Effects of cadmium, copper, magnesium, and zinc on the decomposition of citrate by a Klebsiella sp

Abstract

The effects of Cd2+, Cu2+, Mg2+, and Zn2+ on the decomposition of citric acid by a Klebsiella sp. were studied by monitoring the degradation of [14C]citrate. The carbon concentration used was 10 ,ug of C liter-', and the media were designed to provide at least 95% of the citrate complexed to the metal studied. After 72 h of incubation, 80% of the uncomplexed citric acid and 76% of the magnesium citrate had been decomposed. A marked inhibition was observed when Cd2+, Cu2+, or Zn2+ was bound to the organic anion; only 23% of the cadmium citrate, 14% of the zinc citrate, and 5% of the cuprous citrate had been decomposed. The effects were not the result of toxicity, since experiments run with [14C]glucose (nonchelating compound) instead of citrate resulted in similar decomposition rates regardless of the presence of the metal. To examine whether the binding of a metal to citrate enhanced its uptake by the Klebsiella sp., we studied the relative uptake of 65Zn in citrate-and in glucose-containing media. No such effect could be observed, with the uptake of Zn2+ being higher in the glucose-containing media. The study shows that metals may render low-molecular-weight organic acids, such as citric acid, resistant to bacterial degradation. This stresses the importance of metals in influencing microbial decomposition of organic compounds, not only as a result of toxicity.

Microbial activity and hydrolase activities during decomposition of root exudates released by an artificial root surface in Cd-contaminated soils

“…1 and 2), could be due to the delay in the mineralization of root exudates, which is a common feature of heavy metal contaminated soils (Haanstra and Doelman, 1984;Nordgren et al, 1988) and/or to lower amounts of root exudates metabolized by soil microorganisms due to formation of Cd-root exudates complexes. Low molecular weight organic acids and amino acids can form Cd-complexes (Krishnamurti et al, 1997), which are not readily mineralizable by soil microorganisms (Brynhildsen and Rosswall, 1989;Renella et al, 2004a). However, reduced microbial mineralization and growth rates in Cd-contaminated soils were also observed after treatment with glucose which has no chelating ability, suggesting that the lower metabolic efficiency (i.e.…”

Synthesis and Spectroscopic and Structural Studies of a New Cadmium(II)−Citrate Aqueous Complex. Potential Relevance to Cadmium(II)−Citrate Speciation and Links to Cadmium Toxicity

“…As a result, vital functions such as, e.g., plant uptake of organic substrates or metals for key metabolic processes could be affected. In the case of Cd(II), citrate complexation has been invoked to account for the inability of bacterial organisms to (a) internalize and/or (b) metabolize citrate in the presence of Cd(II), thus emphasizing inhibitory effects of Cd(II) on the physiology of organism(s). , …”

“…It has been elaborated frequently that citrate binding to transition metal ions increases their solubility and ultimate bioavailability. In a number of reports, on the other hand, it has been suggested that complexed forms of Cd(II) with citrate are not transported into the bacterial cells and are consequently not degraded by bacteria . Therefore, citric acid appears to be a very good target for Cd(II), and their interactions are of genuine chemical interest with potential biological ramifications.…”

Biodegradation of thermally treated high-density polyethylene (HDPE) by Klebsiella pneumoniae CH001

“…Klebsiella pneumonia, a Gm-negative bacterium, has shown importance in waste water treatment (Maal et al 2014), citrate decomposition (Brynhildsen and Rosswall 1989), nitrogen fixation (Iniguez et al 2004), and hydrogen production from biodiesel waste containing glycerol (Liu and Fang 2006). Moreover, it qualifies as a suitable microorganism for LDPE degradation (Anbuselvi and Pandey 2015).…”