Kinetic analysis of the uptake of glucose and corn oil used as carbon sources in batch cultures of Gibberella fujikuroi

Identification of a Novel Lactose-Specific PTS Operon in Bacillus licheniformis and Development of Derivative Artificial Operon Modules

Bacillus licheniformis plays a crucial role as a microbial host in the food industry and shows promising potential as a probiotic for human intestinal regulation. It exhibits a remarkable ability to utilize lactose as its sole carbon source. Despite its significance, the lactose-related metabolic pathway in this strain remains unclear. In this study, we identified a novel lactose-specific operon (lacDCAB) in B. licheniformis, consisting of the lacD gene that encodes a unique 6-phospho-β-galactosidase belonging to the GH4 family, and the lacCAB genes encoding a lactose-specific PTS1 system. Notably, we constructed and assessed an array library of transport and catabolic modules specifically for lactose utilization. Among these modules, PDS-lacD-P2-pts1 demonstrated the highest specific lactose consumption rate of 0.64 g/(L·h·OD), which was 8 times higher than that of the control strain. Furthermore, we developed a dual carbon source transport model based on the PDS-lacD-P2-pts1 assembly module, which highlighted efficient coutilization of glucose/sucrose, lactose/sucrose, lactose/galactose, and lactose/2,3-butanediol. This study provides insight into the lactose-specific metabolic pathway of B. licheniformis and presents a promising strategy for enhancing lactose utilization efficiency and mixed carbon source coutilization.

Fungal dynamics and potential functions during anaerobic digestion of food waste

Fungi could play an important role during anaerobic digestion (AD), but have received less attention than prokaryotes. Here, AD bioreactors of food waste were performed to explore fungal succession and their potential ecological and engineering value. We found that similar patterns in fungal biomass and diversity, decreasing from the initial time point (Day 0) to the lowest value within 3-6 days and then started to rise and stabilized between 9 and 42 days. Throughout the entire AD process, variations in fungal community composition were observed and dominant fungal taxa have the potential ability to degrade complex organic matter and alleviate fatty acid and ammonia accumulation. Furthermore, we found that deterministic processes gradually dominated fungal assembly succession (up to 84.85% at the final stage), suggesting changing environmental status responsible for fungal community dynamics and specifically, fungal community structure, diversity and biomass were regulated by different environmental variables or the same variables with opposite effects. AD bioreactors could directionally select specific fungal taxa over time, but some highly abundant fungi could not be mapped to any fungal species with defined function in the reference database, so function prediction relying on PICRUSt2 may underestimate fungal function in AD systems. Collectively, our study confirmed fungi have important ecological and engineering values in AD systems.

Alternative methods for gibberellic acid production, recovery and formulation: A case study for product cost reduction

The aim of this work was to develop a new production, recovery and formulation process of gibberellic acid (GA₃). Low-cost byproducts - citrus pulp (CP) and soybean hulls (SH) - were employed as substrate for GA₃ production by Gibberella fujikuroi in semisolid fermentation. A CP/SH mixture (70%/30%) promoted high productivities both in bubble column reactor (1.66 mg L/h), and in stirred tank reactor (2.13 mg L/h). GA₃ production medium cost (US$ 6.70/m³) was reduced by 85% when compared to previously reported synthetic media (US$ 44.96/m³). It was described that GA₃ fermented extract has low stability, and that liquid and powder formulation of the fermented extract maintained the biomolecule activity over 6 months. Alginate and alginate/kefiran beads containing GA₃ showed encapsulation efficiency of 70% and 60%, respectively. This work supports good perspectives for GA₃ production using cheap substrates and simple formulation of clarified extract to favour its use in agricultural countries.

Enhancement of gibberellic acid production from Fusarium fujikuroi by mutation breeding and glycerol addition

Gibberellic acid (GA₃) is a natural plant growth hormone that has been widely used in agriculture and horticulture. To obtain higher GA₃ producing strains, the method of screening the strains for resistance to simvastatin was used after treatment with nitrosoguanidine (NTG) and gamma rays. The rationale for the strategy was that mutants showing simvastatin resistance were likely to be high GA₃ producers, as their activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is relatively more effective. GA₃ yield of mutant S109 increased by 14.2% than that of the original strain. The GA₃ production ability in mutant S109 remained relatively stable after ten generations. With the addition of 0.4 g glycerol on the 5th day during the fermentation process in Erlenmeyer flask, maximum GA₃ production of 2.7 g/L was achieved by this mutant, exhibiting 28.6% increase compared with original strain. Furthermore, we also achieved 2.8 g/L GA₃ and had a 33.3% increase with addition 20 g glycerol on the 5th day during the fermentation process in a 5-L bioreactor. Our results indicated efficient GA₃ production could be achieved on the condition that the supply of glycerol at the suitable conditions. This study would lay a foundation for industrial production of GA₃.

Improvement of gibberellin production by a newly isolated Fusarium fujikuroi mutant

AIMS

To obtain and investigate the potential mechanism for GA₃ production in Fusarium fujikuroi GA-251, a high GA₃ producer.

METHODS AND RESULTS

Fusarium fujikuroi IMI 58289 was bred with Cobalt-60 (⁶⁰ Co) radiation and lithium chloride treatment. The best mutant strain GA-251 was obtained for the subsequent optimization of fermentation conditions. The yield of GA₃ by GA-251 was 2100 mg l^-1 , while the wild-type strain was 100 mg l^-1 , which is a 21-fold increase in the yield. To elucidate the mechanism of high GA₃ yield of GA-251, the genome was sequenced and compared with wild-type strain IMI 58289. The results showed 2295 single nucleotide polymorphisms, 1242 small indels and 30 structural variants. These mutations were analysed and enriched in the MAPK signalling pathway, the mRNA surveillance pathway and endocytosis. The potential reasons for the improved GA₃ biosynthesis were investigated.

CONCLUSIONS

The potential mechanism of high GA₃ yield was attributed to endocytosis pathway and histone modification proteins family.

SIGNIFICANCE AND IMPACT OF THE STUDY

A mutant strain GA-251 in this work that could potentially be utilized in the industrial yield of GA₃ . The comparative genome analysis would shed light onto the mechanism of yield improvement and be a theoretical guide for further metabolic engineering.

Development of a multi-stage continuous fermentation strategy for docosahexaenoic acid production by Schizochytrium sp

Docosahexaenoic acid (DHA) has wide-ranging benefits for normal development of the visual and nervous systems in infants. A sustainable source of DHA production through fermentation using Schizochytrium sp. has been developed. In this paper, we present the discovery of growth-uncoupled DHA production by Schizochytrium sp. and the development of corresponding kinetic models of fed-batch fermentations, which can be used to describe and predict the cell growth and substrate utilization as well as lipid and DHA production. Based on this kinetic model, a predictive model of multi-stage continuous fermentation process was established and used to analyze, optimize and design the process parameters. Optimal predicted processes of two-stage and three-stage continuous fermentation were developed and verified in lab-scale bioreactor based on the predicted process parameters. A successful three-stage continuous fermentation was achieved, which increased the lipid, DHA content and DHA productivity by 47.6, 64.3 and 97.1%, respectively, compared with two-stage continuous fermentation.

Current advances in gibberellic acid (GA3) production, patented technologies and potential applications

Gibberellic acid is a plant growth hormone that promotes cell expansion and division. Studies have aimed at optimizing and reducing production costs, which could make its application economically viable for different cultivars. Gibberellins consist of a large family of plant growth hormones discovered in the 1930s, which are synthesized via the terpenes route from the geranylgeranyl diphosphate and feature a basic structure formed by an ent-gibberellane tetracyclic skeleton. Among them, only four have biological activity, including gibberellic acid (GA₃), which acts as a natural plant growth regulator, especially for stem elongation, seed germination, and increased fruit size. It can be obtained from plants, fungi, and bacteria. There are also some reports about microalgae GA₃ producers. Fungi, especially Gibberella fujikuroi, are preferred for GA₃ production via submerged fermentation or solid-state fermentation. Many factors may affect its production, some of which are related to the control and scale-up of fermentation parameters. Different GA₃ products are available on the market. They can be found in liquid or solid formulations containing only GA₃ or a mixture of other biological active gibberellins, which can be applied on a wide variety of cultivars, including crops and fruits. However, the product's cost still limits its large and continuous application. New low-cost and efficient GA₃ production alternatives are surely welcome. This review deals with the latest scientific and technological advances on production, recovery, formulation, and applications of this important plant growth hormone.