Magill, C. | bioRxiv Science

bioRxiv2022

The genome of the oomycete Peronosclerospora sorghi, a cosmopolitan pathogen of maize and sorghum, is inflated with dispersed pseudogenes

Several species in the oomycete genus Peronosclerospora cause downy mildew on maize and can result in significant yield losses in Asia. Biosurveillance of these pathogens is a high priority to prevent epidemics on maize in the US and consequent damage to the US economy. The unresolved taxonomy and dearth of molecular resources for Peronosclerospora spp. hinder these efforts. P. sorghi is a pathogen of sorghum and maize with a global distribution, for which limited diversity has been detected in the southern USA. We characterized the genome, transcriptome, and mitogenome of an isolate, representing the US pathotype 6. The highly homozygous genome was assembled using 10x Genomics linked reads and scaffolded using Hi-C into 13 chromosomes. The total assembled length was 319.6 Mb--larger than any other oomycete previously assembled. The mitogenome was 38 kb, similar in size to other oomycetes, although it had a unique gene order. Nearly 20,000 genes were annotated in the nuclear genome, more than described for other downy mildew causing oomycetes. The 13 chromosomes of P. sorghi were highly syntenic with the 17 chromosomes of Peronospora effusa with conserved centromeric regions and distinct chromosomal fusions. The increased assembly size and gene count of P. sorghi is due to extensive retrotransposition, resulting in putative pseudogenization. Ancestral genes had higher transcript abundance and were enriched for differential expression. This study provides foundational resources for analysis of Peronosclerospora and comparisons to other oomycete genera. Further genomic studies of global Peronosclerospora spp. will determine the suitability of the mitogenome, ancestral genes, and putative pseudogenes for marker development and taxonomic relationships.

genomics↗

bioRxiv2020

Response and oil degradation activities of a northeast Atlantic bacterial community to biogenic and synthetic surfactants.

BackgroundAlthough synthetic dispersants are effective in dispersing crude oil, they can alter the natural microbial response to oil and potentially hinder its biodegradation. Biosurfactants, however, are naturally derived products that play a similar role to synthetic dispersants in oil spill response but are easily biodegradable and less toxic. This study investigated the microbial community dynamics, ecological drivers, functional diversity, and oil biodegradation potential of a northeast Atlantic marine microbial community to crude oil when exposed to rhamnolipid or synthetic dispersant Finasol OSR52. ResultsWe found the microbial community composition and diversity were markedly different in the rhamnolipid-amended treatment compared to that with Finasol, with key aromatic hydrocarbon-degrading bacteria like Cycloclasticus being suppressed in the Finasol treatment but not in oil-only and rhamnolipid-amended treatments. Psychrophilic Colwellia and Oleispira dominated the community in both the rhamnolipid and Finasol OSR52 treatments initially but later community structure across treatments diverged significantly: Rhodobacteraceae and Vibrio dominated the Finasol-amended treatment and Colwellia, Oleispira, and later Cycloclasticus and Alcanivorax, dominated the rhamnolipid-amended treatment. Vibrio abundance increased substantially in treatments receiving Finasol, suggesting a potentially important role for these organisms in degrading dispersant components. In fact, Finasol was linked with a negative impact on alpha diversity. Deterministic environmental filtering played a dominant role in regulating the community assembly in all treatments but was strongest in the dispersant-amended treatments. Rhamnolipid-amended and oil-only treatments had the highest functional diversity, however, the overall oil biodegradation was greater in the Finasol treatment, but aromatic biodegradation was highest in the rhamnolipid treatment. ConclusionOverall, the natural marine microbial community in the northeast Atlantic responded differently to crude oil dispersed with either synthetic or biogenic surfactants over time, but oil degradation was more enhanced by the synthetic dispersant. Collectively, our results advance the understanding of how rhamnolipid biosurfactants affect the natural marine microbial community, supporting their potential application in oil spills.

genomics↗