Shuang Hu

Changes of microbial population structure related to lignin degradation during lignocellulosic waste composting

Microbial populations and their relationship to bioconversion during lignocellulosic waste composting were studied by quinone profiling. Nine quinones were observed in the initial composting materials, and 15 quinones were found in compost after 50days of composting. The quinone species Q-9(H2), Q-10 and Q-10(H2) which are indicative of certain fungi appeared at the thermophilic stage but disappeared at the cooling stage. Q-10, indicative of certain fungi, and MK-7, characteristic of certain bacteria, were the predominant quinones during the thermophilic stage and were correlated with lignin degradation at the thermophilic stage. The highest lignin degradation ratio (26%) and good cellulose degradation were found at the cooling stage and were correlated with quinones Q-9, MK-7 and long-chain menaquinones attributed to mesophilic fungi, bacteria and actinomycetes, respectively. The present findings will improve the understandings of microbial dynamics and roles in composting, which could provide useful references for development of composting technology.

Mycelial growth and solid-state fermentation of lignocellulosic waste by white-rot fungus Phanerochaete chrysosporium under lead stress

Lignocellulosic biomass is an abundant renewable resource difficult to degrade. Its bioconversion plays important roles in carbon cycles in nature, which may be influenced by heavy metals in environment. Mycelial growth and the degradation of lignocellulosic waste by lignin-degrading fungus Phanerochaete chrysosporium under lead stress were studied. It was shown that P. chrysosporium could grow in liquid media with 400 mg L⁻¹ Pb(II), and mycelial dry weight was reduced by 54% compared to the control. Yellow mycelia in irregular short-strip shape formed in Pb-containing media, whereas the control showed ivory-white regular mycelial pellets. Two possible responses to Pb stress were: dense hyphae, and secretion from mycelia to resist Pb. During solid-state fermentation of straw, fungal colonization capability under Pb stress was positively correlated with the removal efficiency of soluble-exchangeable Pb when its content was higher than 8.2 mg kg⁻¹ dry mass. Carboxymethyl cellulase activity and cellulose degradation were inhibited at different Pb concentrations, whereas low Pb concentrations increased xylanase and ligninolytic enzyme activities and the hemicellulose and lignin degradation. Cluster analyses indicated that Pb had similar effects on the different microbial indexes related to lignin and hemicellulose degradation. The present findings will advance the understandings of lignocellulose degradation by fungi under Pb pollution, which could provide useful references for developing metal-polluted waste biotreatment technology.

Oxalate production at different initial Pb2+ concentrations and the influence of oxalate during solid-state fermentation of straw with Phanerochaete chrysosporium

The production of oxalate at different initial Pb(2+) concentrations during solid-state fermentation of straw with Phanerochaete chrysosporium was investigated. It was found that the maximal peak value of oxalate concentration (22.84 mM) was detected at the initial Pb(2+) concentration of 200 mg kg(-1) dry straw, while the minimum (15.89 mM) at the concentration of 600 mg Pb(2+)kg(-1) dry straw, and at moderate concentration of Pb(2+) the capability of oxalic acid secretion was enhanced. In addition, it was also found that more oxalic acid accumulation went together with better Pb(2+) passivation effect and higher manganese peroxidase (MnP) activity. The present findings will improve the understandings of the interactions of heavy metals with white-rot fungi and the role of oxalate in lignin degradation system, which could provide useful references for more efficient treatment of Pb-contaminated lignocellulosic waste.

Biotransformation of rice straw by Phanerachaete chrysosporium and the related ligninolytic enzymes.

Biotransformation of lignin is related to the biomass utilisation of agricultural wastes. Ligninolytic enzyme from Phanerochaete chrysosporium plays an important role in biodegrading lignin and is specially concerned by researchers. The aim of the study is to optimise the conditions for producing ligninolytic enzymes in solid-state fermentation, and to biotransform the rice straw for the biomass utilisation. The effects of five factors on enzyme activity in state-solid medium were studied using orthogonal experiments, which were expected to offer reference for condition design of enzyme production in solid-state fermentation. The results indicated that the optimal condition for enzyme production by P. chrysosporium during solid-state fermentation could be realised when fungi were domesticated for 8 days, 0.8% fungi suspension (weight ratio) inoculated, temperature kept at 37?C, water content of the solid substrate maintained by 85% and 0.3% Tween80 added, respectively. Also, it was found that the temperature and water content were the foremost influencing factors for the ligninolytic enzyme production of P. chrysosporium during solid-state fermentation. The lignocellulose of rice straw was reduced significantly. The structures of the untreated straw and the straw degraded under the optimal fermentation condition were analysed through ultraviolet spectroscopy and infrared spectroscopy. It could be observed that long-bond and difficult-to-biodegrade hydrocarbons of giant molecule were degraded into short-bond hydrocarbons of small molecule, which could be easily biodegraded.

Form Distribution and Transformation of Pb in Composting of Pb-Polluted Lignocellulosic Waste with White-Rot Fungi

A major limitation of land application of compost is the potential heavy metal pollution, and lead (Pb) has been recognized as one of the most hazardous heavy metal. To reduce the hazards of Pb to the compost application, composting of Pb- polluted wastes by inoculating white-rot fungi was investigated. The parallel waste composting with no inoculants was performed as control. The form distribution and transformation of Pb during composting were discussed. Results showed that the active Pb ion was transformed into the inactive phase during composting. The soluble-exchangeable Pb with high toxicity in composting with white-rot fungi was reduced to 0 mg/kg dry weight compost at day 50, while that of the control only achieved 100.5 mg/kg till day 60. The higher content of organic-bound Pb (121.0 mg/kg) and residual Pb (141.9 mg/kg) with low toxicity was found after 60-day composting with white-rot fungi, compared to those in control. Meanwhile, the higher microbial biomass was observed in composting with white-rot fungi, and Pb concentrations correlated to the microbial biomass. All the results indicated that the method of composting with white-rot fungi reduced the transfer and bioavailability of Pb in compost so as to alleviate the potential stress of metal, and also improved the microbial growth.