Mechanisms of response to pH shock in microbial fermentation

Mechanism of carbonized humic acid and magnesium aluminum-layered double hydroxide promoting biohydrogen generation

Dark fermentation (DF) is prone to low hydrogen (H2) yield. In this work, magnesium aluminum-layered double hydroxide and carbonized humic acid (MgAl-LDH/CHA) was synthesized by co-precipitation to reveal the mechanism in rising bioH2 generation. The results indicated that MgAl-LDH released Mg and Al ions slowly in DF system, improving the activity of H2-producing microbes (HPM) for more H2. The H2 yield increased from 169.3 mL/g glucose to 244.9 mL/g glucose, which was 44.7 % higher than that for the control yield. MgAl-LDH/CHA increased Proteobacteria content from 30.9 % to 43.7 %, making it form a complex microbial community and participate in DF metabolism with Firmicutes and other microbes together. Besides, MgAl-LDH/CHA could serve as an electron shuttle that likely effectively promotes electron transfer in DF, significantly reduced the energy requirements of HPM, thus raising metabolic activity. It provides direction for the multi-element composite applied in DF system.

Production-optimized fermentation of antifungal compounds by bacillus velezensis LZN01 and transcriptome analysis

Fusarium wilt is one of the major constraints on global watermelon production, and Fusarium oxysporum f. sp. niveum (Fon) is the causative agent of Fusarium wilt in watermelon and results in severe yield and quality losses worldwide. The enhancement of antifungal activity from antagonistic bacteria against Fon is highly practical for managing Fusarium wilt in watermelon. The aim of this study was to maximize the antifungal activity of Bacillus velezensis LZN01 by optimizing fermentation conditions and analysing its regulatory mechanism via transcriptome sequencing. The culture and fermentation conditions for strain LZN01 were optimized by single-factor and response surface experiments. The optimum culture conditions for this strain were as follows: the addition of D-fructose at 35 g/L and NH4Cl at 5 g/L in LB medium, pH 7, and incubation at 30°C for 72 h. The fungal inhibition rate for strain LZN01 reached 71.1%. The improvement of inhibition rate for strain LZN01 in optimization fermentation was supported by transcriptomic analysis; a total of 491 genes were upregulated, while 736 genes were downregulated. Transcriptome analysis revealed that some differentially expressed genes involved in carbon and nitrogen metabolism, oxidation-reduction, fatty acid and secondary metabolism; This optimization process could potentially lead to significant alterations in the production levels and types of antimicrobial compounds by the strain. Metabolomics and UPLC/Q-Exactive Orbitrap MS analysis revealed that the production yields of antimicrobial compounds, such as surfactin, fengycin, shikimic acid, and myriocin, increased or were detected in the cell-free supernatant (CFS) after the fermentation optimization process. Our results indicate that fermentation optimization enhances the antifungal activity of the LZN01 strain by influencing the expression of genes responsible for the synthesis of antimicrobial compounds.

Potential for curdlan recovery from aerobic granular sludge wastewater treatment systems - A review

The aerobic granular sludge (AGS) biotechnology has been explored for wastewater treatment for over two decades. AGS is gaining increased interest due to its enhanced treatment performance ability and the potential for resource recovery from AGS-based wastewater treatment systems. Resource recovery from AGS is a promising approach to sustainable wastewater treatment and attaining a circular economy in the wastewater management industry. Currently, research is at an advanced stage on recovering value-added resources such as phosphorus, polyhydroxyalkanoates, alginate-like exopolysaccharides, and tryptophan from waste aerobic granules. Recently, other value-added resources, including curdlan, have been identified in the aerobic granule matrix, and this may increase the sustainability of biotechnology in the wastewater industry. This paper provides an overview of AGS resource recovery potential. In particular, the potential for enhanced curdlan biosynthesis in the granule matrix and its recovery from AGS wastewater treatment systems is outlined.

Revealing the roles of carbonized humic acid in biohydrogen production

For low yield in dark fermentation (DF), in this study, the carbonized humic acid (CHA) was produced and added to DF for enhancing biohydrogen (bioH2) yield at mesophilic condition. The highest bioH2 yield was 151.08 mL/g glucose with the addition of CHA at 80 mg/L, which was 35.27% and 16.53% higher than those of 0 mg/L CHA and 80 mg/L mineral humic acid (MHA) groups, respectively. Electrons preferentially conducted via the butyrate pathway due to CHA amendments, which corresponded to the prediction of relevant functional genes. Furthermore, CHA possessed distinctive advantages over MHA, which acted as an electron shuttle to facilitate electron transfer, released metal ions as an essential signal mediator and favored the reduction of ferredoxin, obtaining more H2. The use of CHA in the field of H2-DF depicted the high-value utilization and industrial chain extension of MHA.

Physiological analysis of the improved ε-polylysine production induced by reactive oxygen species

INTRODUCTION

Epsilon-poly-L-lysine (ε-PL) is produced by Streptomyces species in acidic and aerobic conditions, which inevitably induces rapid generation of reactive oxygen species (ROS). The devastating effects of ROS on biomolecules and cell vitality have been well-studied, while the positive effects of ROS are rarely reported.

RESULTS

In this study, we found that a proper dose of intracellular ROS (about 3.3 μmol H₂O₂ /g DCW) could induce a physiological modification to promote the ε-PL production (from 1.2 to 1.5 g/L). It resulted in larger sizes of colony and mycelial pellets as well as vibrant, aggregated, and more robust mycelia, which were of high capability of ROS detoxication. Physiological studies showed that appropriate doses of ROS activated the metabolism of the pentose phosphate pathway at both transcriptional and enzymatic levels, which was beneficial for biomass accumulation. The biosynthesis of lysine was also promoted in terms of transcriptional regulatory overexpression, increased transcription and enzymatic activity of key genes, larger pools of metabolites in the TCA cycle, replenishment pathway, and diaminoheptanedioic acid pathway. In addition, energy provision was ensured by activated metabolism of the TCA cycle, a larger pool of NADH, and higher activity of the electron transport system. Increased transcription of HrdD and pls further accelerated the ε-PL biosynthesis.

SIGNIFICANCE

These results indicated that ROS at proper intracellular dose could act as an inducing signal to activate the ε-PL biosynthesis, which laid a foundation for further process regulation to maintain optimal ROS dose in industrial ε-PL production and was of theoretical and practical significance.

KEY POINTS

• A proper dose of intracellular ROS positively influences the ε-PL production. • Proper dose of ROS enhanced the mycelial activity and antioxidative capability. • ROS increased lysine synthesis metabolism, energy provision and pls expression.

Transcriptome and Metabolome Analysis Revealing the Improved ε-Poly-l-Lysine Production Induced by a Microbial Call from Botrytis cinerea

ε-Poly-l-lysine (ε-PL) is a wide-spectrum antimicrobial agent, while its biosynthesis-inducing signals are rarely reported. This study found that Botrytis cinerea extracts could act as a microbial call to induce a physiological modification of Streptomyces albulus for ε-PL efficient biosynthesis and thereby resulted in ε-PL production (34.2 g/liter) 1.34-fold higher than control. The elicitors could be primary isolated by ethanol and butanol extraction, which resulted in more vibrant, aggregate and stronger mycelia. The elicitor-derived physiological changes focused on three aspects: ε-PL synthase, energy metabolism, and lysine biosynthesis. After elicitor addition, upregulated sigma factor hrdD and improved transcription and expression of pls directly contributed to the high ε-PL productivity; upregulated genes in tricarboxylic acid (TCA) cycle and energy metabolism promoted activities of citrate synthase and the electron transport system; in addition, pool enlargements of ATP, ADP, and NADH guaranteed the ATP provision for ε-PL assembly. Lysine biosynthesis was also increased based on enhancements of gene transcription, key enzyme activities, and intracellular metabolite pools related to carbon source utilization, the Embden-Meyerhof pathway (EMP), the diaminopimelic acid pathway (DAP), and the replenishment pathway. Interestingly, the elicitors stimulated the gene transcription for the quorum-sensing system and resulted in upregulation of genes for other antibiotic production. These results indicated that the Botrytis cinerea could produce inducing signals to change the Streptomyces mycelial physiology and accelerate the ε-PL biosynthesis. IMPORTANCE This work identified the role of microbial elicitors on ε-PL production and disclosed the underlying mechanism through analysis of gene transcription, key enzyme activities, and intracellular metabolite pools, including transcriptome and metabolome analysis. It was the first report for the inducing effects of the "microbial call" to Streptomyces albulus and ε-PL biosynthesis, and these elicitors could be potentially obtained from decayed fruits infected by Botrytis cinerea; hence, this may be a way of turning a biohazard into bioproduct wealth. This study provided a reference for application of microbial signals in secondary metabolite production, which is of theoretical and practical significance in industrial antibiotic production.

Biosynthesis and applications of curdlan

Curdlan is widely applied in the food and pharmaceutical industries. This review focuses on the biosynthetic pathways, regulatory mechanisms and metabolic engineering strategies for curdlan production. Firstly, curdlan biosynthesis is discussed. Furthermore, various strategies to increase curdlan production are summarized from four aspects, including the overexpression of genes for curdlan biosynthesis, weakening/knockdown of genes from competing pathways, increasing the supply of curdlan precursors, and optimization of fermentation conditions. Moreover, the emerging and advanced applications of curdlan are introduced. Finally, the challenges that are frequently encountered during curdlan biosynthesis are noted with a discussion of directions for curdlan production.