Chromate Resistance Mechanisms in Leucobacter chromiiresistens

Abstract

Chromate is one of the major anthropogenic contaminants on Earth. Leucobacter chromiiresistens is a highly chromate-resistant strain, tolerating chromate concentrations in LB medium of up to 400 mM. In response to chromate stress, L. chromiiresistens forms biofilms, which are held together via extracellular DNA. Inhibition of biofilm formation leads to drastically decreased chromate tolerance. Moreover, chromate is reduced intracellularly to the less-toxic Cr(III). The oxidation status and localization of chromium in cell aggregates were analyzed by energy-dispersive X-ray spectroscopy coupled to scanning transmission electron microscopy and X-ray absorption spectroscopy measurements. Most of the heavy metal is localized as Cr(III) at the cytoplasmic membrane. As a new cellular response to chromate stress, we observed an increased production of the carotenoid lutein. Carotenoid production could increase membrane stability and reduce the concentration of reactive oxygen species. Bioinformatic analysis of the L. chromiiresistens genome revealed several gene clusters that could enable heavy-metal resistance. The extreme chromate tolerance and the unique set of resistance factors suggest the use of L. chromiiresistens as a new model organism to study microbial chromate resistance. IMPORTANCE Chromate is a highly toxic oxyanion. Extensive industrial use and inadequate waste management has caused the toxic pollution of several field sites. Understanding the chromate resistance mechanisms that enable organisms to thrive under these conditions is fundamental to develop (micro)biological strategies and applications aiming at bioremediation of contaminated soils or waters. Potential detoxifying microorganisms are often not sufficient in their resistance characteristics to effectively perform, e.g., chromate reduction or biosorption. In this study, we describe the manifold strategies of L. chromiiresistens to establish an extremely high level of chromate resistance. The multitude of mechanisms conferring it make this organism suitable for consideration as a new model organism to study chromate resistance.

Bioremediation of Hexavalent Chromium by Chromium Resistant Bacteria Reduces Phytotoxicity

“…Various microorganisms are found in the industrial effluents discharging area and are capable of protecting themselves from the toxicity of existing heavy metals in the effluents [ 21 , 22 , 23 , 24 ]. These microorganisms including bacteria, fungi, algae, and protozoa use diverse systems for survival against heavy metal toxicity, such as uptake of heavy metal, adsorption, oxidation, methylation, and reduction of heavy metals to nontoxic forms [ 21 , 25 ]. Toxic Cr(VI) reduction to its nontoxic Cr(III) form is one of the mechanisms used by many organisms to survive in Cr(VI) contaminated effluents [ 24 ].…”

Machine-assisted cultivation and analysis of biofilms

“…L . chromiiresistens has the ability to tolerate the highest chromate concentrations reported so far 37–39 . It is an aerobic organism whose chromate tolerance stems from its capability to efficiently reduce toxic Cr(VI) to Cr(III) species, the latter of which are highly insoluble and therefore less toxic.…”

Decoding microbiome and protein family linkage to improve protein structure prediction

“…Interestingly, 526 sequences of the bacteria-sourced sequences in Pfam sequences (73.8%=526/713) are classified into phylum Proteobacteria, the dominant phyla in the Soil biome that counts for 93.0% of the homologous sequences supplemented in the MSA (Figure 3B). Further functional analysis reveals its role in the Soil biome: Bacteria that hosts in plant produce the proteins identified as PF09828 to reduce the accumulation of chromate in plant (33). The reduction of chromate in plant could promote the growth of plant and prevent the transmission of cadmium to humans through the food chain leads to cadmium poisoning (34).…”