Enhancing nemadectin production by Streptomyces cyaneogriseus ssp. noncyanogenus through quantitative evaluation and optimization of dissolved oxygen and shear force

Characteristic analysis and fermentation optimization of a novel Aureobasidium pullulans RM1603 with high pullulan yield

A high-yielding microbial polysaccharide-producing strain, named RM1603, was isolated from rhizosphere soil and identified by morphological and phylogenetic analysis. The extracellular polysaccharides (EPS) were identified by thin-layer chromatography and infrared spectroscopy. The fermentation conditions were optimized by single factor experiments in shake flasks and a 5-L fermentor. The results of morphological and phylogenetic tree analysis showed that RM1603 was a strain of Aureobasidium pullulans. Its microbial polysaccharide was identified as pullulan, and the EPS production capacity reached 33.07 ± 1.03 g L-1 in shake flasks. The fermentation conditions were optimized in a 5-L fermentor, and were found to encompass an initial pH of 6.5, aeration rate of 2 vvm, rotor speed of 600 rpm, and inoculum size of 2 %. Under these conditions, the pullulan yield of RM1603 reached 62.52 ± 0.24 g L-1. Thus, this study contributes RM1603 as a new isolation with high-yielding pullulan and potential application value in biotechnology.

Quantification and modeling of macroparticle-induced mechanical stress for varying shake flask cultivation conditions

In biotechnological processes, filamentous microorganisms are known for their broad product spectrum and complex cellular morphology. Product formation and cellular morphology are often closely linked, requiring a well-defined level of mechanical stress to achieve high product concentrations. Macroparticles were added to shake flask cultures of the filamentous actinomycete Lentzea aerocolonigenes to find these optimal cultivation conditions. However, there is currently no model concept for the dependence of the strength and frequency of the bead-induced stress on the process parameters. Therefore, shake flask simulations were performed for combinations of bead size, bead concentration, bead density and shaking frequency. Contact analysis showed that the highest shear stresses were caused by bead-bottom contacts. Based on this, a newly generated characteristic parameter, the stress area ratio (SAR), was defined, which relates the bead wall shear and normal stresses to the total shear area. Comparison of the SAR with previous cultivation results revealed an optimum pattern for product concentration and mean product-to-biomass related yield coefficient. Thus, this model is a suitable tool for future optimization, comparison and scaling up of shear-sensitive microorganism cultivation. Finally, the simulation results were validated using high-speed recordings of the bead motion on the bottom of the shake flask.

Genome-guided approaches and evaluation of the strategies to influence bioprocessing assisted morphological engineering of Streptomyces cell factories

Streptomyces genera serve as adaptable cell factories for secondary metabolites with various and distinctive chemical structures that are relevant to the pharmaceutical industry. Streptomyces' complex life cycle necessitated a variety of tactics to enhance metabolite production. Identification of metabolic pathways, secondary metabolite clusters, and their controls have all been accomplished using genomic methods. Besides this, bioprocess parameters were also optimized for the regulation of morphology. Kinase families were identified as key checkpoints in the metabolic manipulation (DivIVA, Scy, FilP, matAB, and AfsK) and morphology engineering of Streptomyces. This review illustrates the role of different physiological variables during fermentation in the bioeconomy coupled with genome-based molecular characterization of biomolecules responsible for secondary metabolite production at different developmental stages of the Streptomyces life cycle.

Efficient biosynthesis of exopolysaccharide in Candida glabrata by a fed-batch culture

Polysaccharides are important natural biomacromolecules. In particular, microbial exopolysaccharides have received much attention. They are produced by a variety of microorganisms, and they are widely used in the food, pharmaceutical, and chemical industries. The Candida glabrata mutant 4-C10, which has the capacity to produce exopolysaccharide, was previously obtained by random mutagenesis. In this study we aimed to further enhance exopolysaccharide production by systemic fermentation optimization. By single factor optimization and orthogonal design optimization in shaking flasks, an optimal fermentation medium composition was obtained. By optimizing agitation speed, aeration rate, and fed-batch fermentation mode, 118.6 g L⁻¹ of exopolysaccharide was obtained by a constant rate feeding fermentation mode, with a glucose yield of 0.62 g g⁻¹ and a productivity of 1.24 g L⁻¹ h⁻¹. Scaling up the established fermentation mode to a 15-L fermenter led to an exopolysaccharide yield of 113.8 g L⁻¹, with a glucose yield of 0.60 g g⁻¹ and a productivity of 1.29 g L⁻¹ h⁻¹.

Application of autothermal thermophilic aerobic digestion as a sustainable recycling process of organic liquid waste: Recent advances and prospects

Autothermal thermophilic aerobic digestion (ATAD) has been used to stabilize organic waste since the 1960s and is considered sustainable technology. ATAD has several advantages, including high biodegradation efficiency, pathogen inactivation, and ease of operation. Although ATAD research has a long history, the number of studies on ATAD is much lower than those on similar aerobic processes, particularly composting. Previous review articles addressed the origin, design, operational experiences, metabolism, and the microorganisms at the thermophilic stage of ATAD. This article reviews the digestion systems, applications, and characteristics of ATAD; compares system performance and microbial community structure of ATAD with those of other biological processes such as composting, activated sludge, and anaerobic digestion; and discusses the physicochemical properties and factors of ATAD. The challenges, opportunities, and prospects for the application of ATAD are also discussed. This review suggests that ATAD is feasible for treating organic liquid waste (1-6% total solid content) in small-sized towns and can help establish a sustainable society.

Streptomyces derivatives as an insecticide: Current perspectives, challenges and future research needs for mosquito control

The pervasiveness of arboviruses in wreaking havoc on public health has lingered on international health agendas. A scarcity of mosquito-borne disease vaccines and therapies demands prompt attention, as billions of people worldwide are at risk of infections. It is widely known that vector control continues, and in some diseases, remains the only resort in suppressing disease transmissions we presently possess at its disposal. But the use of commercial insecticides is being crippled by the widespread insecticide resistance, which greatly menaces their efficacies, toxicological repercussions such as environmental pollution and human health risk. Rather, an environmentally benign technique of employing Streptomyces isolates from settings such as terrestrial soils, marine sediments, and mangrove soils for Culicidae management has recently received a lot of positive attention. Streptomyces' capacities to produce a wide range of bioactive secondary metabolites that contribute to pharmaceutical, agricultural and veterinarian, Streptomyces-derived bioactive compounds are increasingly being considered for use in vector control. Herein, we compiled all of the available datasets on the effectiveness of Streptomyces-derived compounds against major mosquito vectors of medical importance. Aedes, Anopheles, and Culex are used to assess the toxicity of crude extracts or fractions. This paper reviewed the promising ovicidal, larvicidal, and pupacidal effects of different Streptomyces strains. Notably, no research into the adulticidal effect of Streptomyces-derived compounds has yet been done. Aside from the genetic makeup, the production of secondary metabolites from Streptomyces depends on the growing conditions. And that, to optimise the maximum yield of highly potent bioactive compounds being extracted, solvents' choice is of paramount importance. Thus, both cultivation parameters and the choice of organic solvents for secondary metabolites extraction will be discussed. Furthermore, biases derived from different studies have implied the need for standardizing experimental procedures. While entomological data should be collected consistently across all studies to expedite evidence-based policymaking of bioinsecticides, the quality of data from vector control interventions - particularly the experimental design, execution, analysis, and presentation of results of vector control studies - will be thoroughly reviewed. Lastly, to promote consistency and reliability, these knowledge gaps are identified, along with a discussion of current perspectives on vector control, global bioinsecticide trends, challenges on commercializing bioinsecticides and future research needs.

Effect of Agitation and Aeration on Keratinase Production in Bioreactors Using Bioprocess Engineering Aspects

Streptomyces sp. 2M21 was evaluated for keratinase production in bioreactors using chicken feathers. Firstly, optimization of bioengineering parameters (agitation and aeration rates) using Response Surface Methodology was carried out in 2 L bioreactors. Optimized conditions identified by the modified quadratic model were verified as 150 rpm and 1 vvm experimentally corresponding to 351 U/ml of keratinase activity. Moreover, scaling up sequentially to 20 L bioreactors was implemented using constant impeller tip speed and constant mass transfer coefficient as key scale-up parameters. The keratinase activity in 5, 10 and 20 L bioreactors showed similar results with the one of shake flasks (412 U/ml) and 2 L bioreactors (351 U/ml)with respect to the keratinase activity values of 336, 385 and 344 U/ml, respectively. The results suggest keratinase production by evaluating chicken feathers in commercial level. Furthermore, this study has potential to contribute industrial scale production of keratinase by Streptomyces sp. 2M21 using the proposed bioreactor conditions.

Streptomycetes as platform for biotechnological production processes of drugs

Streptomyces is one of the most versatile genera for biotechnological applications, widely employed as platform in the production of drugs. Although streptomycetes have a complex life cycle and metabolism that would need multidisciplinary approaches, review papers have generally reported only studies on single aspects like the isolation of new strains and metabolites, morphology investigations, and genetic or metabolic studies. Besides, even if streptomycetes are extensively used in industry, very few review papers have focused their attention on the technical aspects of biotechnological processes of drug production and bioconversion and on the key parameters that have to be set up. This mini-review extensively illustrates the most innovative developments and progresses in biotechnological production and bioconversion processes of antibiotics, immunosuppressant, anticancer, steroidal drugs, and anthelmintic agents by streptomycetes, focusing on the process development aspects, describing the different approaches and technologies used in order to improve the production yields. The influence of nutrients and oxygen on streptomycetes metabolism, new fed-batch fermentation strategies, innovative precursor supplementation approaches, and specific bioreactor design as well as biotechnological strategies coupled with metabolic engineering and genetic tools for strain improvement is described. The use of whole, free, and immobilized cells on unusual supports was also reported for bioconversion processes of drugs. The most outstanding thirty investigations published in the last 8 years are here reported while future trends and perspectives of biotechnological research in the field have been illustrated. KEY POINTS: • Updated Streptomyces biotechnological processes for drug production are reported. • Innovative approaches for Streptomyces-based biotransformation of drugs are reviewed. • News about fermentation and genome systems to enhance secondary metabolite production.

Fermentation Titer Optimization and Impact on Energy and Water Consumption during Downstream Processing

A common focus of fermentation process optimization is the product titer. Different strategies to boost fermentation titer target whole-cell biocatalyst selection, process control, and medium composition. Working at higher product concentrations reduces the water that needs to be removed in the case of aqueous systems and, therefore, lowers the cost of downstream separation and purification. Different approaches to achieve higher titer in fermentation are examined. Energy and water consumption data collected from different Cargill fermentation plants, i.e., ethanol, lactic acid, and 2-keto-L-gulonic acid, confirm that improvements in fermentation titer play a decisive role in downstream economics and environmental footprint.