Abstract 

Xyloglucans are the main hemicellulosic polysaccharides found in the primary cell walls of dicots and nongraminaceous monocots, where they are thought to interact with cellulose to form a three-dimensional network that functions as the principal load-bearing structure of the primary cell wall. To determine whether two Arabidopsis thaliana genes that encode xylosyltransferases, XXT1 and XXT2, are involved in xyloglucan biosynthesis in vivo and to determine how the plant cell wall is affected by the lack of expression of XXT1, XXT2, or both, we isolated and characterized xxt1 and xxt2 single and xxt1 xxt2 double T-DNA insertion mutants. Although the xxt1 and xxt2 mutants did not have a gross morphological phenotype, they did have a slight decrease in xyloglucan content and showed slightly altered distribution patterns for xyloglucan epitopes. More interestingly, the xxt1 xxt2 double mutant had aberrant root hairs and lacked detectable xyloglucan. The reduction of xyloglucan in the xxt2 mutant and the lack of detectable xyloglucan in the xxt1 xxt2 double mutant resulted in significant changes in the mechanical properties of these plants. We conclude that XXT1 and XXT2 encode xylosyltransferases that are required for xyloglucan biosynthesis. Moreover, the lack of detectable xyloglucan in the xxt1 xxt2 double mutant challenges conventional models of the plant primary cell wall.

Download the entire paper here.

Annual Meeting of the West Lakes Division of the Association of American
Geographers; Bloomington, IN; November 13-15, 2008.

AGROFUELS AND FOOD SYSTEMS: GEOGRAPHIC SCIENCE IN STUDY OF AGROECOSYSTEM SUSTAINABILITY (more…)

Summary

Triacylglycerols produced by plants are one of the most energy-rich and abundant forms of reduced carbon available from nature. Given their chemical similarities, plant oils represent a logical substitute for conventional diesel, a non-renewable energy source. However, as plant oils are too viscous for use in modern diesel engines, they are converted to fatty acid esters. The resulting fuel is commonly referred to as biodiesel, and offers many advantages over conventional diesel. Chief among these is that biodiesel is derived from renewable sources. In addition, the production and subsequent consumption of biodiesel results in less greenhouse gas emission compared to conventional diesel. However, the widespread adoption of biodiesel faces a number of challenges. The biggest of these is a limited supply of biodiesel feedstocks. Thus, plant oil production needs to be greatly increased for biodiesel to replace a major proportion of the current and future fuel needs of the world. An increased understanding of how plants synthesize fatty acids and triacylglycerols will ultimately allow the development of novel energy crops. For example, knowledge of the regulation of oil synthesis has suggested ways to produce triacylglycerols in abundant non-seed tissues. Additionally, biodiesel has poor cold-temperature performance and low oxidative stability. Improving the fuel characteristics of biodiesel can be achieved by altering the fatty acid composition. In this regard, the generation of transgenic soybean lines with high oleic acid content represents one way in which plant biotechnology has already contributed to the improvement of biodiesel.

Read the full study here.

Summary

Plant cell walls represent the most abundant renewable resource on this planet. Despite their great abundance, only 2% of this resource is currently used by humans. Hence, research into the feasibility of using plant cell walls in the production of cost-effective biofuels is desirable. The main bottleneck for using wall materials is the recalcitrance of walls to efficient degradation into fermentable sugars. Manipulation of the wall polysaccharide biosynthetic machinery or addition of wall structure-altering agents should make it possible to tailor wall composition and architecture to enhance sugar yields upon wall digestion for biofuel fermentation. Study of the biosynthetic machinery and its regulation is still in its infancy and represents a major scientific and technical research challenge. Of course, any change in wall structure to accommodate cost-efficient biofuel production may have detrimental effects on plant growth and development due to the diverse roles of walls in the life of a plant. However, the diversity and abundance of wall structures present in the plant kingdom gives hope that this challenge can be met.

Read the full study here.

Abstract

Aims: To understand factors that impact solar-powered electricity generation by Rhodobacter sphaeroides in a single-chamber microbial fuel cell (MFC). Methods and Results: The MFC used submerged platinum-coated carbon paper anodes and cathodes of the same material, in contact with atmospheric oxygen. Power was measured by monitoring voltage drop across an external resistance. Biohydrogen production and in situ hydrogen oxidation were identified as the main mechanisms for electron transfer to the MFC circuit. The nitrogen source affected MFC performance, with glutamate and nitrate-enhancing power production over ammonium.

Conclusions: Power generation depended on the nature of the nitrogen source and on the availability of light. With light, the maximum point power density was 790 mW m)2 (2Æ9 W m)3). In the dark, power output was less than 0Æ5 mW m)2 (0Æ008 W m)3). Also, sustainable electrochemical activity was possible in cultures that did not receive a nitrogen source.

Significance and Impact of the Study: We show conditions at which solar energy can serve as an alternative energy source for MFC operation. Power densities obtained with these one-chamber solar-driven MFC were comparable with densities reported in nonphotosynthetic MFC and sustainable for longer times than with previous work on two-chamber systems using photosynthetic
bacteria.

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*GLBRC Principal Investigator Tim Donohue contributed to this paper.

Abstract

“The ammonia fiber expansion (AFEX) process has been shown to be an effective pretreatment for lignocellulosic biomass. Technological advances in AFEX have been made since previous cost estimates were developed for this process. Recent research has enabled lower overall ammonia requirements, reduced
ammonia concentrations, and reduced enzyme loadings while still maintaining high conversions of glucan and xylan to monomeric sugars. A new ammonia recovery approach has also been developed. Capital and operating costs for the AFEX process, as part of an overall biorefining system producing fuel ethanol
from biomass have been developed based on these new research results. These new cost estimates are presented and compared to previous estimates. Two biological processing options within the overall biorefinery are also compared, namely consolidated bioprocessing (CBP) and enzymatic hydrolysis followed
by fermentation. Using updated parameters and ammonia recovery configurations, the cost of ethanol production utilizing AFEX is calculated. These calculations indicate that the minimum ethanol selling price (MESP) has been reduced from $1.41/gal to $0.81/gal.”

Read the entire paper here.

*GLBRC Researcher Bruce Dale contributed to this paper.

Agrecol | June 2008 | Porter et. al.

Executive Summary

… The study found that switchgrass can be grown successfully and cost effectively in Wisconsin. It does not require any new technology and can be grown with existing farm practices and equipment. It is also a strong candidate for pelleting. Pelleting allows switchgrass to overcome many logistics inherent to agricultural biomass: the uniform size allows it to be handled and stored easily, transported more economically and burned more efficiently.

By converting to switchgrass pellets the businesses in this study reduced their fuel costs an average of 42%, with the greatest savings coming from facilities that switched from LP to pellets.

The study found that a 100,000 marginal acres (highly erodible and environmentally sensitive) could realistically produce 500,000 tons of switchgrass while markedly improving water quality, wildlife habitat and reducing global warming pollution. This volume of biomass represents $70 million of farmer grown energy and would replace
the estimated $72 - $174 million now exported for natural gas, LP or fuel oil. The money retained in the state would produce farm profits, new business enterprises for harvesting, transportation and processing biomass along with new employment opportunities for workers in the clean energy economy. It is well understood that locally grown and owned projects generate more jobs and more rural economic benefit than those with outside ownership.

In addition the study found that switchgrass, even when grown on marginal sub-prime land in Wisconsin produces more than nine times the energy per acre of land than does the leading biofuels technology of corn (grain) ethanol. This high efficiency in energy production is the result of several factors: switchgrass efficiently captures solar energy, the entire plant is utilized for fuel processing, the bioconversion process retains all the energy captured in the field and the production/conversion process is more energy efficient than corn ethanol…

Read the entire report here.

Harnessing plant biomass for biofuels and biomaterials

By Christoph Benning and Eran Pichersky

…Concerned citizens from scientists to policy makers have recognized the need for a reliable, renewable and affordable source of carbon in its chemically reduced form that can sustain future economic developments without having a negative impact on the environment. Discussion of solutions to overcome the current dependence on fossil carbon is conducted at all levels of society. The conversion of light energy into chemical energy by plant photosynthesis ranks prominently among the natural processes that can potentially meet the challenge. Plant biologists and biochemists are therefore at the forefront of developing schemes and ideas for an emerging bioeconomy that sustainably harnesses plant biomass.

To contribute to the ongoing discussion in this area, we present in this special issue a series of reviews that describe the multiple biochemical processes that plants can or could use to convert their fixed carbon into fuels and other useful products. Rather than advocate a specific process or compound, these invited peer-reviewed articles by leading plant biologists and biochemists focus on the scientific facts behind the production of plant biofuels such as ethanol or biodiesel, as well as other important chemicals that are often unique to plants…

SPECIAL ISSUE: Harnessing plant biomass for biofuels and biomaterials

GLBRC researchers Christoph Benning, Kenneth Keegstra, John Ohlrogge and Markus Pauly contributed to this issue.

Microbial fuel cells (MFC) can generate electricity from renewable sources— in some prototype models, using sunlight via photosynthetic bacteria for power, according to microbiologist Tim Donohue at the University of Wisconsin-Madison (UWM), and his collaborators. Although Rhodobacter sphaeroides-driven MFCs operate in the milliwatt range, they do so harnessing sunlight and waste materials while transiently producing hydrogen and fixing carbon dioxide.

The UWM prototype MFC relies on photosynthetic R. sphaeroides to generate hydrogen that, in turn, is converted to electricity. In light, the maximum power density reaches 790 milliwattsm-2, which falls to 0.5 milliwatts m-2 in the dark. Additional details appear in the October 10, 2007 Journal of Applied Bacteriology. (Read the paper here). In addition to scaling up the MFC and improving its production of hydrogen, Donohue and his collaborators are exploring ways to harness the carbon dioxide that is fixed but then released when R. sphaeroides cells revert to a nonphotosynthetic mode of growth. If fixed carbon dioxide can be converted into high-value byproducts, “we can get two bangs for one buck,” he says. (more…)