Zinc toxicity stimulates microbial production of extracellular polymers in a copiotrophic acid soil

Abstract

The production of extracellular polymeric substances (EPS) is crucial for biofilm structure, microbial nutrition and proximal stability of habitat in a variety of environments. However, the production patterns of microbial EPS in soils as affected by heavy metal contamination remain uncertain. Here we investigate the extracellular response of the native microbial biomass in a grassland soil treated with refined glycerol or crude unrefined biodiesel co-product (BCP) with and without ZnCl2. We extracted microbial EPS and more readily soluble microbial products (SMP), and quantified total polysaccharide, uronic acid, and protein content in these respective extracts. Organic addition, especially BCP, significantly stimulated the production of EPS-polysaccharide and protein but had no impact on EPS-uronic acids, while in the SMP-fraction, polysaccharides and uronic acids were both significantly increased. In response to the inclusion of Zn2+, both EPS- and SMP-polysaccharides increased. This implies firstly that a tolerance mechanism of soil microorganisms against Zn2+ toxicity exists through the stimulation of SMP and EPS production, and secondly that co-products of biofuel industries may have value-added use in bioremediation efforts to support in-situ production of microbial biopolymers. Microbial films and mobile polymers are likely to impact a range of soil properties. The recent focus on EPS research in soils is anticipated to help contribute an improved understanding of biofilm dynamics in other complex systems - such as continuously operated bioreactors.

Influence of surface copper content onStenotrophomonas maltophiliabiofilm control using chlorine and mechanical stress

“…For example, Pal and Paul (2013) reported a decrease in EPS production with an increase in nickel concentration. On the other hand, Redmile-Gordon and Chen (2017) found that zinc may stimulate EPS production.…”

Zinc tolerant plant growth promoting bacteria alleviates phytotoxic effects of zinc on maize through zinc immobilization

“…Zinc contaminated soil has negative impacts on plants as well as soil microbiome however, such soils are enriched with Zn tolerant PGPR hence, the soil sampling is one of the critical criteria for the isolation of such Zn tolerant PGPRs 17 . Many areas in Rajasthan including the Zawar region are contaminated with the toxic amounts of Zn and other heavy metals due to ore mining and other human activities 18 .…”

Acceleration of dolomitization by zinc in saline waters

“…The importance of Zn in accelerating carbonate formation is also identified in marine organisms, where CA, a Zn-containing enzyme, regulates biogenic carbonate formation, as documented in corals 49 , sponges 28 , and other metazoans 50 . The catalytic mechanism of CA involves the attack of Zn-bound OH − on a CO 2 molecule loosely bound in the active center of the enzyme, and the resulting Zn-coordinated HCO 3 − ion is then displaced from the metal ion by H 2 O. Zinc also stimulates the production of extracellular polymeric substances 51 , which have been shown to catalyse dolomitization 20 . Zinc is an essential trace nutrient for marine microorganisms, as demonstrated by the typical nutrient cycling profile of Zn concentrations in the ocean, with surface depletion due to phytoplankton uptake and regeneration at depth by remineralization of sinking organic matter.…”