Optimization of the “in-silico” mate-pair method improved contiguity
and accuracy of genome assembly
Abstract
A combination of next-generation sequencing technologies and mate-pair
libraries of large insert sizes is used as a standard method to generate
genome assemblies with high contiguity. The third-generation sequencing
techniques also are used to improve the quality of assembled genomes.
However, both mate-pair libraries and the third-generation libraries
require high-molecular-weight DNA, making the use of these libraries
inappropriate for samples with only degraded DNA. An in silico method
that generates mate-pair libraries using a reference genome was devised
for the task of assembling target genomes. Although the contiguity and
completeness of assembled genomes were significantly improved by this
method, a high level of errors manifested in the assembly, further to
which the methods for using reference genomes were not optimized. Here,
we tested different strategies for using reference genomes to generate
in silico mate-pairs. The results showed that using a closely related
reference genome from the same genus was more effective than using
divergent references. Conservation of in silico mate-pairs by comparing
two references and using those to guide genome assembly reduced the
number of misassemblies (18.6% – 46.1%) and increased the contiguity
of assembled genomes (9.7% – 70.7%), while maintaining gene
completeness at a level that was either similar or marginally lower than
that obtained via the current method. Finally, we compared the optimized
method with another reference-guided assembler, RaGOO. We found that
RaGOO produced longer scaffolds (17.8 Mbp vs 3.0 Mbp), but resulted in a
much higher misassembly rate (85.68%) than our optimized in silico
mate-pair method.