Enhanced Natamycin production by Streptomyces natalensis in shake-flasks and stirred tank bioreactor under batch and fed-batch conditions

Utilization of carbon catabolite repression for efficiently biotransformation of anthraquinone O-glucuronides by Streptomyces coeruleorubidus DM

Carbon catabolite repression (CCR) is a highly conserved mechanism that regulates carbon source utilization in Streptomyces. CCR has a negative impact on secondary metabolite fermentation, both in industrial and research settings. In this study, CCR was observed in the daunorubicin (DNR)-producing strain Streptomyces coeruleorubidus DM, which was cultivated in high concentration of carbohydrates. Unexpectedly, DM exhibited a high ability for anthraquinone glucuronidation biotransformation under CCR conditions with a maximum bioconversion rate of 95% achieved at pH 6, 30°C for 24 h. The co-utilization of glucose and sucrose resulted in the highest biotransformation rate compared to other carbon source combinations. Three novel anthraquinone glucuronides were obtained, with purpurin-O-glucuronide showing significantly improved water solubility, antioxidant activity, and antibacterial bioactivity. Comparative transcript analysis revealed that glucose and sucrose utilization were significantly upregulated as DM cultivated under CCR condition, which strongly enhance the biosynthetic pathway of the precursors Uridine diphosphate glucuronic acid (UDPGA). Meanwhile, the carbon metabolic flux has significantly enhanced the fatty acid biosynthesis, the exhaust of acetyl coenzyme A may lead to the complete repression of the biosynthesis of DNR, Additionally, the efflux transporter genes were simultaneously downregulated, which may contribute to the anthraquinones intracellular glucuronidation. Overall, our findings demonstrate that utilizing CCR can be a valuable strategy for enhancing the biotransformation efficiency of anthraquinone O-glucuronides by DM. This approach has the potential to improve the bioavailability and therapeutic potential of these compounds, opening up new possibilities for their pharmaceutical applications.

Understanding the Streptomyces albulus response to low-pH stress at the interface of physiology and transcriptomics

Streptomyces albulus is a well-established cell factory for ε-poly-L-lysine (ε-PL) production. It has been reported that ε-PL biosynthesis is strictly regulated by pH and that ε-PL can accumulate at approximately pH 4.0, which is outside of the general pH range for natural product production by Streptomyces species. However, how S. albulus responds to low pH is not clear. In this study, we attempted to explore the response of S. albulus to low-pH stress at the physiological and global gene transcription levels. At the physiological level, S. albulus maintained intracellular pH homeostasis at ~pH 7.5, increased the unsaturated fatty acid ratio, extended the fatty acid chain length, enhanced ATP accumulation, increased H⁺-ATPase activity, and accumulated the basic amino acids L-lysine and L-arginine. At the global gene transcription level, carbohydrate metabolism, oxidative phosphorylation, macromolecule protection and repair, and the acid tolerance system were found to be involved in combating low-pH stress. Finally, we preliminarily evaluated the effect of the acid tolerance system and cell membrane fatty acid synthesis on low-pH tolerance via gene manipulation. This work provides new insight into the adaptation mechanism of Streptomyces to low-pH stress and a new opportunity for constructing robust S. albulus strains for ε-PL production. KEY POINTS: • S. albulus consistently remained pH _i at ~7.4 regardless of the environmental pH. • S. albulus combats low-pH stress by modulating lipid composition of cell membrane. • Overexpression of cfa in S. albulus could improve low-pH tolerance and ɛ-PL titer.

Bioprotective cultures and bacteriocins as food preservatives

Food preservation technologies face the challenge of extending product shelf life applying different factors to prevent the microbiological spoilage of food and inhibit/inactivate food borne pathogens maintaining or even enhancing its quality. One such preservation strategy is the application of bacteriocins or bacteriocin-producer cultures as a kind of food biopreservation. Bacteriocins are ribosomally synthesized small polypeptide molecules that exert antagonistic activity against closely related and unrelated bacteria without harming the producing strain by specific immunity proteins. This chapter aims to contribute to current knowledge about innovative natural preservative agents and their application in the food industry. Specifically, its purpose is to analyze the classification of bacteriocins from lactic acid bacteria (LAB), desirable characteristics of bacteriocins that position them in a privileged place in food biopreservation technology, their success story as well as the bacteriocinogenic LAB in various food systems. Finally, challenges and barrier strategies used to enhance the efficiency of the bacteriocins antimicrobial effect are presented in this chapter.

Double-reporter-guided targeted activation of the oxytetracycline silent gene cluster in Streptomyces rimosus M527

In Streptomyces rimosus M527, the oxytetracycline (OTC) biosynthetic gene cluster is not expressed under laboratory conditions. In this study a reported-guided mutant selection (RGMS) procedure was used to activate the cluster. The double-reporter plasmid pAGT was constructed in which gusA encoding a β-glucuronidase and tsr encoding a thiostrepton resistance methyltransferase were placed under the control of the native promoter of oxyA gene (P_oxyA ). Plasmid pAGT was introduced and integrated into the chromosome of S. rimosus M527 by conjugation, yielding initial strain M527-pAGT. Subsequently, mutants of M527-pAGT were generated by using ribosome engineering technology. The mutants harboring activated OTC gene cluster were selected based on visual observation of GUS activity and thiostrepton resistance. Finally, mutant M527-pAGT-R7 was selected producing OTC in a concentration of 235.2 mg/L. In this mutant transcriptional levels of oxy_sr genes especial oxyA_sr gene were increased compared to wild-type strain S. rimosus M527. The mutant M527-pAGT-R7 showed antagonistic activities against Gram-negative and Gram-positive strains. All data indicate that the OTC gene cluster was successfully activated using the RGMS method.

Multi-Omics Approach in Amelioration of Food Products

Determination of the quality of food products is an essential key factor needed for safe-guarding the quality of food for the interest of the consumers, along with the nutritional and sensory improvements that are necessary for delivering better quality products. Bacteriocins are a group of ribosomally synthesized antimicrobial peptides that help in maintaining the quality of food. The implementation of multi-omics approach has been important for the overall enhancement of the quality of the food. This review uses various recent technologies like proteomics, transcriptomics, and metabolomics for the overall enhancement of the quality of food products. The matrix associated with the food products requires the use of sophisticated technologies that help in the extraction of a large amount of information necessary for the amelioration of the food products. This review would provide a wholesome view of how various recent technologies can be used for improving the quality food products and for enhancing their shelf-life.

Natamycin: a natural preservative for food applications-a review

Natamycin is a natural antimicrobial peptide produced by the strains of Streptomyces natalensis. It effectively acts as an antifungal preservative on various food products like yogurt, khoa, sausages, juices, wines, etc. Additionally, it has been used as a bio preservative and is listed as generally recognized as a safe ingredient for various food applications. In this review, natamycin properties, production methods, toxicity, and application as a natural preservative in different foods are emphasized. This review also focuses on optimal condition and process control required in natamycin production. The mode of action and inhibitory effect of natamycin on yeast and molds inhibition and its formulation and dosage to preserve various food products, coating, and hurdle applications are summarized. Understanding the scientific factors in natamycin's production process, its toxicity, and its efficiency as a preservative will open its practical application in various food products.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00981-1.

Improvement of tacrolimus production in Streptomyces tsukubaensis by mutagenesis and optimization of fermentation medium using Plackett-Burman design combined with response surface methodology

OBJECTIVE

This study was conducted to enhance the production of tacrolimus in Streptomyces tsukubaensis by strain mutagenesis and optimization of the fermentation medium.

RESULTS

A high tacrolimus producing strain S. tsukubaensis FIM-16-06 was obtained by ultraviolet mutagenesis coupled with atmospheric and room temperature plasma mutagenesis.Then, nine variables were screened using Plackett-Burman experimental design, in which soluble starch, peptone and Tween 80 showed significantly affected tacrolimus production. Further studies were carried out employing central composite design to elucidate the mutual interaction between the variables and to work out optimal fermentation medium composition for tacrolimus production. The optimum fermentation medium was found to contain 61.61 g/L of soluble starch, 20.61 g/L of peptone and 30.79 g/L of Tween 80. In the optimized medium, the production of tacrolimus reached 1293 mg/L in shake-flask culture, and reached 1522 mg/L while the scaled-up fermentation was conducted in a 1000 L fermenter, which was about 3.7 times higher than that in the original medium.

CONCLUSIONS

Combining compound mutation with rational medium optimization is an effective approach for improving tacrolimus production, and the optimized fermentation medium could be efficiently used for industrial production.

Recent developments on solid-state fermentation for production of microbial secondary metabolites: Challenges and solutions

Microbial secondary metabolites (SMs) are the intermediate or the product of metabolism produced during fermentation process. SMs are produced during stationary phase and play a major role in competition, antagonism and self defence mechanisms. These metabolites finds application in the pharmaceuticals, food, cosmetics etc. These are produced besides primary key metabolites (e.g., amino acids, lipids, carbohydrates etc.). Growth condition in solid-state fermentation (SSF) resembles microorganism's own native environment allowing the microorganisms to adapt best. Recent developments in bioprocessing has identified specific SSF practices that have a significant impact on SMs production. The practice of SSF, representing new opportunities to design better bioprocessing with potential genetic development goals for expanding the list of exciting SMs. Current updates cover advanced techniques on SSF to improve microbial SMs production and their ease of operation and cost-effective production strategies. Various factors affecting the SSF have been discussed with respect to sustainable development of novel SSF strategies for SMs production.

Application of bacteriocins in food preservation and infectious disease treatment for humans and livestock: a review

Infectious diseases caused by bacteria that can be transmitted via food, livestock and humans are always a concern to the public, as majority of them may cause severe illnesses and death. Antibacterial agents have been investigated for the treatment of bacterial infections. Antibiotics are the most successful antibacterial agents that have been used widely for decades to ease human pain caused by bacterial infections. Nevertheless, the emergence of antibiotic-resistant bacteria has raised awareness amongst public about the downside of using antibiotics. The threat of antibiotic resistance to global health, food security and development has been emphasized by the World Health Organization (WHO), and research studies have been focused on alternative antimicrobial agents. Bacteriocin, a natural antimicrobial peptide, has been chosen to replace antibiotics for its application in food preservation and infectious disease treatment for livestock and humans, as it is less toxic.

Killing or inhibition actions of (a) antibiotics and (b) bacteriocin on gut microbiota.

Medium Optimization by Response Surface Methodology for Improved Cholesterol Oxidase Production by a Newly Isolated Streptomyces rochei NAM-19 Strain

Cholesterol oxidase is an alcohol oxidoreductase flavoprotein with wide biotechnological applications. The current work describes the isolation of a potential cholesterol oxidase producing streptomycete from Egyptian soil. The isolated strain produced cholesterol oxidase in submerged culture using a medium containing glucose, yeast extract, malt extract, and CaCO₃ with the addition of cholesterol as an inducer. The isolated strain was identified as Streptomyces rochei NAM-19 based on 16S rRNA sequencing and phylogeny. Optimization of cholesterol oxidase production has been carried out using response surface methodology. The Plackett-Burman design method was used to evaluate the significant components of the production medium followed by Box-Behnken experimental design to locate the true optimal concentrations, which are significantly affecting enzyme production. Results showed that the predicted enzyme response could be closely correlated with the experimentally obtained production. Furthermore, the applied optimization strategy increased volumetric enzyme production by 2.55 times (65.1 U/mL) the initial production obtained before medium optimization (25.5 U/mL).

Characterization of the Metabolic Response of Streptomyces clavuligerus to Shear Stress in Stirred Tanks and Single-Use 2D Rocking Motion Bioreactors for Clavulanic Acid Production

Streptomyces clavuligerus is a gram-positive filamentous bacterium notable for producing clavulanic acid (CA), an inhibitor of β-lactamase enzymes, which confers resistance to bacteria against several antibiotics. Here we present a comparative analysis of the morphological and metabolic response of S. clavuligerus linked to the CA production under low and high shear stress conditions in a 2D rocking-motion single-use bioreactor (CELL-tainer ^®) and stirred tank bioreactor (STR), respectively. The CELL-tainer^® guarantees high turbulence and enhanced volumetric mass transfer at low shear stress, which (in contrast to bubble columns) allows the investigation of the impact of shear stress without oxygen limitation. The results indicate that high shear forces do not compromise the viability of S. clavuligerus cells; even higher specific growth rate, biomass, and specific CA production rate were observed in the STR. Under low shear forces in the CELL-tainer^® the mycelial diameter increased considerably (average diameter 2.27 in CELL-tainer^® vs. 1.44 µm in STR). This suggests that CA production may be affected by a lower surface-to-volume ratio which would lead to lower diffusion and transport of nutrients, oxygen, and product. The present study shows that there is a strong correlation between macromorphology and CA production, which should be an important aspect to consider in industrial production of CA.