannosamine and galactosamine in soils may be useful for elucidating the microbial origin of soil organic nitrogen. Therefore, a method was developed to determine the aldononitrile acetate derivatives of the four amino sugars simultaneously in the 6 m HCl hydrolysates of soil samples by means of high resolution gas liquid chromatography. This method was sensitive enough to detect less than 10 μg muramic acid ml−1 and less than 20 μg ml−1 of the other three amino sugars. The maximum release of amino sugars was found after 6 to 8 h hydrolysis at 105°C. Impurities in the acidic hydrolysates were removed simply by neutralisation with KOH solution. The recovery of amino sugars after hydrolysis and purification was more than 90% on average. The method was applied to determine amino sugars in eight soils with different properties. The coefficients of variation averaged 6.1% for glucosamine and galactosamine and 10.9% for muramic acid and mannosamine.

Abstract: Agricultural management practices have been shown to influence the decomposer community in soils, with no-tillage (NT) systems favoring fungi as compared with conventional tillage (CT) systems. In this study, we examined six North American agroecosystems with respect to the effects of NT vs. CT management systems on the accrual of microbial cell-wall residues in surface soil. We used total amino sugar contents to estimate living and decomposing microbial cell-wall mass in soil and the contents of glucosamine and muramic acid to separate fungal and bacterial contributions to microbial-derived soil organic matter (SOM). Compared with estimates of glucosamine and muramic acid present in living biomass of fungi and bacteria, total concentrations of these compounds (745-2076 mg glucosamine kg -1 soil and 37-79 mg muramic acid kg -1 soil) were larger by factors of 54 to 745 and 26 to 82, respectively. At three sites, the ratios of glucosamine to muramic acid in NT soils (32.0, 30.0, 42.2) significantly exceeded those in the respective CT soils (18.8, 22.1, 23.0) because of a higher enrichment of glucosamine. This coincided with higher values for fungal biomass, particulate organic matter carbon (POM-C), mean weight diameter of water-stable aggregates (MWD), and total organic carbon (TOC). Analysis of aggregate-size classes showed that the additional glucosamine accumulated in >53-mm aggregates but not in smaller particles. The enrichment of SOM in fungal-derived glucosamine suggests that the accrual of hyphal cell-wall residues is an important process in the three NT agroecosystems which leads to higher SOM storage in surface soil concurrent with an increase in aggregate stability. The other soils, having a lower clay plus silt content, exhibited no significant differences in POM-C, MWD, and total amino sugars between NT and CT management systems. We suggest that at lower clay plus silt contents the beneficial potential for NT to sequester microbial-derived SOM is lower because of limited physical stabilization.

Abstract: Fifteen plants species were grown in the greenhouse on the same soil and sampled at flowering to obtain rhizosphere soil and root material. In both fractions, the data on fungal and bacterial tissue obtained by amino sugar analysis were compared with the total microbial biomass based on fumigation-extraction and ergosterol data. The available literature on glucosamine concentrations in fungi and on muramic acid concentrations in bacteria was reviewed to prove the possibility of generating conversion values for general use in root material. All microbial properties analysed revealed strong species-specific differences in microbial colonisation of plant roots. The root material contained considerable amounts of microbial biomass C and biomass N, reaching mean levels of 10.9 and 1.4 mg g −1 dry weight, respectively. However, the majority of CHCl 3 labile C and N, i.e. 89 and 55% was root derived. The average amount of ergosterol was 13 μg g −1 dry weight and varied between 0.0 for Phacelia roots and 45.5 μg g −1 dry weight for Vicia roots. The ergosterol content in root material of mycorrhizal and non-mycorrhizal plant species did not differ significantly. Fungal glucosamine was converted to fungal C by multiplication by 9 giving a range of 7.1–25.9 mg g −1 dry weight in the root material. Fungal C and ergosterol were significantly correlated. Bacterial C was calculated by multiplying muramic acid by 45 giving a range from 1.7 to 21.6 mg g −1 dry weight in the root material. In the root material of the 15 plant species, the ratio of fungal C-to-bacterial C ranged from 1.0 in mycorrhizal Trifolium roots to 9.5 in non-mycorrhizal Lupinus roots and it was on average 3.1. These figures mean that the microbial tissue in the root material consists on average of 76% fungal C and 24% bacterial C. The differences in microbial colonisation of the roots were reflected by differences in microbial indices found in the rhizosphere soil, most strongly for microbial biomass C and ergosterol, but to some extent also for glucosamine and muramic acid.