TY - JOUR

T1 - Bacterial impact on the wetting properties of soil minerals

AU - Achtenhagen, Jan

AU - Goebel, Marc O.

AU - Miltner, Anja

AU - Woche, Susanne K.

AU - Kästner, Matthias

N1 - Funding information: We would like to thank the German Research Foundation (Priority Programme 1315 “Biogeochemical Interfaces in Soil”, MI 598/2-2 and BA 1359/9-2) for funding. We also thank A. Prager (Institute of Surface Modification, Leipzig, Germany) for her kind help with the SEM and J. Reichenbach and L. Y. Wick (both UFZ, Leipzig, Germany) for their help with the CA measurements. We thank three anonymous reviewers for their comments, which improved the manuscript significantly.

PY - 2015/2

Y1 - 2015/2

N2 - Soil–water repellency (SWR) is a widely observed phenomenon with severe impacts, but a physicochemical framework to explain the process of SWR development is still a major field of research. Recent studies have shown that microbial biomass residues, in particular cell fragments, contribute significantly to the formation of soil organic matter (SOM) and can decrease wettability. It was also shown that osmotic stress increases the hydrophobicity of bacterial cell surfaces. If microorganisms are an important source of SOM, the attachment of cells and their residues on mineral grains should decrease wettability of minerals, and the effect should be more pronounced in case of osmotic stress. Cultures of Pseudomonas putida, either unstressed or exposed to osmotic stress, and cell fragments were mixed with minerals and the impact on surface wetting properties was investigated by determining the solid-water contact angle (CA). Attachment of bacteria to quartz surfaces resulted in a significant increase in hydrophobicity of the surfaces (CA increase by up to 90°), in particular for stressed cells. Cell fragments and cytosol were also found to decrease wettability significantly (CAs of up to 100°). These findings may explain various phenomena related to SWR, like critical soil–water content, and may be one important explanation for the formation of SWR after irrigation with treated sewage effluents. The results also support the hypothesis of a microbial origin of SWR, in which macromolecular biological structures may have a greater impact than specific classes of organic compounds.

AB - Soil–water repellency (SWR) is a widely observed phenomenon with severe impacts, but a physicochemical framework to explain the process of SWR development is still a major field of research. Recent studies have shown that microbial biomass residues, in particular cell fragments, contribute significantly to the formation of soil organic matter (SOM) and can decrease wettability. It was also shown that osmotic stress increases the hydrophobicity of bacterial cell surfaces. If microorganisms are an important source of SOM, the attachment of cells and their residues on mineral grains should decrease wettability of minerals, and the effect should be more pronounced in case of osmotic stress. Cultures of Pseudomonas putida, either unstressed or exposed to osmotic stress, and cell fragments were mixed with minerals and the impact on surface wetting properties was investigated by determining the solid-water contact angle (CA). Attachment of bacteria to quartz surfaces resulted in a significant increase in hydrophobicity of the surfaces (CA increase by up to 90°), in particular for stressed cells. Cell fragments and cytosol were also found to decrease wettability significantly (CAs of up to 100°). These findings may explain various phenomena related to SWR, like critical soil–water content, and may be one important explanation for the formation of SWR after irrigation with treated sewage effluents. The results also support the hypothesis of a microbial origin of SWR, in which macromolecular biological structures may have a greater impact than specific classes of organic compounds.

KW - Bacterial cell wall fragments, lipids and proteins

KW - Contact angle

KW - Environmental scanning microscopy

KW - Microbial biomass

KW - Osmotic stress

KW - Soil water repellency

UR - http://www.scopus.com/inward/record.url?scp=84922005045&partnerID=8YFLogxK

U2 - 10.1007/s10533-014-0040-9

DO - 10.1007/s10533-014-0040-9

M3 - Article

AN - SCOPUS:84922005045

VL - 122

SP - 269

EP - 280

JO - BIOGEOCHEMISTRY

JF - BIOGEOCHEMISTRY

SN - 0168-2563

IS - 2-3

ER -