Hadden J.A.,University of Georgia |
French A.D.,Southern Regional Research Center |
Woods R.J.,University of Georgia |
Woods R.J.,National University of Ireland
Biopolymers | Year: 2013
Molecular dynamics (MD) simulations of cellulose microfibrils are pertinent to the paper, textile, and biofuels industries for their unique capacity to characterize dynamic behavior and atomic-level interactions with solvent molecules and cellulase enzymes. While high-resolution crystallographic data have established a solid basis for computational analysis of cellulose, previous work has demonstrated a tendency for modeled microfibrils to diverge from the linear experimental structure and adopt a twisted conformation. Here, we investigate the dependence of this twisting behavior on computational approximations and establish the theoretical basis for its occurrence. We examine the role of solvent, the effect of nonbonded force field parameters [partial charges and van der Waals (vdW) contributions], and the use of explicitly modeled oxygen lone pairs in both the solute and solvent. Findings suggest that microfibril twisting is favored by vdW interactions, and counteracted by both intrachain hydrogen bonds and solvent effects at the microfibril surface. © 2013 Wiley Periodicals, Inc.
Ehrlich K.C.,Southern Regional Research Center
Frontiers in Microbiology | Year: 2014
Aspergillus flavus is a diverse assemblage of strains that include aflatoxin-producing and non-toxigenic strains with cosmopolitan distribution. The most promising strategy currently being used to reduce preharvest contamination of crops with aflatoxin is to introduce non-aflatoxin (biocontrol) A. flavus into the crop environment. Whether or not introduction of biocontrol strains into agricultural fields is enough to reduce aflatoxin contamination to levels required for acceptance of the contaminated food as fit for consumption is still unknown. There is no question that biocontrol strains are able to reduce the size of the populations of aflatoxin-producing strains but the available data suggests that at most only a four- to five-fold reduction in aflatoxin contamination is achieved. There are many challenges facing this strategy that are both short term and long term. First, the population biology of A. flavus is not well understood due in part to A. flavus's diversity, its ability to form heterokaryotic reproductive forms, and its unknown ability to survive for prolonged periods after application. Second, biocontrol strains must be selected that are suitable for the environment, the type of crop, and the soil into which they will be introduced. Third, there is a need to guard against inadvertent introduction of A. flavus strains that could impose an additional burden on food safety and food quality, and fourth, with global warming and resultant changes in the soil nutrients and concomitant microbiome populations, the biocontrol strategy must be sufficiently flexible to adapt to such changes. Understanding genetic variation within strains of A. flavus is important for developing a robust biocontrol strategy and it is unlikely that a "one size fits all" strategy will work for preharvest aflatoxin reduction. © 2014 Ehrlich.
He Z.,Southern Regional Research Center |
Olk D.C.,U.S. Department of Agriculture |
Cade-Menun B.J.,Agriculture and Agri Food Canada
Soil Science Society of America Journal | Year: 2011
Phosphorus has long been known to be present in soil humic fractions, but little is known about specific P forms in humic fractions or their lability. We extracted the mobile humic acid (MHA) and recalcitrant calcium humate (CaHA) fractions from a Nebraska Hord silt loam soil (a fine-silty, mixed, superactive, mesic Cumulic Haplustoll) under continuous corn (Zea mays L.) receiving either inorganic fertilizer or animal manure. Solution 31P nuclear magnetic resonance spectroscopy demonstrated that P in both MHA and CaHA was predominantly present in organic forms, mostly as orthophosphate monoesters. Spiking experiments indicated no phytate present in these humic fractions, but scyllo-inositol P was identified in all samples. Potato phosphatase hydrolyzed some humicbound P. Fungal phytase released more humic-bound P, which may come from scyllo-inositol P. No additional P was released by including nuclease. Ultraviolet (UV) irradiation increased soluble inorganic P in MHA fractions, but total hydrolyzable P in MHA fractions did not increase, suggesting that the portion of P that was UV labile was also enzymatically hydrolyzable. In contrast, UV irradiation increased soluble inorganic P and total hydrolysable P in CaHA fractions, which suggests that UV-labile P in CaHA fractions did not overlap wiThenzymatically hydrolyzable P. Fertilization management did not significantly alter the lability of humic P in these humic fractions. This research has the potential to improve P management by increasing our knowledge of P lability for more efficient crop uptake. © Soil Science Society of America.
Calvo A.M.,Northern Illinois University |
Cary J.W.,Southern Regional Research Center
Frontiers in Microbiology | Year: 2015
Fungal secondary metabolism and morphological development have been shown to be intimately associated at the genetic level. Much of the literature has focused on the co-regulation of secondary metabolite production (e.g., sterigmatocystin and aflatoxin in Aspergillus nidulans and Aspergillus flavus, respectively) with conidiation or formation of sexual fruiting bodies. However, many of these genetic links also control sclerotial production. Sclerotia are resistant structures produced by a number of fungal genera. They also represent the principal source of primary inoculum for some phytopathogenic fungi. In nature, higher plants often concentrate secondary metabolites in reproductive structures as a means of defense against herbivores and insects. By analogy, fungi also sequester a number of secondary metabolites in sclerotia that act as a chemical defense system against fungivorous predators. These include antiinsectant compounds such as tetramic acids, indole diterpenoids, pyridones, and diketopiperazines. This chapter will focus on the molecular mechanisms governing production of secondary metabolites and the role they play in sclerotial development and fungal ecology, with particular emphasis on Aspergillus species. The global regulatory proteins VeA and LaeA, components of the velvet nuclear protein complex, serve as virulence factors and control both development and secondary metabolite production in many Aspergillus species. We will discuss a number of VeA- and LaeA-regulated secondary metabolic gene clusters in A. flavus that are postulated to be involved in sclerotial morphogenesis and chemical defense. The presence of multiple regulatory factors that control secondary metabolism and sclerotial formation suggests that fungi have evolved these complex regulatory mechanisms as a means to rapidly adapt chemical responses to protect sclerotia from predators, competitors and other environmental stressors. © 2015 Calvo and Cary.
Shih F.F.,Southern Regional Research Center
JAOCS, Journal of the American Oil Chemists' Society | Year: 2012
Because of the large amount of rice produced annually, milled rice co-products, such as rice flour, rice bran, rice bran oil, wax, and rice hulls are plentiful and readily available. These co-products are valuable sources of food ingredients, but they are currently under-utilized. Rice bran and flour contain different levels of protein. When treated with carbohydrate-hydrolyzing enzymes, high-protein products can be produced, which are nutritious and used widely in health and baby food formulations. Recently, subcritical water processing has also been studied, in which water is put under high pressure to maintain its liquid state and used as an environmental-friendly media for the recovery of rice bran proteins. Rice flour contains more than 90% rice starch (RS), and functional properties of RS are normally modified to suit the needs for food applications. For example, the addition of small amounts of phosphorylated RS esters or pregelatinized rice flour to frying batters made of rice flour was found to impart superior sensory characteristics and lower the amount of oil-uptake. Reductions in oil uptake of up to 50% were observed with the rice based formulations compared with batters made from traditional wheat ingredients. Treatment of RS with octenylsuccinic anhydride produces modified starch products that are useful as an emulsifying agent for the encapsulation of lipophilic compounds. Similarly, other rice-based products, such as microcrystalline celluloses from rice hulls, edible films formed with rice wax, various components with antioxidant properties, and germinated brown rice flours have also been developed. © 2011 AOCS (outside the USA).