Management of proximal tibial stress fracture associated with advanced knee osteoarthritis: A systematic review.

PURPOSE: Tibial stress fracture associated with knee osteoarthritis is an unusual and difficult clinical scenario. There is no clear existing treatment guideline for this uncommon clinical disease. The aim of this study is to review the impact of various treatment options for patients with advanced knee osteoarthritis associated with proximal tibial stress fracture. METHODS: The study was performed using the databases of PubMed and Scopus. Methodological index for non-randomized studies score was used to evaluate the included studies' bias. The concluded data included the treatment approach, reported outcome measure, and time to fracture union. The literature search was started in December 2021 and accomplished at January 2022. A narrative description of the different methods and comparison of their results were done. RESULTS: Out of total assessed 69 studies, 9 studies were included in our review. The commonest treatment approach used was total knee arthroplasty by long tibial stem extension. The mean preoperative knee society score and knee functional score were 30.62 and 23.17, respectively. The mean postoperative knee society knee score was 86.87, while the functional score was 83.52. The average reported time to achieve fracture union was 4 months (ranging 2.07-5.50 months). CONCLUSION: The optimal clinical outcome for treating either acute or mobile tibial stress fracture in patients with advanced knee osteoarthritis can be achieved with long stem total knee arthroplasty. However, due to heterogeneity of data, comparison of different treatment options for chronic proximal tibial stress fracture mal-union/non-union coexisting with knee osteoarthritic and such inferences need to be judged cautiously.

Medial tibial bone resorption following total knee arthroplasty comparing a traditional with a kinematic design.

BACKGROUND: New total knee prostheses are being designed to improve clinical outcome, survivorship and patient satisfaction following total knee arthroplasty (TKA). A new knee system was developed with improvements in patellofemoral joint, trochlear geometry, polyethylene formulation and tibial baseplate. Aim of this study was to compare the newer kinematic knee system with its existing predecessor knee system in terms of clinical outcome, revision rates, radiographic outcomes specifically medial tibial bone resorption. METHODS: The prospective matched-pair study included 88 TKA surgeries using newer kinematic design knee prostheses, performed between January 2015 and December 2016, out of which 82 patients were available for final follow-up. The control cohort of 82 traditional TKA prosthesis was matched in terms of age, gender and body mass index. All surgeries were performed by the single surgeon using medial parapatellar arthrotomy and posterior stabilized implants were used. Clinical outcomes were assessed using knee society score, range of motion (ROM), anterior knee pain and crepitation. Radiological examinations included recording of radiolucent lines and medial tibial bone resorption. RESULTS: At the 5-year follow-up, no significant differences were noted in terms of mean knee society score (93.3 ± 6.6 vs 94.2 ± 8.1), knee function score (88.5 ± 10.5 vs 89.1 ± 11.2) and ROM. The incidences of anterior knee pain and crepitation were lower in the newer group (8.5% vs 21.9% and 14.6% vs 32.9%, respectively) compared to the traditional prosthesis group. No cases of aseptic loosening were observed in either cohort. No significant difference was seen in terms of radiolucent lines (29.3% vs 26.8%) and medial tibial resorption (2.43% in each group) incidences. CONCLUSIONS: At the 5 years follow-up no significant differences were noted between the two groups in terms of clinical and radiological outcomes, except the former proved to be better for anterior knee pain and crepitation. LEVEL OF EVIDENCE: II.

The application of low-dose dexamethasone in total knee arthroplasty: finding out the best route and dosage schedule.

BACKGROUND: The use of dexamethasone as additive to multimodal analgesic regimen in total knee arthroplasty has been well established, but the most suitable route, effectiveness, safety and dose schedule of low-dose dexamethasone is not known. METHODS: We conducted a prospective, randomized, double-blinded trial to investigate and compare the analgesic and antiemetic effects and safety of low-dose (8 mg) dexamethasone introduced as periarticular injection or intravenous (as a single dose or in two divided doses of 4 mg separated by 24 h) in unilateral total knee arthroplasty patients. RESULTS: The single dose intravenous administration as well as the periarticular administration of dexamethasone had similar mean visual analogue scores which were significantly lower than divided dose group at 24 and 48 h postoperatively. The rate of postoperative nausea and vomiting was lowest among single intravenous dose group and highest among interval dose group at 24 h, while no difference was noted at 48 h. No significant differences were noted in terms of knee flexion angle at 48 h and modified Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score at 6 weeks. CONCLUSION: Single low-dose intravenous dexamethasone is the most appropriate dose which can safely be given to TKA patients and is only moderately associated with rise in blood sugar not causing any significant complication. Alternatively, periarticular infiltration of low-dose dexamethasone can produce equivalent analgesic effect as SDIV in first 24 h without causing significant blood sugar rise and wound complications, but its antiemetic effect remains subtle. Therefore, it is recommended to further study the combination of intraoperative periarticular and postoperative intravenous dexamethasone for their possible additive effect.

"Floating Hip" and "Floating Knee" Associated with Hip Dislocation, Sciatic Nerve Palsy, and Patella Fracture: A Case Report.

CASE: We report a very rare case of simultaneous ipsilateral floating hip and floating knee (SIFHFK) injury with the neck of the femur and patella fracture and hip dislocation associated with sciatic nerve injury in a 45-year-old man after a road traffic accident. We adopted a staged approach for surgical fixation of the fractures after stabilization. At the latest 2 years follow-up, the patient was asymptomatic with satisfactory clinical outcome. CONCLUSION: SIFHFK injuries present a challenging and emergent clinical scenario and require extensive clinical experience, careful planning, and multidisciplinary teamwork because of the paucity of specific treatment protocols for the treatment of this complex injury.

A three-dimensional gadolinium organic framework based on a pyridinedicarboxylic acid organic linker with a paddle-wheel-type network structure.

A new gadolinium(III)-pyridine-2,5-dicarboxylic acid (GdIII-2,5-H2pdc)-based three-dimensional coordination polymer, namely, poly[dimethylazanium [bis(µ-pyridine-2,5-dicarboxylato)gadolinium(III)]], {[(CH3)2NH2][Gd(C7H3NO4)2]}n, CP-1, has been synthesized via a typical solvothermal method. The as-synthesized material was characterized in the solid state using single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and FT-IR spectroscopy. During the synthesis of CP-1, the in situ dimethylformamide (DMF) promotes the formation of a dimeric unit and these act as secondary building blocks in the assembly of a three-dimensional anionic {[Gd(pdc)2]-}∞ framework. The framework has channels along the c axis which are filled by dimethylazanium cations. Interestingly, the framework shows a helical-type assembly running down the a axis. A Hirshfeld surface analysis of CP-1 suggests that extra stability is provided by hydrogen-bonding interactions. The magnetic properties of CP-1 showed weak antiferromagnetic couplings between adjacent Gd3+ ions.

Analysis of clinical and radiological outcomes of long tibial stemmed total knee arthroplasty in knee osteoarthritis complicated by tibial stress fracture.

OBJECTIVE: Knee arthritis associated with tibial stress fractures represents an uncommon and difficult clinical scenario to treat. The use of long, fluted tibial extension rods has been vital in the management of such cases owing to immediate fracture stability and single-stage surgery without the need to open the fracture site. This study investigates clinical and radiological outcomes following total knee arthroplasty using a tibial extension stem in cases of knee osteoarthritis with tibial stress fracture. METHODS: From February 2015 to December 2020, 17 patients who had total knee arthroplasty implanted with a long stemmed tibial component were included in the study. Patient data were analyzed for knee range of motion, deformities, Knee Society score, knee function score, and time to fracture union in the pre- and postoperative periods. RESULTS: The mean follow-up duration was 22.7 ± 11.68 months (range 12-60 months), and mean time to fracture healing was 10.23 ± 2.81 weeks (range 8-20 weeks). The preoperative mean fixed flexion deformity improved from 8.53 ± 3.43° to a mean of 0.29°, and knee flexion improved from 79.4 ± 13.90° to 125.29 ± 8.74° on postoperative assessment. The Knee Society score improved from a mean preoperative score of 18.94 ± 5.55 (range 8-28) to 89.41 ± 7.5 (range 74-102, p value < 0.001). Similarly, the knee function score improved significantly from a mean preoperative score of 15.5 ± 4.48 (range 8-26) to a mean of 85 ± 6.09 (range 72-94, p value < 0.001). CONCLUSION: Total knee arthroplasty using long tibial extenders has been an effective and safe surgical option for patients with advanced osteoarthritis with tibial stress fractures.

Calcaneal osteomyelitis caused by Acremonium sp in an immunocompetent adult - A case report.

Fungal osteomyelitis of calcaneus is rare in immunocompetent adults. A case of fungal osteomyelitis of calcaneus in a 19 year old immunocompetent female without any history of trauma caused by Acremonium sp is presented. The patient was treated with surgical debridement, autogenous iliac crest bone grafting and antifungal chemotherapy for 6 months. At latest follow up after 2 years, patient is asymptomatic and the osteolytic lesion is healed with no signs of recurrence. This case report highlights a rare presentation of chronic painful calcaneal osteomyelitis with an osteolytic lesion.

Clinical and Surgical Insights on Bilateral Total Knee Arthroplasty in Ochronotic Arthropathy: A Case-based Review.

Introduction: Ochronotic arthropathy (OcA) is a consequence of alkaptonuria, a rare systemic-inherited metabolic disorder leading to accumulation of homogentisic acid in articular cartilage and subsequent early degeneration of the joints. Only few cases of OcA managed with bilateral total knee arthroplasty (TKA) has been described in the literature so far. We aim to discuss surgical pearls, pitfalls, and clinical outcome of OcA of knees managed with simultaneous bilateral TKA. Case Presentation: The patient was a 52-year-old female presented to outpatient facility with severe bilateral knee pain and difficult ambulation. After clinical and radiological diagnosis of osteoarthritis, she was posted for bilateral TKA. During arthrotomy, blackening of articular cartilage, quadriceps and patellar tendon, and synovium was noted. Subchondral bone was free of pigmentation though, seemed osteopenic while taking bone cuts. Right knee was implanted with cruciate retaining components with ultracongruent insert; while on the left side, posterior stabilized components were used. Diagnosis of ochronosis was made retrospectively with characteristic subtle pigmentation of nails, palms, pinnae, and urine homogentisic levels. Two years follow-up of the patient remained satisfactory without any major complications. Conclusion: OcA may present with intra-operative surprise to the surgeon if not anticipated preoperatively. Simultaneous bilateral TKA is safe and effective treatment for end-stage arthritis. However, it is difficult to diagnose it preoperatively; a high clinical suspicion leads to meticulous assessment and counseling regarding potential anesthetic concerns, choice of implant, and possible intra-operative and post-operative complications reported sporadically though.

Clinical, Functional, and Midterm Survival Analysis on Sigma Curved Plus Ultracongruent Polyethylene Insert in Primary Total Knee Arthroplasty: A Retrospective Study.

BACKGROUND: Posterior-stabilized (PS) total knee arthroplasty (TKA) poses problems such as the need for intercondylar notch bone resection as well as cam and post wear and patella clunk. Owing to its heightened anterior profile, an ultracongruent polyethylene insert prevents the excessive posterior translation of tibia in the case of a deficient or scarified posterior cruciate ligament (PCL). This study aimed to determine whether an ultracongruent insert provides satisfactory clinical and functional outcomes and midterm survival benefits. METHODS: Based on the reviewed medical records of 200 patients, 240 primary TKA cases involving the use of Sigma Curved Plus (DePuy International, Ltd., Leeds, UK) ultracongruent insert were retrospectively enrolled in this study. Follow-up data were used to evaluate the clinical and radiological outcomes and to conduct a Kaplan-Meier survival analysis. RESULTS: The mean follow-up duration for 224 knees was 5.8 years (range 5-6.5 years). A revision was made due to infection in two patients and due to periprosthetic fractures in two other patients. The mean knee flexion improved from 101.97° ± 9.43° (range 85°-125°) to 125.75° ± 9.58° (range 100°-140°) at the final follow-up. The mean Knee Society score improved from 43.1 ± 9.76 to 88.3 ± 3.2, and the function score improved from 44.95 ± 7.26 to 90.16 ± 3.71. None of the patients showed radiographic loosening of either insert component, but 22 (5%) patients showed radiolucent lines (<2 mm). The Kaplan-Meier analysis showed that the five-year survival of the insert with an endpoint of revision for any reason was 98.1% (confidence interval, CI, 95.7-99.6%). CONCLUSION: The Sigma Curved Plus insert showed a low failure rate with good clinical, functional, and midterm survival outcomes in comparison to standard outcomes reported in earlier studies. Further follow-up studies are warranted to determine whether the insert's performance is maintained in the long term.

Stress Fracture of Isolated Middle Cuneiform Bone in a Trainee Physician: A Case Report and Review.

Stress fractures are chronic fatigue failure of bone from repetitive subthreshold loads. Insufficiency fractures occur in bones that are already osteopenic and fail to withstand normal loads over time. Stress fractures of cuneiform bones are extremely rare and usually reported to happen in athletes or recruits. We describe a case of middle cuneiform insufficiency fracture that occurred in a young trainee physician with severe hypovitaminosis D, who joined his training a few weeks before it happened. Magnetic resonance imaging remains the modality of choice of diagnosis of foot stress injuries because it detects even stress reactions with reasonable sensitivity. Cuneiform stress fractures, like other low-risk stress fractures, heal with immobilization only and do not require surgical intervention.

Genetic Biosensor Design for Natural Product Biosynthesis in Microorganisms.

Low yield and low titer of natural products are common issues in natural product biosynthesis through microbial cell factories. One effective way to resolve such bottlenecks is to design genetic biosensors to monitor and regulate the biosynthesis of target natural products. In this review, we evaluate the most recent advances in the design of genetic biosensors for natural product biosynthesis in microorganisms. In particular, we examine strategies for selection of genetic parts and construction principles for the design and evaluation of genetic biosensors. We also review the latest applications of transcription factor- and riboswitch-based genetic biosensors in natural product biosynthesis. Lastly, we discuss challenges and solutions in designing genetic biosensors for the biosynthesis of natural products in microorganisms.

Disassembly of Components of a Monoblock Bipolar Hip Prosthesis Following Dislocation: A Case Report and Review on "Bottle Opener Effect".

INTRODUCTION: Bipolar hemiarthroplasty has been reliable and successful treatment for geriatric patients following neck of femur fractures. Dissociation/disassembly of bipolar prosthesis is a rare complication in which separation of outer head from inner head leads to failure of prosthesis and needs revision surgery. The disassembly though commonly seen after years of primary surgery as a result of polyethylene wear leading to fixed varus position of outer head but it can happen in an acute setting anytime in immediate or late post-operative period following posterior dislocation with closed reduction attempt. We describe a rare case of disassembly of monoblock (non-modular) bipolar prosthesis following attempt of closed reduction for posterior dislocation of the prosthesis. CASE REPORT: The patient was a 70-year-old male with 3 weeks prior bipolar hemiarthroplasty of hip joint, presented with posterior dislocation. While manipulation during closed reduction maneuvers, the outer head got locked behind acetabulum and component dissociation happened through bottle opener phenomena. The patient managed with revision surgery in the form of bipolar extraction and revision with total hip joint prosthesis. CONCLUSION: Disassembly of bipolar prosthesis is a rare and unforeseen complication which obviates for revision surgery. A modular bipolar prosthesis can be reassembled or can be managed with shell, liner, and head exchange with retention of femoral stem but it is impossible to reassemble a non-modular bipolar due to its characteristic locking mechanism. It is vital to look for proper orientation and stability of components, integrity of abductor mechanism and short external rotators, and restoration of horizontal and vertical offsets during revision.

Synthesis and characterization of carbonate-encapsulated ytterbium- and yttrium-containing polyoxotungstates.

A sandwiched-type carbonate-encapsulated yttrium-containing arsenotungstate(III) has been synthesized under mild reaction conditions. The polyanion [NaCH3COO{Y2(H2O)3(B-α-AsW9O33)2(W2O5)(CO3)}]12- (1) was isolated as a solid crystalline material by the reaction of a YIII salt with the sodium salt of trilacunary [AsW9O33]9- in sodium acetate solution. The sodium salt of the polyanion, i.e. Na12[Na(CH3COO){Y2(AsW9O33)2(W2O5)(CO3)(H3O)3}]·22H2O (1a), was characterized by various analytical techniques, such as FT-IR, single-crystal X-ray diffraction (SC-XRD), TGA (thermogravimetric analysis), 13C NMR and ESI-MS (electrospray ionization mass spectrometry). SC-XRD studies revealed that the polyanion crystallizes in the triclinic space group P-1. The structure showed that the polyanion is a carbonate-encapsulated sandwich-type species, consisting of two trilacunary B-α-[AsW9O33]9-, with a lone-pair-containing AsIII heteroatom, together with two extra tungsten centres and two yttrium cations at the sandwich position, where CH3COO- and Na+ ions act as linkers between the two polyanion units. In addition, we have also synthesized two carbonate-encapsulated germanotungstates(IV), without lone-pair-containing heteroatoms, with the formula [Ln3(A-ß-GeW9O34)2(CO3)(H2O)3]13- [Ln = YIII (2) and YbIII (3)], i.e. Y2K3Na4[Y3(A-ß-GeW9O34)2(CO3)(H2O)3]·19H2O (2a) and YbK8Na2[Yb(A-ß-GeW9O34)2(CO3)(H2O)3]·16H2O (3a), and characterized them by FT-IR, SC-XRD, TGA and ESI-MS. Here, the lanthanide ions act as linkers, extending the structures into higher dimensions. Sodium and potassium ions also play a key role as linkers, further extending the structure. The packing shows the presence of certain hydrophilic pores within the structure.

Biological Reconstruction of Knee Joint by Pedicled Patellar Transplant in a Recurrent Giant-cell Tumor of Lateral Femoral Condyle: A Case Report.

INTRODUCTION: Giant-cell tumors (GCTs) are benign tumors of musculoskeletal system, commonly occur around knee. High-grade GCTs have a high tendency to recur after intralesional curettage. Reconstruction of joint after excision of such aggressive juxta-articular GCT has been challenging task. We describe a case of recurrence in GCT of lateral femoral condyle managed with tumor excision and pedicled patellar transplant to reconstruct the joint. CASE REPORT: A 25-year-old male patient reported to us after 22 months after he had undergone curettage and bone grafting for GCT of lateral femoral condyle of his right knee with recurrence of primary tumor. After tumor resection, we restored the lost articular surface with musculovascular pedicled patella and managed dead space with corticocancellous bone graft and fibular strut. 2-year follow-up exhibited good functional outcome without any sign of recurrence. CONCLUSION: Biological reconstruction with patellar transplant can be a good option for young patients in whom endoprosthesis placement poses significant concerns about longevity, cost, and revision surgeries.

Short Term Outcome of Varus Derotation Osteotomy in Late Presenting Perthes Disease.

BACKGROUND: Untreated Perthes disease can lead to osteoarthritis by the fourth decade. The treatment is conservative for children <6 years, operative within the age group of 6-9 years. Late onset Perthes, older than 9 years or more, are notorious with the aggressive course with poor outcome. However, literature do not come to a consensus between conservative and operative management. This study evaluates the clinical and radiological outcome of varus derotation osteotomy (VDRO) in Perthes disease presenting late with age 8 years or more. MATERIALS AND METHODS: 15 children (13 males and 2 females) with the mean age of 9.4 years belonging to modified Elizabethtown classification Stage IB, IIA, IIB treated with open wedge VDRO between 2008 and 2014 were included in this study. Seven patients (46.67%) were of >10 years of age at presentation. All patients had limitation of abduction and internal rotation. Eight patients (53.33%) had pain at the hip and 12 patients (80%) had limp. Mean time between diagnosis and corrective surgery was 3 weeks. RESULTS: The evaluation was done using caput index (CI) and epiphyseal quotient (EQ) and articulotrochanteric distance radiologically, range of motion and Harris Hip Score for clinical outcome. All the measurements were carried out on pre- and postoperative X-rays after 3 years followup and compared with the contralateral normal hip. After a mean followup period of 3.4 years, we noted the statistically significant difference between pre- and postoperative values. We noted that all (100%) children in Stage IB, IIA and 50% children in Stage IIB achieved satisfactory results. There was a significant change (P = 0.000) in CI among all the patients after surgery. The final EQ after 3 years of VDRO was 0.606 and was significant (P = 0.0000). CONCLUSION: In our opinion, based on the encouraging short term radiological and clinical outcomes, VDRO may be regarded as a treatment procedure for late presenting Perthes disease in stage IB, IIA, IIB.

Synthetic Consortium of Escherichia coli for n-Butanol Production by Fermentation of the Glucose-Xylose Mixture.

The microbial production of n-butanol using glucose and xylose, the major components of plant biomass, can provide a sustainable and renewable fuel as crude oil replacement. However, Escherichia coli prefers glucose to xylose as programmed by carbohydrate catabolite repression (CCR). In this study, a synthetic consortium consisting of two strains was developed by transforming the CCR-insensitive strain into a glucose-selective strain and a xylose-selective strain. Furthermore, the dual culture was reshaped by distribution of the synthetic pathway of n-butanol into two strains. Consequently, the co-culture system enabled effective co-utilization of both sugars and production of 5.2 g/L n-butanol at 30 h. The result leads to the conversion yield and productivity accounting for 63% of the theoretical yield and 0.17 g L-1 h-1, respectively. Overall, the technology platform as proposed is useful for production of other value-added chemicals, which require complicated pathways for their synthesis by microbial fermentation of a sugar mixture.

Metabolic engineering of Escherichia coli for production of n-butanol from crude glycerol.

BACKGROUND: Crude glycerol in the waste stream of the biodiesel production process is an abundant and renewable resource. However, the glycerol-based industry is usually afflicted by the cost for refinement of crude glycerol. This issue can be addressed by developing a microbial process to convert crude glycerol to value-added chemicals. In this study, Escherichia coli was implemented for the production of n-butanol based on the reduced nature of glycerol. RESULTS: The central metabolism of E. coli was rewired to improve the efficiency of glycerol metabolism and provide the reductive need for n-butanol in E. coli. This was carried out in several steps by (1) forcing the glycolytic flux through the oxidation pathway of pyruvate, (2) directing the gluconeogenic flux into the oxidative pentose phosphate pathway, (3) enhancing the anaerobic catabolism for glycerol, and (4) moderately suppressing the tricarboxylic acid cycle. Under the microaerobic condition, the engineered strain enabled the production of 6.9 g/L n-butanol from 20 g/L crude glycerol. The conversion yield and the productivity reach 87% of the theoretical yield and 0.18 g/L/h, respectively. CONCLUSIONS: The approach by rational rewiring of metabolic pathways enables E. coli to synthesize n-butanol from glycerol in an efficient way. Our proposed strategies illustrate the feasibility of manipulating key metabolic nodes at the junction of the central catabolism. As a result, it renders the intracellular redox state adjustable for various purposes. Overall, the developed technology platform may be useful for the economic viability of the glycerol-related industry.

Sorption kinetics and isotherm modelling of imidacloprid on bentonite and organobentonites.

Bentonite was modified by quaternary ammonium cations viz. cetytrimethylammonium (CTA), cetylpyridinium (CP), rioctylmethylammonium (TOM) and pcholine (PTC) at 100% cation exchange capacity of bentonite and was characterized by X-ray diffraction, CHNS elemental analyser and Fourier transform infrared spectroscopy. The sorption of imidacloprid on organobentonites/bentonite was studied by batch method. Normal bentonite could adsorb imidacloprid only upto 19.31-22.18% while all organobentonites except PTC bentonite (PTCB), enhanced its adsorption by three to four times. Highest adsorption was observed in case of TOM bentonite (TOMB) (76.94-83.16%). Adsorption kinetic data were fitted to pseudo-first-order, pseudo-second-order and intraparticle diffusion models. For normal bentonite data were best fitted to pseudo-first-order kinetic, while for organobentonites fitted to pseudo-second-order kinetics. Sorption data were analysed using Freundlich, Langmuir, Temkin and Dubinin-Radushkevich isotherm models. Data were well fitted to Freundlich adsorption isotherm. Product of Freundlich adsorption constant and heterogeneity parameter (Kf.1/n) was in following order: TOMB (301.87) > CTA bentonite (CTAB) (152.12) > CP bentonite (CPB) (92.58) > bentonite (27.25). Desorption study confirmed hysteresis and concentration dependence. The present study showed that the organobentonite could be a good sorbent for removal of imidacloprid from natural water sample also. Percentage adsorption and Distribution coefficient (mL g-1) value of different adsorbent was in following order: TOMB (74.85% and 297.54) > CTAB (55.78% and 126.15) > CPB (45.81% and 84.55) > bentonite (10.65% and 11.92).

Systematic engineering of the central metabolism in Escherichia coli for effective production of n-butanol.

BACKGROUND: Microbes have been extensively explored for production of environment-friendly fuels and chemicals. The microbial fermentation pathways leading to these commodities usually involve many redox reactions. This makes the fermentative production of highly reduced products challenging, because there is a limited NADH output from glucose catabolism. Microbial production of n-butanol apparently represents one typical example. RESULTS: In this study, we addressed the issue by adjustment of the intracellular redox state in Escherichia coli. This was initiated with strain BuT-8 which carries the clostridial CoA-dependent synthetic pathway. Three metabolite nodes in the central metabolism of the strain were targeted for engineering. First, the pyruvate node was manipulated by enhancement of pyruvate decarboxylation in the oxidative pathway. Subsequently, the pentose phosphate (PP) pathway was amplified at the glucose-6-phosphate (G6P) node. The pathway for G6P isomerization was further blocked to force the glycolytic flux through the PP pathway. It resulted in a growth defect, and the cell growth was later recovered by limiting the tricarboxylic acid cycle at the acetyl-CoA node. Finally, the resulting strain exhibited a high NADH level and enabled production of 6.1 g/L n-butanol with a yield of 0.31 g/g-glucose and a productivity of 0.21 g/L/h. CONCLUSIONS: The production efficiency of fermentative products in microbes strongly depends on the intracellular redox state. This work illustrates the flexibility of pyruvate, G6P, and acetyl-CoA nodes at the junction of the central metabolism for engineering. In principle, high production of reduced products of interest can be achieved by individual or coordinated modulation of these metabolite nodes.

Production of biobutanol from cellulose hydrolysate by the Escherichia coli co-culture system.

The commercialization of the n-butanol bioprocess is largely dependent on the price of feedstocks. Renewable cellulose appears to be an appealing feedstock. The microbial production of n-butanol still remains challenging because of the limited availability of intracellular NADH. To address this issue, an Escherichia coli strain carrying the clostridial CoA-dependent pathway was supplied with heterologous formate dehydrogenase. With the cellulose hydrolysate of rice straw, this single strain produced cellulosic biobutanol with a production yield at 35% of the theoretical and a productivity of 0.093 g L(-1) h(-1). In an alternative method, the production involved a co-culture system consisting of two separate strains provided with the full CoA-dependent pathway. This system achieved a production yield and productivity reaching 62.8% of the theoretical and 0.163 g L(-1) h(-1), respectively. The result indicates that the E. coli co-culture system is technically promising for the production of cellulosic biobutanol.