Microbial nanowires with genetically modified peptide ligands to sustainably fabricate electronic sensing devices

Nanowires have substantial potential as the sensor component in electronic sensing devices. However, surface functionalization of traditional nanowire and nanotube materials with short peptides that increase sensor selectivity and sensitivity requires complex chemistries with toxic reagents. In contrast, microorganisms can assemble pilin monomers into protein nanowires with intrinsic conductivity from renewable feedstocks, yielding an electronic material that is robust and stable in applications, but also biodegradable. Here we report that the sensitivity and selectivity of protein nanowire-based sensors can be modified with a simple plug and play genetic approach in which a short peptide sequence, designed to bind the analyte of interest, is incorporated into the pilin protein that is microbially assembled into nanowires. We employed a scalable Escherichia coli chassis to fabricate protein nanowires that displayed either a peptide previously demonstrated to effectively bind ammonia, or a peptide known to bind acetic acid. Sensors comprised of thin films of the nanowires amended with the ammonia-specific peptide had a ca. 100-fold greater response to ammonia than sensors made with unmodified protein nanowires. Protein nanowires with the peptide that binds acetic acid yielded a 4-fold higher response than nanowires without the peptide. The protein nanowire-based sensors had greater responses than previously reported sensors fabricated with other nanomaterials. The results demonstrate that protein nanowires with enhanced sensor response for analytes of interest can be fabricated with a flexible genetic strategy that sustainably eliminates the energy, environmental, and health concerns associated with other common nanomaterials.

Mechanisms for Electron Uptake by Methanosarcina acetivorans during Direct Interspecies Electron Transfer

Direct interspecies electron transfer (DIET) between bacteria and methanogenic archaea appears to be an important syntrophy in both natural and engineered methanogenic environments. However, the electrical connections on the outer surface of methanogens and the subsequent processing of electrons for carbon dioxide reduction to methane are poorly understood. Here, we report that the genetically tractable methanogen Methanosarcina acetivorans can grow via DIET in coculture with Geobacter metallireducens serving as the electron-donating partner. Comparison of gene expression patterns in M. acetivorans grown in coculture versus pure-culture growth on acetate revealed that transcripts for the outer-surface multiheme c-type cytochrome MmcA were higher during DIET-based growth. Deletion of mmcA inhibited DIET. The high aromatic amino acid content of M. acetivorans archaellins suggests that they might assemble into electrically conductive archaella. A mutant that could not express archaella was deficient in DIET. However, this mutant grew in DIET-based coculture as well as the archaellum-expressing parental strain in the presence of granular activated carbon, which was previously shown to serve as a substitute for electrically conductive pili as a conduit for long-range interspecies electron transfer in other DIET-based cocultures. Transcriptomic data suggesting that the membrane-bound Rnf, Fpo, and HdrED complexes also play a role in DIET were incorporated into a charge-balanced model illustrating how electrons entering the cell through MmcA can yield energy to support growth from carbon dioxide reduction. The results are the first genetics-based functional demonstration of likely outer-surface electrical contacts for DIET in a methanogen. IMPORTANCE The conversion of organic matter to methane plays an important role in the global carbon cycle and is an effective strategy for converting wastes to a useful biofuel. The reduction of carbon dioxide to methane accounts for approximately a third of the methane produced in anaerobic soils and sediments as well as waste digesters. Potential electron donors for carbon dioxide reduction are H2 or electrons derived from direct interspecies electron transfer (DIET) between bacteria and methanogens. Elucidating the relative importance of these electron donors has been difficult due to a lack of information on the electrical connections on the outer surfaces of methanogens and how they process the electrons received from DIET. Transcriptomic patterns and gene deletion phenotypes reported here provide insight into how a group of Methanosarcina organisms that play an important role in methane production in soils and sediments participate in DIET.

Geobacter pickeringii sp. nov., Geobacter argillaceus sp. nov. and Pelosinus fermentans gen. nov., sp. nov., isolated from subsurface kaolin lenses

The goal of this project was to isolate representative Fe(III)-reducing bacteria from kaolin clays that may influence iron mineralogy in kaolin. Two novel dissimilatory Fe(III)-reducing bacteria, strains G12(T) and G13(T), were isolated from sedimentary kaolin strata in Georgia (USA). Cells of strains G12(T) and G13(T) were motile, non-spore-forming regular rods, 1-2 mum long and 0.6 mum in diameter. Cells had one lateral flagellum. Phylogenetic analyses using the 16S rRNA gene sequence of the novel strains demonstrated their affiliation to the genus Geobacter. Strain G12(T) was most closely related to Geobacter pelophilus (94.7 %) and Geobacter chapellei (94.1 %). Strain G13(T) was most closely related to Geobacter grbiciae (95.3 %) and Geobacter metallireducens (95.1 %). Based on phylogenetic analyses and phenotypic differences between the novel isolates and other closely related species of the genus Geobacter, the isolates are proposed as representing two novel species, Geobacter argillaceus sp. nov. (type strain G12(T)=ATCC BAA-1139(T)=JCM 12999(T)) and Geobacter pickeringii sp. nov. (type strain G13(T)=ATCC BAA-1140(T)=DSM 17153(T)=JCM 13000(T)). Another isolate, strain R7(T), was derived from a primary kaolin deposit in Russia. The cells of strain R7(T) were motile, spore-forming, slightly curved rods, 0.6 x 2.0-6.0 microm in size and with up to six peritrichous flagella. Strain R7(T) was capable of reducing Fe(III) only in the presence of a fermentable substrate. 16S rRNA gene sequence analysis demonstrated that this isolate is unique, showing less than 92 % similarity to bacteria of the Sporomusa-Pectinatus-Selenomomas phyletic group, including 'Anaerospora hongkongensis' (90.2 %), Acetonema longum (90.6 %), Dendrosporobacter quercicolus (90.9 %) and Anaerosinus glycerini (91.5 %). On the basis of phylogenetic analysis and physiological tests, strain R7(T) is proposed to represent a novel genus and species, Pelosinus fermentans gen. nov., sp. nov. (type strain R7(T)=DSM 17108(T)=ATCC BAA-1133(T)), in the Sporomusa-Pectinatus-Selenomonas group.

Synthesis and cytotoxic action of 3,5-isoxazolidinediones and 2-isoxazolin-5-ones in murine and human tumors

The 3,5-isoxazolidinediones and 2-isoxazolin-5-ones demonstrated potent cytotoxicity against the growth of human Tmolt3 T cell leukemia, murine P388 and L1210 leukemias, as well as human HeLa-S3 uterine carcinoma and glioma tumor cell growth. The specificity of the 3,5-isoxazolidinedione and 2-isoxazoline-5-one derivatives as cytotoxic agents varied with the histological type of tumor cell. Selected compounds were active against solid HeLa uterine. KB nasopharynx, skin A431, SW-480 adenocarcinoma, osteosarcoma and glioma growth. Selected compounds demonstrated in vivo antineoplastic activity against Ehrlich ascites carcinoma growth. In L-1210 leukemia cells, the agents blocked DNA and protein synthesis at 25, 50 and 100 microM over 60 min. The agents were effective in reducing rate limiting enzymes in the de novo purine and pyrimidine pathways. In addition they suppressed dihydrofolate reductase and ribonucleoside reductase activities with moderate inhibition of DNA and RNA polymerase activities. DNA itself was not a target of the agents.

Investigation of 3,5-isoxazolidinediones as hypolipidemic agents in rodents

A series of 2-benzoyl-4,4-dialkyl-3,5-isoxazolidinediones proved to have potent hypolipidemic activity, lowering both serum cholesterol and triglyceride levels at 10 or 20 mg/kg/day, IP and orally in rodents. 2-(3,4,5-Trimethoxybenzoyl)-4,4-diethyl-3,5-isoxazolidinedione+ ++ (4) afforded the best hypolipidemic activity lowering normolipidemic CF1 mouse serum cholesterol levels 49% and serum triglyceride levels 34% at 20 mg/kg/day, IP. Compound 4 was selected as a typical derivative of the chemical class for further detailed studies. Serum cholesterol levels in normolipidemic Sprague Dawley male rats were reduced 45% after 8 weeks at 10 and 20 mg/kg/day of compound, orally. Serum triglyceride levels were reduced 38-49% at 10 and 20 mg/kg/day, orally. In vitro liver enzyme activities studies in normolipidemic CF1 mice showed the compound inhibited mitochondrial citrate exchange, acetyl CoA synthetase, HMG CoA reductase, acyl CoA cholesterol acyl transferase, acetyl CoA carboxylase, sn-glycerol-3-phosphate acyl transferase, phosphatidylate phosphohydrolase and heparin-induced lipoprotein lipase activities with increases in the activities of cholesterol ester hydrolase and ATP-dependent citrate lyase. Similar enzyme activities were inhibited in vivo except HMG CoA reductase activity was not inhibited in rat liver or small intestinal mucosa after 8 weeks drug administration. Cholesterol levels were reduced in tissues after 8 weeks administration of compound 4 in normolipidemic rats. Bile cholesterol and triglyceride levels were elevated after two weeks administration to rats at 20 mg/kg/day. Serum lipoprotein levels in normolipidemic and hyperlipidemic rats showed the cholesterol levels in VLDL and LDL fractions after 4, 6 and 8 weeks at 10 and 20 mg/kg/day were reduced whereas HDL-cholesterol levels were significantly elevated. Studies demonstrated that 3H-cholesterol and 14C-palmitic acid incorporation into lipids of the lipoprotein fraction was reduced by the drug but 32P-incorporation was generally elevated. The agent demonstrated no observable toxicity in rats after 8 weeks administration, orally. The acute toxicity study in normolipidemic mice at 20, 40 and 100 mg/kg/day, IP, demonstrated no observable harmful effects of the drug.

The antineoplastic and cytotoxicity of benzohydroxamic acids and related derivatives in murine and human tumor cells

Benzohydroxamic acids proved to be potent cytotoxic agents suppressing the growth of a number of murine and human cell lines grown in tissue culture, e.g. leukemia, colon, uterine and glioma. Selected compounds demonstrated activity against the growth KB nasopharynx, bronchogenic lung, osteosarcoma and skin cancer. In vivo activity against Ehrlich ascites carcinoma growth was shown with certain compounds. In L1210 cells compound 2 inhibited DNA synthesis significantly within 60 min. the site of action of the agent appears to involve the purine de novo synthesis pathway at PRPP amido transferase and IMP dehydrogenase. Dihydrofolate reductase and nucleoside kinase activities were inhibited by the agent. The levels of d(NTP)s in L1210 cells were reduced after drug treatment. The drug did not appear to affect the DNA template directly causing any damage which might alter transcription and replication nor was there any inhibition of HeLa topoisomerase activity by the drug. Thus the drug appears to be a metabolic inhibitor of nucleoside metabolism.

Hypolipidemic activity of benzohydroxamic acids and dibenzohydroxamic acids in rodents

A series of benzo- and dibenzohydroxamic acids were shown to have potent hypolipidemic activity in mice and rats lowering both serum cholesterol and triglyceride levels at 20 mg/kg/day. Selected derivatives lowered tissue lipids, i.e. liver, small intestine and aorta, and accelerated fecal lipid excretion in rats. The VLDL and LDL cholesterol content was reduced and HDL cholesterol was significantly elevated after 14 days administration, orally. The agents were not HMG CoA reductase inhibitors; however, other lipid regulator enzyme activities were inhibited, e.g. acyl CoA cholesterol acyl transferase, ATP-dependent citrate lyase and acetyl CoA synthetase. The triglyceride levels were probably reduced due to the derivatives inhibiting the enzymatic activities of sn-glycerol-3-phosphate acyl transferase and phosphatidylate phosphohydrolase.

Correction of uremic cellular injury with a protein-restricted amino acid-supplemented diet

Untreated patients with uremia show an abnormally low resting transmembrane potential (Em) of skeletal muscle cells. This finding corresponds to impaired sodium transport. Adequate hemodialysis corrects this abnormality. Toxins derived from protein precursors have been implicated as the hypothetical cause of impaired transport and membrane depolarization in untreated uremia. To inferentially examine this hypothesis in further detail, we deliberately reduced dialysis time until Em fell in six uremic patients in whom it had been previously corrected. When Em fell, we examined the effect of reducing crude protein in their diet in conjunction with adding an essential amino acid supplement. Five of six patients who complied with the diet showed correction of their abnormally low Em despite continued reduction of dialysis time. These findings support the notion that in patients with uremia, a product of crude dietary protein may be responsible for membrane depolarization and, in addition, direct measurement of resting muscle transmembrane potential may be a useful index to determine adequacy of dialysis therapy.

Resting skeletal muscle membrane potential as an index of uremic toxicity. A proposed new method to assess adequacy of hemodialysis

Electrochemical disturbances of skeletal muscle cells in untreated uremia are characterized by an increase in the intracellular sodium and chloride content, a decrease in intracellular potassium, and a low resting membrane potential. In this study, we have reexamined the foregoing and, in addition, have examined the effects of hemodialysis. Three groups of patients were studied. In the first group of 22 uncomplicated uremic patients, whose creatinine clearance (Ccr) ranged from 2 to 12 cm(3)/min per 1.73 m(2), resting transmembrane potential difference (Em) of skeletal muscle cells was measured. In each of the nine patients whose Ccr ranged between 6.3 and 12 cm(3)/min, the Em was normal (i.e., -90.8+/-0.9 mV, mean+/-SEM). However, as Ccr dropped below 6.3 cm/min, the Em became progressively reduced and assumed a linear relationship with the Ccr. In the second study, nine individuals with end-stage renal disease, whose mean Ccr was 4.3 cm(3)/min, underwent measurement of Em and intracellular electrolyte concentration before and after 7 wk of hemodialysis. Before dialysis, the Em was -78.5+/-2.1 mV, intracellular sodium and chloride were elevated, and the intracellular potassium was reduced. After 7 wk of hemodialysis the Em rose to -87.8+/-1.3 mV, and the intracellular sodium, chloride, and potassium became normal. In the third study, seven patients who were stable on 6-h thrice-weekly dialysis were studied before and after reduction of dialysis to 6 h twice weekly. In those individuals whose Em remained normal after 6 wk, dialysis time was reduced further. On thrice-weekly dialysis the Em was -91.2+/-1.0 mV. With reduced dialysis, the Em fell to -80.1+/-0.8 mV (P < 0.001). In each case, the Em became abnormal before significant signs or symptoms of uremia were noted. These findings demonstrate that end-stage renal disease is associated with serious electrochemical changes in the muscle cell which are reversed by hemodialysis and recur when dialysis time is reduced. Thus, serial observations of muscle Em may be a potentially powerful tool to assess adequacy of dialysis therapy.