Selenite reduction by the obligate aerobic bacterium Comamonas testosteroni S44 isolated from a metal-contaminated soil

Abstract

BackgroundSelenium (Se) is an essential trace element in most organisms but has to be carefully handled since there is a thin line between beneficial and toxic concentrations. Many bacteria have the ability to reduce selenite (Se(IV)) and (or) selenate (Se(VI)) to red elemental selenium that is less toxic.ResultsA strictly aerobic bacterium, Comamonas testosteroni S44, previously isolated from metal(loid)-contaminated soil in southern China, reduced Se(IV) to red selenium nanoparticles (SeNPs) with sizes ranging from 100 to 200 nm. Both energy dispersive X-ray Spectroscopy (EDX or EDS) and EDS Elemental Mapping showed no element Se and SeNPs were produced inside cells whereas Se(IV) was reduced to red-colored selenium in the cytoplasmic fraction in presence of NADPH. Tungstate inhibited Se(VI) but not Se(IV) reduction, indicating the Se(IV)-reducing determinant does not contain molybdenum as co-factor. Strain S44 was resistant to multiple heavy and transition metal(loid)s such as Se(IV), As(III), Cu(II), and Cd(II) with minimal inhibitory concentrations (MIC) of 100 mM, 20 mM, 4 mM, and 0.5 mM, respectively. Disruption of iscR encoding a transcriptional regulator negatively impacted cellular growth and subsequent resistance to multiple heavy metal(loid)s.ConclusionsC. testosteroni S44 could be very useful for bioremediation in heavy metal(loid) polluted soils due to the ability to both reduce toxic Se(VI) and Se(IV) to non-toxic Se (0) under aerobic conditions and to tolerate multiple heavy and transition metals. IscR appears to be an activator to regulate genes involved in resistance to heavy or transition metal(loid)s but not for genes responsible for Se(IV) reduction.

Bacillus cereus, selenite-reducing bacterium from contaminated lake of an industrial area: a renewable nanofactory for the synthesis of selenium nanoparticles

“…(Bajaj et al 2012), Zooglea ramigera (Srivastava and Mukhopadhyay 2013), Streptomyces minutiscleroticus M10A62 (Ramya et al 2015), Acinetobacter sp. E6.2 (Durán et al 2015), Comamonas testosteroni S44 (Zheng et al 2014), Klebsiella pneumonia (Fesharaki et al 2010), Lactobacillus sp, Bifidobacter sp., and Streptococcus thermophilus (Eszenyi et al 2011).…”

“…In addition, from the soil of a antimony mine from Lengshuijiang, southern China (Zheng et al 2014), soil of a magnesite mine from Salem, India (Ramya et al 2015), soil of a coal mine from West Bengal, India (Dhanjal and Cameotra 2010), selenium laden agricultural soil of North-East Punjab, India (Bajaj et al 2012), soil of mangrove forest from Bhitarkanika, Orissa, India (Mishra et al 2011), rhizosphere soil of a selenium hyperaccumulator legume grown in seleniferous mine from Sardina, Italy (Lampis et al 2014), rhizosphere of wheat grown in herbicide contaminated soil (Dwivedi et al 2013), and rhizosphere of cereal plants grown in ash-derived volcanic soil of southern Chile (Durán et al 2015). Others include rock fragments of black oil shale from Haenam, Korea (Tam et al 2010), food wastes collected from local market of Giza, Egypt (Khiralla and El-Deeb 2015), sub gingival dental plaque (Pearce et al 2008) etc.…”

Microbial selenite reduction with organic carbon and electrode as sole electron donor by a bacterium isolated from domestic wastewater

“…1a), indicating that the microaerobic condition was favorable for growth of strain THL1. Aerobic selenite reduction to elemental selenium by Pseudomonas stutzeri NT-I (Kuroda et al, 2011a), Comamonas testosteroni S44 (Zheng et al, 2014), and Rhizobium selenitireducens (Hunter, 2014) has been reported. Different pathways have been suggested to be involved in microbial selenite reduction, including the Paintertype reaction, the thioredoxin reductase system, siderophoremediated reduction, sulfide-mediated reduction, and dissimilatory reduction (Nancharaiah and Lens, 2015a,b).…”

“…Different pathways have been suggested to be involved in microbial selenite reduction, including the Paintertype reaction, the thioredoxin reductase system, siderophoremediated reduction, sulfide-mediated reduction, and dissimilatory reduction (Nancharaiah and Lens, 2015a,b). Several enzymes were proposed to be involved in microbiological selenite reduction but no sole gene product was identified (Zheng et al, 2014). Bacterial selenite reduction is believed to occur in the cytoplasm or periplasm, following which the product is transported out of the cell to form elemental selenium nanoparticles (Bajaj et al, 2012;Zheng et al, 2014).…”

“…The mechanisms of microbial reduction of selenate to selenite and selenite to elemental selenium through anaerobic respiration and detoxification have been characterized in both gram-negative and gram-positive bacteria (Debieux et al, 2011;Kuroda et al, 2011b;Schröder et al, 1997). Microbial reduction of selenite to elemental selenium is typically regarded as a detoxification mechanism, which has been observed in a wide range of microorganisms under both aerobic (Kuroda et al, 2011a;Zheng et al, 2014) and anaerobic conditions (Ayano et al, 2014;Basaglia et al, 2007;Hunter, 2014;Li et al, 2014). In all cases, the microbial detoxification of soluble selenium requires an adequate organic substrate as the electron donor.…”