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bioRxiv2020

First Glimpse of Gut Microbiota of Quarantine Insects in China

Quarantine insects are economically important pests that frequently invade new habitats. A rapid and accurate monitoring method to trace the geographical source of invaders is therefore needed for prevention, detection, and eradication. Current methods based on insect genetics are often too slow. We developed a novel tracing method based on insect gut microbiota. The source location of microbiota of insects can be used to rapidly determine the insects geographic origin. We analyzed 179 gut microbiota samples belonging to 591 individuals of 22 quarantine insect species collected from 36 regions in China and abroad. The gut microbiotas of these insects mainly included Actinobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Proteobacteria, and Tenericutes. The diversity of the insect gut microbiota was closely related to geographic and environmental factors. Different insect species could be distinguished at the phylum level of microbiota. Populations of individual insect species from different regions could be distinguished at the genus level of microbiota. A method for determining the geographical origin of invasive insect species was tentatively established, but its practical applicability requires further study.

microbiology↗

bioRxiv2020

Genome engineering of Nannochloropsis with large deletions for constructing microalgal minigenomes

Industrial microalgae are promising photosynthetic cell factories, yet tools for targeted genome engineering are limited. Here for the model industrial oleaginous microalga Nannochloropsis oceanica we established a method to precisely and serially delete large genome fragments of ~100 kb from its 30.01-Mb nuclear genome. We started by identifying the "non-essential" chromosomal regions (i.e., low-expression region or LER) based on minimal gene expression under N-replete and N-depleted conditions. The largest such LER (LER1) is ~98 kb in size, located near the telomere of the 502.09 kb-long Chromosome 30 (Chr 30). We deleted 81 kb and further distal and proximal deletions of up to 110 kb (21.9% of Chr 30) in LER1 by dual targeting the boundaries with the episome-based CRISPR/Cas9 system. The telomere-deletion mutants showed normal telomeres consisting of CCCTAA repeats, revealing telomere regeneration capability after losing distal part of Chr 30. Interestingly, the deletions caused no significant alteration in growth, lipid production or photosynthesis (transcript-abundance change for < 3% genes under N depletion). We also performed double-deletion of both LER1 and LER2 (from Chr 9) that totals ~214 kb, and phenotypes are essentially normal. Therefore, loss of the large yet "non-essential" regions does not necessarily sacrifice important traits. Such serial targeted deletions of large genomic regions have not been reported in plants or microalgae, and will accelerate crafting minimal genomes as chassis for photosynthetic production.

biochemistry↗