Streptomyces polyketides mediate bacteria–fungi interactions across soil environments

Although the interaction between prokaryotic and eukaryotic microorganisms is crucial for the functioning of ecosystems, information about the processes driving microbial interactions within communities remains scarce. Here we show that arginine-derived polyketides (arginoketides) produced by Streptomyces species mediate cross-kingdom microbial interactions with fungi of the genera Aspergillus and Penicillium, and trigger the production of natural products. Arginoketides can be cyclic or linear, and a prominent example is azalomycin F produced by Streptomyces iranensis, which induces the cryptic orsellinic acid gene cluster in Aspergillus nidulans. Bacteria that synthesize arginoketides and fungi that decode and respond to this signal were co-isolated from the same soil sample. Genome analyses and a literature search indicate that arginoketide producers are found worldwide. Because, in addition to their direct impact, arginoketides induce a secondary wave of fungal natural products, they probably contribute to the wider structure and functioning of entire soil microbial communities

Lichen-like association of Chlamydomonas reinhardtii and Aspergillus nidulans protects algal cells from bacteria

Organismal interactions within microbial consortia and their responses to harmful intruders remain largely understudied. An important step toward the goal of understanding functional ecological interactions and their evolutionary selection is the study of increasingly complex microbial interaction systems. Here, we discovered a tripartite biosystem consisting of the fungus Aspergillus nidulans , the unicellular green alga Chlamydomonas reinhardtii , and the algicidal bacterium Streptomyces iranensis . Genetic analyses and MALDI-IMS demonstrate that the bacterium secretes the algicidal compound azalomycin F upon contact with C. reinhardtii . In co-culture, A. nidulans attracts the motile alga C. reinhardtii , which becomes embedded and surrounded by fungal mycelium and is shielded from the algicide. The filamentous fungus Sordaria macrospora was susceptible to azalomycin F and failed to protect C. reinhardtii despite chemotactically attracting the alga. Because S. macrospora was susceptible to azalomycin F, this data imply that for protection the fungus needs to be resistant. Formation of the lichen-like association between C. reinhardtii and A. nidulans increased algal growth. The protection depends on the increased amounts of membrane lipids provided by resistant fungi, thereby generating a protective shelter against the bacterial toxin. Our findings reveal a strategy whereby algae survive lethal environmental algicides through cooperation with fungi

Achlya mitochondrial DNA: gene localization and analysis of inverted repeats

Mitochondrial DNA from four strains of the oomycete Achlya has been compared and nine gene loci mapped, including that of the ribosomal protein gene, var1 . Examination of the restriction enzyme site maps showed the presence of four insertions relative to a map common to all four strains. All the insertions were found in close proximity to genic regions. The four strains also cotained the inverted repeat first observed in A. ambisexualis (Hudspeth et al. 1983), allowing an examination by analysis of retained restriction sites of the evolutionary stability of repeated DNA sequences relative to single copy sequences. Although the inverted repeat is significantly more stable than single copy sequences, more detailed analysis indicated that this stability is limited to the portion encoding the ribosomal RNA genes. Thus, the apparent evolutionary stability of the repeat does not appear to derive from the inverted repeat structure per se.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47563/1/438_2004_Article_BF00330510.pd

Characterization of fracture processes by continuum and discrete modelling

A large number of methods to describe fracture mechanical features of structures on basis of computational algorithms have been developed in the past due to the importance of the topic. In this paper, current and promising numerical approaches for the characterization of fracture processes are presented. A fracture phenomenon can either be depicted by a continuum formulation or a discrete notch. Thus, starting point of the description is a micromechanically motivated formulation for the development of a local failure situation. A current, generalized method without any restriction to material modelling and loading situation in order to describe an existing crack in a structure is available through the material force approach. One possible strategy to simulate arbitrary crack growth is based on an adaptive implementation of cohesive elements in combination with the standard discretization of the body. In this case, crack growth criteria and the determination of the crack propagation direction in combination with the modification of the finite element mesh are required. The nonlinear structural behaviour of a fibre reinforced composite material is based on the heterogeneous microstructure. A two-scale simulation is therefore an appropriate and effective way to take into account the scale differences of macroscopic structures with microscopic elements. In addition, fracture mechanical structural properties are far from being sharp and deterministic. Moreover, a wide range of uncertainties influence the ultimate load bearing behaviour. Therefore, it is evident that the deterministic modelling has to be expanded by a characterization of the uncertainty in order to achieve a reliable and realistic simulation result. The employed methods are illustrated by numerical examples

Novel roles for GAPDH in cell death and carcinogenesis

Publicado en línea el 25 de septiembre de 2009Growing evidence points to the fact that glucose metabolism has a central role in carcinogenesis. Among the enzymes controlling this energy production pathway, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is of particular interest. Initially identified as a glycolytic enzyme and considered as a housekeeping gene, this enzyme is actually tightly regulated and is involved in numerous cellular functions. Particularly intriguing are recent reports describing GAPDH as a regulator of cell death. However, its role in cell death is unclear; whereas some studies point toward a proapoptotic function, others describe a protective role and suggest its participation in tumor progression. In this study, we highlight recent findings and discuss potential mechanisms through which cells regulate GAPDH to fulfill its diverse functions to influence cell fate.This work was supported in part by l’Association pour la Recherche sur le Cancer, by l’Agence Nationnal de la Recherche, la Fondation de France, Plan Nacional I+D SAF2008-04974 and by grants from The U.S. National Institutes of Health. J-E.R. is a recipient of a contrat d’interface INSERM-CHU de Nice.Peer reviewe

Ubiquitous bacterial polyketides induce cross-kingdom microbial interactions

AbstractAlthough the interaction of prokaryotic and eukaryotic microorganisms is critical for the functioning of ecosystems, knowledge of the processes driving microbial interactions within communities is in its infancy. We previously reported that the soil bacterium Streptomyces iranensis specifically triggers the production of natural products in the fungus Aspergillus nidulans. Here, we discovered that arginine-derived polyketides serve as the bacterial signals for this induction. Arginine-derived polyketide-producing bacteria occur world wide. These producer bacteria and the fungi that decode and respond to this signal can be co-isolated from the same soil sample. Arginine-derived polyketides impact surrounding microorganisms both directly as well as indirectly, by inducing the production of natural products in fungi that further influence the composition of microbial consortia.One-Sentence SummaryUbiquitous bacterial polyketides are universal components of the chemical network for microbial communication</jats:sec