Walter F. Schmidt

Large contribution of arbuscular mycorrhizal fungi to soil carbon pools in tropical forest soils

The origins and composition of soil organic matter (SOM) are still largely uncertain. Arbuscular mycorrhizal fungi (AMF) are recognized as indirect contributors through their influence on soil aggregation, plant physiology, and plant community composition. Here we present evidence that AMF can also make large, direct contributions to SOM. Glomalin, a recently discovered glycoprotein produced by AMF hyphae, was detected in tropical soils in concentrations of over 60 mg cm−3. Along a chronosequence of soils spanning ages from 300 to 4.1 Mio years, a pattern of glomalin concentrations is consistent with the hypothesis that this protein accumulates in soil. Carbon dating of glomalin indicated turnover at time scales of several years to decades, much longer than the turnover of AMF hyphae (which is assumed to be on the order of days to weeks). This suggests that contributions of mycorrhizae to soil carbon storage based on hyphal biomass in soil and roots may be an underestimate. The amount of C and N in glomalin represented a sizeable amount (ca. 4–5%) of total soil C and N in the oldest soils. Our results thus indicate that microbial (fungal) carbon that is not derived from above- or below-ground litter can make a significant contribution to soil carbon and nitrogen pools and can far exceed the contributions of soil microbial biomass (ranging from 0.08 to 0.2% of total C for the oldest soils).

Brain-specific lipids from marine, lacustrine, or terrestrial food resources: potential impact on early African Homo sapiens ☆

The polyunsaturated fatty acid (PUFA) composition of the mammalian central nervous system is almost wholly composed of two long-chain polyunsaturated fatty acids (LC-PUFA), docosahexaenoic acid (DHA) and arachidonic acid (AA). PUFA are dietarily essential, thus normal infant/neonatal brain, intellectual growth and development cannot be accomplished if they are deficient during pregnancy and lactation. Uniquely in the human species, the fetal brain consumes 70% of the energy delivered to it by mother. DHA and AA are needed to construct placental and fetal tissues for cell membrane growth, structure and function. Contemporary evidence shows that the maternal circulation is depleted of AA and DHA during fetal growth. Sustaining normal adult human brain function also requires LC-PUFA.Homo sapiens is unlikely to have evolved a large, complex, metabolically expensive brain in an environment which did not provide abundant dietary LC-PUFA. Conversion of 18-carbon PUFA from vegetation to AA and DHA is considered quantitatively insufficient due to a combination of high rates of PUFA oxidation for energy, inefficient and rate limited enzymatic conversion and substrate recycling. The littoral marine and lacustrine food chains provide consistently greater amounts of pre-formed LC-PUFA than the terrestrial food chain. Dietary levels of DHA are 2.5-100 fold higher for equivalent weights of marine fish or shellfish vs. lean or fat terrestrial meats. Mammalian brain tissue and bird egg yolks, especially from marine birds, are the richest terrestrial sources of LC-PUFA. However, land animal adipose fats have been linked to vascular disease and mental ill-health, whereas marine lipids have been demonstrated to be protective. At South African Capesites, large shell middens and fish remains are associated with evidence for some of the earliest modern humans. Cape sites dating from 100 to 18 kya cluster within 200 km of the present coast. Evidence of early H. sapiens is also found around the Rift Valley lakes and up the Nile Corridor into the Middle East; in some cases there is an association with the use of littoral resources. Exploitation of river, estuarine, stranded and spawning fish, shellfish and sea bird nestlings and eggs by Homo could have provided essential dietary LC-PUFA for men, women, and children without requiring organized hunting/fishing, or sophisticated social behavior. It is however, predictable from the present evidence that exploitation of this food resource would have provided the advantage in multi-generational brain development which would have made possible the advent of H. sapiens. Restriction to land based foods as postulated by the savannah and other hypotheses would have led to degeneration of the brain and vascular system as happened without exception in all other land based apes and mammals as they evolved larger bodies.

Evidence for the unique function of docosahexaenoic acid during the evolution of the modern hominid brain

The African savanna ecosystem of the large mammals and primates was associated with a dramatic decline in relative brain capacity associated with little docosahexaenoic acid (DHA), which is required for brain structures and growth. The biochemistry implies that the expansion of the human brain required a plentiful source of preformed DHA. The richest source of DHA is the marine food chain, while the savanna environment offers very little of it. ConsequentlyHomo sapiens could not have evolved on the savannas. Recent fossil evidence indicates that the lacustrine and marine food chain was being extensively exploited at the time cerebral expansion took place and suggests the alternative that the transition from the archaic to modern humans took place at the land/water interface. Contemporary data on tropical lakeshore dwellers reaffirm the above view with nutritional support for the vascular system, the development of which would have been a prerequisite for cerebral expansion. Both arachidonic acid and DHA would have been freely available from such habitats providing the double stimulus of preformed acyl components for the developing blood vessels and brain. The n-3 docosapentaenoic acid precursor (n-3 DPA) was the major n-3-metabolite in the savanna mammals. Despite this abundance, neither it nor the corresponding n-6 DPA was used for the photoreceptor nor the synapse. A substantial difference between DHA and other fatty acids is required to explain this high specificity. Studies on fluidity and other mechanical features of cell membranes did not reveal a difference of such magnitude between even α-linolenic acid and DHA sufficient to explain the exclusive use of DHA. We suggest that the evolution of the large human brain depended on a rich source of DHA from the land/water interface. We review a number of proposals for the possible influence of DHA on physical properties of the brain that are essential for its function.

The potential role for arachidonic and docosahexaenoic acids in protection against some central nervous system injuries in preterm infants

The risk of central nervous, visual, and auditory damage increases from 2/1000 live births in the normal birthweight to >200/1000 as birthweight falls below 1500 g. Such babies are most likely to be born preterm. Advances in infant care have led to increasing numbers of very-low-birthweight, preterm infants surviving to school age with moderate to severe brain damage. Steroids are one of the current treatments, but they cause significant, long-term problems. The evidence reported here suggests an additional approach to protecting the very preterm infant by supporting neurovascular membrane integrity. The complications of preterm, very-low-birthweight babies include bronchopulmonary dysplasia, retinopathy of prematurity, intraventricular hemorrhage, periventricular leukomalacia, and necrotizing enterocolitis, all of which have a vascular component. Arachidonic acid (AA) and DHA are essential, structural, and functional constituents of cell membranes. They are especially required for the growth and function of the brain and vascular systems, which are the primary biofocus of human fetal growth. Molecular dynamics and experimental evidence suggest that DHA could be the ligand for the retinoid X receptor (RXR) in neural tissue. RXR activation is an obligatory step in signaling to the nucleus and in the regulation of gene expression. Very preterm babies are born with minimal fat stores and suboptimal circulating levels of these nutrients. Postanatally, they lose the biomagnification of the proportions of AA and DHA by the placenta for the fetus. No current nutritional management repairs these deficits. The placental biomagnification profile highlights AA rather than DHA. The resultant fetal FA profile closely resembles that of the vascular endothelium and not the brain. Without this nourishment, cell membrane abnormalities would be predicted. We present a scientific rationale for a common pathogenic process in the complications of prematurity.

Isolation of flavipin, a fungus compound antagonistic to plant-parasitic nematodes

An isolate of the fungus Chaetomium globosum produced culture broths that inhibited in vitro egg hatch and juvenile mobility of root-knot nematode (Meloidogyne incognita) and hatch of soybean cyst nematode (Heterodera glycines). Extraction and bioassay-directed fractionation of the culture broth filtrate determined that flavipin, a low molecular weight compound, was the fungus metabolite responsible for most of the nematode-antagonistic activity. Synthesis of flavipin permitted evaluation of the compound as a suppressor of nematode populations on plants in glasshouse studies. Muskmelon (Cucumis melo) plants in steamed and unsteamed soil were inoculated with root-knot nematodes and various concentrations of flavipin were applied to the soil. Contrary to expectations from the in vitro studies, the number of galls per g of roots increased with flavipin treatment at the 14-day harvest. No effect of flavipin on nematode populations was found at the 55-day harvest. In general, plant growth and nematode populations were greater in plants grown in steamed soil.

Characterization and structure by NMR and FTIR spectroscopy, and molecular modeling of chromium(III) picolinate and nicotinate complexes utilized for nutritional supplementation

Chromium picolinate (CrPic) and chromium nicotinate preparations (CrNicl, CrNic2, CrNic3) were investigated with tH and 13C NMR, FTIR, and molecular modeling. CrPic is crystalline and bidentately coordinated. Cr-PicA bonding broadens the NMR signal or shifts it so far downfieid that it is not detectable. All CrNic preparations are noncrystalline, and results provide no evidence that nicotinic acid (NicA) is O-coordinated to Cr. The complex colors may be due to O-coordination with 1-120 and~or OH, not NicA. I H NMR spectra of CrNic l have two sets of peaks. One set has a significant 8 with respect to NicA, indicating that NicA is more strongly associated with Cr. CrNicl 13C data show small, uniform 8 with respect to NicA, indicating that strong localized Cr-COOH bonding is unlikely. The magnitude of 8, :3C, and 1H exchange data suggests that limited Cr-N bonding may occur in CrNicl. CrNic2 and CrNic3 show little difference from NicA spectra. FTIR spectra of all CrNic complexes, but not CrPic, PicA, or NicA, show bound OH and~ or HzO. CrNic complexes are probably olates, with Cr and NicA OHpolymerized. CrPic exchanges with CrNicl in DMSO. This exchange may provide a mechanism for the absorption and active transport of Cr in biological systems. []ournal of Inorganic Biochemistry 66, 119-130 (1997) @ 1997 Elsevier Science Inc.

Nematode-Antagonistic Trichothecenes from Fusarium equiseti

A strain of the fungus Fusarium equiseti isolated from soybean cyst nematode secretes nematode-antagonistic compounds. Bioassay-guided fractionation of an extract of the culture broth was undertaken to identify the compounds. Fractions were assayed for activity against a root-knot nematode (Meloidogyne incognita), a plant pathogen that attacks the roots of numerous plant species. Two trichothecene compounds were isolated that inhibited egg hatch and immobilized second-stage juveniles of this nematode: 4,15-diacetoxy-12,13-epoxy-3,7-dihydroxytrichothec-9-en-8-one (4,15-diacetylnivalenol) and 4,15-diacetoxy-12,13-epoxy-trichothec-9-en-3-ol ( diacetoxyscirpenol). This is the first published report of these compounds affecting plant-parasitic nematodes.

Stereochemical Effects in an Insect Repellent

Abstract Racemic 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine repels blood-feeding arthropods such as mosquitoes, chiggers, and ticks. The compound contains two asymmetric carbon atoms and the racemate consists of four stereoisomers. Quantitative mosquito bioassays using Aedes aegypti (L.) showed that (1S,2′S) and (1R,2′S) configurations were 2.8–3.1 and 1.6–1.8 times more effective, respectively, than the other two stereoisomers in reducing mosquito bites. (1S,2′S) was 2.5 more repellent than the racemate. Biological data show that an interaction of the (2′S)-2-methylpiperidine configuration with a repellent receptor system in A. aegypti is apparently important to repellent activity. Nuclear magnetic resonance spectra and molecular mechanics calculations for the stereoisomers provided insight into the conformation of the (2′S)-group. Results indicate that enhanced repellent effects can be realized through formulation of the most active stereoisomers of the compound.

Biodegradability of injection molded bioplastic pots containing polylactic acid and poultry feather fiber

The biodegradability of three types of bioplastic pots was evaluated by measuring carbon dioxide produced from lab-scale compost reactors containing mixtures of pot fragments and compost inoculum held at 58 °C for 60 days. Biodegradability of pot type A (composed of 100% polylactic acid (PLA)) was very low (13 ± 3%) compared to literature values for other PLA materials. Near infrared spectroscopy (NIRS) results suggest that the PLA undergoes chemical structural changes during polymer extrusion and injection molding. These changes may be the basis of the low biodegradability value. Biodegradability of pot types B (containing 5% poultry feather, 80% PLA, 15% starch), and C (containing 50% poultry feather, 25% urea, 25% glycerol), were 53 ± 2% and 39 ± 3%, respectively. More than 85% of the total biodegradation of these bioplastics occurred within 38 days. NIRS results revealed that poultry feather was not degraded during composting.

Flavonoids as markers for Erythroxylum Taxa: E. coca var. ipadu and E. novogranatense var. truxillense

Abstract Leaf extracts of Erythroxylum coca var. ipadu Plowman (E. c. var. ipadu) produced five O-conjugates of taxifolin and one O-conjugate of quercetin flavonoids, while the equivalent extract from Erythroxylum novogranatense var. truxillense (Rusby) Plowman (E. n. var. truxillense) afforded four flavonoids: (a) the first, an O-conjugate of quercetin; (b) the second, an O-conjugate of fisetin; and (c) the third and fourth O-conjugates of kaempferol. The flavonols of E. n. var. truxillense contained 4′-OEt whereas in E. c. var. ipadu none was found. E. n. var. truxillense contained the flavonol fisetin which was not found in E. c. var. ipadu and has not been previously reported for the taxa. The major sugars in leaf extracts were acylated rhamnosides with either 7, 3 or 4′ linkage or combinations thereof. Flavonoids of the four cultivated Erythroxylum taxa, all of which contain the cocaine alkaloid, differ, and may be used as chemotaxonomic markers for the taxa.