浅水 俊平

Abstract Microorganisms in nature form communities through diverse interactions, such as mutualism and competition, to adapt to their ecological environments. These interactions seem to be mediated by extracellular metabolites (exometabolites), yet the chemical and biological diversity underlying these processes remains largely unexplored. In this study, we examined the chemical basis of cell-cell communication in the fission yeast Schizosaccharomyces pombe by a genome-wide screen employing 3,420 viable gene deletion mutants. We identified 37 strains that exhibited growth defects in monoculture on a minimal medium but exhibited growth recovery in the vicinity of wild-type colonies (co-culture), suggesting that exometabolites secreted by wild-type cells compensated for the gene deletion. Both lipophilic and water-soluble fractions obtained by solvent partitioning of the wild-type culture supernatant promoted growth recovery. Among the 11 mutants rescued by the water-soluble fraction, six were cysteine auxotrophs, prompting analyses of thiol-containing metabolites by liquid chromatography-mass spectrometry (LC-MS), revealing the presence of glutathione (GSH) in the culture supernatant. GSH restored growth in most strains as a nutrient source. In contrast, GSH rescued cell morphology defects in the hob3 Δ mutant, lacking the Bin/Amphiphysin/Rvs (BAR) adaptor protein Hob3, through a mechanism independent of nutrition. This research advances understanding of exometabolite-mediated interactions in S. pombe by highlighting the role of GSH as one of the communication molecules that influence cellular processes and shape microbial communities. Author summary Microorganisms secrete a wide range of metabolites that control microbial community behavior. These extracellular metabolites (exometabolites) include not only well-studied signaling molecules but also diverse primary and secondary metabolites, suggesting complex interactions among microbes. However, the molecular basis of these interactions remains poorly understood, partly due to challenges in detecting them experimentally. In this study, we surveyed exometabolites involved in cell-cell interactions in the model eukaryotic microorganism Schizosaccharomyces pombe . S. pombe secretes a wide variety of metabolites, including previously reported nitrogen signaling factors (NSFs) and glutathione identified in this work. By analyzing gene deletion mutants that depend on GSH for growth, we provide new insights into how microbes regulate collective behavior by sharing exometabolites.

Contractile injection systems (CISs) are derivatives of phage tails and widely distributed in prokaryotes. CISs load cognate effectors and eject them through contractile actions resembling those of phage tails. Ejected effectors play central roles in CIS functionality by acting on target cells and mediating various biological processes. Here, we report a novel group of CIS effectors related to phage tapemeasure protein, the transmembrane component of the phage infection machinery. This group is broadly distributed within the class actinobacteria, one of the bacterial classes in which CIS gene clusters are highly conserved, and is represented by Sle1, a cognate effector of the intracellularly localised Streptomyces lividans phage tail-like nanoparticle (SLP). This effector is associated with Sle2, which contains a CIS effector core domain and interacts with the SLP core component. Sle1 is packaged inside SLP and is translocated to lipid membranes along with SLPs. The functional domain of Sle1, probably through interactions with ribosome-containing subcellular fractions, upregulates the membrane-associated proteome in S. lividans and E. coli . This effect modifies the physiological properties of S. lividans , ultimately enhancing its adaptation to microbial competition. In addition, we revealed that Sle1-type effectors conserved among actinobacterial species are structurally and functionally diverse in their functional domains. One of them from Micromonospora eburnea constitutes a novel toxin-antitoxin system and introducing its functional domain into Sle1 reprogrammes the phenotypic responsiveness of S. lividans to neighbouring bacteria. Our findings illustrate that phage elements can be incorporated into CISs as reconfigurable platforms for bacterial adaptation to various environmental conditions.

Abstract Chemical cross talks between Mycolicibacterium septicum HEK138M and Bacillus subtilis 168 affect the bacterial morphology of Streptomyces variegatus HEK138A. We found that S. variegatus exhibits unusual hyphae branching by the bacterial interaction. We aimed to elucidate the mechanism by performing activity guided purification of substances that induce the unusual cell morphology. We found that pyrogallol, a redox active aromatic small molecule induced significant hyphae branching in S. variegatus and the activity was also observed in some of other Streptomyces species. Interestingly, the pyrogallol activity was diminished by adding catalase, which broke down H ₂ O ₂ . To further confirm the involvement, H ₂ O ₂ was tested and similar activity which induced hyphal branching was observed. This indicates that reactive oxygen species (ROS) generated by redox-active compound (RAC) is the inducing factor of hyphae branching. Further investigation revealed that pyrogallol was generated by NahG enzyme homolog of M. septicum using 2,3-dihydroxybenzoic acid as substrate by heterologous expression in E. coli . Moreover, co-culture with gene knock-out mutants revealed that 2,3-dihydroxybenzoic acid was supplied by B. subtilis produced as intermediate of bacterial siderophore bacillibactin. Since the hyphae branching of vegetative mycelium can increase the density of filamentous network and consequently help secure the milieu in soil, our results suggested that those filamentous soil bacteria use ROS which can be supplied from plant derived RAC as a signal. As those RAC ubiquitously exist in soil environment, the system will be beneficial for sensing the nutrient sources in addition to the generally considered defensive response to oxidative stress. Importance The characterization of interactions between three or more bacteria are lacking as these interactions are visually imperceptible in general. Our current study revealed changes of morphological behavior by the bacterial interaction. This study showed that hydrogen peroxide generated by redox-active compound derived from a breakdown product of siderophore can significantly increase the number of hyphae tip extension in filamentous bacteria. Our result implies the existence of oxidative response system using a low amount of reactive oxygen species as an integrated signal to sense the plant-derived carbon source by the filamentous soil bacteria. As a result of sensing, filamentous soil bacteria may decide whether the hypha tip should be extended to further explore the area or increase the tips to densify filamentous network to monopolize the nutrients in the milieu.