Significant amounts of cell wall degrading (CWD) enzymes are required to degrade lignocellulosic biomass into its component sugars. One strategy for reducing exogenous enzyme production requirements is to produce the CWD enzymes in planta. For this work, various CWD enzymes were expressed in maize (Zea mays). Following growth and dry down of the plants, harvested maize stover was tested to determine the impact of the expressed enzymes on the production of glucose and xylose using different exogenous enzyme loadings. In this study, a consolidated pretreatment and hydrolysis process consisting of a moderate chemical pretreatment at temperatures below 75°C followed by enzymatic hydrolysis using an in-house enzyme cocktail was used to evaluate engineered transgenic feedstocks. The carbohydrate compositional analysis showed no significant difference in the amounts of glucan and xylan between the transgenic maize plants expressing CWD enzyme(s) and the control plants. Hydrolysis results demonstrated that transgenic plants expressing CWD enzymes achieved up to 141% higher glucose yield and 172% higher xylose yield over the control plants from enzymatic hydrolysis under the experimental conditions. The hydrolytic performance of a specific xylanase (XynA) expressing transgenic event (XynA.2015.05) was heritable in the next generation, and the improved properties can be achieved even with a 25% reduction in exogenous enzyme loading. Simultaneous saccharification and fermentation of biomass hydrolysates from two different transgenic maize lines with yeast (Saccharomyces cerevisiae D5A) converted 65% of the biomass glucan into ethanol, versus only a 42% ethanol yield with hydrolysates from control plants, corresponding to a 55% improvement in ethanol production.

The chemical interaction between plants and bacteria in the root zone can lead to soil decontamination. Bacteria that degrade polycyclic aromatic hydrocarbons (PAHs) have been isolated from the rhizospheres of plant species with varied biological traits; however, it is not known what phytochemicals promote contaminant degradation. One monocot and two dicotyledon plants were grown in PAH-contaminated soil from a manufactured gas plant (MGP) site. A phytotoxicity assay confirmed greater soil decontamination in rhizospheres when compared to bulk soil controls. Bacteria were isolated from plant roots (rhizobacteria) and selected for growth on anthracene and chrysene on PAH-amended plates. Rhizosphere isolates metabolized 3- and 4-ring PAHs and PAH catabolic intermediates in liquid incubations. Aromatic root exudate compounds, namely flavonoids and simple phenols, were also substrates for isolated rhizobacteria. In particular, the phenolic compounds-morin, caffeic acid, and protocatechuic acid-appear to be linked to bacterial degradation of 3- and 4-ring PAHs in the rhizosphere.

Bacterial associations with plant roots are thought to contribute to the success of phytoremediation. We tested the effect of addition of a polycyclic aromatic hydrocarbon contaminated soil on the structure of the rhizosphere microbial communities of wheat (Triticum aestivum), lettuce (Lactuca sativa var. Tango), zucchini (Cucurbita pepo spp. pepo var. Black Beauty), and pumpkin (C. pepo spp. pepo var. Howden) 16S rDNA terminal restriction fragment length polymorphism (T-RFLP) profiles of rhizosphere microbial communities from different soil/plant combinations were compared with a pairwise Pearson correlation coefficient. Rhizosphere microbial communities of zucchini and pumpkin grown in the media amended with highest degree of contaminated soil clustered separately, whereas communities of these plants grown in unamended or amended with lower concentrations of contaminated soil, grouped in a second cluster. Lettuce communities grouped similarly to cucurbits communities, whereas wheat communities did not display an obvious clustering. The variability of 16S rDNAT-RFLP profiles among the different plant/soil treatments were mostly due to the difference in relative abundance rather than presence/ absence of T-RFLP fragments. Our results suggest that in highly contaminated soils, the rhizosphere microbial community structure is governed more by the degree of contamination rather than the plant host type.

No abstract