Longer Average Chain Length Research Articles

Foundation species enhance food web complexity through non-trophic facilitation.

Food webs are an integral part of every ecosystem on the planet, yet understanding the mechanisms shaping these complex networks remains a major challenge. Recently, several studies suggested that non-trophic species interactions such as habitat modification and mutualisms can be important determinants of food web structure. However, it remains unclear whether these findings generalize across ecosystems, and whether non-trophic interactions affect food webs randomly, or affect specific trophic levels or functional groups. Here, we combine analyses of 58 food webs from seven terrestrial, freshwater and coastal systems to test (1) the general hypothesis that non-trophic facilitation by habitat-forming foundation species enhances food web complexity, and (2) whether these enhancements have either random or targeted effects on particular trophic levels, functional groups, and linkages throughout the food web. Our empirical results demonstrate that foundation species consistently enhance food web complexity in all seven ecosystems. Further analyses reveal that 15 out of 19 food web properties can be well-approximated by assuming that foundation species randomly facilitate species throughout the trophic network. However, basal species are less strongly, and carnivores are more strongly facilitated in foundation species' food webs than predicted based on random facilitation, resulting in a higher mean trophic level and a longer average chain length. Overall, we conclude that foundation species strongly enhance food web complexity through non-trophic facilitation of species across the entire trophic network. We therefore suggest that the structure and stability of food webs often depends critically on non-trophic facilitation by foundation species.

Modulation of the digestibility and multi-scale structure of cassava starch by controlling the cassava growth period

Starch digestibility is the dominant factor affecting the nutrition of starchy food. Starch with different digestibility can be obtained through tailoring the starch multi-scale structures by controlling the crop growth period. Here, the multi-scale structure and digestibility of cassava starch obtained from different cassava growth periods were investigated, and the structure-digestibility relationships were revealed. The results indicated that the cassava starch synthesized during different growth periods showed differences in digestibility. The combined total content of slowly digestible starch (SDS) and resistant starch (RS) was highest at the growth period of 7 months, and the individual content of SDS and RS was highest at the growth periods of 10 and 11 months, respectively. The multi-scale structure changes during different growth periods demonstrated that smaller weight-average molecular molar mass, larger molecular density, more ordered short-range structure, and thinner amorphous lamellae decreased starch digestion, while higher amylose content and B2 chain ratio, longer average chain length, thicker crystalline lamellae, and repeated semicrystalline lamellae contributed the formation of RS fractions. Hence, specific starch structures can be tailored by simply controlling the growth period for obtaining slow and resistant digestible cassava starch to improve its nutritional value.

A Fatty Acyl Coenzyme A Reductase Promotes Wax Ester Accumulation in Rhodococcus jostii RHA1.

Many rhodococci are oleaginous and, as such, have considerable potential for the sustainable production of lipid-based commodity chemicals. Herein, we demonstrated that Rhodococcus jostii RHA1, a soil bacterium that catabolizes a wide range of organic compounds, produced wax esters (WEs) up to 0.0002% of its cellular dry weight during exponential growth on glucose. These WEs were fully saturated and contained primarily 31 to 34 carbon atoms. Moreover, they were present at higher levels during exponential growth than under lipid-accumulating conditions. Bioinformatics analyses revealed that RHA1 contains a gene encoding a putative fatty acyl coenzyme A (acyl-CoA) reductase (FcrA). The purified enzyme catalyzed the NADPH-dependent transformation of stearoyl-CoA to stearyl alcohol with a specific activity of 45 ± 3 nmol/mg · min and dodecanal to dodecanol with a specific activity of 5,300 ± 300 nmol/mg · min. Deletion of fcrA did not affect WE accumulation when grown in either carbon- or nitrogen-limited medium. However, the ΔfcrA mutant accumulated less than 20% of the amount of WEs as the wild-type strain under conditions of nitric oxide stress. A strain of RHA1 overproducing FcrA accumulated WEs to ∼13% cellular dry weight under lipid-accumulating conditions, and their acyl moieties had longer average chain lengths than those in wild-type cells (C17 versus C16). The results provide insight into the biosynthesis of WEs in rhodococci and facilitate the development of this genus for the production of high-value neutral lipids.IMPORTANCE Among the best-studied oleaginous bacteria, rhodococci have considerable potential for the sustainable production of lipid-based commodity chemicals, such as wax esters. However, many aspects of lipid synthesis in these bacteria are poorly understood. The current study identifies a key enzyme in wax ester synthesis in rhodococci and exploits it to significantly improve the yield of wax esters in bacteria. In so doing, this work contributes to the development of novel bioprocesses for an important class of oleochemicals that may ultimately allow us to phase out their unsustainable production from sources such as petroleum and palm oil.

Effect of diurnal photosynthetic activity on the fine structure of amylopectin from normal and waxy barley starch

The impact of diurnal photosynthetic activity on the fine structure of the amylopectin fraction of starch synthesized by normal barley (NBS) and waxy barley (WBS), the latter completely devoid of amylose biosynthesis, was determined following the cultivation under normal diurnal or constant light growing conditions. The amylopectin fine structures were analysed by characterizing its unit chain length profiles after enzymatic debranching as well as its φ,β-limit dextrins and its clusters and building blocks after their partial and complete hydrolysis with α-amylase from Bacillus amyloliquefaciens, respectively. Regardless of lighting conditions, no structural effects were found when comparing both the amylopectin side-chain distribution and the internal chain fragments of these amylopectins. However, the diurnally grown NBS and WBS both showed larger amylopectin clusters and these had lower branching density and longer average chain lengths than clusters derived from plants grown under constant light conditions. Amylopectin clusters from diurnally grown plants also consisted of a greater number of building blocks, and shorter inter-block chain lengths compared to clusters derived from plants grown under constant light. Our data demonstrate that the diurnal light regime influences the fine structure of the amylopectin component both in amylose and non-amylose starch granules.

The importance of chain length for the polyphosphate enhancement of acidic potassium permanganate chemiluminescence

Sodium polyphosphate is commonly used to enhance chemiluminescence reactions with acidic potassium permanganate through a dual enhancement mechanism, but commercially available polyphosphates vary greatly in composition. We have examined the influence of polyphosphate composition and concentration on both the dual enhancement mechanism of chemiluminescence intensity and the stability of the reagent under analytically useful conditions. The average chain length (n) provides a convenient characterisation, but materials with similar values can exhibit markedly different distributions of phosphate oligomers. There is a minimum polyphosphate chain length (∼6) required for a large enhancement of the emission intensity, but no further advantage was obtained using polyphosphate materials with much longer average chain lengths. Providing there is a sufficient average chain length, the optimum concentration of polyphosphate is dependent on the analyte and in some cases, may be lower than the quantities previously used in routine detection. However, the concentration of polyphosphate should not be lowered in permanganate reagents that have been partially reduced to form high concentrations of the key manganese(III) co-reactant, as this intermediate needs to be stabilised to prevent formation of insoluble manganese(IV).

End product yields from the extraruminal fermentation of various polysaccharide, protein and nucleic acid components of biofuels feedstocks

"Extraruminal" fermentations employing in vitro incubation of mixed ruminal bacterial consortia, are capable of converting a complex array of biomass materials to mixtures of volatile fatty acids (VFA), methane, and carbon dioxide. Most of the potential energy in the biomass feedstock is retained in the VFA products, which are potential reactants for electrochemical conversion to hydrocarbon fuels. Quantitative data on VFA yields and proportions from biomass components are necessary for determining industrial feasibility, but such measurements have not been systematically reported. VFA yields and proportions were determined for a variety of carbohydrates, proteins and nucleic acids. Carbohydrates yielded primarily acetic and propionic acids, while proteins also yielded a more favorable product mix (longer average chain length and branched chain VFAs). Addition of certain co-substrates (e.g., glycerol) favorably improved the VFA product mix. The results have implications for hydrocarbon fuel generation from biomass materials by hybrid fermentation/chemical processes.

Affinity purification and kinetics of pea cotyledon starch phosphorylases

Affinity purification of two phosphorylases from pea cotyledons has been achieved by chromatography on amylopectin bound to Concanavalin A—Sepharose. Cytoplasmic enzyme bound to amylopectin from normal-starch but the plastid enzyme required the amylopectin from high-amylose starch, with a longer average chain length. The V max/ K m values for a series of branched α-glucans with differing average chain lengths were linearly related to average external chain length. Rabbit-muscle phosphorylase limit-dextrin competitively inhibited the cytoplasmic enzyme with a K is of 13 μM non-reducing end-groups. Progress curves of phosphorolysis with both enzymes showed no product inhibition by d-glucose α-1-phosphate. A study of molecular models of the two reactions suggests that separate binding patterns of glucan may not be necessary for phosphorolysis and synthesis.

Possible involvement of acetyl coenzyme A carboxylase as well as fatty acid synthetase in the temperature-controlled synthesis of fatty acids in Saccharomyces cerevisiae.

Fatty acid synthetase (FAS) preparations from Saccharomyces cerevisiae cells grown at either 35 or 10 degrees C produced the same products at different temperatures and showed quite similar temperature-dependencies in Arrhenius plots, with break points at 25 degrees C. This break point does not appear to reflect a phase transition of phospholipids present in the purified FAS preparations but rather is associated with protein conformational changes. S. cerevisiae cells grown at 35 degrees C and then shifted to 10 degrees C produced fatty acids with a shorter average chain length than those fatty acids synthesized at 10 degrees C by cells already adapted to 10 degrees C (hyper response). Acetyl-CoA carboxylase activity was relatively higher in the cells grown at 35 degrees C than in the cells grown at 10 degrees C; moreover, fatty acids with longer average chain lengths were synthesized in vitro at higher malonyl-CoA concentrations, which was consistent with the difference in the average chain lengths of newly synthesized fatty acids in cells grown at 35 and 10 degrees C. However, the activity levels of acetyl-CoA carboxylase and fatty acid synthetase alone did not account for the hyper response phenomena.

Transport of hydrogen and carbon monoxide in highly crosslinked poly(propylene glycol) networks

AbstractPrevious interpretations of gas transport data in crosslinked networks have been hindered by an inability to accurately control and evaluate the network parameters. We have recently prepared a series of model networks by reacting poly(propylene glycol) with a triisocyanate crosslinking agent. The poly(propylene glycol)s had narrow molecular weight distributions and average molecular weights between 425 and 3000, so the resulting networks had uniform average molecular weights between crosslinks. Hydrogen and carbon monoxide permeabilities in membranes formed from these networks increase with decreasing crosslink density. These results indicate increased cooperative molecular motions in the networks with longer average chain lengths between crosslinks. Increasing the average molecular weight between crosslinks also reduces the discrimination between these two gases so that the separation factors decrease. For networks prepared from mixtures of poly(propylene glycol)s with different molecular weights the gas permeabilities (but not the separation factors) depend on the molecular weight distribution.

Biochemical studies of metachromatic leukodystrophy in three siblings.

Biochemical analyses were performed on cerebral biopsies from three siblings with metachromatic leukodystrophy, and from autopsy tissue obtained 6 months later. The lipids of all gray matter samples were relatively normal, with the exception of an elevated sulfatide: cerebroside ratio. The white matter samples were grossly abnormal and showed a progression in severity of biochemical abnormalities with duration of the disease. Sulfatides were 4-8-fold higher than normal, and the ratio of cerebrosides to sulfatides ranged from 0.13 to 0.26, compared to the normal value of about 4.0. Myelin was isolated in very low yield, but had normal morphology. As others have reported, it had the same chemical defect as whole white matter; sulfatides were 7-8 times higher than normal and cerebrosides were reduced by more than half. The fatty acid compositions of the myelin sphingolipids were found to be of much longer average chain length than those in affected white matter. In myelin, the unsubstituted fatty acids of cerebrosides and sphingomyelin had a higher percentage of short chains than found in normal myelin, but were less abnormal than those in whole white matter, whereas the unsubstituted and alpha-hydroxy acids of sulfatides and the alpha-hydroxy acids of cerebrosides were not deficient in long chains. These data indicate that there are at least two compartments of sphingolipids in MLD white matter, each having different average chain lengths.

RNA polymerase of nuclear sap and chromatin fractions of walker tumor

1. 1. Walker tumor RNA polymerase II consists of two activities, lIa and IIb, distinguishable by their intranuclear distribution and template preference. 2. 2. RNA polymerase IIa, localized in nuclear sap, preferentially utilizes denatured DNA template, while RNA polymerase IIb, obtained from chromatin (nuclear sap-free nuclei), is more active with native DNA template. 3. 3. The two activities show similarities in response to divalent metal ions, salt concentration, and sensitivity to α-amanitin. 4. 4. The RNA synthesized by the two polymerases show similar nearest neighbor frequences and base ratios. 5. 5. However, RNA product synthesized by RNA polymerase IIa has a much longer average chain length than that synthesized by RNA polymerase IIb, while the RNA product of polymerase IIb shows significantly more self-complementarity than the product of polymerase IIa.

Activated transcription from rat liver chromatin by non-histone proteins

1. 1. The non-histone proteins partially purified from rat liver DNA-protein complex have been shown to stimulate chromatin-templated RNA synthesis in vitro. This stimulation is not the result of contaminating DNA or proteases. 2. 2. The RNA transcribed from chromatin stimulated by the non-histone proteins has a different nucleotide composition, and hybridizes more with homologous DNA in saturation hybridization and competition hybridization experiments than RNA transcribed from control chromatin. 3. 3. In ribosomal amino acid incorporation system in vitro, the RNA transcribed from the activated chromatin codes different polypeptides than RNA transcribed from control chromatin. 14C-labeled polypeptides translated by the activated RNA product are shown to have a longer average chain length. These data suggest an activation of the genome, resulting in increased transcription of additional genome sequences.