Reduction of acetate synthesis, enhanced arginine export, and supply of precursors, cofactors, and energy for improved synthesis of L-arginine by Escherichia coli.

L-arginine (L-Arg) is a semi-essential amino acid with many important physiological functions. However, achieving efficient manufacture of L-Arg on an industrial scale using Escherichia coli (E. coli) remains a major challenge. In previous studies, we constructed a strain of E. coli A7, which had good L-Arg production capacity. In this study, E. coli A7 was further modified, and E. coli A21 with more efficient L-Arg production capacity was obtained. Firstly, we reduced the acetate accumulation of strain A7 by weakening the poxB gene and overexpressing acs gene. Secondly, we improved the L-Arg transport efficiency of strains by overexpressing the lysE gene from Corynebacterium glutamicum (C. glutamicum). Finally, we enhanced the supplies of precursors for the synthesis of L-Arg and optimized the supplies of cofactor NADPH and energy ATP in strain. After fermentation in a 5-L bioreactor, the L-Arg titer of strain A21 was found to be 89.7 g/L. The productivity was 1.495 g/(L·h) and the glucose yield was 0.377 g/g. Our study further narrowed the titer gap between E. coli and C. glutamicum in the synthesis of L-Arg. In all recent studies on the L-Arg production by E. coli, this was the highest titer recorded. In conclusion, our study further promotes the efficient mass synthesis of L-Arg by E. coli. KEY POINTS: • The acetate accumulation of starting strain A7 was decreased. • Overexpression of gene lysE of C. glutamicum enhanced L-Arg transport in strain A10. • Enhance the supplies of precursors for the synthesis of L-Arg and optimize the supplies of cofactor NADPH and energy ATP. Finally, Strain A21 was detected to have an L-Arg titer of 89.7 g/L in a 5-L bioreactor.

Simplified LDPC-assisted CNC algorithm for entropy-loaded discrete multi-tone in a 100G flexible-rate PON.

Passive optical networks (PONs) have been widely used in optical access networks to meet the requirement of the rapidly growing data traffic. However, the optical power budget of the worst optical network unit certainly limits the maximum capacity of PON. In this paper, we demonstrate a flexible-rate PON based on entropy-loaded clipping discrete multi-tone (DMT) for increasing the capacity. Meanwhile, clipping operation and simplified low-density parity-check (LDPC) assisted clipping-noise-cancellation (CNC) algorithm are proposed to improve the performance of DMT in peak-power constrained PON. In the simplified LDPC-assisted CNC algorithm, the iteration number of the sum-product algorithm in the LDPC decoding can be reduced to decrease the computational complexity almost without performance loss. The experimental results show that the simplified CNC algorithm can achieve approximately 1.8dB improvement of the optical receiver sensitivity at the 20% soft-decision forward-error-correction limit. The proposed flexible-rate PON has a wide-range data-rate adjustment from 12.5Gb/s to 100Gb/s under the optical power budget from 40dB to 26dB.

Metabolic engineering of Escherichia coli for efficient production of L-arginine.

As an important semi-essential amino acid, L-arginine (L-Arg) has important application prospects in medicine and health care. However, it remains a challenge to efficiently produce L-Arg by Escherichia coli (E. coli). In the present study, we obtained an E. coli A1 with L-Arg accumulation ability, and carried out a series of metabolic engineering on it, and finally obtained an E. coli strain A7 with high L-Arg production ability. First, genome analysis of strain A1 was performed to explore the related genes affecting L-Arg accumulation. We found that gene speC and gene speF played an important role in the accumulation of L-Arg. Second, we used two strategies to solve the feedback inhibition of the L-Arg pathway in E. coli. One was the combination of a mutation of the gene argA and the deletion of the gene argR, and the other was the combination of a heterologous insertion of the gene argJ and the deletion of the gene argR. The combination of exogenous argJ gene insertion and argR gene deletion achieved higher titer accumulation with less impact on strain growth. Finally, we inserted the gene cluster argCJBDF of Corynebacterium glutamicum (C. glutamicum) to enhance the metabolic flux of the L-Arg pathway in E. coli. The final strain obtained 70.1 g/L L-Arg in a 5-L bioreactor, with a yield of 0.326 g/g glucose and a productivity of 1.17 g/(L· h). This was the highest level of L-Arg production by E. coli ever reported. Collectively, our findings provided valuable insights into the possibility of the industrial production of L-Arg by E. coli. KEY POINTS: • Genetic background of E. coli A1 genome analysis. • Heterologous argJ substitution of argA mutation promoted excessive accumulation of L-Arg in E. coli A1. • The overexpression of L-Arg synthesis gene cluster argCJBDF of Corynebacterium glutamicum (C. glutamate) promoted the accumulation of L-Arg, and 70.1 g/L L-Arg was finally obtained in fed-batch fermentation.

Processing for dispersive intensity-modulation and direct-detection fiber-optic communications.

In intensity-modulation and direct-detection (IM/DD) fiber-optic communications, it is hard to pre- or post-compensate for chromatic dispersion (CD) by digital signal processing due to one-dimensional modulation and detection. In this Letter, we propose joint optical and digital signal processing to effectively compensate for CD-caused distortions for IM/DD optical systems. As a reasonable optical signal processing, negative chirp based on self-phase modulation can suppress a part of CD to take pressure off digital signal processing. Digital signal processing is designed based on the model of a dispersive channel to accurately compensate for CD-caused distortions. To the best of our knowledge, we present a record C-band 72 Gbit/s optical on-off keying over 100 km dispersion-uncompensated link (i.e., ∼1700ps/nm dispersion), achieving a 7% hard-decision forward error correction limit. We conclude that joint optical and digital signal processing is effective in dealing with CD-caused distortions to achieve a higher capacity-distance product in IM/DD fiber-optic communications.

C-band 56 Gbit/s on/off keying system over a 100 km dispersion-uncompensated link using only receiver-side digital signal processing: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 758 (2020)OPLEDP0146-959210.1364/OL.384168.

C-band 56 Gbit/s on/off keying system over a 100 km dispersion-uncompensated link using only receiver-side digital signal processing.

In this Letter, we present a record C-band 56 Gbit/s intensity-modulation/direct-detection optical on/off keying (OOK) system over a 100 km dispersion-uncompensated link using only the receiver-side digital signal processing (DSP). The proposed DSP mainly includes an adaptive moment estimation (Adam)-based polynomial nonlinear equalizer (PNLE), autoregression (AR)-based post filter, and maximum likelihood sequence estimation (MLSE). Due to square-law detection, chromatic dispersion induces 11 nulls on the 28 GHz spectrum of the 56 Gbit/s OOK signal after the 100 km standard-single-mode-fiber transmission. Adam-based PNLE eliminates major linear and nonlinear distortions, but it cannot compensate the nulls. After the Adam-based PNLE, the AR-based post filter and MLSE further deal with the inter-symbol interference caused by the nulls to improve the system performance. The proposed C-band 56 Gbit/s OOK system shows great potential for future metro networks and data center networks.

Adaptive moment estimation for polynomial nonlinear equalizer in PAM8-based optical interconnects.

Adaptive moment estimation (Adam) is a popular optimization method to estimate large-scale parameters in neural networks. This paper proposes the first use of Adam algorithm to fast and stably converge large-scale tap coefficients of polynomial nonlinear equalizer (PNLE) for 129-Gbit/s PAM8-based optical interconnects. PNLE is one of simplified Volterra nonlinear equalizer for making a trade-off between complexity and performance. Different from serial least-mean square (LMS) adaptive algorithm, Adam algorithm is a parallel processing algorithm, which can obtain globally optimal tap coefficients without being trapped in locally optimal tap coefficients. Timing error is one of the main obstacles to the PAM systems with high baud rate and high modulation order. Owing to parallel processing and global optimization, Adam algorithm has much better performance on resisting the timing error, which can achieve faster, more-stable and lower-MSE convergence compared to LMS adaptive algorithm. In conclusion, Adam algorithm shows great potential for converging the tap coefficients of PNLE in PAM8-based optical interconnects.

Analysis of the Complete Genome Sequence of Bacillus atrophaeus GQJK17 Reveals Its Biocontrol Characteristics as a Plant Growth-Promoting Rhizobacterium.

Bacillus atrophaeus GQJK17 was isolated from the rhizosphere of Lycium barbarum L. in China, which was shown to be a plant growth-promoting rhizobacterium as a new biological agent against pathogenic fungi and gram-positive bacteria. We present its biological characteristics and complete genome sequence, which contains a 4,325,818 bp circular chromosome with 4,181 coding DNA sequences and a G+C content of 43.3%. A genome analysis revealed a total of 8 candidate gene clusters for producing antimicrobial secondary metabolites, including surfactin, bacillaene, fengycin, and bacillibactin. Some other antimicrobial and plant growth-promoting genes were also discovered. Our results provide insights into the genetic and biological basis of B. atrophaeus strains as a biocontrol agent for application in agriculture.

Complete Genome Sequence of Bacillus velezensis GQJK49, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity.

Bacillus velezensis GQJK49 is a plant growth-promoting rhizobacterium with antifungal activity, which was isolated from Lycium barbarum L. rhizosphere. Here, we report the complete genome sequence of B. velezensis GQJK49. Twelve gene clusters related to its biosynthesis of secondary metabolites, including antifungal and antibacterial antibiotics, were predicted.

Complete Genome Sequence of Biocontroller Bacillus velezensis Strain JTYP2, Isolated from Leaves of Echeveria laui.

Bacillus velezensis JTYP2 was isolated from the leaves of Echeveria laui in Qingzhou, China, and may control some of the fungal pathogens of the plant. Here, we present the complete genome sequence of B. velezensis JTYP2. Several gene clusters related to its biosynthesis of antimicrobial compounds were predicted.

Complete Genome Sequence of Bacillus subtilis GQJK2, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity.

Bacillus subtilis GQJK2 is a plant growth-promoting rhizobacterium with antifungal activity which was isolated from Lycium barbarum L. rhizosphere. Here, we report the complete genome sequence of B. subtilis GQJK2. Ten gene clusters involved in the biosynthesis of antagonistic compounds were predicted.

Complete Genome Sequence of Bacillus paralicheniformis MDJK30, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity.

Bacillus paralicheniformis MDJK30 was isolated from the rhizosphere of a peony. It could control the pathogen of peony root rot. Here, we report the complete genome sequence of B. paralicheniformis MDJK30. Eleven secondary metabolism gene clusters were predicted.