Live and death of streptomyces in soil—what happens to the biomass?

Abstract

The formation of soil organic matter (SOM) has been proposed to depend on fragmentation of biomass after cell death. However, this is hard to mimic in laboratory experiments showing the process directly. We used heavy metal contamination in order to provide an environment in which one Streptomyces strain, the heavy metal resistant S. mirabilis P16B-1, could survive while the sensitive strain S. lividans TK24 was expected to die and disintegrate; the necromass fragments would then contribute to SOM formation. Both strains were grown for 30 d in sterile mesocosms containing either highly metal-contaminated soil from a former uranium-mining site in Ronneburg, Germany, or control soil from a municipal park, Jena, Germany. The fate and morphology of living and dead bacterial biomass (necromass) was observed using scanning electron microscopy. Attachment of soil particles to the intact mycelium as well as decay of dead biomass was observed. Dead bacterial biomass was identified in form of patchy fragments while the superordinate filamentous structure of the hyphae was still visible and obviously stabilized in soil. The fate of cytosolic compounds was followed using the example of a nickel-containing superoxide dismutase (NiSOD) which was found to be released after death of cells grown in liquid soil-extract medium. Activity of the enzyme was proven for concentrated media supernatant by a gel-based qualitative activity assay. This indicates that NiSOD remains active in soil after cell death. Hence, bacterial cell death results in the release of cytosolic compounds, e.g., intact proteins, as well as the formation of residual cell-envelope fragments contributing to SOM formation.

Microbial consortia at steady supply

“…Populations of the various cell types exchange building blocks with the external resource pool via import and passive transport, and also via biomass release upon cell death (Simpson et al, 2007; Schütze et al, 2013). Conservation of extracellular building block $i$ prescribes the dynamics of the external concentration $c_i^{\mathrm{ext}}$ (see Appendix 2),${\dot{c}}_i^{\mathrm{ext}}=s_i-\mu c_i^{\mathrm{ext}}-true\frac{v}{V-Nv}\left(true\underset{\sigma }{truefalsetrue\sum }{n}_{\sigma }{\varphi }_{i,\sigma }\right),$…”

Bacterial cartels at steady supply

“…where the only nonlinearity is due to the growth function g. Populations of the various cell types exchange building blocks with the external resource pool via import and leakage, and also via biomass release upon cell death [18,19]. Conservation of extracellular building block i prescribes the dynamics of the external concentration…”

How does sonication affect the mineral and organic constituents of soil aggregates?—A review

“…The application of ultrasound is used to extract enzymes and bacteria from the bulk soil or soil fractions. Sonication leads at certain energy levels to the perforation of the microbial cell envelope and its disintegration into flakes and fragments resulting in the release of the cytosol (Schütze et al, 2013) and to the destruction of macromolecules such as enzymes (Stemmer et al, 1998). Such disaggregation can redistribute microbial cells and metabolites and spread lysed microbial cell material extensively over particle surfaces (Ahmed and Oades, 1984).…”