ABSTRACT
【Objective】 To explore the influence of common methods of reducing non-viral nucleic acid on the abundance of plasma virus group. 【Methods】 Three kinds of library construction, five kinds of centrifugation conditions, two kinds of filters, four kinds of enzymes and four concentrations of chloroform were used to treat plasma samples added quantitatively 2.16 mL of pseudorabies virus(PRV) and 2.16 mL of porcine parvovirus(PPV). A total of 21.6 mL of plasma samples were processed, including 54 samples. Subsequently, nucleic acid was extracted, mitochondrial DNA(mtDNA) and two viruses were quantitated, the library of the next generation sequencing was constructed, Illumina NovaSeq 6000 was used for the next generation sequencing. The sequencing data were compared with Kraken Py 2.0 software, and the species annotation analysis was conducted. The corresponding species classification information of each segment was obtained to analyze the impact of different reducing non-viral nucleic acid methods on the relative abundance of microorganisms and two indicator viruses. 【Results】 After sequencing by Illumina NovaSeq 6000, 306.27 GB raw data and 193.17 GB clean data were obtained, with Q20>90%, Q30>85%, Error Rate of 0.03%, and average GC Content of 45.02%. The DNA library construction process significantly increased the proportion of microbial sequences and the PRV abundance [(91.8±0.5)%](P<0.05); RNA library construction and combined library construction can increase the abundance of Pestivirus, an RNA virus, and the PRV abundance was(17.7±3.3)% and(8.1±1.5)% respectively. The Ct value of mtDNA was increased and the proportion of human sequence decreased to less than(89.5±1)%, while the proportion of microbial sequence increased to (2.4±0.03)% after treatment of five centrifugation conditions(P<0.05); After centrifugation at 4℃, 100 g, 30 min, the PRV abundance was increased to (40.6±6)%, and centrifugation at 4℃, 4 000 g, 45 min reduced the PRV abundance to (4.1±0.01)%(P<0.05). Both of 0.22-μm filter and 0.45-μm filter increased the Ct value of mtDNA to above 25.56±0.13, decreased the proportion of human sequence to less than (86.1±0.6)%, increased the proportion of microbial sequence to (3.1±0.1)% and (3.4±0.2)%, and decreased the PRV abundance to (1.6±0.3)% and (4.1±0.7)%(P<0.05), while there was no statistical difference in the effect on PPV concentration and abundance. DNase Ⅰ and Benzonase increased the Ct value of PPV to 25.65±0.06 and 25.36±0.45, decreased the proportion of human sequence to (81.7±5.6)% and (72.8±6.7)%, and increased the proportion of microbial sequence and PRV abundance to (11.0±4.1)% and (16.1±4.7)%, (55.8±2.3)% and (39.0±8.9)%, respectively(P<0 05); After treatment with RNase A, the Ct value of PRV increased to 25.20±0.11, and the human sequence proportion decreased to (85.4±5.6)%(P<0 05); Lysozyme had no effect on removing non-viral nucleic acid. The chloroform of 1%, 5%, 10% and 20% increased Ct value of PRV and mtDNA to no less than 27.17±0.21 and 25.68±0.04; Only 10% chloroform increased the proportion of microbial sequences to (3.1±1.2)%(P<0.05); The abundance of PRV with 1% and 5% chloroform treatment was increased to (48.7±13.3)% and (42.1±5.5)%(P<0.05), while 10% and 20% chloroform reduced PRV abundance to (1.0±0.5)% and (3.4±2.8)%(P<0.05). There was no statistical difference in the effect of chloroform with four contents on PPV abundance. 【Conclusion】 Centrifugation at 4℃, 5 000 g, 10 min is suitable for increasing the overall abundance of virus, and centrifugation at 4℃, 100 g, 30 min is suitable for increasing the content of virus similar to PRV. 0.45-μm filter, DNase Ⅰ, Benzonase and low concentration chloroform can effectively reduce the proportion of non-viral nucleic acid sequence in plasma to increase the abundance of the indicated virus group. Thus, the enrichment effect of plasma meta-virome is closely related to the nature of the virus, and the appropriate virus enrichment method should be selected according to the research purpose to establish the corresponding enrichment strategy.
ABSTRACT
Although viruses are the most common cause of acute gastroenteritis (AGE) in humans, details about the causative viruses in AGE are largely unknown because many causative viruses are unable to be cultured by current culture techniques. In our study, fecal samples from 10 children under five years of age with unexplained AGE and 10 healthy children were investigated for RNA viruses using random priming (RP)-mediated sequence-independent single primer amplification (SISPA). The causative viruses in cases of cryptogenic diarrhea were then assessed for their potential diagnostic value. Of the 1,129 viral clones identified, rotavirus was most commonly associated with AGE (125 sequences, 22.4%). In contrast, bacteriophage was most common (43 sequences, 13.6%) in healthy children. The remaining 515 viral clones were unidentifiable. These findings suggest that investigation of cases or outbreaks of unexplained diarrhea using a metaviromic strategy is a new avenue for diagnosis.