Gram-positive bacteria of the genus Streptomyces are industrially important microorganisms, producing >70% of commercially important antibiotics. The production of these compounds is often regulated by low-molecular-weight bacterial hormones called autoregulators. Although 60% of Streptomyces strains may use γ-butyrolactone–type molecules as autoregulators and some use furan-type molecules, little is known about the signaling molecules used to regulate antibiotic production in many other members of this genus. Here, we purified a signaling molecule (avenolide) from Streptomyces avermitilis —the producer of the important anthelmintic agent avermectin with annual world sales of $850 million—and determined its structure, including stereochemistry, by spectroscopic analysis and chemical synthesis as (4 S ,10 R )-10-hydroxy-10-methyl-9-oxo-dodec-2-en-1,4-olide, a class of Streptomyces autoregulator. Avenolide is essential for eliciting avermectin production and is effective at nanomolar concentrations with a minimum effective concentration of 4 nM. The aco gene of S. avermitilis, which encodes an acyl-CoA oxidase, is required for avenolide biosynthesis, and homologs are also present in Streptomyces fradiae , Streptomyces ghanaensis , and Streptomyces griseoauranticus , suggesting that butenolide-type autoregulators may represent a widespread and another class of Streptomyces autoregulator involved in regulating antibiotic production.
Methanotrophs play a key role in the global carbon cycle, in which they affect methane emissions and help to sustain diverse microbial communities through the conversion of methane to organic compounds. To investigate the microbial interactions that cause positive effects on methanotrophs, cocultures were constructed using Methylovulum miyakonense HT12 and each of nine nonmethanotrophic bacteria, which were isolated from a methane-utilizing microbial consortium culture established from forest soil. Three rhizobial strains were found to strongly stimulate the growth and methane oxidation of M. miyakonense HT12 in cocultures. We purified the stimulating factor produced by Rhizobium sp. Rb122 and identified it as cobalamin. Growth stimulation by cobalamin was also observed for three other gammaproteobacterial methanotrophs. These results suggest that microbial interactions through cobalamin play an important role in methane oxidation in various ecosystems.Methane is the second most important greenhouse gas, and mitigating emissions of methane has become a major global concern (17). Aerobic methanotrophs are the major terrestrial methane sink and are widespread in a large variety of ecosystems (26). They belong to the Gammaproteobacteria (type I), Alphaproteobacteria (type II), and Verrucomicrobia (26). Methanotrophs utilize methane as a single source of carbon and energy, but only some methanotrophic strains in the class Alphaproteobacteria can assimilate substrates with C-C bonds (8).Mutual interactions that occur between methanotrophs and other organisms, ranging from microbes to plants and animals, may affect the global methane cycle in various ways. Stable isotope probing (SIP) experiments revealed that methane-derived carbon was incorporated into methylotrophic or heterotrophic bacteria when they were incubated with methanotrophs (5,14,20,22,23), indicating an important role of methanotrophs in supplying nutrients in the form of carbon sources to other nonmethanotrophic organisms. At deep-sea hydrothermal vents and cold seeps, invertebrates form symbiotic associations with gammaproteobacterial methanotrophs living in their tissues (21,26). Some invertebrates can derive most of their carbon nutrition from methane, indeed acquiring it from methane-derived metabolites of methanotrophs or by digestion of methanotrophs. Inversely, the hosts provide methanotrophs with simultaneous access to methane and oxygen by positioning themselves appropriately and also by providing a stable environment. In peat bogs, Sphagnum mosses associate with alphaproteobacterial methanotrophs and utilize carbon dioxide that is generated from methane by methanotrophic symbionts (18,24). Although previous studies have demonstrated that methanotrophs serve as food suppliers for other organisms, less attention has been paid to the specific benefits that methanotrophs acquire from such interactions.Previously, we established a forest soil-based microbial consortium utilizing methane as the single carbon and energy source, from which we isolate...
A novel methanotroph, designated strain HT12T, was isolated from forest soil in Japan. Cells of strain HT12T were Gram-reaction-negative, aerobic, non-motile, coccoid and formed pale-brown colonies. The strain grew only with methane and methanol as sole carbon and energy sources. Cells grew at 5–34 °C (optimum 24–32 °C). The strain possessed both particulate and soluble methane monooxygenases and assimilated formaldehyde using the ribulose monophosphate pathway. The major cellular fatty acids were C16 : 0 (46.9 %) and C14 : 0 (34.2 %), whereas unsaturated C16 fatty acids, typical of type I methanotrophs, were absent. Comparative 16S rRNA gene sequence analysis showed that the most closely related strains were Methylosoma difficile LC 2T (93.1 % sequence similarity) and Methylobacter tundripaludum SV96T (92.6 % similarity). Phylogenetic analysis based on the pmoA gene indicated that strain HT12T formed a distinct lineage within the type I methanotrophs and analysis of the deduced pmoA amino acid sequence of strain HT12T showed that it had a 7 % divergence from that of its most closely related species. The DNA G+C content was 49.3 mol%. Based on this evidence, strain HT12T represents a novel species and genus of the family Methylococcaceae, for which the name Methylovulum miyakonense gen. nov., sp. nov. is proposed. The type strain of the type species is HT12T ( = NBRC 106162T = DSM 23269T = ATCC BAA-2070T).
This study investigated the potential local CH4 sink in various plant parts as a boundary environment of CH4 emission and consumption. By comparing CH4 consumption activities in cultures inoculated with parts from 39 plant species, we observed significantly higher consumption of CH4 associated with aquatic plants than other emergent plant parts such as woody plant leaves, macrophytic marine algae, and sea grass. In situ activity of CH4 consumption by methanotrophs associated with different species of aquatic plants was in the range of 3.7–37 μmol·h−1·g−1 dry weight, which was ca 5.7–370-fold higher than epiphytic CH4 consumption in submerged parts of emergent plants. The qPCR-estimated copy numbers of the particulate methane monooxygenase-encoding gene pmoA were variable among the aquatic plants and ranged in the order of 105–107 copies·g−1 dry weight, which correlated with the observed CH4 consumption activities. Phylogenetic identification of methanotrophs on aquatic plants based on the pmoA sequence analysis revealed a predominance of diverse gammaproteobacterial type-I methanotrophs, including a phylotype of a possible plant-associated methanotroph with the closest identity (86–89%) to Methylocaldum gracile.
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