Fermentative production of lactic acid from biomass: an overview on process developments and future perspectives

The concept of utilizing excess biomass or wastes from agricultural and agro-industrial residues to produce energy, feeds or foods, and other useful products is not necessarily new. Recently, fermentation of biomass has gained considerable attention due to the forthcoming scarcity of fossil fuels and also due to the necessity of increasing world food and feed supplies. A cost-effective viable process for lactic acid production has to be developed for which several attempts have been initiated. Fermentation techniques result in the production of either d (−) or l (+) lactic acid, or a racemic mixture of both, depending on the type of organism used. The interest in the fermentative production of lactic acid has increased due to the prospects of environmental friendliness and of using renewable resources instead of petrochemicals. Amylolytic bacteria Lactobacillus amylovorus ATCC 33622 is reported to have the efficiency of full conversion of liquefied cornstarch to lactic acid with a productivity of 20 g l⁻¹ h⁻¹. A maximum of 35 g l⁻¹ h⁻¹ was reported using a high cell density of L. helveticus (27 g l⁻¹) with a complete conversion of 55- to 60-g l⁻¹ lactose present in whey. Simultaneous saccharification and fermentation is proved to be best in the sense of high substrate concentration in lower reactor volume and low fermentation cost. In this review, a survey has been made to see how effectively the fermentation technology explored and exploited the cheaply available source materials for value addition with special emphasis on lactic acid production.     

Segment- and nest-specific determination in the histoblasts of the housefly

Summary Using a novel grafting procedure for histoblasts, we have transplanted the fifth dorsal or ventral histoblast nests to heterotopic positions in the abdomen of the prepupa of the housefly to find out how rigid are these imaginai cells in their commitment to form their respective segmental pattern. Our results clearly show that these histoblasts survive in their new positions and form patterns according to their original determined state.     

Roles of semiquinone species in proton pumping mechanism by complex I

Complex I (NDH-1) translocates protons across the membrane using electron transfer energy. Two different coupling mechanisms are currently being discussed for complex I: direct (redox-driven) and indirect (conformation-driven). Semiquinone (SQ) intermediates are suggested to be key for the coupling mechanism. Recently, using progressive power saturation and simulation techniques, three distinct SQ species were resolved by EPR analysis of E. coli complex I reconstituted into proteoliposomes. The fast-relaxing SQ (SQ_Nf) signals completely disappeared in the presence of the uncoupler gramicidin D or the potent E. coli complex I inhibitor squamotacin. The slow-relaxing SQ (SQ_Ns) signals were insensitive to gramicidin D, but they were sensitive to squamotacin. The very slow-relaxing SQ (SQ_Nvs) signals were insensitive to both gramicidin D and squamotacin. Interestingly, no SQ_Ns signal was observed in the ΔNuoL mutant, which lacks transporter module subunits NuoL and NuoM. Furthermore, we sought out the effect of using menaquinone (which has a lower redox potential compared to that of ubiquinone) as an electron acceptor on the proton pumping stoichiometry by in vitro reconstitution experiments with ubiquinone-rich or menaquinone-rich double knock-out membrane vesicles, which contain neither complex I nor NDH-2 (non-proton translocating NADH dehydrogenase). No difference in the proton pumping stoichiometry between menaquinone and ubiquinone was observed in the ΔNuoL and D178N mutants, which are considered to lack the indirect proton pumping mechanism. However, the proton pumping stoichiometry with menaquinone decreased by half in the wild-type. The roles and relationships of SQ intermediates in the coupling mechanism of complex I are discussed.     

Two Sweetclover (Melilotus alba Desr.) Mutants Temperature Sensitive for Chlorophyll Expression

The nonallelic sweetclover (Melilotus alba Desr.) mutants U371 (ch10/ch10 genotype) and U372 (ch11/ch11 genotype) are derived from the U389 (+/+ genotype) parental strain. Growth of the U389 strain at a temperature of 17 or 26[deg]C results in plants normally green in appearance. The U371 and U372 mutant plants grown at 26[deg]C are slightly to moderately chlorophyll (Chl) deficient and have decreased Chl b/a ratios. Growth of the mutants at 17[deg]C results in plants severely deficient in Chl a, with markedly reduced levels of carotenoids except for violaxanthin, and with negligible amounts of Chl b or apoproteins for the light-harvesting complex of photosystem II. If mutant plants grown at 17[deg]C are transferred to 26[deg]C, during the next 20 d the amount of Chl per fresh weight will increase 5-fold and both the Chl b/a ratio and the expression of the light-harvesting complex apoproteins will progressively increase. Studies of the U371 mutant during the temperature-induced greening demonstrate progressive changes in chloroplast ultra-structure and leaf carbon isotope fractionation that parallel the increases in Chl. Changes observed in the leaf carbon isotope fractionation in the mutant suggest that, in addition to the already known effects of various abiotic factors, structural and metabolic internal factors can also influence whether the limitation in CO2 fixation is at the level of diffusion or carboxylation. Such temperature-initiated progressive greening in these and similar mutants may make them useful tools to elucidate not only the biosynthesis and assembly of the photosynthetic apparatus, but also physiological phenomena such as the influence of light-driven energy production on the overall carbon isotope fractionation during photosynthesis.     

Riboflavin/UVA collagen cross-linking-induced changes in normal and keratoconus corneal stroma

Purpose

To determine the effect of Ultraviolet-A collagen cross-linking with hypo-osmolar and iso-osmolar riboflavin solutions on stromal collagen ultrastructure in normal and keratoconus ex vivo human corneas.

Methods

Using small-angle X-ray scattering, measurements of collagen D-periodicity, fibril diameter and interfibrillar spacing were made at 1 mm intervals across six normal post-mortem corneas (two above physiological hydration (swollen) and four below (unswollen)) and two post-transplant keratoconus corneal buttons (one swollen; one unswollen), before and after hypo-osmolar cross-linking. The same parameters were measured in three other unswollen normal corneas before and after iso-osmolar cross-linking and in three pairs of swollen normal corneas, in which only the left was cross-linked (with iso-osmolar riboflavin).

Results

Hypo-osmolar cross-linking resulted in an increase in corneal hydration in all corneas. In the keratoconus corneas and unswollen normal corneas, this was accompanied by an increase in collagen interfibrillar spacing (p<0.001); an increase in fibril diameter was also seen in two out of four unswollen normal corneas and one unswollen keratoconus cornea (p<0.001). Iso-osmolar cross-linking resulted in a decrease in tissue hydration in the swollen normal corneas only. Although there was no consistent treatment-induced change in hydration in the unswollen normal samples, iso-osmolar cross-linking of these corneas did result in a compaction of collagen fibrils and a reduced fibril diameter (p<0.001); these changes were not seen in the swollen normal corneas. Collagen D-periodicity was not affected by either treatment.

Conclusion

The observed structural changes following Ultraviolet-A cross-linking with hypo-osmolar or iso-osmolar riboflavin solutions are more likely a consequence of treatment-induced changes in tissue hydration rather than cross-linking.     

The hedgehog pathway is a modulator of retina regeneration

The embryonic chick has the ability to regenerate its retina after it has been completely removed. Here, we provide a detailed characterization of retina regeneration in the embryonic chick at the cellular level. Retina regeneration can occur in two distinct manners. The first is via transdifferentiation, which is induced by members of the Fibroblast growth factor (Fgf) family. The second type of retinal regeneration occurs from the anterior margin of the eye, near the ciliary body (CB) and ciliary marginal zone (CMZ). We show that regeneration from the CB/CMZ is the result of proliferating stem/progenitor cells. This type of regeneration is also stimulated by Fgf2, but we show that it can be activated by Sonic hedgehog (Shh) overexpression when no ectopic Fgf2 is present. Shh-stimulated activation of CB/CMZ regeneration is inhibited by the Fgf receptor (Fgfr) antagonist, PD173074. This indicates that Shh-induced regeneration acts through the Fgf signaling pathway. In addition, we show that the hedgehog (Hh) pathway plays a role in maintenance of the retina pigmented epithelium (RPE), as ectopic Shh expression inhibits transdifferentiation and Hh inhibition increases the transdifferentiation domain. Ectopic Shh expression in the regenerating retina also results in a decrease in the number of ganglion cells present and an increase in apoptosis mostly in the presumptive ganglion cell layer (GCL). However, Hh inhibition increases the number of ganglion cells but does not have an effect on cell death. Taken together, our results suggest that the hedgehog pathway is an important modulator of retina regeneration.     

Three-dimensional characterization of regional lung deformation

The deformation of the lung during inspiration and expiration involves regional variations in volume change and orientational preferences. Studies have reported techniques for measuring the displacement field in the lung based on imaging or image registration. However, means of interpreting all the information in the displacement field in a physiologically relevant manner is lacking. We propose three indices of lung deformation that are determinable from the displacement field: the Jacobian--a measure of volume change, the anisotropic deformation index--a measure of the magnitude of directional preference in volume change and a slab-rod index--a measure of the nature of directional preference in volume change. To demonstrate the utility of these indices, they were determined for six human subjects using deformable image registration on static CT images, registered from FRC to TLC. Volume change was elevated in the inferior-dorsal region as should be expected for breathing in the supine position. The anisotropic deformation index was elevated in the inferior region owing to proximity to the diaphragm and in the lobar fissures owing to sliding. Vessel regions in the lung had a significantly rod-like deformation compared to the whole lung. Compared to upper lobes, lower lobes exhibited significantly greater volume change (19.4% and 21.3% greater in the right and left lungs on average; p<0.005) and anisotropy in deformation (26.3% and 21.8% greater in the right and left lungs on average; p<0.05) with remarkable consistency across subjects. The developed deformation indices lend themselves to exhaustive and physiologically intuitive interpretations of the displacement fields in the lung determined through image-registration techniques or finite element simulations.     

A novel role of the hedgehog pathway in lens regeneration

Lens regeneration in the adult newt is a classic example of replacing a lost organ by the process of transdifferentiation. After lens removal, the pigmented epithelial cells of the dorsal iris proliferate and dedifferentiate to form a lens vesicle, which subsequently differentiates to form a new lens. In searching for factors that control this remarkable process, we investigated the expression and role of hedgehog pathway members. These molecules are known to affect retina and pigment epithelium morphogenesis and have been recently shown to be involved in repair processes. Here we show that Shh, Ihh, ptc-1, and ptc-2 are expressed during lens regeneration. The expression of Shh and Ihh is quite unique since these genes have never been detected in lens. Interestingly, both Shh and Ihh are only expressed in the regenerating and developing lens, but not in the intact lens. Interfering with the hedgehog pathway results in considerable inhibition of the process of lens regeneration, including decreased cell proliferation as well as interference with lens fiber differentiation in the regenerating lens vesicle. Down-regulation of ptc-1 was also observed when inhibiting the pathway. These results provide the first evidence of a novel role for the hedgehog pathway in specific regulation of the regenerating lens.