High-Yield Expression of Heterologous [FeFe] Hydrogenases in Escherichia coli

BACKGROUND: The realization of hydrogenase-based technologies for renewable H(2) production is presently limited by the need for scalable and high-yielding methods to supply active hydrogenases and their required maturases. PRINCIPAL FINDINGS: In this report, we describe an improved Escherichia coli-based expression system capable of producing 8-30 mg of purified, active [FeFe] hydrogenase per liter of culture, volumetric yields at least 10-fold greater than previously reported. Specifically, we overcame two problems associated with other in vivo production methods: low protein yields and ineffective hydrogenase maturation. The addition of glucose to the growth medium enhances anaerobic metabolism and growth during hydrogenase expression, which substantially increases total yields. Also, we combine iron and cysteine supplementation with the use of an E. coli strain upregulated for iron-sulfur cluster protein accumulation. These measures dramatically improve in vivo hydrogenase activation. Two hydrogenases, HydA1 from Chlamydomonas reinhardtii and HydA (CpI) from Clostridium pasteurianum, were produced with this improved system and subsequently purified. Biophysical characterization and FTIR spectroscopic analysis of these enzymes indicate that they harbor the H-cluster and catalyze H(2) evolution with rates comparable to those of enzymes isolated from their respective native organisms. SIGNIFICANCE: The production system we describe will facilitate basic hydrogenase investigations as well as the development of new technologies that utilize these prolific H(2)-producing enzymes. These methods can also be extended for producing and studying a variety of oxygen-sensitive iron-sulfur proteins as well as other proteins requiring anoxic environments

New Insights into the Bacterial Fitness-Associated Mechanisms Revealed by the Characterization of Large Plasmids of an Avian Pathogenic E. coli

Extra-intestinal pathogenic E. coli (ExPEC), including avian pathogenic E. coli (APEC), pose a considerable threat to both human and animal health, with illness causing substantial economic loss. APEC strain χ7122 (O78∶K80∶H9), containing three large plasmids [pChi7122-1 (IncFIB/FIIA-FIC), pChi7122-2 (IncFII), and pChi7122-3 (IncI(2))]; and a small plasmid pChi7122-4 (ColE2-like), has been used for many years as a model strain to study the molecular mechanisms of ExPEC pathogenicity and zoonotic potential. We previously sequenced and characterized the plasmid pChi7122-1 and determined its importance in systemic APEC infection; however the roles of the other pChi7122 plasmids were still ambiguous. Herein we present the sequence of the remaining pChi7122 plasmids, confirming that pChi7122-2 and pChi7122-3 encode an ABC iron transport system (eitABCD) and a putative type IV fimbriae respectively, whereas pChi7122-4 is a cryptic plasmid. New features were also identified, including a gene cluster on pChi7122-2 that is not present in other E. coli strains but is found in Salmonella serovars and is predicted to encode the sugars catabolic pathways. In vitro evaluation of the APEC χ7122 derivative strains with the three large plasmids, either individually or in combinations, provided new insights into the role of plasmids in biofilm formation, bile and acid tolerance, and the interaction of E. coli strains with 3-D cultures of intestinal epithelial cells. In this study, we show that the nature and combinations of plasmids, as well as the background of the host strains, have an effect on these phenomena. Our data reveal new insights into the role of extra-chromosomal sequences in fitness and diversity of ExPEC in their phenotypes

"We fear the police, and the police fear us": structural and individual barriers and facilitators to HIV medication adherence among injection drug users in Kiev, Ukraine

Ukraine has one of the most severe HIV/AIDS epidemics in Europe, with an estimated 1.63% of the population living with HIV/AIDS in 2007. Injection drug use (IDU) remains the predominant mode of transmission in Kiev - the capital and largest city. Prior reports suggest that the HIV infection rate among IDUs in Kiev reaches 33%, and many have poor and inequitable access to highly active antiretroviral therapy (HAART). Among those with access to HAART, little is understood about barriers and facilitators to HAART medication adherence. In May 2009, two semi-structured focus groups were conducted with HIV-infected IDUs seeking treatment at the City AIDS Center, Kiev. The goal was to use this information to adapt and tailor, to Ukrainian culture, an evidence-based intervention for improving adherence to HAART. All 16 participants attributed HIV infection to IDU. Their average age was 31.6 (SD=7.0), average time with HIV 5.7 years (SD=4.0), average time on HAART 2.5 years (SD=1.7), average time as IDU 14.6 years (SD=6.8), and 88% were on opioid substitution therapy. The most salient themes related to adherence barriers included: (1) harassment and discrimination by police; (2) opioid dependence; (3) complexity of drug regimen; (4) side effects; (5) forgetting; (6) co-occurring mental health problems; and (7) HIV stigma. Facilitators of adherence included: (1) cues for pill taking; (2) support and reminders from family, significant other, and friends; (3) opioid substitution therapy; and (4) wanting improved health. Additional factors explored included: (1) knowledge about HAART; (2) storage of medications; and (3) IDU and sexual risk behaviors. Findings highlighted structural and individual barriers to adherence. At the structural level, police discrimination and harassment was reported to be a major barrier to adherence to opioid substitution therapy and HAART. Privacy and stigma were barriers at the individual level. Recommendations for adherence interventions included education, training, and identification cards to show police that medication was for treatment of HIV, not for abuse; and involving family members and other systems of support for HIV treatment

“We fear the police, and the police fear us”: structural and individual barriers and facilitators to HIV medication adherence among injection drug users in Kiev, Ukraine

Ukraine has one of the most severe HIV/AIDS epidemics in Europe, with an estimated 1.63% of the population living with HIV/AIDS in 2007. Injection drug use (IDU) remains the predominant mode of transmission in Kiev—the capital and largest city. Prior reports suggest that the HIV infection rate among IDUs in Kiev reaches 33%, and many have poor and inequitable access to highly active antiretroviral therapy (HAART). Among those with access to HAART, little is understood about barriers and facilitators to HAART medication adherence. In 5/2009, two semi-structured focus groups were conducted with HIV-infected IDUs seeking treatment at the City AIDS Center, Kiev. The goal was to use this information to adapt and tailor, to Ukrainian culture, an evidence-based intervention for improving adherence to HAART. All 16 participants attributed HIV infection to IDU. Their average age was 31.6 (SD=7.0), average time with HIV 5.7 years (SD=4.0), average time on HAART 2.5 years (SD=1.7), average time as IDU 14.6 years (SD=6.8), and 88% were on opioid substitution therapy. The most salient themes related to adherence barriers included: (1) harassment and discrimination by police; (2) opioid dependence; (3) complexity of drug regimen; (4) side effects; (5) forgetting; (6) co-occurring mental health problems; and (7) HIV stigma. Facilitators of adherence included: (1) cues for pill taking; (2) support and reminders from family, significant other, and friends; (3) opioid substitution therapy; and (4) wanting improved health. Additional factors explored included: 1) knowledge about HAART; (2) storage of medications; and (3) IDU and sexual risk behaviors. Findings highlighted structural and individual barriers to adherence. At the structural level, police discrimination and harassment was reported to be a major barrier to adherence to opioid substitution therapy and HAART. Privacy and stigma were barriers at the individual level. Recommendations for adherence interventions included education, training, and identification cards to show police that medication was for treatment of HIV, not for abuse; and involving family members and other systems of support for HIV treatment

Exciton Dynamics in MoS2-Pentacene and WSe2-Pentacene Heterojunctions

We measured the exciton dynamics in van der Waals heterojunctions of transition metal dichalcogenides (TMDCs) and organic semiconductors (OSs). TMDCs and OSs are semiconducting materials with rich and highly diverse optical and electronic properties. Their heterostructures, exhibiting van der Waals bonding at their interfaces, can be utilized in the field of optoelectronics and photovoltaics. Two types of heterojunctions, MoS2-pentacene and WSe2-pentacene, were prepared by layer transfer of 20 nm pentacene thin films as well as MoS2and WSe2monolayer crystals onto Au surfaces. The samples were studied by means of transient absorption spectroscopy in the reflectance mode. We found that A-exciton decay by hole transfer from MoS2to pentacene occurs with a characteristic time of 21 ± 3 ps. This is slow compared to previously reported hole transfer times of 6.7 ps in MoS2-pentacene junctions formed by vapor deposition of pentacene molecules onto MoS2on SiO2. The B-exciton decay in WSe2shows faster hole transfer rates for WSe2-pentacene heterojunctions, with a characteristic time of 7 ± 1 ps. The A-exciton in WSe2also decays faster due to the presence of a pentacene overlayer; however, fitting the decay traces did not allow for the unambiguous assignment of the associated decay time. Our work provides important insights into excitonic dynamics in the growing field of TMDC-OS heterojunctions