Iterative cycle of widely targeted metabolic profiling for the improvement of 1-butanol titer and productivity in Synechococcus elongatus

BACKGROUND

Metabolomics is the comprehensive study of metabolites that can demonstrate the downstream effects of gene and protein regulation, arguably representing the closest correlation with phenotypic features. Hence, metabolomics-driven approach offers an effective way to facilitate strain improvement. Previously, targeted metabolomics on the 1-butanol-producing cyanobacterial strain Synechococcus elongatus BUOHSE has revealed the reduction step from butanoyl-CoA to butanal, catalyzed by CoA-acylating propionaldehyde dehydrogenase (PduP), as a rate-limiting step in the CoA-dependent pathway. Moreover, an increase in acetyl-CoA synthesis rate was also observed in this strain, by which the increased rate of release of CoA from butanoyl-CoA was used to enhance formation of acetyl-CoA to feed into the pathway.

RESULTS

In the present study, a new strain (DC7) with an improved activity of PduP enzyme, was constructed using BUOHSE as the background strain. DC7 showed a 33% increase in 1-butanol production compared to BUOHSE. For a deeper understanding of the metabolic state of DC7, widely targeted metabolomics approach using ion-pair reversed-phase LC/MS was performed. Results showed a decreased level of butanoyl-CoA and an increased level of acetyl-CoA in DC7 compared to BUOHSE. This served as an indication that the previous bottleneck has been solved and free CoA regeneration increased upon the improvement of the PduP enzyme. In order to utilize the enhanced levels of acetyl-CoA in DC7 for 1-butanol production, overexpression of acetyl-CoA carboxylase (ACCase) in DC7 was performed by inserting the gene encoding an ACCase subunit from Yarrowia lipolytica into the aldA site. The resulting strain, named DC11, was able to reach a production titer of 418.7 mg/L in 6 days, compared to DC7 that approached a similar titer in 12 days. A maximum productivity of 117 mg/L/day was achieved between days 4 and 5 in DC11.

CONCLUSIONS

In this study, the iterative cycle of genetic modification based on insights from metabolomics successfully resulted in the highest reported 1-butanol productivity for engineered Synechococcus elongatus PCC 7942.

beta-amyloid peptide-induced death of PC 12 cells and cerebellar granule cell neurons is inhibited by long-term lithium treatment

Treatment of rat pheochromocytoma cells (PC 12) cells with beta-amyloid peptide-(1-42) for 24 h induced a concentration-dependent decrease in cellular redox activity in the dose range of 1 to 20 microM. These effects were markedly attenuated by pretreatment with 2 mM LiCl for 7 days, whereas 1-day pretreatment was ineffective. Measurements of live and dead cells by double-staining with fluorescein diacetate and propidium iodide, respectively revealed that protracted lithium pretreatment attenuated PC 12 cell death induced by beta-amyloid-(1-42) and cerebellar granule cell death induced by beta-amyloid-(25-35). Preceding PC 12 cell death, beta-amyloid peptide elicited a slight decrease in protein levels of Bcl-2. Conversely, 7-day pretreatment with lithium resulted in an approximate doubling of Bcl-2 protein levels in cells treated with or without beta-amyloid peptide-(1-42). Lithium-induced Bcl-2 upregulation was temporally associated with the cytoprotective effects of this drug. Thus, lithium protection against beta-amyloid peptide neurotoxicity might involve Bcl-2 overexpression, and lithium treatment for Alzheimer's disease should be reexamined.

Blood glucose dependence of visual flicker threshold

BACKGROUND

Published research indicated that fluctuations in blood glucose concentration (BGC) change the biochemical balance of the retina and may alter the sensitivity of retinal cells. Low-contrast flicker was used in this research to measure the changes in sensitivity of the retina accompanying shifts in BGC.

METHODS

In five subjects without diabetes and four subjects with diabetes, simultaneous measurements of flicker thresholds, using a two-alternative, forced choice psychometric test, and BGC, were made every 15 to 30 minutes for several hours, while BGC was allowed to fluctuate spontaneously.

RESULTS

Flicker thresholds were found to rise and fall, generally tracking BGC in each subject. First-day flicker threshold measurements were used to "calibrate" the method for each subject, and subsequent days' measurements were used to infer blood glucose. The resulting inferred blood glucose values correlated with BGC measured from blood samples in the range of 70 mg/dL to 500 mg/dL with a maximum error of +/-33% in 97% of the measurements.

CONCLUSIONS

The feasibility of using flicker sensitivity for monitoring blood glucose levels noninvasively is discussed. Improvements in the testing method can potentially reach +/-18% error margin with 1-minute measurements, according to computer simulations. Devices using a visual test would be inexpensive to manufacture and would need no disposable supplies. Planned research will assess the long-term stability of flicker threshold measurements and will determine the applicability of the technique in diabetic retinopathy, in hypoglycemia and in the presence of fatigue and inattention.

Microvascular free posterior interosseous flap and a comparison with the pedicled posterior interosseous flap

The posterior interosseous flap has been used as a pedicled flap for coverage of hand wounds. However, the pedicled flap is associated with partial or even complete loss when there is venous congestion. This happens because it depends on retrograde venous drainage. Another pitfall of the pedicled posterior interosseous flap is the undetected damage to the communicating vessels between the anterior and posterior interosseous arteries before surgery. This would result in failure if the flap is used as a distally based flap. Thirty-four patients had been reconstructed with the microvascular free posterior interosseous flap. The free flap has a large draining vein. Flap survival rate was 97%. There was no venous congestion and no partial loss of the flap. It is thin, sensate, and reliable. The free posterior interosseous flap is indicated for coverage of the following wounds: (1) first web space and thumb, (2) radial side of the index and ulnar side of the small finger if a cross-finger flap cannot be used, and (3) defects at the dorsum of multiple fingers. It can also be used as a free fascial flap. The free posterior interosseous flap provides a reliable option for coverage of hand wounds. Previously, another 14 patients with hand wounds had been reconstructed with a pedicled posterior interosseous flap. The results of pedicled and free posterior interosseous flaps are compared.

Transposed replantation of fingers at forearm bones in severe segmental injuries across the hand and wrist

There are situations in which amputated hands or fingers cannot be replanted directly back to their original positions. When there is severe segmental injury across the hand and wrist but one or several fingers are still healthy, the fingers can be selected to be replanted at the forearm bones to restore pinch function. This is different from the toe to antebrachial stump transplantation presented by Dr. Vilkki. From the results in four patients, the following conclusions are drawn: (1) When the fingers are replanted at the forearm bone(s), only pinch function can be obtained. There is no opposition. (2) Grip function is weak because the intrinsics are lost and only a few fingers are replanted. The forearm bones are often shortened, as are the flexors. (3) Of particular importance is the creation of a large web space between the radial digit and ulnar digit(s), because fingers are longer than toes. (4) The sensory recovery is not so good as in ordinary finger replantation. However, this is a salvage procedure. Regardless of these facts, the patients are still satisfied with the results out of such severe injuries. With good pinch function, not only are they independent in daily life, but they also can do a lot of work. It is a worthwhile procedure. A functional prosthesis can be added distally after this replantation.

A translocation-associated ribosomal conformational change detected by hydrogen exchange and sedimentation velocity

Translocation in ribosomes consists of transposition of peptidyl-tRNA from the aminoacyl to the peptidyl site and, probably concomitantly, the movement of ribosomes on mRNA. Does a conformational change in the ribosome provide the motive force for this process? Hydrogen exchange and sedimentation velocity experiments indicate that the Escherichia coli ribosome does undergo a conformational change associated with translocation. When pretranslocational ribosomes carrying acetyldiphenylalanyl-tRNA in the aminoacyl site were incubated with G factor and GTP, translocation occurred, with a concomitant increase in hydrogen exchange rate and a decrease in sedimentation constant. These changes did not occur when GTP was replaced by a nonhydrolyzable analogue, GDP-CH(2)-P, and they were blocked by the antibiotics fusidic acid and thiostrepton. When posttranslocational ribosomes were cycled back to the pretranslocational state by T factor, GTP, and phenylalanyl-tRNA, the sedimentation constant reverted to the original value. Whether or not this conformation change drives translocation requires further study.