Rubisco mutants of Chlamydomonas reinhardtii display divergent photosynthetic parameters and lipid allocation.

Photosynthesis and lipid allocation were investigated in Rubisco small subunit mutants of the microalga Chlamydomonas reinhardtii. Comparative analyses were undertaken with cells grown photoheterotrophically under sulphur-replete or sulphur-depleted conditions. The Y67A Rubisco mutant, which has previously demonstrated a pronounced reduction in Rubisco levels and higher hydrogen production rates than the wild type, also shows the following divergences in photosynthetic phenotype and lipid allocation: (i) low Fv/Fm (maximum photochemical efficiency), (ii) low effective quantum yield of photosystem II (ΦPSII), (iii) low effectiveness at protection against high light intensities, (iv) a higher level of total lipids per pigment and (v) changes in the relative proportions of different fatty acids, with a marked decrease in unsaturated fatty acids (FAs). The most abundant thylakoid membrane lipid, monogalactosyldiacylglycerol, decreased in amount, while the neutral lipid/polar lipid ratio increased in the mutant. The low amount and activity of the mutated Rubisco Y67A enzyme seems to have an adverse effect on photosynthesis and causes changes in carbon allocation in terms of membrane fatty acid composition and storage lipid accumulation. Our results suggest that Rubisco mutants of Chlamydomonas might be useful in biodiesel production.

Nitrogen balancing and xylose addition enhances growth capacity and protein content in Chlorella minutissima cultures.

This study aimed to examine the metabolic changes in Chlorella minutissima cells grown under nitrogen-deficient conditions and with the addition of xylose. The cell density, maximum photochemical efficiency, and chlorophyll and lipid levels were measured. The expression of two photosynthetic proteins, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the beta subunit (AtpB) of adenosine triphosphate synthase, were measured. Comparison of cells grown in medium with a 50% reduction in the nitrogen concentration versus the traditional medium solution revealed that the cells grown under nitrogen-deficient conditions exhibited an increased growth rate, higher maximum cell density (12.7×10(6)cellsmL(-1)), optimal PSII efficiency (0.69) and decreased lipid level (25.08%). This study has taken the first steps toward protein detection in Chlorella minutissima, and the results can be used to optimize the culturing of other microalgae.

Rubisco mutants of Chlamydomonas reinhardtii enhance photosynthetic hydrogen production.

Molecular hydrogen (H2) is an ideal fuel characterized by high enthalpy change and lack of greenhouse effects. This biofuel can be released by microalgae via reduction of protons to molecular hydrogen catalyzed by hydrogenases. The main competitor for the reducing power required by the hydrogenases is the Calvin cycle, and rubisco plays a key role therein. Engineered Chlamydomonas with reduced rubisco levels, activity and stability was used as the basis of this research effort aimed at increasing hydrogen production. Biochemical monitoring in such metabolically engineered mutant cells proceeded in Tris/acetate/phosphate culture medium with S-depletion or repletion, both under hypoxia. Photosynthetic activity, maximum photochemical efficiency, chlorophyll and protein levels were all measured. In addition, expression of rubisco, hydrogenase, D1 and Lhcb were investigated, and H2 was quantified. At the beginning of the experiments, rubisco increased followed by intense degradation. Lhcb proteins exhibited monomeric isoforms during the first 24 to 48 h, and D1 displayed sensitivity under S-depletion. Rubisco mutants exhibited a significant decrease in O2 evolution compared with the control. Although the S-depleted medium was much more suitable than its complete counterpart for H2 production, hydrogen release was observed also in sealed S-repleted cultures of rubisco mutated cells under low-moderate light conditions. In particular, the rubisco mutant Y67A accounted for 10-15-fold higher hydrogen production than the wild type under the same conditions and also displayed divergent metabolic parameters. These results indicate that rubisco is a promising target for improving hydrogen production rates in engineered microalgae.

Alanine-scanning mutagenesis of the small-subunit beta A-beta B loop of chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase: substitution at Arg-71 affects thermal stability and CO2/O2 specificity.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) enzymes from different species differ with respect to carboxylation catalytic efficiency and CO2/O2 specificity, but the structural basis for these differences is not known. Whereas much is known about the chloroplast-encoded large subunit, which contains the alpha/beta-barrel active site, much less is known about the role of the nuclear-encoded small subunit in Rubisco structure and function. In particular, a loop between beta-strands A and B contains 21 or more residues in plants and green algae, but only 10 residues in prokaryotes and nongreen algae. To determine the significance of these additional residues, a mutant of the green alga Chlamydomonas reinhardtii, which lacks both small-subunit genes, was used as a host for transformation with directed-mutant genes. Although previous studies had indicated that the betaA-betaB loop was essential for holoenzyme assembly, Ala substitutions at residues conserved among land plants and algae (Arg-59, Tyr-67, Tyr-68, Asp-69, and Arg-71) failed to block assembly or eliminate function. Only the Arg-71 --> Ala substitution causes a substantial decrease in holoenzyme thermal stability. Tyr-68 --> Ala and Asp-69 --> Ala enzymes have lower K(m)(CO2) values, but these improvements are offset by decreases in carboxylation V(max) values. The Arg-71 --> Ala enzyme has a decreased carboxylation V(max) and increased K(m)(CO2) and K(m)(O2) values, which account for an observed 8% decrease in CO2/O2 specificity. Despite the fact that Arg-71 is more than 20 A from the large-subunit active site, it is apparent that the small-subunit betaA-betaB loop region can influence catalytic efficiency and CO2/O2 specificity.

[External version in pelvic presentation]. / Versión externa en presentación pélvica.

We made a prospective, population-based study of external version attempt in the department of obstetrics at Hospital, Clínica y Maternidad Conchita A.C. at Monterrey, N.L. 45 patients were enrolled with diagnosis of breech presentation. We tested the hypothesis to determined the average of success and how this procedure can reduce the primary C section rate. Of the 45 patients, 48.9% were primiparous, we had success in the external version in 27 patients (60%), 81.4% had vaginal delivery and 18.6% C section. During the study the incidence of primary C section in breech presentation shown low rates from 15.3% to 9.3%. We did'nt have complications in the procedure. With these results, we concluded that the attempt of external version is more safety and had less risks for the mother and fetus that breech delivery, and we can reduced the primary C section rate for this indication.

[Incidence of fetal macrosomia: maternal and fetal morbidity]. / Incidencia de macrosomía fetal. Morbilidad materna y fetal.

The macrosomia is an obstetric eventuality associated to high maternal-fetal morbidity-mortality. This assay was planned in order to know the incidence of macrosomia in our institution, the relation between vaginal and abdominal deliveries and the fetal-maternal morbidity we reviewed 3590 records and we found 5.6% incidence of macrosomia in the global obstetric population. There was 58% of vaginal deliveries, 68% of the newborn were male. The main complications were in the C. sections, 2 laceration of the hysterectomy, and 2 peroperative atonias. In the vaginal deliveries, the lacerations of III and IV grade were 9 of each grade. The main fetal complications were 5 slight to severe asphyxia and 4 shoulder dystocias. This assay concludes that the macrosomia in our service is similar to the already published ones, a 42% were C. section and the maternal-fetal morbidity was low.

[Syringomyelia and pregnancy. A case report]. / Siringomielia y embarazo. Informe de un caso.

This report refers to the case of a 39-year-old woman, fourth gestation, who during her first pregnancy developed neurologic deficit of the left hand, which slowly progressed getting to affect during seven years, all the left upper extremity and the right hand. During this time, she had two abortions, and between the third and fourth pregnancies, because of the clinical suspicion, laboratory tests were done, finding by electromyography, lesion of anterior process of spinal chord at cervical level. During this fourth pregnancy, neurologic deficit increased and it was decided to interrupt pregnancy by cesarean section under epidural block at 38 weeks of gestation. According to our knowledge this syringomyelia case and pregnancy, is the first one reported in our country.