Photofermentative hydrogen production by immobilized Rhodopseudomonas sp. S16-VOGS3 cells in photobioreactors

One of the most important solutions to overcome energy and environmental problems and to replace the fossil fuel-based economy could be the use of photosynthetic microorganisms.The use of photosynthetic microorganisms is a potential alternative to energy generation from fossil fuels because they efficiently produce hydrogen(H_(2)).Immobilization of photosynthetic microorganisms is used for many biotechnological applications such as H_(2) production.This method appears attractive because it restricts cell movement in an entrapped matrix.Immobilization of Rhodopseudomonas sp.S16-VOGS3 cells is a promising way to improve H_(2) production.In this work,the ability of immobilized Rhodopseudomonas sp.S16-VOGS3 cells to produce H_(2) was investigated in two types of PBRs.The PBRs used in this work were a cylindrical one with 0.2 L working volume(C-PBR)and a flat Roux type with 0.6 L working volume(FRT-PBR).The calcium alginate beads prepared were resistant to culture mixing and showed little leakage of cells,and the immobilized cells continued the photofermentation process in both PBRs.The immobilized cells in the C-PBR produced 936.8 mL of H_(2) with an average H_(2) production rate of 2.99 mL/h.The average productivity was 126.4μL(H_(2))/mg(cells)/h or 14.96 mL(H_(2))/L(culture)/h,and the light conversion efficiency was 2.37%.The immobilized cells in the FRT-PBR produced a total of 662.2 mL of H_(2) with an average H_(2) production rate of 1.55 mL/h.The average productivity was 31.1μL(H_(2))/mg(cells)/h or 2.58 mL(H_(2))/L(culture)/h,and the light conversion efficiency was 0.52%.The more uniform and therefore more efficient degree of bacterial cell mixing achieved in the C-PBR with cylindrical configuration played an important role compared to the FRT-PBR.In the FRT-PBR,the beads were aggregated at the bottom,which limited light penetration and resulted in low H_(2) production efficiency.

Does divergence from normal patterns of integration increase as chromosomal fusions increase in number?A test on a house mouse hybrid zone

Chromosomal evolution is widely considered an important driver of speciation because it can promote the establishment of reproductive barriers.Karyotypic reorganization is also expected to affect the mea n phe no type,as well as its developme nt and patter ns of phenotypic in tegrati on,through processes such as variation in genetic linkage between quantitative trait loci or between regulatory regions and their targets.Here we explore the relationship between chromosomal evolution and phenotypic integration by analyzing a well-known house mouse parapatric contact zone between a highly derived Robertsonian(Rb)race(2n=22)and populations with standard karyotype(2n=40).Populations with hybrid karyotypes are scattered throughout the hybrid zone connecting the two parental races.Using mandible shape data and geometric morphometries,we test the hypothesis that patter ns of in tegration progressively diverge from the"normal"integration pattern observed in the standard race as they accumulate Rb fusions.We find that the main pattern of integration observed between the posterior and anterior part of the mandible can be largely attributed to allometry.We find no support for a gradual increase in divergence from normal patterns of integration as fusions accumulate.Surprisingly,however,we find that the derived Rb race(2n=22)has a distinct allometric trajectory compared with the standard race.Our results suggest that either individual fusions disproportionately affect patterns of integration or that there are mechanisms which"purge"extreme variants in hybrids(e.g.reduced fitness of hybrid shape).