Yuehui Chen

Characterization and genomic analysis of kraft lignin biodegradation by the beta-proteobacterium Cupriavidus basilensis B-8

BackgroundLignin materials are abundant and among the most important potential sources for biofuel production. Development of an efficient lignin degradation process has considerable potential for the production of a variety of chemicals, including bioethanol. However, lignin degradation using current methods is inefficient. Given their immense environmental adaptability and biochemical versatility, bacterial could be used as a valuable tool for the rapid degradation of lignin. Kraft lignin (KL) is a polymer by-product of the pulp and paper industry resulting from alkaline sulfide treatment of lignocellulose, and it has been widely used for lignin-related studies.ResultsBeta-proteobacterium Cupriavidus basilensis B-8 isolated from erosive bamboo slips displayed substantial KL degradation capability. With initial concentrations of 0.5–6 g L-1, at least 31.3% KL could be degraded in 7 days. The maximum degradation rate was 44.4% at the initial concentration of 2 g L-1. The optimum pH and temperature for KL degradation were 7.0 and 30°C, respectively. Manganese peroxidase (MnP) and laccase (Lac) demonstrated their greatest level of activity, 1685.3 U L-1 and 815.6 U L-1, at the third and fourth days, respectively. Many small molecule intermediates were formed during the process of KL degradation, as determined using GC-MS analysis. In order to perform metabolic reconstruction of lignin degradation in this bacterium, a draft genome sequence for C. basilensis B-8 was generated. Genomic analysis focused on the catabolic potential of this bacterium against several lignin-derived compounds. These analyses together with sequence comparisons predicted the existence of three major metabolic pathways: β-ketoadipate, phenol degradation, and gentisate pathways.ConclusionThese results confirmed the capability of C. basilensis B-8 to promote KL degradation. Whole genomic sequencing and systematic analysis of the C. basilensis B-8 genome identified degradation steps and intermediates from this bacterial-mediated KL degradation method. Our findings provide a theoretical basis for research into the mechanisms of lignin degradation as well as a practical basis for biofuel production using lignin materials.

Cr (VI) remediation by indigenous bacteria in soils contaminated by chromium-containing slag

Hexavalent chromium (Cr) is a toxic element causing serious environmental threat. Recently, more and more attention is paid to the bio-remediation of Cr (VI) in the contaminated soils. Cr (VI) remediation by indigenous bacteria in soils contaminated by chromium-containing slag at a steel-alloy factory in Hunan Province, China, was investigated in the present study. The results showed that when sufficient nutrients were amended into the contaminated soils, total Cr (VI) concentration declined from the initial value of 462.8 to 10 mg kg(-1) at 10 days and the removal rate was 97.8%. Water soluble Cr (VI) decreased from the initial concentration of 383.8 to 1.7 mg kg(-1). Exchangeable Cr (VI) and carbonates-bound Cr (VI) were removed by 92.6% and 82.4%, respectively. Meanwhile, four Cr (VI) resistant bacterial strains were isolated from the soil under the chromium-containing slag. Only one strain showed a high ability for Cr (VI) reduction in liquid culture. This strain was identified as Pannonibacter phragmitetus sp. by gene sequencing of 16S rRNA. X-ray photoelectron spectroscope (XPS) analysis indicated that Cr (VI) was reduced into trivalent chromium. The results suggest that indigenous bacterial strains have potential application for Cr (VI) remediation in the soils contaminated by chromium-containing slag.

Biodegradation of kraft lignin by a bacterial strain Comamonas sp. B-9 isolated from eroded bamboo slips.

Aims:  The aim was to obtain evidences for lignin degradation by unicellular bacterium Comamonas sp. B‐9.

Kraft lignin biodegradation by Novosphingobium sp. B-7 and analysis of the degradation process

This study focused on the biodegradation of kraft lignin (KL) by Novosphingobium sp. B-7 using KL as sole carbon source. Results revealed that Novosphingobium sp. B-7 reduced the chemical oxygen demand (COD) by 34.7% in KL mineral salt medium after 7days of incubation. Additionally, the maximum activities of manganese peroxidase (MnP) of 3229.8Ul(-1) and laccase (Lac) of 1275Ul(-1) were observed at 4th and 5th day, respectively. GC-MS analysis indicated that after incubated with Novosphingobium sp. B-7, low molecular weight alcohols and lignin-related monomer compounds such as ethanediol, p-hydroxy benzoic acid and vanillic acid were formed in the system, which strongly confirmed the degradation of KL by Novosphingobium sp. B-7.

Environmentally safe treatment of black liquor with Comamonas sp. B-9 under high-alkaline conditions

The strain Comamonas sp. B‐9 was isolated from steeping fluid of erosive bamboo slips derived from Kingdom Wu during the Three‐Kingdoms Dynasty of ancient China (A.D. 220–280). It could be used to treat black liquor (BL) with high‐alkaline pH and with an initial chemical oxygen demand (COD) of 18,000–25,000 mg L−1, without the addition of other carbon and nitrogen sources. The results revealed that Comamonas sp. B–9 was capable of reducing the COD, color, and lignin content of BL by up to 56.8, 35.3, and 43.5%, respectively. High levels of laccase, manganese peroxidase, cellulase, and xylanase enzymatic activities were also observed, and these enzymes could play an important role in the biotreatment of BL. Further, GC–MS analysis showed that most of the compounds detected in BL after biotreatment with Comamonas sp. B‐9 were diminished, while 4‐methyl benzaldehyde, 3,4,5‐trihydroxybenzoic acid ethyl ester, and 4‐hydroxy‐3,5‐dimethoxy benzaldehyde were produced as metabolites. The presented results indicate that Comamonas sp. B‐9 has potential application for the treatment of wastewaters from pulp and paper processing with high COD load under high‐alkaline conditions.