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Does Osmotic Stress Affect Natural Product Expression in Fungi?

ABSTRACT: The discovery of new natural products from fungi isolated from the marine environment has increased dramatically over the last few decades, leading to the identification of over 1000 new metabolites. However, most of the reported marine-derived species appear to be terrestrial in origin yet at the same time, facultatively halo- or osmotolerant. An unanswered question regarding the apparent chemical productivity of marine-derived fungi is whether the common practice of fermenting strains in seawater contributes to enhanced secondary metabolism? To answer this question, a terrestrial isolate of Aspergillus aculeatus was fermented in osmotic and saline stress conditions in parallel across multiple sites. The ex-type strain of A. aculeatus was obtained from three different culture collections. Site-to-site variations in metabolite expression were observed, suggesting that subculturing of the same strain and subtle variations in experimental protocols can have pronounced effects upon metabolite expression. Replicated experiments at individual sites indicated that secondary metabolite production was divergent between osmotic and saline treatments. Titers of some metabolites increased or decreased in response to increasing osmolite (salt or glycerol) concentrations. Furthermore, in some cases, the expression of some secondary metabolites in relation to osmotic and saline stress was attributed to specific sources of the ex-type strains.

SUBMITTER: Overy D

PROVIDER: S-EPMC5577608 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Does Osmotic Stress Affect Natural Product Expression in Fungi?

Overy David D Correa Hebelin H Roullier Catherine C Chi Wei-Chiung WC Pang Ka-Lai KL Rateb Mostafa M Ebel Rainer R Shang Zhuo Z Capon Rob R Bills Gerald G Kerr Russell R

Marine drugs 20170813 8

The discovery of new natural products from fungi isolated from the marine environment has increased dramatically over the last few decades, leading to the identification of over 1000 new metabolites. However, most of the reported marine-derived species appear to be terrestrial in origin yet at the same time, facultatively halo- or osmotolerant. An unanswered question regarding the apparent chemical productivity of marine-derived fungi is whether the common practice of fermenting strains in seawa ...[more]

PMID: 28805714

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Project description:Contractile injection systems (CISs) are a large group of phage tail-like nanostructures conserved among bacteria. Despite their wide distribution, the biological significance of CISs in bacteria remains largely unclear except for a few unicellular bacteria. Here, we show that Streptomyces lividans-a model organism of filamentous Gram-positive bacteria with highly conserved CIS-related gene clusters-produces intracellular CIS-like nanostructures (Streptomyces phage tail-like particles [SLPs]) that affect phenotypes of this bacterium under hyperosmotic conditions. In contrast to typical CISs released from the cells, SLPs are localized in the cytoplasm of S. lividans. In addition, loss of SLPs leads to (i) delayed erection of aerial mycelia on hyperosmotic solid medium and (ii) decreased growth during the transition from exponential growth phase to stationary phase in hyperosmotic liquid medium. Localization of fluorescent protein-tagged SLPs showed partial correlation with cell wall synthesis-related proteins, including MreB, an actin-like cytoskeleton protein. Our pulldown assay and subsequent quantitative proteome analysis also suggest that 30S ribosomal proteins and cell wall-related proteins, including MreB, are coeluted with SLPs. Furthermore, an interaction assay using the recombinant proteins revealed a direct interaction between a sheath protein of SLP and ribosomal protein S16. Results of cross-linking experiments show indirect interactions between SLPs and translation elongation factors. These findings collectively suggest that SLPs are directly or indirectly associated with a protein interaction network within the cytoplasm of S. lividans and that SLP loss ultimately affects the susceptibility of the bacterium to certain stress conditions. IMPORTANCE Recent bioinformatic analyses have revealed that CIS-related gene clusters are highly conserved in Gram-positive actinomycetes, especially members of the genus Streptomyces known for their ability to produce therapeutic antibiotics. While typical CISs are released from the cells and can act as protein translocation systems that inject effector proteins into the target cells, our results indicate the unique intracellular localization of SLPs, CIS-related nanostructures produced by S. lividans. In addition, the direct and indirect interactions of SLPs with cytoplasmic proteins and SLP localization within specific regions of mycelia suggest that the biological significance of SLPs is related to intracellular processes. Further, SLP loss leads to increased susceptibility of S. lividans to osmotic stress, suggesting that production of these phage tail-like nanostructures ultimately affects the fitness of the bacterium under certain stress conditions. This work will provide new insight into the phage tail-like nanostructures highly conserved in Streptomyces species.

Project description:BackgroundSaccharomyces cerevisiae senses hyperosmotic conditions via the HOG signaling network that activates the stress-activated protein kinase, Hog1, and modulates metabolic fluxes and gene expression to generate appropriate adaptive responses. The integral control mechanism by which Hog1 modulates glycerol production remains uncharacterized. An additional Hog1-independent mechanism retains intracellular glycerol for adaptation. Candida albicans also adapts to hyperosmolarity via a HOG signaling network. However, it remains unknown whether Hog1 exerts integral or proportional control over glycerol production in C. albicans.ResultsWe combined modeling and experimental approaches to study osmotic stress responses in S. cerevisiae and C. albicans. We propose a simple ordinary differential equation (ODE) model that highlights the integral control that Hog1 exerts over glycerol biosynthesis in these species. If integral control arises from a separation of time scales (i.e. rapid HOG activation of glycerol production capacity which decays slowly under hyperosmotic conditions), then the model predicts that glycerol production rates elevate upon adaptation to a first stress and this makes the cell adapts faster to a second hyperosmotic stress. It appears as if the cell is able to remember the stress history that is longer than the timescale of signal transduction. This is termed the long-term stress memory. Our experimental data verify this. Like S. cerevisiae, C. albicans mimimizes glycerol efflux during adaptation to hyperosmolarity. Also, transient activation of intermediate kinases in the HOG pathway results in a short-term memory in the signaling pathway. This determines the amplitude of Hog1 phosphorylation under a periodic sequence of stress and non-stressed intervals. Our model suggests that the long-term memory also affects the way a cell responds to periodic stress conditions. Hence, during osmohomeostasis, short-term memory is dependent upon long-term memory. This is relevant in the context of fungal responses to dynamic and changing environments.ConclusionsOur experiments and modeling have provided an example of identifying integral control that arises from time-scale separation in different processes, which is an important functional module in various contexts.

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Does Osmotic Stress Affect Natural Product Expression in Fungi?

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Does Osmotic Stress Affect Natural Product Expression in Fungi?

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