Enzymatic biofilm digestion in soil aggregates facilitates the release of particulate organic matter by sonication

Abstract

Abstract. The stability of soil aggregates against shearing and compressive forces as well as water-caused dispersion is an integral marker of soil quality. High stability results in less compaction and erosion and has been linked to enhanced water retention, dynamic water transport and aeration regimes, increased rooting depth, and protection of soil organic matter (SOM) against microbial degradation. In turn, particulate organic matter is supposed to support soil aggregate stabilization. For decades the importance of biofilm extracellular polymeric substances (EPSs) regarding particulate organic matter (POM) occlusion and aggregate stability has been canonical because of its distribution, geometric structure and ability to link primary particles. However, experimental proof is still missing. This lack is mainly due to methodological reasons. Thus, the objective of this work is to develop a method of enzymatic biofilm detachment for studying the effects of EPSs on POM occlusion. The method combines an enzymatic pre-treatment with different activities of α-glucosidase, β-galactosidase, DNAse and lipase with a subsequent sequential ultrasonic treatment for disaggregation and density fractionation of soils. POM releases of treated samples were compared to an enzyme-free control. To test the efficacy of biofilm detachment the ratio of bacterial DNA from suspended cells and the remaining biofilm after enzymatic treatment were measured by quantitative real-time PCR. Although the enzyme treatment was not sufficient for total biofilm removal, our results indicate that EPSs may attach POM within soil aggregates. The tendency to additional POM release with increased application of enzymes was attributed to a slight loss in aggregate stability. This suggests that an effect of agricultural practices on soil microbial populations could influence POM occlusion/aggregate stability and thereby carbon cycle/soil quality.

The impact of microplastic weathering on interactions with the soil environment: a review

“…In contrast, for PP and PVC neither degrading enzymes nor observed decay were reported (Danso et al, 2019). The practical side is, that enzymes, that have not been shown to target on plastics, are applied to purify extracted soil microplastic by degrading biofilms, that stabilize soil structure, or co-extracted organic matter (Büks and Kaupenjohann, 2016;Löder et al, 2017).…”

Soil biofilms: microbial interactions, challenges, and advanced techniques for ex-situ characterization

“…For example, EPS can store 15 to 20 times its own weight in water (Chenu and Roberson, 1996), thus significantly increase the water holding capacity of soils (Adessi et al, 2018). EPS also contributes to the formation and stability of soil aggregates (Bezzate et al, 2000;Büks and Kaupenjohann, 2016), in which the magnitude of the effect is largely dependent on the characteristics of EPS (Chenu and Cosentino, 2011) and soil physico-chemical properties (Martin and Aldrich, 1955).…”

Particles under stress: ultrasonication causes size and recovery rate artifacts with soil-derived POM but not with microplastics

“…These origins of MP are characterized by a different composition of the size and shape of the extracted items (e.g., Zhang and Liu, 2018;Ding et al, 2020). In laboratory experiments, MP in the observed size range was shown to influence soil biogeochemical properties such as water-holding capacity, soil structure, microbial activity and the health of soil biota, with a strong dependence on the size and shape of the applied particles (de Souza Machado et al, 2018;Büks et al, 2020). Furthermore, the mobility within the soil pore space and preferential flow channels, which is crucial for the accessibility of soil microplastic to groundwaters and surface waters, is also highly dependent on particle size (O'Connor et al, 2019;Zubris and Richards, 2005).…”