Metal accumulation by sunflower (Helianthus annuus L.) and the efficacy of its biomass in enzymatic saccharification

PLoS One. 2017 Apr 24;12(4):e0175845. doi: 10.1371/journal.pone.0175845. eCollection 2017.

Abstract

Accumulation of metal contaminants in soil as a result of various industrial and anthropogenic activities has reduced soil fertility significantly. Phytoextraction of metal contaminants can improve soil fertility and provide inexpensive feedstock for biorefineries. We investigated the hyperaccumulation capacity of sunflower (Helianthus annuus) biomass by cultivating these plants in various concentrations of metal contaminants. Sunflowers were grown in soils contaminated with various levels of heavy metals (10-2,000 mg/kg dry soil). The degree of metal uptake by different parts of the biomass and the residual concentration in the soil were estimated through inductively coupled plasma mass spectrometry. An almost 2.5-fold hyperaccumulation of Zn2+ was observed in the leaf and flower biomass compared with the concentration in the soil. For the subsequent saccharification of biomass with hyperaccumulated contaminants, a fungal lignocellulosic consortium was used. The fungal consortium cocktail retained more than 95% filter paper activity with 100 mM Ni2+ ions even after 36 h. The highest saccharification yield (SY, 87.4%) was observed with Ni2+ as the contaminant (10 mg/kg dry wt), whereas Pb2+ (251.9 mg/kg dry wt) was the strongest inhibitor of biomass hydrolysis, resulting in only a 30% SY. Importantly, the enzyme cocktail produced by the fungal consortium resulted in almost the same SY (%) as that obtained from a combination of commercial cellulase and β-glucosidase. Significant sugar conversion (61.7%) from H. annuus biomass hydrolysate occurred, resulting in the production of 11.4 g/L of bioethanol. This is the first study to assess the suitability of phytoremediated sunflower biomass for bioethanol production.

MeSH terms

  • Biodegradation, Environmental*
  • Biomass*
  • Helianthus / chemistry*
  • Metals, Heavy / analysis*
  • Plant Leaves / chemistry
  • Soil / chemistry
  • Soil Pollutants / analysis*

Substances

  • Metals, Heavy
  • Soil
  • Soil Pollutants

Grants and funding

This research was supported by Korea Ministry of Environment as GAIA Project (G112-00055-0023-0). This study was also supported by the Energy Efficiency & Resources Core Technology Program of the KETEP (20153010092130 and 20153030091450). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.