Identification of a solo acylhomoserine lactone synthase from the myxobacterium Archangium gephyra

Considered a key taxon in soil and marine microbial communities, myxobacteria exist as coordinated swarms that utilize a combination of lytic enzymes and specialized metabolites to facilitate predation of microbes. This capacity to produce specialized metabolites and the associated abundance of biosynthetic pathways contained within their genomes have motivated continued drug discovery efforts from myxobacteria. Of all myxobacterial biosynthetic gene clusters deposited in the antiSMASH database, only one putative acylhomoserine lactone (AHL) synthase, agpI, was observed, in genome data from Archangium gephyra. Without an AHL receptor also apparent in the genome of A. gephyra, we sought to determine if AgpI was an uncommon example of an orphaned AHL synthase. Herein we report the bioinformatic assessment of AgpI and discovery of a second AHL synthase from Vitiosangium sp. During axenic cultivation conditions, no detectible AHL metabolites were observed in A. gephyra extracts. However, heterologous expression of each synthase in Escherichia coli provided detectible quantities of 3 AHL signals including 2 known AHLs, C8-AHL and C9-AHL. These results suggest that A. gephyra AHL production is dormant during axenic cultivation. The functional, orphaned AHL synthase, AgpI, is unique to A. gephyra, and its utility to the predatory myxobacterium remains unknown.

Axenic in-vitro cultivation of nineteen peat-moss (Sphagnum L.) species as a resource for basic biology, biotechnology and paludiculture

SummaryThe cultivation of Sphagnum mosses reduces CO2 emissions by rewetting drained peatlands and by substituting peat with renewable biomass. ‘Sphagnum farming’ requires large volumes of founder material, which can only be supplied sustainably by axenic cultivation in bioreactors.We established axenic in-vitro cultures from sporophytes of 19 Sphagnum species collected in Austria, Germany, Latvia, Netherlands, Russia and Sweden, namely S. angustifolium, S. balticum, S. capillifolium, S. centrale, S. compactum, S. cuspidatum, S. fallax, S. fimbriatum, S. fuscum, S. lindbergii, S. medium/divinum, S. palustre, S. papillosum, S. rubellum, S. russowii, S. squarrosum, S. subnitens, S. subfulvum, and S. warnstorfii. These species cover five of the six European Sphagnum sections, namely Acutifolia, Cuspidata, Rigida, Sphagnum and Squarrosa.Their growth was measured in axenic suspension cultures, whereas their ploidy was determined by flow cytometry and compared with the genome size of Physcomitrella patens. We identified haploid and diploid Sphagnum species, found that their cells are predominantly arrested in the G1-phase of the cell cycle, and did not find a correlation between plant productivity and ploidy.With this collection, high-quality founder material for diverse large-scale applications but also for basic Sphagnum research is available from the International Moss Stock Center (IMSC).

Cryptic, solo acylhomoserine lactone synthase from predatory myxobacterium suggests beneficial contribution to prey quorum signaling

Considered a key taxon in microbial communities, myxobacteria exist as coordinated swarms that utilize an excreted combination of lytic enzymes and specialized metabolites to facilitate predation of numerous microbial phyla. This capacity to produce biologically active metabolites and the associated abundance of natural product biosynthetic pathways contained within their genomes have motivated continued drug discovery efforts from myxobacteria. Of all the biosynthetic gene clusters associated with myxobacteria deposited in the antiSMASH database (∼1,000 total), only one putative acylhomoserine lactone synthase, agpI, was observed in genome data from the myxobacterium Archangium gephyra. Without an acylhomoserine lactone (AHL) receptor also apparent in the genome of A. gephyra, we sought to determine if AgpI was the first example of an orphaned AHL synthase. Herein we report the bioinformatic assessment of AgpI and discovery of a second myxobacterial AHL synthase from Vitiosangium sp. strain GDMCC 1.1324. During axenic cultivation conditions, no detectible AHL metabolites were observed in A. gephyra extracts. However, heterologous expression of each synthase in Escherichia coli provided detectible quantities of 3 AHL signals including 2 known AHLs, C8-AHL and C9-AHL. These results suggest that A. gephyra AHL production is dormant during axenic cultivation conditions and requires an unknown external cue for activation. The orphaned AHL synthase, AgpI, is the first to be reported from a predatory myxobacterium, and predator production of prey quorum signals provides unique insight into interspecies crosstalk within polymicrobial communities.ImportanceThe presence of orphaned quorum signal receptors and associated recognition and response to exogenous acylhomoserine lactone quorum signals observed in microbial communities provides evidence for small molecule-mediated interspecies interactions. While the high occurrence of orphaned AHL receptors from bacteria that do not produce cognate AHL signals suggests the involvement of AHL signals as a shared chemical resource in polymicrobial communities, no orphaned AHL synthases have been determined to be functional in a species without an associated AHL receptor. An orphan signal synthase from a predatory myxobacterium provides an alternative perspective on the evolution and benefits of quorum signaling systems within these communities.