Salt‐enhanced cultivation as a morphology engineering tool for filamentous actinomycetes: Increased production of labyrinthopeptin A1 in Actinomadura namibiensis

Abstract

Salt‐enhanced cultivation as a morphology engineering tool for the filamentous actinomycete Actinomadura namibiensis was evaluated in 500‐mL shaking flasks (working volume 100 mL) with the aim of increasing the concentration of the pharmaceutically interesting peptide labyrinthopeptin A1. Among the inorganic salts added to a complex production medium, the addition of (NH4)2SO4 led to the highest amount of labyrinthopeptin A1 production. By using 50 mM (NH4)2SO4, the labyrinthopeptin A1 concentration increased up to sevenfold compared to the non‐supplemented control, resulting in 325 mg L−1 labyrinthopeptin A1 after 10 days of cultivation. The performance of other ammonium‐ and sulfate‐containing salts (e.g., NH4Cl, K2SO4) was much lower than the performance of (NH4)2SO4. A positive correlation between the uptake of glycerol as one of the main carbon sources and nongrowth‐associated labyrinthopeptin productivity was found. The change in the cell morphology of A. namibiensis in conjunction with increased osmolality by the addition of 50 mM (NH4)2SO4, was quantified by image analysis. A. namibiensis always developed a heterogeneous morphology with pellets and loose mycelia present simultaneously. In contrast to the non‐supplemented control, the morphology of (NH4)2SO4‐supplemented cultures was characterized by smaller and circular pellets that were more stable against disintegration in the stationary production phase.

Challenges of influencing cellular morphology by morphology engineering techniques and mechanical induced stress on filamentous pellet systems—A critical review

“…These challenges are accepted because many filamentous bacteria and fungi produce substances that are interesting for food or pharmaceutical industry [34]. The bacterial filamentous Actinomycetes, including Actinomadura namibiensis and Lentzea aerocolonigenes , are of special interest, because of the production of mainly pharmaceutically relevant secondary metabolites such as labyrinthopeptin and rebeccamycin, respectively [6,8,35]. In 2000, 60% of the known biologically active secondary metabolites were isolated from Actinomycetes [35].…”

“…The production of citric acid [17,50], glucose oxidase [44], glucoamylase [29], and polygalacturonidase [51] is favoured in pellet growth by Aspergillus niger . Compared to mycelium cultures, pellet morphologies have also been used to achieve higher productivity in the production of nikkomycin by Streptomyces tendae [52], avermectin by Streptomyces avermitilis [53], rebeccamycin by Lentzea (formerly Lechevalieria ) aerocolonigenes [7,19,54,55], and the new peptide antibiotic labyrinthopeptin A1 by Actinomadura namibiensis [8]. For these reasons, a large number of studies focus exclusively on pellet‐like cultivations and the interaction between mechanically induced morphological changes and product formation.…”

“…In addition to the techniques of microparticle‐ and macroparticle‐enhanced cultivation, the manipulation of osmolality by adding inorganic salts to the cultivation broth was found to be another method to adapt the cell morphology [66]. In analogy to MPEC this tool of morphology engineering was refered to as salt‐enhanced cultivation [8,92]. Compared to an unsupplemented cultivation the increase in osmolality or osmolarity through the addition of salt leads to significantly higher productivity in some filamentous microorganisms such as A. niger for the production of fructofuranosidase or glucoamylase and Actinomadura namibiensis for the production of labyrinthopeptin [8,66].…”

“…In analogy to MPEC this tool of morphology engineering was refered to as salt‐enhanced cultivation [8,92]. Compared to an unsupplemented cultivation the increase in osmolality or osmolarity through the addition of salt leads to significantly higher productivity in some filamentous microorganisms such as A. niger for the production of fructofuranosidase or glucoamylase and Actinomadura namibiensis for the production of labyrinthopeptin [8,66]. The pellet size is reduced while the pellet porosity is increased and a stronger mycelial growth occurred which caused this productivity increase.…”

“…Filamentous microorganisms are in the focus of many industrial biotechnological processes for the production of organic acids, enzymes, and pharmaceutical agents such as antibiotics, and are often cultivated as disperse mycelia or pellets in shaken and stirred tank bioreactors [1–5]. Beside filamentous growing eukaryotic fungi like from the family of Aspergilli , also bacterial filamentous microorganisms, actinomycetes, especially Streptomyces species, are of great pharmaceutical interest due to their production of various secondary metabolites [6–8].…”