Sporulation of Aspergillus niger and Aspergillus ochraceus in Continuous Submerged Liquid Culture

Broderick, A. J.; Greenshields, R. N.

doi:10.1099/00221287-126-1-193

Cited by 15 publications

(17 citation statements)

References 25 publications

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“…This is opposite to truly starved cultures, which would rely purely on mobilized endogenous nutrients. Other investigations (15,56,65) have shown that the maximal extent of submerged sporulation in carbon-limited cultures of Aspergillus and Penicillium is achieved with a low external supply of the carbon source. In this study we have shown that net growth in the retentostat cultures was accounted for by small melanized particles from days 4 to 7, which suggests that the cultures were fully committed to conidiospore formation in this period.…”

Section: Discussionmentioning

confidence: 96%

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confidence: 99%

“…During subaerial growth, A. niger produces chains of black spores from biseriate conidiophores (55), but like other molds (15,16,56,62) it also conidiates in submerged culture in response to severe nitrogen or carbon limitation (15,27,46). More recent molecular studies have shown that the transcription factor BrlA plays a central role as a positive regulator of conidiation in liquid as well as aerial environments (1,2,25,40,67,74) and that nutrient starvation is associated with induction of brlA transcription (62).…”

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Transcriptomic Insights into the Physiology of Aspergillus niger Approaching a Specific Growth Rate of Zero

Jørgensen

Nitsche

Lamers

et al. 2010

Appl Environ Microbiol

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The physiology of filamentous fungi at growth rates approaching zero has been subject to limited study and exploitation. With the aim of uncoupling product formation from growth, we have revisited and improved the retentostat cultivation method for Aspergillus niger. A new retention device was designed allowing reliable and nearly complete cell retention even at high flow rates. Transcriptomic analysis was used to explore the potential for product formation at very low specific growth rates. The carbon-and energy-limited retentostat cultures were highly reproducible. While the specific growth rate approached zero (<0.005 h ؊1 ), the growth yield stabilized at a minimum (0.20 g of dry weight per g of maltose). The severe limitation led to asexual differentiation, and the supplied substrate was used for spore formation and secondary metabolism. Three physiologically distinct phases of the retentostat cultures were subjected to genome-wide transcriptomic analysis. The severe substrate limitation and sporulation were clearly reflected in the transcriptome. The transition from vegetative to reproductive growth was characterized by downregulation of genes encoding secreted substrate hydrolases and cell cycle genes and upregulation of many genes encoding secreted small cysteine-rich proteins and secondary metabolism genes. Transcription of known secretory pathway genes suggests that A. niger becomes adapted to secretion of small cysteine-rich proteins. The perspective is that A. niger cultures as they approach a zero growth rate can be used as a cell factory for production of secondary metabolites and cysteine-rich proteins. We propose that the improved retentostat method can be used in fundamental studies of differentiation and is applicable to filamentous fungi in general.The filamentous fungus Aspergillus niger is one of the most important microorganisms in industrial biotechnology because of its ability to produce high levels of enzymes and organic acids (6,50,57). Apart from their biotechnological importance, filamentous fungi in the Aspergillus section Nigri (the black aspergilli) represent some of the most widespread storage molds which contaminate food and feedstocks with mycotoxins (26,37,48).Both metabolic engineering approaches and the search for optimal cultivation conditions have long been used to improve A. niger as a production host (e.g., 14, 22, 41). With the availability of the A. niger genome sequence (50), systems biology tools are being developed (4, 5, 33) which, together with new efficient methods for constructing gene knockout mutants (43), open new possibilities for further improvement of A. niger as a cell factory.A major ongoing challenge for microbial production processes is to minimize the amount of biomass formed while maintaining high productivity. Solutions to uncouple product formation from biomass accumulation or growth are therefore highly desirable. However, production at zero growth is difficult to achieve when nutrients are supplied to allow formation of a desired product. Carbon-a...

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Section: Discussionmentioning

confidence: 96%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Transcriptomic Insights into the Physiology of Aspergillus niger Approaching a Specific Growth Rate of Zero

Jørgensen

Nitsche

Lamers

et al. 2010

Appl Environ Microbiol

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“…The four A. niger strains N402, MA93.1, JP5.1, and MA146.1 were propagated on solidified CM to produce a conidial inoculum for submerged cultivation. The CM agar plates contained (per liter) 10.0 g glucose, 6.0 g NaNO 3 [43]). The pH of the medium was adjusted to 5.8 with NaOH prior to autoclaving.…”

Section: Strainsmentioning

confidence: 99%

“…A low growth rate is a common consequence of substrate-limited growth during prolonged fed-batch cultivation and poor mixing in large volumes of dense culture broth. Severe limitation of nutrients and low specific growth rates () trigger submerged conidiation and secondary metabolism in both fed and starved cultures of aspergilli (6,8,37,40). Retentostat cultures are continuous cultures with cell retention, which, instead of maintaining a fixed specific growth rate, forces into a transient decline to approach zero.…”

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confidence: 99%

Submerged Conidiation and Product Formation by Aspergillus niger at Low Specific Growth Rates Are Affected in Aerial Developmental Mutants

Jørgensen

Nielsen

Arentshorst

et al. 2011

Appl Environ Microbiol

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Exposure to an aerial environment or severe nutrient limitation induces asexual differentiation in filamentous fungi. Submerged cultivation of Aspergillus niger in carbon-and energy-limited retentostat cultures both induces and fuels conidiation. Physiological and transcriptomic analyses have revealed that this differentiation strongly affects product formation. Since conidiation is inherent in the aerial environment, we hypothesized that product formation near zero growth can be influenced by affecting differentiation or development of aerial hyphae in general. To investigate this idea, three developmental mutants (⌬fwnA, scl-1, and scl-2 mutants) that have no apparent vegetative growth defects were cultured in maltose-limited retentostat cultures. The secondary-metabolite profile of the wild-type strain defined flavasperone, aurasperone B, tensidol B, and two so far uncharacterized compounds as associated with conidium formation, while fumonisins B 2 , B 4 , and B 6 were characteristic of early response to nutrient limitation by the vegetative mycelium. The developmental mutants responded differently to the severe substrate limitation, which resulted in distinct profiles of growth and product formation. fwnA encodes the polyketide synthase responsible for melanin biosynthesis during aerial differentiation, and we show that conidial melanin synthesis in submerged retentostat cultures and aurasperone B production are fwnA dependent. The scl-1 and scl-2 strains are two UV mutants generated in the ⌬fwnA background that displayed reduced asexual conidiation and formed sclerotium-like structures on agar plates. The reduced conidiation phenotypes of the scl-1 and scl-2 strains are reflected in the retentostat cultivation and are accompanied by elimination or severely reduced accumulation of secondary metabolites and distinctly enhanced accumulation of extracellular protein. This investigation shows that submerged conidiation and product formation of a mitosporic fungus cultured at low specific growth rates can be fundamentally affected by interfering with the genetic program for differentiation of aerial hyphae, opening new perspectives for tailoring industrial performance.The black-spored ascomycete Aspergillus niger is a ubiquitous saprophyte in nature and occurs as a common spoilage mold on stored food and feed (15,26,30). Its successful occupation of these ecological niches results at least partially from an ability to secrete a wide array of substrate-degrading enzymes, which, like organic acid biosynthesis, is exploited in industrial production (32, 34). Also contributing to its economic importance are less desirable traits, such as conditional production of toxic secondary metabolites or mycotoxins, like ochratoxin A and fumonisins (30,36). Secondary-metabolite accumulation in the genus Aspergillus and its relatives is most diverse and abundant under subaerial growth conditions on solid media that allow differentiation or development of vegetative hyphae into conidia, sclerotia, or cleistothecia (2, 45).Despit...

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Peppermint Essential Oil and Its Major Volatiles as Protective Agents against Soft Rot Caused by Fusarium sambucinum in Cera Pepper (Capsicum pubescens)

Pérez-Vázquez

Hernández

Lozoya‐Gloria

et al. 2021

Chemistry & Biodiversity

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Cera pepper (Capsicum pubescens) is an exotic fruit considered as a rich source of nutraceuticals with known benefits for human health and also an economic resource for local producers in Mexico. The present investigation reports on the in vitro and in situ antifungal activity of the essential oil from Mentha piperita and its two major volatiles (menthol and menthone) against Fusarium sambucinum, which is a causal agent of soft rot in cera pepper. The application of these components in pepper fruits previously infected with F. sambucinum caused a significant delay (p < 0.05) in the emergence of soft rot symptoms. This effect was reflected in the maintenance of pH and fruit firmness during a period of 10 days. The nutrimental content of the fruits (protein, fiber, fat and other proximate parameters) was conserved in the same period of time. The nutraceutical content of these fruits was estimated by the quantification of seven carotenoids (violaxanthin, cis-violaxanthin, luteoxanthin, antheraxanthin, lutein, zeaxanthin and β-carotene), ascorbic acid and capsaicinoids (capsaicin and dihydrocapsaicin). According to our results, the essential oil from M. Piperita and its major volatiles exerted a preservative effect on these metabolites. Our findings demonstrated that the essential oil of M. Piperita and its major volatiles represent an ecological alternative for the control of fusariosis caused by F. sambucinum in cera peppers under postharvest conditions.

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Sporulation of Aspergillus niger and Aspergillus ochraceus in Continuous Submerged Liquid Culture

Cited by 15 publications

References 25 publications

Transcriptomic Insights into the Physiology of Aspergillus niger Approaching a Specific Growth Rate of Zero

Transcriptomic Insights into the Physiology of Aspergillus niger Approaching a Specific Growth Rate of Zero

Submerged Conidiation and Product Formation by Aspergillus niger at Low Specific Growth Rates Are Affected in Aerial Developmental Mutants

Peppermint Essential Oil and Its Major Volatiles as Protective Agents against Soft Rot Caused by Fusarium sambucinum in Cera Pepper (Capsicum pubescens)

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