Fermentation Strategy Research Articles

Current trends in medium‐chain‐length polyhydroxyalkanoates: Microbial production, purification, and characterization

AbstractPolyhydroxyalkanoates (PHAs) have gained interest recently due to their biodegradability and versatility. In particular, the chemical compositions of medium‐chain‐length (mcl)‐PHAs are highly diverse, comprising different monomers containing 6–14 carbon atoms. This review summarizes different feedstocks and fermentation strategies to enhance mcl‐PHA production and briefly discusses the downstream processing. This review also provides comprehensive details on analytical tools for determining the composition and properties of mcl‐PHA. Moreover, this study provides novel information by statistically analyzing the data collected from several reports on mcl‐PHA to determine the optimal fermentation parameters (specific growth rate, PHA productivity, and PHA yield from various structurally related and unrelated substrates), mcl‐PHA composition, molecular weight (MW), and thermal and mechanical properties, in addition to other relevant statistical values. The analysis revealed that the median PHA productivity observed in the fed‐batch feeding strategy was 0.4 g L−1 h−1, which is eight times higher than that obtained from batch feeding (0.05 g L−1 h−1). Furthermore, 3‐hydroxyoctanoate and ‐decanoate were the primary monomers incorporated into mcl‐PHA. The investigation also determined the median glass transition temperature (−43°C) and melting temperature (47°C), which indicated that mcl‐PHA is a flexible amorphous polymer at room temperature with a median MW of 104 kDa. However, information on the monomer composition or heterogeneity and the associated physical and mechanical data of mcl‐PHAs is inadequate. Based on their mechanical values, the mcl‐PHAs can be classified as semi‐crystalline polymers (median crystallinity 23%) with rubber‐like properties and a median elongation at break of 385%. However, due to the limited mechanical data available for mcl‐PHAs with known monomer composition, identifying suitable processing tools and applications to develop mcl‐PHAs further is challenging.

Fed-batch fermentation of Mucor circinelloides reveals significant improvement in biomass and lipid accumulation through performance evaluation, chemical analysis, and expression profiling

This study aimed to improve the lipid and biomass yields of Mucor circinelloides WJ11 by implementing four different fed-batch fermentation strategies, varied in time and glucose concentration (S1-S4). The S1 fermentation strategy yielded the highest biomass, lipid, and fatty acid content (22 ± 0.7 g/L, 53 ± 1.2 %, and 28 ± 1.6 %) after 120 and 144 h, respectively. The γ-linolenic acid titer of 0.75 ± 0.0 g/L was greatest in S3 after 48 h. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was used to analyze the transcription of key genes involved in lipid accumulation. The glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and ATP-citrate lyase genes showed increased expression levels. Fourier-transform infrared (FTIR) spectroscopy was used to analyze the biochemical profile during fermentation strategies. Optimal abiotic factors for production efficiency included pH 6.5, 25–26 °C, 15 % (v/v) inoculum, 500 rpm, 20 %-30 % dissolved oxygen, and 120 h fermentation. Glucose co-feeding offers valuable insights to develop effective fermentation strategies for lipid production.

Streptomycetes as Microbial Cell Factories for the Biotechnological Production of Melanin.

Melanins are complex, polymeric pigments with interesting properties like UV-light absorbance ability, metal ion chelation capacity, antimicrobial action, redox behaviors, and scavenging properties. Based on these characteristics, melanins might be applied in different industrial fields like food packaging, environmental bioremediation, and bioelectronic fields. The actual melanin manufacturing process is not environmentally friendly as it is based on extraction and purification from cuttlefish. Synthetic melanin is available on the market, but it is more expensive than animal-sourced pigment and it requires long chemical procedures. The biotechnological production of microbial melanin, instead, might be a valid alternative. Streptomycetes synthesize melanins as pigments and as extracellular products. In this review, the melanin biotechnological production processes by different Streptomyces strains have been revised according to papers in the literature. The different fermentation strategies to increase melanin production such as the optimization of growth conditions and medium composition or the use of raw sources as growth substrates are here described. Diverse downstream purification processes are also reported as well as all the different analytical methods used to characterize the melanin produced by Streptomyces strains before its application in different fields.

Efficient Secretory Expression of Leghemoglobin in Saccharomyces cerevisiae

Leghemoglobin (LegH) is a plant-derived hemoglobin that can be used as a food additive to confer red color and meat flavor to plant-based meat products. Although LegH has been expressed in Saccharomyces cerevisiae, the productivity is low at the shaking-flask level, and the downstream process of purification is complicated. Herein, the intracellular expression of LegH reached 151.2 mg/L through initial promoter modification. Then, the fermentation strategy was optimized, and the titer of LegH reached 544.8 mg/L (5.2 mg/L/OD600 per unit yield) in the two-stage fed-batch fermentation in a 5-L fermenter. After the modification of signal peptide and knockout of proteases, the secretory expression of LegH was achieved in recombinant S. cerevisiae, and the final secretory titer of LegH reached 88.5 mg/L at the 5-L fermenter level. Based on the results of this study, the secreted LegH can be widely applied in the fields of food processing and biocatalysis in the future.

Pilot-scale acetone-butanol-ethanol fermentation from corn stover

Biobutanol is an advanced biofuel that can be produced from excess lignocellulose via acetone-butanol-ethanol (ABE) fermentation. Although significant technological progress has been made in this field, attempts at large-scale lignocellulosic ABE production remain scarce. In this study, 1 m3 scale ABE fermentation was investigated using high inhibitor tolerance Clostridium acetobutylicum ABE-P1201 and steam-exploded corn stover hydrolysate (SECSH). Before expanding the fermentation scale, the detoxification process for SECSH was simplified by process engineering. Results revealed that appropriate pH management during the fed-batch cultivation could largely decrease the inhibition of the toxic components in undetoxified SECSH to the solventogenesis phase of the ABE-P1201 strains, avoiding “acid crash”. Therefore, after naturalizing the pH by Ca(OH)2, the undetoxified SECSH, without removal of the solid components, reached 17.68 ± 1.30 g/L of ABE production with 0.34 ± 0.01 g/g of yield in 1 L scale bioreactor. Based on this strategy, the fermentation scale gradually expanded from laboratory-scale apparatus to pilot-scale bioreactors. Finally, 17.05 ± 1.20 g/L of ABE titer and 0.32 ± 0.01 g/g of ABE yield were realized in 1 m3 bioreactor, corresponding to approximately 145 kg of ABE production from 1 t of dry corn stover. The pilot-scale ABE fermentation demonstrated excellent stability during repeated operations. This study provided a simplified ABE fermentation strategy and verified the feasibility of the pilot process, providing tremendous significance and a solid foundation for the future industrialization of second-generation ABE plants.

Application of Aqueous Two-Phase Systems with Thermoseparating Polymers (EOPO) as a Method for Extractive Fermentation with Neochloris oleoabundans

Extractive fermentation is an in situ method for the production and recovery of biomolecules of interest. Aqueous two-phase systems (ATPS) allow the product to be recovered in one phase of the system, reducing unit operations in the bioprocess. Thermosensitive polymers such as EOPOs are an interesting alternative to be applied in ATPS. In this work, different EOPOs were tested in an extractive fermentation strategy with the green microalgae Neochloris oleoabundans to provide a basis for future implementations of these systems in microalgae bioprocesses. Extractive fermentations were carried out with two EOPOs of different molecular weights (3900 and 12,000 g/mol) at concentrations of 10% and 15% (w/v). The microalga was incubated axenically under two different sets of conditions for 21 and 45 days, respectively. Cell counts were performed, and cell growth curves were obtained. Additionally, a semi-continuous and batch extractive fermentation assay was performed. The extractive fermentation with EOPO showed lower cell growth and a longer adaptation time of the microalgae in the fermentation, and EPS production yields of up to 8–23 g/L were obtained. Extractive fermentation is an interesting method to be implemented in microalgae cultures; however, further conditions need to be explored to achieve an appropriate bioprocess.

Production optimization of food functional factor ergothioneine in wild-type red yeast Rhodotorula mucilaginosa DL-X01.

Ergothioneine (EGT) is a high-value food functional factor that cannot be synthesized by humans and other vertebrates, and the low yield limits its application. In this study, the optimal fermentation temperature, fermentation time, initial pH, inoculum age, and inoculation ratio on EGT biosynthesis of Rhodotorula mucilaginosa DL-X01 were optimized. In addition, the effects of three key precursor substances - histidine, methionine, and cysteine - on fungal EGT synthesis were verified. The optimal conditions were further obtained by response surface optimization. The EGT yield of R. mucilaginosa DL-X01 under optimal fermentation conditions reached 64.48 ± 2.30 mg L-1 at shake flask fermentation level. Finally, the yield was increased to 339.08 ± 3.31 mg L-1 (intracellular) by fed-batch fermentation in a 5 L bioreactor. To the best of our knowledge, this is the highest EGT yield ever reported in non-recombinant strains. The fermentation strategy described in this study will promote the efficient biosynthesis of EGT in red yeast and its sustainable production in the food industry. © 2024 Society of Chemical Industry.

Waste Tea-Derived Theabrownins for Solar-Driven Steam Generation.

Solar-driven seawater desalination has been considered an effective and sustainable solution to mitigate the global freshwater crisis. However, the substantial cost associated with photothermal materials for evaporator fabrication still hinders large-scale manufacturing for practical applications. Herein, we successfully obtained high yields of theabrownins (TB), which were oxidation polymerization products of polyphenols from waste and inferior tea leaves using a liquid-state fermentation strategy. Subsequently, a series of photothermal complexes were prepared based on the metal-phenolic networks assembled from TB and metal ions (Fe(III), Cu(II), Ni(II), and Zn(II)). Also, the screened TB@Fe(III) complexes were directly coated on a hydrophilic poly(vinylidene fluoride) (PVDF) membrane to construct the solar evaporation device (TB@Fe(III)@PVDF), which not only demonstrated superior light absorption property and notable hydrophilicity but also achieved a high water evaporation rate of 1.59 kg m-2 h-1 and a steam generation efficiency of 90% under 1 sun irradiation. More importantly, its long-term stability and exceptionally low production cost enabled an important step toward the possibility of large-scale practical applications. We believe that this study holds the potential to pave the way for the development of sustainable and cost-effective photothermal materials, offering new avenues for utilization of agriculture resource waste and solar-driven water remediation.

Approaches for Producing Fungal Cellulases Through Submerged Fermentation.

Fungal cellulases are the most sought-after biological molecules produced from microbial sources in the last four decades. Owing to their emerging applications in the bioenergy industry for hydrolyzing cellulose, for which they are the most abundant source on this planet, research trends are shifting heavily toward adapting to submerged fermentation. However, filamentous fungal species, which are efficient cellulase producers, are well-adapted to low-moisture solid support as the substrate, such as in nature. Therefore, various fermentation strategies are currently being investigated to adapt them to submerged fermentation for large and high-quality production of cellulases. Emerging research trends, such as the use of inexpensive feedstocks, nutrient and/or culture optimization, innovative bioreactor designs, microparticle-assisted fungal growth, and innovative genetic engineering approaches, are some of the recent efforts by researchers to exploit the full potential of these biological molecules. This review discusses some of these strategies and their success rates in various research conditions. In addition, specific focus was provided to both increasing the market value of cellulases and the innovative strategies required to enhance their production on an industrial scale.

Recycling Fermentation Strategy for Waste Cellular Residues in the Production of Polyunsaturated Fatty Acids

Cellular residues after lipid extraction are the primary waste by-products of microbial polyunsaturated fatty acid production. To mitigate the discharge of cellular residues and reduce the cost of DHA and ARA production, this study examined the utilization of enzymatically hydrolyzed Aurantiochytrium cellular residues (ACRs) and Mortierella alpina cellular residues (MCRs) as nitrogen sources. Results demonstrated that ACRs and MCRs could partially substitute yeast extract (YE) without adverse effects on DHA and ARA fermentation. Moreover, the implementation of a new fermentation medium incorporating ACRs, MCRs, and YE as mixed nitrogen sources resulted in DHA and ARA yields of 17.78 and 5.77 g/L, respectively. These values represented increases of 10.37% and 9.28% compared to traditional cultural methods, while simultaneously reducing the usage of YE by 80% and 60%, respectively. Therefore, the strategy of recycling waste cellular residues presents a novel approach for reducing the costs and environmental impact associated with microbial fermentations.

Anaerobic gut fungal communities in marsupial hosts.

The anaerobic gut fungi (AGF) inhabit the alimentary tracts of herbivores. In contrast to placental mammals, information regarding the identity, diversity, and community structure of AGF in marsupials is extremely sparse. Here, we characterized AGF communities in 61 fecal samples from 10 marsupial species belonging to four families in the order Diprotodontia: Vombatidae (wombats), Phascolarctidae (koalas), Phalangeridae (possums), and Macropodidae (kangaroos, wallabies, and pademelons). An amplicon-based diversity survey using the D2 region of the large ribosomal subunit as a phylogenetic marker indicated that marsupial AGF communities were dominated by eight genera commonly encountered in placental herbivores (Neocallimastix, Caecomyces, Cyllamyces, Anaeromyces, Orpinomyces, Piromyces, Pecoramyces, and Khoyollomyces). Community structure analysis revealed a high level of stochasticity, and ordination approaches did not reveal a significant role for the animal host, gut type, dietary preferences, or lifestyle in structuring marsupial AGF communities. Marsupial foregut and hindgut communities displayed diversity and community structure patterns comparable to AGF communities typically encountered in placental foregut hosts while exhibiting a higher level of diversity and a distinct community structure compared to placental hindgut communities. Quantification of AGF load using quantitative PCR indicated a significantly smaller load in marsupial hosts compared to their placental counterparts. Isolation efforts were only successful from a single red kangaroo fecal sample and yielded a Khoyollomyces ramosus isolate closely related to strains previously isolated from placental hosts. Our results suggest that AGF communities in marsupials are in low abundance and show little signs of selection based on ecological and evolutionary factors.IMPORTANCEThe AGF are integral part of the microbiome of herbivores. They play a crucial role in breaking down plant biomass in hindgut and foregut fermenters. The majority of research has been conducted on the AGF community in placental mammalian hosts. However, it is important to note that many marsupial mammals are also herbivores and employ a hindgut or foregut fermentation strategy for breaking down plant biomass. So far, very little is known regarding the AGF diversity and community structure in marsupial mammals. To fill this knowledge gap, we conducted an amplicon-based diversity survey targeting AGF in 61 fecal samples from 10 marsupial species. We hypothesize that, given the distinct evolutionary history and alimentary tract architecture, novel and unique AGF communities would be encountered in marsupials. Our results indicate that marsupial AGF communities are highly stochastic, present in relatively low loads, and display community structure patterns comparable to AGF communities typically encountered in placental foregut hosts. Our results indicate that marsupial hosts harbor AGF communities; however, in contrast to the strong pattern of phylosymbiosis typically observed between AGF and placental herbivores, the identity and gut architecture appear to play a minor role in structuring AGF communities in marsupials.

Effects of fermentation with different probiotics on the quality, isoflavone content, and flavor of okara beverages.

The present study aimed to prepare and evaluate a new probiotic functional beverage, using single-probiotic and compound probiotic fermentation on okara. Four different forms of fermentation microorganisms used were Lacticaseibacillus rhamnosus S24 (Lr), Lacticaseibacillus paracasei 6244 (Lp), Lactobacillus acidophilus 11,073 (La), and mixed fermentation (Lr + Lp + La). The physicochemical properties, antioxidant activity, flavor change, and storage period of fermented okara beverages with probiotics were investigated. The results showed that different fermentation schemes could significantly improve the physicochemical properties, antioxidant activity, and sensory quality of the okara beverages. The number of viable bacteria in the Lp group (3.53 × 108 CFU/mL), isoflavone content (0.514 μg/mL) were the highest; total phenol and flavonoid content were 3.32 and 5.68 times higher than in the CK group, respectively. DPPH and ABTS+ free radical scavenging rates were increased by 11.32% and 20%, respectively (p < .05). Through SPME/GC-MS analysis, 44 volatile compounds were identified in the Lr + Lp + La groups, mainly as a result of changes in alcohols and aldehydes produced by fermentation metabolism. It enhances the floral and fruity aroma of the okara beverage. All probiotic-fermented okara beverages can be stored at 4°C for 15 days, with probiotic activity greater than 107 CFU/mL. This study can obtain a probiotic okara beverage rich in soybean isoflavones and with good flavor. Overall, okara can be used to develop functional beverages containing probiotics and contribute to a zero-waste approach in the food industry.

Perspectives and Progress in Bioethanol Processing and Social Economic Impacts

The liquid biofuel bioethanol is widely produced worldwide via fermenting sugars extracted from a variety of raw materials, including lignocellulose biomass, one of the world’s most abundant renewable resources. Due to its recalcitrant character, lignocellulose is usually pretreated by mechanical, chemical, and biological methods to maximize sugar recovery. Pretreated lignocellulose biomass undergoes a fermentation process performed sequentially or simultaneously to saccharification. The different fermentation strategies (e.g., separate or simultaneous hydrolysis and fermentation or co-fermentation) and conditions (e.g., inoculum type load, agitation, temperature, and pH) affect ethanol yield. Genetic modification of the inoculum has been focused recently to improve ethanol tolerance and as well as to use different sugars to enhance the performance of the microorganisms involved in fermentation. Nonetheless, these improvements result in a substantial increase in costs and have certain environmental costs. This review offers an overview of advancements in bioethanol production, with a primary focus on lignocellulosic feedstock, while also considering other feedstocks. Furthermore, it provides insights into the economic, social, and environmental impacts associated with bioethanol production.

Sustainable paramylon production from food waste by Euglena gracilis using a waste-based cell immobilisation technique

Microalga represents a promising platform for numerous valuable bioproducts, but the production cost and efficiency remain major challenges for the industrial implementation. In this study, the production of paramylon (polysaccharides) from microalga Euglena gracilis using food waste hydrolysate and cell immobilisation cultivation was assessed. Synthetic medium supplemented with food waste hydrolysate proved to be a feasible option and achieved the paramylon productivity of 1.46 g/L/day in the heterotrophic (HT) cultivation. In addition, waste-based supporting materials were investigated for cell immobilisation cultivation, and waste sponge demonstrating good cell viability and paramylon productivity with maximum of 2.22 g/L/day was achieved using the synthetic medium in HT condition. However, sugarcane bagasse was not suitable for E. gracilis immobilisation as it induced serious cell lysis and oxidative stress under heterotrophic cultivation. The subsequent utilisation of the hydrolysate-based medium coupled with waste-based cell immobilisation cultivation resulted in the paramylon productivity of 1.77 g/L/day, demonstrating a promising fermentation strategy for sustainable and efficient paramylon production. This study serves as a noteworthy example of producing microalgal metabolites from the food waste hydrolysate using waste-based cell immobilisation technique. Overall, our findings provide valuable insights into green and sustainable production of microalgal biorefineries, and contributes to the advancement of the circular bioeconomy.

Indigo production goes green: a review on opportunities and challenges of fermentative production.

Indigo is a widely used dye in various industries, such as textile, cosmetics, and food. However, traditional methods of indigo extraction and processing are associated with environmental and economic challenges. Fermentative production of indigo using microbial strains has emerged as a promising alternative that offers sustainability and cost-effectiveness. This review article provides a critical overview of microbial diversity, metabolic pathways, fermentation strategies, and genetic engineering approaches for fermentative indigo production. The advantages and limitations of different indigo production systems and a critique of the current understanding of indigo biosynthesis are discussed. Finally, the potential application of indigo in other sectors is also discussed. Overall, fermentative production of indigo offers a sustainable and bio-based alternative to synthetic methods and has the potential to contribute to the development of sustainable and circular biomanufacturing.

Biotechnological lactic acid production from low-cost renewable sources via anaerobic microbial processes.

Lactic acid (LA) production from microbial fermentation using low-cost renewable sources has emerged as an attractive alternative to the use of petroleum-based products. This approach not only offers sustainable solutions for waste management but also enables the production of value-added products in an eco-friendly manner. However, to make this approach economically viable, optimizing the production process for high yield, productivity, and purity while minimizing costs is crucial. To address these challenges, various approaches have been proposed, including the use of neutralizing agents, high cell density cultures, co-cultures, fed-batch fermentation, and product removal strategies. Overall, this review underscores the potential of microbial fermentation for LA production as a sustainable and cost-effective solution to meet the growing demand for eco-friendly products. Further optimization of fermentation processes and the development of new microbial strains and fermentation techniques are key to advancing this approach. The production of LA through microbial fermentation presents a sustainable and eco-friendly solution to the increasing demand for eco-friendly products. With continued innovation, we can expect to see a significant reduction in the environmental impact of industrial processes, coupled with a more cost-effective and high-purity source of lactic acid for various industries.

Enhancing menaquinone-7 biosynthesis through strengthening precursor supply and product secretion.

Menaquinone-7 (MK-7) is an important class of vitamin K2 that is essential in human health and can prevent osteoporosis and cardiovascular disease. However, due to the complex synthesis pathway, the synthesis efficiency is low. The main objective of this study was to explore the effect of enhanced supply of precursors in Bacillus natto. Three precursors of pyruvate, shikimic acid, and sodium glutamate were chosen to investigate the effect of enhanced supply of precursors on MK-7 synthesis. Then, the optimal concentrations, different combinations, and different adding times were systematically studied, respectively. Results showed that the combination of shikimic acid and sodium glutamate could boost MK-7 production by 2 times, reaching 50mg/L of MK-7 titer and 0.52mg/(L·h) of MK-7 productivity. Furthermore, adding shikimic acid and sodium glutamate initially and feeding pyruvate at 48h and 72h increased MK-7 production to 58mg/L. At the same time, the expression of the three related genes was also significantly upregulated. Subsequently, a new fermentation strategy combining the precursors enhancement and product secretion was proposed to enhance MK-7 yield and MK-7 productivity to 63mg/L and 0.45mg/(L·h). This study proposed a new fermentation regulation strategy for the enhancement of vitamin K2 biosynthesis.

Strategies for high cell density cultivation of Akkermansia muciniphila and its potential metabolism.

Currently, there is significant interest in Akkermansia muciniphila as a promising next-generation probiotic, making it a hot topic in scientific research. However, to achieve efficient industrial production, there is an urgent need to develop an in vitro culture method to achieve high biomass using low-cost carbon sources such as glucose. This study aims to explore the high-density fermentation strategy of A. muciniphila by optimizing the culture process. This study also employs techniques such as LC-MS and RNA-Seq to explain the possible regulatory mechanism of high-density cell growth and increased cell surface hydrophobicity facilitating cell colonization of the gut in vitro culture. Overall, this research sheds light on the potential of A. muciniphila as a probiotic and provides valuable insights for future industrial production.

Two wastes into one resource: Carbide slag-driven anaerobic fermentation of excess sludge towards short-chain fatty acids recovery

The anaerobic fermentation has been regarded as promising technology for short-chain fatty acids (SCFAs) recovery from excess sludge. Despite that various treatment approaches have been developed, the sustainable waste utilization of carbide slag in enhancing anaerobic fermentation has rarely been reported. It demonstrated that the carbide slag-derived alkaline condition dominantly contributed to triggering extracellular polymeric substance disruption and microbial cell lysis by protein molecule deconstruction. Considerable sludge hydrolysis was facilitated owing to extracellular and intracellular organic matter release, solubilizing 14.73 % of total solid organic matters in 4-h treatment. Correspondingly, massive SCFAs of 2219.70 mg COD/L (mainly acetate) were produced through 8-day anaerobic fermentation, with the improved acidification and the inhibited methanogenesis. Approximately 83.03–96.21 % of the recoverable SCFAs were extracted after sludge conditioning and solid–liquid separation, providing remarkable economic benefit of 196.23 CNY/ton VSS and carbon-emission reduction of 0.069–0.347 ton CO2/ton VSS. The findings proposed an innovative and sustainable carbide slag-driven anaerobic fermentation strategy for SCFAs recovery and waste stabilization, with low heavy metal residual and negligible environmental risks in “two wastes into one resource” pattern.

Biotechnological production of ectoine: current status and prospects.

Ectoine is an important natural secondary metabolite in halophilic microorganisms. It protects cells against environmental stressors, such as salinity, freezing, drying, and high temperatures. Ectoine is widely used in medical, cosmetic, and other industries. Due to the commercial market demand of ectoine, halophilic microorganisms are the primary method for producing ectoine, which is produced using the industrial fermentation process "bacterial milking." The method has some limitations, such as the high salt concentration fermentation, which is highly corrosive to the equipment, and this also increases the difficulty of downstream purification and causes high production costs. The ectoine synthesis gene cluster has been successfully heterologously expressed in industrial microorganisms, and the yield of ectoine was significantly increased and the cost was reduced. This review aims to summarize and update microbial production of ectoine using different microorganisms, environments, and metabolic engineering and fermentation strategies and provides important reference for the development and application of ectoine.