DNA storage-from natural biology to synthetic biology

Photophysics of Nitro-Substituted Unnatural Nucleic Acid Base

The unnatural nucleic acid base (uNAB), 6-amino-3-methyl-5-nitropyridin-2(1H)one, often referred to as Z can form a base pair with the uNAB 2-aminoimidazo[1,2-a]-1,3,5-triazin-4(8H)-one (referred to as P) and is analogous to a guanine-cytosine (G-C) pair. However, it is well-known that the nonradiative decay pathway of the P-Z pair is significantly different from that of the G-C pair (Cui et al., Front. Chem. 2020, 8, 605117-605125). In this work, we study the excited state processes in Z using state-of-the-art multireference methods and dynamical techniques to ascertain the predominant nonradiative channels. We find that unlike in the natural NABs, the excited state processes in Z are driven primarily by the -NO2 group rotation. The electron-withdrawing effect of the -NO2 substituent plays a crucial role. We further ascertained that ultrafast deactivation channels are possible in Z and identified the stationary point geometries that are responsible for these channels.

Efficient data reconstruction: The bottleneck of large-scale application of DNA storage

Over the past decade, the rapid development of DNA synthesis and sequencing technologies has enabled preliminary use of DNA molecules for digital data storage, overcoming the capacity and persistence bottlenecks of silicon-based storage media. DNA storage has now been fully accomplished in the laboratory through existing biotechnology, which again demonstrates the viability of carbon-based storage media. However, the high cost and latency of data reconstruction pose challenges that hinder the practical implementation of DNA storage beyond the laboratory. In this article, we review existing advanced DNA storage methods, analyze the characteristics and performance of biotechnological approaches at various stages of data writing and reading, and discuss potential factors influencing DNA storage from the perspective of data reconstruction.

Massive integration of large gene libraries in the chromosome of Escherichia coli

Large gene libraries are frequently created in Escherichia coli plasmids, which can induce cell toxicity and expression instability due to the high gene dosage. To address these limitations, gene libraries can be integrated in a single copy into the bacterial chromosome. Here, we describe an efficient system for the massive integration (MAIN) of large gene libraries in the E. coli chromosome that generates in-frame gene fusions that are expressed stably. MAIN uses a thermosensitive integrative plasmid that is linearized in vivo to promote extensive integration of the gene library via homologous recombination. Positive and negative selections efficiently remove bacteria lacking gene integration in the target site. We tested MAIN with a library of 107 VHH genes that encode nanobodies (Nbs). The integration of VHH genes into a custom target locus of the E. coli chromosome enabled stable expression and surface display of the Nbs. Next-generation DNA sequencing confirmed that MAIN preserved the diversity of the gene library after integration. Finally, we screened the integrated library to select Nbs that bind a specific antigen using magnetic and fluorescence-activated cell sorting. This allowed us to identify Nbs binding the epidermal growth factor receptor that were not previously isolated in a similar screening of a multicopy plasmid library. Our results demonstrate that MAIN enables large gene library integration into the E. coli chromosome, creating stably expressed in-frame fusions for functional screening.

DBTRG: De Bruijn Trim rotation graph encoding for reliable DNA storage

DNA is a high-density, long-term stable, and scalable storage medium that can meet the increased demands on storage media resulting from the exponential growth of data. The existing DNA storage encoding schemes tend to achieve high-density storage but do not fully consider the local and global stability of DNA sequences and the read and write accuracy of the stored information. To address these problems, this article presents a graph-based De Bruijn Trim Rotation Graph (DBTRG) encoding scheme. Through XOR between the proposed dynamic binary sequence and the original binary sequence, k-mers can be divided into the De Bruijn Trim graph, and the stored information can be compressed according to the overlapping relationship. The simulated experimental results show that DBTRG ensures base balance and diversity, reduces the likelihood of undesired motifs, and improves the stability of DNA storage and data recovery. Furthermore, the maintenance of an encoding rate of 1.92 while storing 510 KB images and the introduction of novel approaches and concepts for DNA storage encoding methods are achieved.