Bioadsorption and bioaccumulation of chromium trivalent in Cr(III)-tolerant microalgae: a mechanisms for chromium resistance

Anthropogenic activity constantly releases heavy metals into the environment. The heavy metal chromium has a wide industrial use and exists in two stable oxidation states: trivalent and hexavalent. While hexavalent chromium uptake in plant cells has been reported that an active process by carrying essential anions, the cation Cr(III) appears to be taken up inactively. Dictyosphaerium chlorelloides (Dc1M), an unicellular green alga is a well-studied cell biological model organism. The present study was carried out to investigate the toxic effect of chromium exposures on wild-type Cr(III)-sensitive (Dc1M(wt)) and Cr(III)-tolerant (Dc1M(Cr(III)R30)) strains of these green algae, and to determine the potential mechanism of chromium resistance. Using cell growth as endpoint to determine Cr(III)-sensitivity, the IC₅₀(₇₂) values obtained show significant differences of sensitivity between wild type and Cr(III)-tolerant cells. Scanning electron microscopy (SEM) showed significant morphological differences between both strains, such as decrease in cell size or reducing the coefficient of form; and transmission electron microscopy (TEM) revealed ultrastructural changes such as increased vacuolization and cell wall thickening in the Cr(III)-tolerant strain with respect to the wild-type strain. Energy dispersive X-ray analysis (SEM/XEDS) revealed that Cr(III)-tolerant D. chlorelloides cells are able to accumulate considerable amounts of chromium distributed in cell wall (bioadsorption) as well as in cytoplasm, vacuoles, and chloroplast (bio-accumulation). Morphological changes of Cr(III)-tolerant D. chlorelloides cells and the presence of these electron-dense bodies in their cell structures can be understood as a Cr(III) detoxification mechanism.

Risk factors associated with Clostridium difficile infection after kidney and pancreas transplantation

BACKGROUND

Clostridium difficile infection (CDI) is a common cause of nosocomial antibiotic-associated diarrhea with an increased incidence reported in solid organ transplant recipients. We sought to determine if kidney and/or pancreas transplant recipients possess unique risk factors for CDI.

METHODS

Between January 2009 and February 2011, 942 kidney and 56 pancreas transplants were performed at the 2 centers. Of these, 28 recipients (kidney, n = 24; pancreas, n = 4) developed CDI. Cases were matched to controls (n = 56) in a 1:2 ratio.

RESULTS

Those with CDI were mostly male patients (82% vs. 48%, P = 0.003), deceased-donor organ recipients (86% vs. 64%, P = 0.045), more likely to have leukopenia (18% vs. 4%, P = 0.038), and had undergone a gastrointestinal procedure within 3 months preceding CDI diagnosis (18% vs. 4%, P = 0.038). Cases had higher cumulative and restricted antimicrobial exposure in days (37 ± 79 vs. 8 ± 12, P = 0.009 and 27 ± 69 vs. 7 ± 10, P = 0.032). Cephalosporin use was more common among cases (43% vs. 16%, P = 0.008).

CONCLUSION

Careful antimicrobial selection and assurance of optimal treatment duration in the kidney and pancreas transplant population is prudent. Clinicians should have a heightened awareness of CDI risk particularly during periods of leukopenia and in the setting of gastrointestinal procedures.

Functional mapping of the neural circuitry of rat maternal motivation: effects of site-specific transient neural inactivation

The present review focuses on recent studies from our laboratory examining the neural circuitry subserving rat maternal motivation across postpartum. We employed a site-specific neural inactivation method by infusion of bupivacaine to map the maternal motivation circuitry using two complementary behavioural approaches: unconditioned maternal responsiveness and choice of pup- over cocaine-conditioned incentives in a concurrent pup/cocaine choice conditioned place preference task. Our findings revealed that, during the early postpartum period, distinct brain structures, including the medial preoptic area, ventral tegmental area and medial prefrontal cortex infralimbic and anterior cingulate subregions, contribute a pup-specific bias to the motivational circuitry. As the postpartum period progresses and the pups grow older, it is further revealed that maternal responsiveness becomes progressively less dependent on the medial preoptic area and medial prefrontal cortex infralimbic activity, and more distributed in the maternal circuitry, such that additional network components, including the medial prefrontal cortex prelimbic subregion, are recruited with maternal experience, and contribute to the expression of late postpartum maternal behaviour. Collectively, our findings provide strong evidence that the remarkable ability of postpartum females to successfully care for their developing infants is subserved by a distributed neural network that carries out efficient and dynamic processing of complex, constantly changing incoming environmental and pup-related stimuli, ultimately allowing the progression of appropriate expression and waning of maternal responsiveness across the postpartum period.