Correction: BiKEGG: a COBRA toolbox extension for bridging the BiGG and KEGG databases

Genome mining discovery of hydrogen production pathway of Klebsiella sp. WL1316 fermenting cotton stalk hydrolysate

Genome sequencing was used to identify key genes for the generation of hydrogen gas through cotton stalk hydrolysate fermentation by Klebsiella sp. WL1316. Genome annotation indicated that the genome size was 5.2 Mb with GC content 57.6%. Xylose was metabolized in the pentose phosphate pathway via the conversion of xylose to xylulose in Klebsiella sp. WL1316. This strain contained diverse formate-hydrogen lyases and hydrogenases with gene numbers higher than closely related species. A metabolic network involving glucose, xylose utilisation, and fermentative hydrogen production was reconstructed. Metabolic analysis of key node metabolites showed that glucose and xylose metabolism influenced biomass synthesis and biohydrogen production. Formic acid accumulated during fermentation at 24-48 h but decreased sharply after 48 h, illustrating the splitting of formic acid to hydrogen gas during early-to-mid fermentation. The Kreb's cycle was the main competitive metabolic branch of biohydrogen synthesis at 24 h of fermentation. Lactic and acetic acid fermentation and late ethanol accumulation competed the carbon skeleton of biohydrogen synthesis after 72 h of fermentation, indicating that these competitive pathways are regulated in middle-to-late fermentation (48-96 h). This study is the first to elucidate the metabolic mechanisms of mixed sugar utilisation and biohydrogen synthesis based on genomic information.

Metabolic pathway analysis of walnut endophytic bacterium Bacillus subtilis HB1310 related to lipid production from fermentation of cotton stalk hydrolysate based on genome sequencing

OBJECTIVES

In this study, genome sequencing and metabolic analysis were used to identify and verify the key metabolic pathways for glucose and xylose utilization and fatty acid synthesis in the walnut endophytic bacterium (WEB) Bacillus subtilis HB1310.

RESULTS

The genome sequence of WEB HB1310 was generated with a size of 4.1 Mb and GC content of 43.5%. Genome annotation indicated that the Embden-Meyerhof-Parnas, pentose phosphate, and fatty acid synthesis pathways were mainly involved in mixed sugar utilization and lipid production. In particular, diverse and abundant fatty acid synthesis genes were observed in a higher number than in other Bacillus strains. The tricarboxylic acid cycle competitively shared the carbon flux flowing before 48 h, and the acetic acid fermentation competed after 72 h. Moreover, fatty acid synthase activity was highly correlated with lipid titer with a correlation coefficient of 0.9626, and NADPH might be more utilized for the lipid synthesis within 48 h.

CONCLUSIONS

This study is the first attempt to explain the metabolic mechanism of mixed sugar utilization and lipid production based on genomic information, which provides a theoretical basis for the metabolic regulation of bacterial lipid production from lignocellulosic hydrolysates.