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Genetically modified organisms are commonly used in disease research and agriculture but the precise genomic alterations underlying transgenic mutations are often unknown. The position and characteristics of transgenes, including the number of independent insertions, influences the expression of both transgenic and wild-type sequences. We used long-read, Oxford Nanopore Technologies (ONT) to sequence and assemble two transgenic strains ofCaenorhabditis eleganscommonly used in the research of neurodegenerative diseases: BY250 (pPdat-1::GFP) and UA44 (GFP and humanα-synuclein), a model for Parkinson’s research. After scaffolding to the reference, the final assembled sequences were ∼102 Mb with N50s of 17.9 Mb and 18.0 Mb, respectively, and L90s of six contiguous sequences, representing chromosome-level assemblies. Each of the assembled sequences contained more than 99.2% of the Nematoda BUSCO genes found in theC. elegansreference and 99.5% of the annotatedC. elegansreference protein-coding genes. We identified the locations of the transgene insertions and confirmed that all transgene sequences were inserted in intergenic regions, leaving the organismal gene content intact. The transgenicC. elegansgenomes presented here will be a valuable resource for Parkinson’s research as well as other neurodegenerative diseases. Our work demonstrates that long-read sequencing is a fast, cost-effective way to assemble genome sequences and characterize mutant lines and strains.

 

Abstract Genome size has been measurable since the 1940s but we still do not understand genome size variation. Caenorhabditis nematodes show strong conservation of chromosome number but vary in genome size between closely related species. Androdioecy, where populations are composed of males and self-fertile hermaphrodites, evolved from outcrossing, female-male dioecy, three times in this group. In Caenorhabditis, androdioecious genomes are 10–30% smaller than dioecious species, but in the nematode Pristionchus, androdioecy evolved six times and does not correlate with genome size. Previous hypotheses include genome size evolution through: 1) Deletions and “genome shrinkage” in androdioecious species; 2) Transposable element (TE) expansion and DNA loss through large deletions (the “accordion model”); and 3) Differing TE dynamics in androdioecious and dioecious species. We analyzed nematode genomes and found no evidence for these hypotheses. Instead, nematode genome sizes had strong phylogenetic inertia with increases in a few dioecious species, contradicting the “genome shrinkage” hypothesis. TEs did not explain genome size variation with the exception of the DNA transposon Mutator which was twice as abundant in dioecious genomes. Across short and long evolutionary distances Caenorhabditis genomes evolved through small structural mutations including gene-associated duplications and insertions. Seventy-one protein families had significant, parallel decreases across androdioecious Caenorhabditis including genes involved in the sensory system, regulatory proteins and membrane-associated immune responses. Our results suggest that within a dynamic landscape of frequent small rearrangements in Caenorhabditis, reproductive mode mediates genome evolution by altering the precise fates of individual genes, proteins, and the phenotypes they underlie. 

The isolation ofBradyrhizobiumstrain I71 expands the distribution of acetylene-consuming microbes to include a group of economically important microorganisms. Members ofBradyrhizobiumare well studied for their abilities to improve plant health and increase crop yields by providing bioavailable nitrogen.

 

We report the genome ofRhodococcus opacusstrain MoAcy1 (DSM 44186), an aerobic soil isolate capable of using acetylene as its primary carbon and energy source (acetylenotrophy). The genome is composed of a single circular chromosome of ∼8 Mbp and two closed plasmids, with a G+C content of 67.3%.

 

Abstract The deleterious effects of inbreeding have been of extreme importance to evolutionary biology, but it has been difficult to characterize the complex interactions between genetic constraints and selection that lead to fitness loss and recovery after inbreeding. Haploid organisms and selfing organisms like the nematode Caenorhabditis elegans are capable of rapid recovery from the fixation of novel deleterious mutation; however, the potential for recovery and genomic consequences of inbreeding in diploid, outcrossing organisms are not well understood. We sought to answer two questions: 1) Can a diploid, outcrossing population recover from inbreeding via standing genetic variation and new mutation? and 2) How does allelic diversity change during recovery? We inbred C. remanei, an outcrossing relative of C. elegans, through brother-sister mating for 30 generations followed by recovery at large population size. Inbreeding reduced fitness but, surprisingly, recovery from inbreeding at large populations sizes generated only very moderate fitness recovery after 300 generations. We found that 65% of ancestral single nucleotide polymorphisms (SNPs) were fixed in the inbred population, far fewer than the theoretical expectation of ∼99%. Under recovery, 36 SNPs across 30 genes involved in alimentary, muscular, nervous, and reproductive systems changed reproducibly across replicates, indicating that strong selection for fitness recovery does exist. Our results indicate that recovery from inbreeding depression via standing genetic variation and mutation is likely to be constrained by the large number of segregating deleterious variants present in natural populations, limiting the capacity for recovery of small populations. 

Bumble bees are ecologically and economically important insect pollinators. Three abundant and widespread species in western North America, Bombus bifarius, Bombus vancouverensis, and Bombus vosnesenskii, have been the focus of substantial research relating to diverse aspects of bumble bee ecology and evolutionary biology. We present de novo genome assemblies for each of the three species using hybrid assembly of Illumina and Oxford Nanopore Technologies sequences. All three assemblies are of high quality with large N50s (> 2.2 Mb), BUSCO scores indicating > 98% complete genes, and annotations producing 13,325 - 13,687 genes, comparing favorably with other bee genomes. Analysis of synteny against the most complete bumble bee genome, Bombus terrestris, reveals a high degree of collinearity. These genomes should provide a valuable resource for addressing questions relating to functional genomics and evolutionary biology in these species. 

A Gram-stain-negative, strictly anaerobic, non-motile, rod-shaped bacterium, designated SFB93^T, was isolated from the intertidal sediments of South San Francisco Bay, located near Palo Alto, CA, USA. SFB93^Twas capable of acetylenotrophic and diazotrophic growth, grew at 22–37 °C, pH 6.3–8.5 and in the presence of 10–45 g l⁻¹NaCl. Phylogenetic analyses based on 16S rRNA gene sequencing showed that SFB93^Trepresented a member of the genusSyntrophotaleawith highest 16S rRNA gene sequence similarities toSyntrophotalea acetylenicaDSM 3246^T(96.6 %),Syntrophotalea carbinolicaDSM 2380^T(96.5 %), andSyntrophotalea venetianaDSM 2394^T(96.7 %). Genome sequencing revealed a genome size of 3.22 Mbp and a DNA G+C content of 53.4 %. SFB93^Thad low genome-wide average nucleotide identity (81–87.5 %) and <70 % digital DNA–DNA hybridization value with other members of the genusSyntrophotalea. The phylogenetic position of SFB93^Twithin the familySyntrophotaleaceaeand as a novel member of the genusSyntrophotaleawas confirmed via phylogenetic reconstruction based on concatenated alignments of 92 bacterial core genes. On the basis of the results of phenotypic, genotypic and phylogenetic analyses, a novel species,Syntrophotalea acetylenivoranssp. nov., is proposed, with SFB93^T(=DSM 106009^T=JCM 33327^T=ATCC TSD-118^T) as the type strain.

 

Many species use dormant stages for habitat selection by tying recovery to informative external cues. Other species have an undiscerning strategy in which they recover randomly despite having advanced sensory systems. We investigated whether elements of a species' habitat structure and life history can bar it from developing a discerning recovery strategy. The nematodeCaenorhabditis eleganshas a dormant stage called the dauer larva that disperses between habitat patches. On one hand,C. eleganscolonization success is profoundly influenced by the bacteria found in its habitat patches, so we might expect this to select for a discerning strategy. On the other hand,C. elegans' habitat structure and life history suggest that there is no fitness benefit to varying recovery, which might select for an undiscerning strategy. We exposed dauers of three genotypes to a range of bacteria acquired from the worms' natural habitat. We found thatC. elegansdauers recover in all conditions but increase recovery on certain bacteria depending on the worm's genotype, suggesting a combination of undiscerning and discerning strategies. Additionally, the worms' responses did not match the bacteria's objective quality, suggesting that their decision is based on other characteristics.