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Complete Genome Sequence of the Red-Pigmented Strain <named-content content-type='genus-species'>Serratia marcescens</named-content> SCQ1 and Its Four Spontaneous Pigment Mutants

Serratia marcescens SCQ1 is a red-pigmented bacterium isolated from silkworm larva with septicemia. Pigment-deficient spontaneous mutants arise when S. marcescens SCQ1 is incubated under relatively stable laboratory conditions for a long time. Here, we present the complete genome sequence of SCQ1 and the resequenced genomes of four spontaneous pigment mutants. S erratia marcescens, a kind of Gram-negative bacterium, belongs to the family Enterobacteriaceae, which is widely distributed in diverse environments, including water, soil, plants, and animals (1). Some strains of S. marcescens may produce a red pigment, prodigiosin, which is a secondary metabolite with multiple bioactivities that has a linear tripyrrole skeleton (2-methyl-3-pentyl-6-methoxyprodiginine) (2–4). S. marcescens SCQ1 was isolated from the hemolymph of diseased silkworm larvae in a sericultural area of Chongqing, China. The hemolymph of silkworm larvae was streaked onto an LB plate and incubated at 28°C for 24h. Red colonies were picked and restreaked onto LB medium 3 times to obtain the axenic strain S. marcescens SCQ1, which was stored at220°C. Strain SCQ1 was then passaged 20 times in liquid LB medium (pH 7), incubated at 28°C with shaking (200 rpm). Every day, 500ml of culture was transferred into 50ml of fresh LB. After 20 transfers, 50ml of the diluted cultures was plated onto LB medium. Colonies with different pigment phenotypes were picked, and the mutant strains SCQ1-1M (pink), SCQ1-2M (white), SCQ1-3M (white), and SCQ1-4M (white sides and red center) were characterized by different colony colors (5). The genetic changes underlying the pigment deficiencies in the S. marcescensmutants have not yet been identified. S. marcescens SCQ1 and the other four spontaneous mutants were cultured in LB broth at 28°C. Genomic DNA was extracted using the E.Z.N.A. bacterial DNA kit (Omega Bio-tek, Norcross, GA). DNA concentration and quality were assessed using a NanoDrop 2000 UV-visible (UV-vis) spectrophotometer (Implen, CA, USA) and 1% agarose gel electrophoresis. Genomic DNA of SCQ1 was sheared into;10-kb fragments using a g-TUBE device (Covaris). A library was constructed for SCQ1 using the SMRTbell Express template preparation kit v2.0 (Pacific Biosciences, USA) and sequenced using single-molecule real-time (SMRT) sequencing technology on the PacBio RS II sequencing platform (6). A total of 3,152,565,048 bases and 320,553 subreads were generated. The mean subread length and N50 value were 9,834bp and 11,305bp, respectively. The reads were assembled using Falcon v2.0.0. Genomic DNA from SCQ1-1M, SCQ1-2M, SCQ1-3M, and SCQ1-4M was sheared into 400to 500-bp fragments using the M220 sonicator (Covaris, Woburn, MA, USA). Paired-end sequencing libraries were prepared for SCQ1-1M, SCQ1-2M, SCQ1-3M, and SCQ1-4M using the NEBNext Ultra DNA library prep kit (NEB, USA). Whole-genome sequencing of SCQ1-1M, SCQ1-2M, and SCQ1-3M was performed using the HiSeq X Ten platform (Illumina, San Diego, CA, USA), and whole-genome sequencing of SCQ1-4M was performed using the Illumina HiSeq 4000 platform to generate 2 150-bp paired-end reads. Quality control on the Illumina data was assessed with FastQC v0.11.5 (7). The adapter sequences, low-quality reads, and reads Citation Xiang T, Liu R, Xu J, Xu C, Wang N, Zhou W, Zhao Y, Luo M, Wan Y. 2021. Complete genome sequence of the redpigmented strain Serratia marcescens SCQ1 and its four spontaneous pigment mutants. Microbiol Resour Announc 10:e01456-20. https://doi.org/10.1128/MRA.01456-20. Editor Julia A. Maresca, University of Delaware Copyright © 2021 Xiang et al. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 International license. Address correspondence to Yongji Wan, canbl3312@126.com. Received 18 December 2020 Accepted 13 March 2021 Published 15 April 2021 Volume 10 Issue 15 e01456-20 mra.asm.org 1 GENOME SEQUENCES