The aim of this study is to investigate the microbial community structure and diversity in a wooddecomposed hollow-stump ecosystem. Microbial communities of SD-1, a lateritic soil sample from forest hollowstump ecosystems in Fuzhou (a southeastern coast city of China), were characterized by constructing and analyzing rRNA gene clone libraries. Sixty-six phylotypes were identified from 112 bacterial clones, including Acidobacteria (71.5%), Proteobacteria (24.1%) and Verrucomicrobia (0.9%). A total of 40 phylotypes were obtained from 138 fungal clones, including Basidiomycota (42.8%), Ascomycota (36.2%), Zygomycota (13.8%), Chytridiomycota (2.9%) and Fungi incertae sedis (4.3%). The results showed a variety of clones related to the reported lignocellulosedecomposing microorganisms. They included some important bacterial decomposers, such as Sphingomonas and Burkholderia, and a number of wood-decaying fungi, including Tricholomataceae, Strophariaceae and Agaricaceae of Basidiomycota; Orbilia, Aspergillus, Phialocephala, Epicoccum and Phoma of Ascomycota and Mucorales of Zygomycota. The result indicated that the lignocellulolytic microorganisms worked synergically with a unique community structure to biodegrade lignocellulose in the hollowstump ecosystem.

This work aimed to develop an efficient L-leucine industrial production strain of Corynebacterium glutamicum by using metabolic engineering. A recombinant C. glutamicum strain was constructed by expressing a feedback-resistant leuA-encoded 2-isopropylmalate synthase (IPMS) that carries three amino acid exchanges (R529H, G532D and L535V) from the mutant strain C. glutamicum ML1-9 which was obtained by screening for structural analogues. In order to improve the expression of IPMS, a strong promoter (tac promoter) was used to ensure efficient expression of the rate-limiting enzyme. In addition, reasonable metabolic modifications on the central carbon metabolic pathway and competitive metabolic pathways to optimize the L-leucine biosynthesis pathway by redistribution of various types of precursors and repression of negative regulation were used aimed for increased L-leucine production. The modifications involved (1) deletion of the gene encoding the repressor LtbR to increase expression of leuBCD, (2) deletion of the gene encoding the AlaT to decrease the concentration of extracellular L-alanine, and increased availability of pyruvate for L-leucine formation, (3) deletion of the gene encoding the threonine dehydratase to abolish L-isoleucine synthesis and to eliminate the intermediate precursor of L-isoleucine biosynthesis competing with L-leucine biosynthesis, (4) inactivation of the pantothenate synthetase to increase α-ketoisovalerate formation, and to enable its further conversion to L-leucine, and (5) inactivation of lactate dehydrogenase to decrease lactate production and its pyruvate consumption, concomitant to decreased glucose consumption rates and prevention of lactic acid to restrict cell growth. The production performance of the engineered strain MDLeu-19/pZ8-1leuA r was characterized with cultivations in a bioreactor. Under fed-batch conditions in a 50-L automated fermentor, the best producer strain accumulated 38.1 g L -1 of L-leucine; the molar product yield being 0.42 mol L-leucine per mole of glucose (glucose conversion rate attained 26.4%). Moreover, during large-scale fermentation using a 150-m 3 fermentor, this strain produced more than 37.5 g L -1 L-leucine and the glucose conversion rate was 25.8%, making this process potentially viable for industrial production.

The aim of this study was to endow an industrial strain of Saccharomyces cerevisiae with the ability to overexpress the xylanase by constructing a homology-driven integration vector. The total mRNA from a xylanase-producing strain of Aspergillus niger IME-216 was extracted and used as the template for the production of endo-β-1,4-xylanase cDNA by reverse transcription. The fusion fragment containing the phosphoglycerate kinase promoter, α-factor signal peptide, xylanase gene encoding the mature peptide, and CYC1 terminator was first generated by overlap extension polymerase chain reaction. Then, the vector pUPX was constructed by inserting the fusion fragment into the S. cerevisiae plasmid pUG6. Then, A 2.2-kb rDNA sequence was further cloned and attached to the SalI-digested pUPX to obtain the integration plasmid pUPXR. The pUPXR was linearized by KpnI, transformed into the industrial strain S. cerevisiae YS2 using the lithium acetate method and integrated into the S. cerevisiae chromosome. The maximum yield of the recombinant xylanase produced by the engineered S. cerevisiae strain YS2_2 was 74.8 U per microliter, which was about 1.5-fold higher than the original 50 U per microliter by Aspergillus niger IME-216 strain under the flask culture at 28 °C for 72 h. The findings of our study can be used for further development of industrial S. cerevisiae strain for producing interested enzymes, or improving the achievement of metabolism, for example, simultaneous fermentation of glucose and xylose to producing bioethanol.

L-valine is an essential branched-amino acid that is widely used in multiple areas such as pharmaceuticals and special dietary products and its use is increasing. As the world market for L-valine grows rapidly, there is an increasing interest to develop an efficient L-valine-producing strain. In this study, a simple, sensitive, efficient, and consistent screening procedure termed 96 well plate-PC-HPLC (96-PH) was developed for the rapid identification of high-yield L-valine strains to replace the traditional L-valine assay. L-valine production by Brevibacterium flavum MDV1 was increased by genome shuffling. The starting strains were obtained using ultraviolet (UV) irradiation and binary ethylenimine treatment followed by preparation of protoplasts, UV irradiation inactivation, multi-cell fusion, and fusion of the inactivated protoplasts to produce positive colonies. After two rounds of genome shuffling and the 96-PH method, six L-valine high-yielding mutants were selected. One genetically stable mutant (MDVR2-21) showed an L-valine yield of 30.1 g/L during shake flask fermentation, 6.8-fold higher than that of MDV1. Under fed-batch conditions in a 30 L automated fermentor, MDVR2-21 accumulated 70.1 g/L of L-valine (0.598 mol L-valine per mole of glucose; 38.9% glucose conversion rate). During large-scale fermentation using a 120 m fermentor, this strain produced > 66.8 g/L L-valine (36.5% glucose conversion rate), reflecting a very productive and stable industrial enrichment fermentation effect. Genome shuffling is an efficient technique to improve production of L-valine by B. flavum MDV1. Screening using 96-PH is very economical, rapid, efficient, and well-suited for high-throughput screening.

Dendrobium is an important source of natural components with high medicinal value. While numerous endophytic fungi associated with these plants have been extensively studied, research on endophytic bacteria remains limited. In this study, an improved tissue separation method was used to isolate endophytic bacteria from Dendrobium nobile and enrich the resources of high-quality biocontrol bacteria with both antibacterial and growth-promoting effects. We assessed the inhibitory effect of the isolated bacteria on pathogenic bacteria and fungi using agar diffusion and plate confrontation methods. We further investigated the growth-promoting effect of bacterial suspensions at various concentrations on corn seeds and Dendrobium nobile plantlets. The obtained endophytic bacterium, JC-3jx, isolated for the first time from the stem of Dendrobium nobile, exhibited significant inhibitory activity against the tested indicator bacteria. Morphologic and phylogenetic analysis confirmed the closest similarity of JC-3jx to Paenibacillus peoriae, leading to its final identification as Paenibacillus peoriae JC-3jx. This bacteria exhibited varying degrees of inhibition against the six pathogenic plant fungi tested, achieving a significant 56% inhibition rate against Pyricularia oryzae. Furthermore, the sterile fermentation supernatant of JC-3jx demonstrated pronounced inhibitory activity against the three tested pathogenic bacteria, particularly the gram-negative Escherichia coli. Moreover, the results demonstrate that the bacterial suspension of JC-3jx significantly promoted the rooting of corn seeds and the growth of Dendrobium nobile plantlets, indicating its excellent antibacterial and growth-promoting potential.