Achieving High-Performance Ge0.92 Bi0.08 Te Thermoelectrics via LaB6 -Alloying-Induced Band Engineering and Multi-Scale Structure Manipulation.

In this work, a LaB6 -alloying strategy is reported to effectively boost the figure-of-merit (ZT) of Ge0.92 Bi0.08 Te-based alloys up to ≈2.2 at 723 K, attributed to a synergy of La-dopant induced band structuring and structural manipulation. Density-function-theory calculations reveal that La dopant enlarges the bandgap and converges the energy offset between the sub-valence bands in cubic-structured GeTe, leading to a significantly increased effective mass, which gives rise to a high Seebeck coefficient of ≈263 µV K-1 and in turn a superior power factor of ≈43 µW cm-1 K-2 at 723 K. Besides, comprehensive electron microscopy characterizations reveal that the multi-scale phonon scattering centers, including a high density of planar defects, Boron nanoparticles in tandem with enhanced boundaries, dispersive Ge nanoprecipitates in the matrix, and massive point defects, contribute to a low lattice thermal conductivity of ≈0.67 W m-1 K-1 at 723 K. Furthermore, a high microhardness of ≈194 Hv is witnessed in the as-designed Ge0.92 Bi0.08 Te(LaB6 )0.04 alloy, derived from the multi-defect-induced strengthening. This work provides a strategy for developing high-performance and mechanical robust middle-temperature thermoelectric materials for practical thermoelectric applications.

Structural Evolution of High-Performance Mn-Alloyed Thermoelectric Materials: A Case Study of SnTe.

Mn alloying in thermoelectrics is a long-standing strategy for enhancing their figure-of-merit through optimizing electronic transport properties by band convergence, valley perturbation, or spin-orbital coupling. By contrast, mechanisms by which Mn contributes to suppressing thermal transports, namely thermal conductivity, is still ambiguous. A few precedent studies indicate that Mn introduces a series of hierarchical defects from the nano- to meso-scale, leading to effective phonon scattering scoping a wide frequency spectrum. Due to insufficient insights at the atomic level, the theory remains as phenomenological and cannot be used to quantitatively predict the thermal conductivity of Mn-alloyed thermoelectrics. Herein, by choosing the SnTe as a case study, aberration-corrected transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) to characterize the lattice complexity of Sn1.02- x Mnx Te is employed. Mn as a "dynamic" dopant that plays an important role in SnTe with respect to different alloying levels or post treatments is revealed. The results indicate that Mn precipitates at x = 0.08 prior to reaching solubility (≈10 mol%), and then splits into MnSn substitution and γ-MnTe hetero-phases via mechanical alloying. Understanding such unique crystallography evolution, combined with a modified Debye-Callaway model, is critical in explaining the decreased thermal conductivity of Sn1.02- x Mnx Te with rational phonon scattering pathways, which should be applicable for other thermoelectric systems.

Two PAAR Proteins with Different C-Terminal Extended Domains Have Distinct Ecological Functions in Myxococcus xanthus.

Bacterial proline-alanine-alanine-arginine (PAAR) proteins are located at the top of the type VI secretion system (T6SS) nanomachine and carry and deliver effectors into neighboring cells. Many PAAR proteins are fused with a variable C-terminal extended domain (CTD). Here, we report that two paar-ctd genes (MXAN_RS08765 and MXAN_RS36995) located in two homologous operons are involved in different ecological functions of Myxococcus xanthusMXAN_RS08765 inhibited the growth of plant-pathogenic fungi, while MXAN_RS36995 was associated with the colony-merger incompatibility of M. xanthus cells. These two PAAR-CTD proteins were both toxic to Escherichia coli cells, while MXAN_RS08765, but not MXAN_RS36995, was also toxic to Saccharomyces cerevisiae cells. Their downstream adjacent genes, i.e., MXAN_RS08760 and MXAN_RS24590, protected against the toxicities. The MXAN_RS36995 protein was demonstrated to have nuclease activity, and the activity was inhibited by the presence of MXAN_RS24590. Our results highlight that the PAAR proteins diversify the CTDs to play divergent roles in M. xanthusIMPORTANCE The type VI secretion system (T6SS) is a bacterial cell contact-dependent weapon capable of delivering protein effectors into neighboring cells. The PAAR protein is located at the top of the nanomachine and carries an effector for delivery. Many PAAR proteins are extended with a diverse C-terminal sequence with an unknown structure and function. Here, we report two paar-ctd genes located in two homologous operons involved in different ecological functions of Myxococcus xanthus; one has antifungal activity, and the other is associated with the kin discrimination phenotype. The PAAR-CTD proteins and the proteins encoded by their downstream genes form two toxin-immunity protein pairs. We demonstrated that the C-terminal diversification of the PAAR-CTD proteins enriches the ecological functions of bacterial cells.

Digitally Controlled Oscillator with High Timing Resolution and Low Complexity for Clock Generation.

This paper presents a digitally controlled oscillator (DCO) with a low-complexity circuit structure that combines multiple delay circuits to achieve a high timing resolution and wide output frequency range simultaneously while also significantly reducing the overall power consumption. A 0.18 µm complementary metal-oxide-semiconductor standard process was used for the design, and measurements showed that the chip had a minimum controllable timing resolution of 4.81 ps and power consumption of 142 µW with an output signal of 364 MHz. When compared with other designs using advanced processes, the proposed DCO demonstrated the best power-to-frequency ratio. Therefore, it can output a signal at the required frequency more efficiently in terms of power consumption. Additionally, because the proposed DCO uses digital logic gates only, a cell-based design flow can be implemented. Hence, the proposed DCO is not only easy to implement in different processes but also easy to integrate with other digital circuits.

Deinococcus terrestris sp. nov., a gamma ray- and ultraviolet-resistant bacterium isolated from soil.

Strain SDU3-2T was isolated from a soil sample collected in Shandong Province, PR China. Cells of SDU3-2T were spherical, Gram-stain-positive, aerobic and non-motile. Cellular growth of the strain occurred at 25-45 °C, pH 5.5-8.5 and with 0-1.5 % (w/v) of NaCl. Phylogenetic analysis based on the 16S rRNA gene sequences showed that strain SDU3-2T was closest to the type strain Deinococcus murrayi ALT-1bT with a similarity of 95.2 %. The draft genome was 3.49 Mbp long with 69.2 mol% G+C content. Strain SDU3-2T exhibited high resistance to gamma radiation (D10 >12 kGy) and UV (D10 >900 J m-2). The strain encoded many genes for resistance to radiation and oxidative stress, which were highly conserved with other Deinococcus species, but possessed interspecific properties. The major fatty acids of SDU3-2T cells were C15 : 1 ω6c, C16 : 1 ω7c/C16 : 1 ω6c, and C17 : 1 ω8c, the major menaquinone was menaquinone-8, and the major polar lipids were an unidentified phosphoglycolipid, four unidentified glycolipids and an unidentified phospholipid. The average nucleotide identity and DNA-DNA hybridization results further indicated that strain SDU3-2T represents a new species in the genus Deinococcus, for which the name Deinococcus terrestris sp. nov. is proposed. The type strain is SDU3-2T (=CGMCC 1.17147T=KCTC 43098T).

Psychroflexus aurantiacus sp. nov., isolated from soil in the Yellow River Delta wetlands.

A Gram-stain-negative, strictly aerobic, non-motile, orange-coloured bacterium, designated YR1-1T, was isolated from a soil sample collected from the Yellow River Delta wetlands (PR China). Growth was observed at a salinity of 1.0-15.0 % NaCl, 4-45 °C and pH 6.0-9.0. The results of phylogenetic analysis based on the 16S rRNA gene sequences indicated that YR1-1T represented a member of the genus Psychroflexus, with the highest sequence similarity to Psychroflexus sediminis YIM-C238T (97.9 %), followed by Psychroflexus aestuariivivens (97.1 %) and Psychroflexus torquis (96.4 %). The average nucleotide identity and digital DNA-DNA hybridization values between YR1-1T and other closely related type strains of species of the genus Psychroflexus were 68.7-86.3% and 17.8-30.9 %. The genome of the strain was 2 899 374 bp in length with 39.8 % DNA G+C content. The predominant fatty acids (>10 %) were iso-C15 : 0 and anteiso-C15 : 0. The major respiratory quinone was menaquinone-6 (MK-6) and the major polar lipids were phosphatidylethanolamine, phospholipid, diphosphatidylglycerol, two unidentified aminolipids and four unidentified lipids. The combined genotypic and phenotypic data indicate that YR1-1T represents a novel species within the genus Psychroflexus, for which the name Psychroflexus aurantiacus sp. nov., is proposed. The type strain is YR1-1T (=KCTC 72794T=CGMCC 1.17458T).

Whole transcriptome analysis and gene deletion to understand the chloramphenicol resistance mechanism and develop a screening method for homologous recombination in Myxococcus xanthus.

BACKGROUND: Myxococcus xanthus DK1622 is a model system for studying multicellular development, predation, cellular differentiation, and evolution. Furthermore, it is a rich source of novel secondary metabolites and is widely used as heterologous expression host of exogenous biosynthetic gene clusters. For decades, genetic modification of M. xanthus DK1622 has mainly relied on kanamycin and tetracycline selection systems. RESULTS: Here, we introduce an alternative selection system based on chloramphenicol (Cm) to broaden the spectrum of available molecular tools. A chloramphenicol-resistant growth phase and a chloramphenicol-susceptible growth phase before and after chloramphenicol-induction were prepared, and later sequenced to identify specific genes related to chloramphenicol-repercussion and drug-resistance. A total of 481 differentially expressed genes were revealed in chloramphenicol-resistant Cm5_36h and 1920 differentially expressed genes in chloramphenicol-dormant Cm_8h. Moreover, the gene expression profile in the chloramphenicol-dormant strain Cm_8h was quite different from that of Cm5_36 which had completely adapted to Cm, and 1513 differentially expression genes were identified between these two phenotypes. Besides upregulated acetyltransferases, several transporter encoding genes, including ABC transporters, major facilitator superfamily transporters (MFS), resistance-nodulation-cell division (RND) super family transporters and multidrug and toxic compound extrusion family transporters (MATE) were found to be involved in Cm resistance. After the knockout of the most highly upregulated MXAN_2566 MFS family gene, mutant strain DK-2566 was proved to be sensitive to Cm by measuring the growth curve in the Cm-added condition. A plasmid with a Cm resistance marker was constructed and integrated into chromosomes via homologous recombination and Cm screening. The integration efficiency was about 20% at different concentrations of Cm. CONCLUSIONS: This study provides a new antibiotic-based selection system, and will help to understand antibiotic resistance mechanisms in M. xanthus DK1622.

CRISPR/dCas9-mediated transcriptional improvement of the biosynthetic gene cluster for the epothilone production in Myxococcus xanthus.

BACKGROUND: The CRISPR/dCas9 system is a powerful tool to activate the transcription of target genes in eukaryotic or prokaryotic cells, but lacks assays in complex conditions, such as the biosynthesis of secondary metabolites. RESULTS: In this study, to improve the transcription of the heterologously expressed biosynthetic genes for the production of epothilones, we established the CRISPR/dCas9-mediated activation technique in Myxococcus xanthus and analyzed some key factors involving in the CRISPR/dCas9 activation. We firstly optimized the cas9 codon to fit the M. xanthus cells, mutated the gene to inactivate the nuclease activity, and constructed the dCas9-activator system in an epothilone producer. We compared the improvement efficiency of different sgRNAs on the production of epothilones and the expression of the biosynthetic genes. We also compared the improvement effects of different activator proteins, the ω and α subunits of RNA polymerase, and the sigma factors σ54 and CarQ. By using a copper-inducible promoter, we determined that higher expressions of dCas9-activator improved the activation effects. CONCLUSIONS: Our results showed that the CRISPR/dCas-mediated transcription activation is a simple and broadly applicable technique to improve the transcriptional efficiency for the production of secondary metabolites in microorganisms. This is the first time to construct the CRISPR/dCas9 activation system in myxobacteria and the first time to assay the CRISPR/dCas9 activations for the biosynthesis of microbial secondary metabolites.

O-Phenylenediamine: a privileged pharmacophore of ferrostatins for radical-trapping reactivity in blocking ferroptosis.

Ferroptosis is a non-apoptotic, iron dependent form of regulated cell death that is characterized by the accumulation of lipid hydroperoxides. It has drawn considerable attention owing to its putative involvement in diverse neurodegenerative diseases. Ferrostatins are the first identified inhibitors of ferroptosis and they inhibit ferroptosis by efficiently scavenging free radicals in lipid bilayers. However, their further medicinal application has been limited due to the deficient knowledge of the lipid peroxyl radical-trapping mechanism. In this study, experimental and theoretical methods were performed to illustrate the possible lipid hydroperoxide inhibition mechanism of ferrostatins. The results show that an ortho-amine (-NH) moiety from ferrostatins can simultaneously interact with lipid radicals, and then form a planar seven-membered ring in the transition state, and finally present greater reactivity. NBO analysis shows that the formed planar seven-membered ring forces ortho-amines into better alignment with the aromatic π-system. It significantly increases the magnitudes of amine conjugation and improves spin delocalization in the transition state. Additionally, a classical H-bond type interaction was discovered between a radical and an o-NH group as another transition state stabilizing effect. This type of radical-trapping mechanism is novel and has not been found in diphenylamine or traditional polyphenol antioxidants. It can be said that o-phenylenediamine is a privileged pharmacophore for the design and development of ferroptosis inhibitors.

Increasing on-target cleavage efficiency for CRISPR/Cas9-induced large fragment deletion in Myxococcus xanthus.

BACKGROUND: The CRISPR/Cas9 system is a powerful tool for genome editing, in which the sgRNA binds and guides the Cas9 protein for the sequence-specific cleavage. The protocol is employable in different organisms, but is often limited by cell damage due to the endonuclease activity of the introduced Cas9 and the potential off-target DNA cleavage from incorrect guide by the 20 nt spacer. RESULTS: In this study, after resolving some critical limits, we have established an efficient CRISPR/Cas9 system for the deletion of large genome fragments related to the biosynthesis of secondary metabolites in Myxococcus xanthus cells. We revealed that the high expression of a codon-optimized cas9 gene in M. xanthus was cytotoxic, and developed a temporally high expression strategy to reduce the cell damage from high expressions of Cas9. We optimized the deletion protocol by using the tRNA-sgRNA-tRNA chimeric structure to ensure correct sgRNA sequence. We found that, in addition to the position-dependent nucleotide preference, the free energy of a 20 nt spacer was a key factor for the deletion efficiency. CONCLUSIONS: By using the developed protocol, we achieved the CRISPR/Cas9-induced deletion of large biosynthetic gene clusters for secondary metabolites in M. xanthus DK1622 and its epothilone-producing mutant. The findings and the proposals described in this paper were suggested to be workable in other organisms, for example, other Gram negative bacteria with high GC content.

A Low-Power All-Digital on-Chip CMOS Oscillator for a Wireless Sensor Node.

This paper presents an all-digital low-power oscillator for reference clocks in wireless body area network (WBAN) applications. The proposed on-chip complementary metal-oxide-semiconductor (CMOS) oscillator provides low-frequency clock signals with low power consumption, high delay resolution, and low circuit complexity. The cascade-stage structure of the proposed design simultaneously achieves high resolution and a wide frequency range. The proposed hysteresis delay cell further reduces the power consumption and hardware costs by 92.4% and 70.4%, respectively, relative to conventional designs. The proposed design is implemented in a standard performance 0.18 µm CMOS process. The measured operational frequency ranged from 7 to 155 MHz, and the power consumption was improved to 79.6 µW (@7 MHz) with a 4.6 ps resolution. The proposed design can be implemented in an all-digital manner, which is highly desirable for system-level integration.

Optical coherent thermal emission by excitation of magnetic polariton in multilayer nanoshell trimer.

A theoretical demonstration is given of coherent thermal emission via the visible region by exciting magnetic polaritons in isolated metal-dielectric-metal multilayer nanoshells and the collective behavior in a trimer comprising multilayer nanoshells. The dipolar metallic core induces magnetic polaritons in the dielectric shell creating a large enhancement of the emissivity, whose mechanism is different from that of film-coupled metamaterials. The coupling effect of the magnetic polaritons and the electric/magnetic modes of symmetric nanoparticle trimers is discussed to understand the collective behavior in self-assembled nanoparticle clusters with potential solar energy utilizations. The concept of hybridization is employed to understand the collective magnetic polaritons of a multilayer nanoshell trimer. The fundamental understanding gained herein opens up new ways to explore, control, and tailor spectral absorptance, thus facilitating rational design of novel self-assembled nanoclusters for energy harvesting.

A high resolution on-chip delay sensor with low supply-voltage sensitivity for high-performance electronic systems.

An all-digital on-chip delay sensor (OCDS) circuit with high delay-measurement resolution and low supply-voltage sensitivity for efficient detection and diagnosis in high-performance electronic system applications is presented. Based on the proposed delay measurement scheme, the quantization resolution of the proposed OCDS can be reduced to several picoseconds. Additionally, the proposed cascade-stage delay measurement circuit can enhance immunity to supply-voltage variations of the delay measurement resolution without extra self-biasing or calibration circuits. Simulation results show that the delay measurement resolution can be improved to 1.2 ps; the average delay resolution variation is 0.55% with supply-voltage variations of ±10%. Moreover, the proposed delay sensor can be implemented in an all-digital manner, making it very suitable for high-performance electronic system applications as well as system-level integration.

All-digital transmit beamformer for portable high-frequency ultrasound imaging systems.

To meet the requirements of high-frequency ultrasound imaging systems, a transmit-beamforming integrated circuit with higher delay resolution than conventional transmit-beamforming circuits, which are typically implemented using field-programmable gate array chips, is presented. It also requires smaller volumes, allowing for portable applications. Its proposed design includes two all-digital delay-locked loops providing a specified digital control code for a counter-based beamforming delay chain (CBDC) to generate stable and suitable delays for exciting the array transducer elements without variations in process, voltage, and temperature. Moreover, to maintain the duty cycle of long propagation signals, this novel CBDC requires only a few delay cells, significantly reducing hardware costs and power consumption. Simulations were conducted, revealing a maximum time delay of 451.9 ns with a time resolution of 652 ps and a maximum lateral resolution error of 0.04 mm at 6.8 mm.

A Dual-Functional Orphan Response Regulator Negatively Controls the Differential Transcription of Duplicate groELs and Plays a Global Regulatory Role in Myxococcus.

Differential transcription of functionally divergent duplicate genes is critical for bacterial cells to properly and competitively function in the environment, but the transcriptional regulation mechanisms remain in mystery. Myxococcus xanthus DK1622 possesses two duplicate groELs with divergent functions. Here, we report that MXAN_4468, an orphan gene located upstream of groEL2, encodes a response regulator (RR) and is responsible for the differential expression regulation of duplicate groELs. This RR protein realizes its negative regulatory role via a novel dual-mode functioning manner: binding to the transcription repressor HrcA to enhance its transcriptional inhibition of duplicate groELs and binding to the 3' end of the MXAN_4468 sequence to specifically decrease the transcription of the following groEL2. Phosphorylation at the conserved 61st aspartic acid is required to trigger the regulatory functions of MXAN_4468. Pull-down experiment and mutation demonstrated that two noncognate CheA proteins, respectively belonging to the Che8 and Che7 chemosensory pathways, are involved in the protein phosphorylation. A transcriptome analysis, as well as the pull-down experiment, suggested that MXAN_4468 plays a global negative regulatory role in M. xanthus. This study elucidates, for the first time, the regulatory mechanism of differential transcription of bacterial duplicate groELs and suggests a global regulatory role of a dual-functional orphan RR. IMPORTANCE Multiply copied groELs require precise regulation of transcriptions for their divergent cellular functions. Here, we reported that an orphan response regulator (RR) tunes the transcriptional discrepancy of the duplicate groELs in Myxococcus xanthus DK1622 in a dual-functional mode. This RR protein has a conserved phosphorylation site, and the phosphorylation is required for the regulatory functions. Transcriptomic analysis, as well as a pull-down experiment, suggests that the RR plays a global regulatory role in M. xanthus. This study highlights that the dual-functional orphan RR might be involved in conducting the transcriptional symphony to stabilize the complex biological functions in cells.

The Regulation of LexA on UV-Induced SOS Response in Myxococcus xanthus Based on Transcriptome Analysis.

SOS response is a conserved response to DNA damage in prokaryotes and is negatively regulated by LexA protein, which recognizes specifically an "SOS-box" motif present in the promoter region of SOS genes. Myxococcus xanthus DK1622 possesses a lexA gene, and while the deletion of lexA had no significant effect on either bacterial morphology, UV-C resistance, or sporulation, it did delay growth. UV-C radiation resulted in 651 upregulated genes in M. xanthus, including the typical SOS genes lexA, recA, uvrA, recN and so on, mostly enriched in the pathways of DNA replication and repair, secondary metabolism, and signal transduction. The UV-irradiated lexA mutant also showed the induced expression of SOS genes and these SOS genes enriched into a similar pathway profile to that of wild-type strain. Without irradiation treatment, the absence of LexA enhanced the expression of 122 genes that were not enriched in any pathway. Further analysis of the promoter sequence revealed that in the 122 genes, only the promoters of recA2, lexA and an operon composed of three genes (pafB, pafC and cyaA) had SOS box sequence to which the LexA protein is bound directly. These results update our current understanding of SOS response in M. xanthus and show that UV induces more genes involved in secondary metabolism and signal transduction in addition to DNA replication and repair; and while the canonical LexA-dependent regulation on SOS response has shrunk, only 5 SOS genes are directly repressed by LexA.

Optimizing Electronic Quality Factor toward High-Performance Ge1- x - y Tax Sby Te Thermoelectrics: The Role of Transition Metal Doping.

Owing to high intrinsic figure-of-merit implemented by multi-band valleytronics, GeTe-based thermoelectric materials are promising for medium-temperature applications. Transition metals are widely used as dopants for developing high-performance GeTe thermoelectric materials. Herein, relevant work is critically reviewed to establish a correlation among transition metal doping, electronic quality factor, and figure-of-merit of GeTe. From first-principle calculations, it is found that Ta, as an undiscovered dopant in GeTe, can effectively converge energy offset between light and heavy conduction band extrema to enhance effective mass at high temperature. Such manipulation is verified by the increased Seebeck coefficient of synthesized Ge1- x - y Tax Sby Te samples from 160 to 180 µV K-1 at 775 K upon doping Ta, then to 220 µV K-1 with further alloying Sb. Characterization using electron microscopy also reveals the unique herringbone structure associated with multi-scale lattice defects induced by Ta doping, which greatly hinder phonon propagation to decrease thermal conductivity. As a result, a figure-of-merit of ≈2.0 is attained in the Ge0.88 Ta0.02 Sb0.10 Te sample, reflecting a maximum heat-to-electricity efficiency up to 17.7% under a temperature gradient of 400 K. The rationalized beneficial effects stemming from Ta doping is an important observation that will stimulate new exploration toward high-performance GeTe-based thermoelectric materials.

32-Channel transmit beamformer with high timing resolution for high-frequency ultrasound imaging systems.

This paper presents a 32-channel high timing resolution transmit-beamforming circuit for use in high-frequency ultrasound imaging systems. Conventional transmit-beamforming circuits are typically implemented using field-programmable gate array (FPGA) chips. However, it is difficult for FPGAs to provide high timing resolution to meet the beamforming requirements of high-frequency ultrasound imaging systems. The proposed transmit-beamforming design can generate stable and suitable delays to excite 32-channel array transducer elements without variations in the process, voltage, and temperature. In addition, the proposed low-complexity architecture can maintain the duty cycle of long prorogation signals with low hardware cost to meet the timing requirements of a large channel number array transducer. The proposed designed transmit beamformer uses 0.18-µm CMOS technology for a 30-MHz high-frequency linear array, and the simulation results show that the proposed transmit-beamforming application-specific integrated circuit can achieve a maximum time delay of 619.5 ns with a time resolution of 617 ps.

Functional Division Between the RecA1 and RecA2 Proteins in Myxococcus xanthus.

Myxococcus xanthus DK1622 has two RecA genes, recA1 (MXAN_1441) and recA2 (MXAN_1388), with unknown functional differentiation. Herein, we showed that both recA genes were induced by ultraviolet (UV) irradiation but that the induction of recA1 was more delayed than that of recA2. Deletion of recA1 did not affect the growth but significantly decreased the UV-radiation survival, homologous recombination (HR) ability, and induction of LexA-dependent SOS genes. In contrast, the deletion of recA2 markedly prolonged the lag phase of bacterial growth and increased the sensitivity to DNA damage caused by hydrogen peroxide but did not change the UV-radiation resistance or SOS gene inducibility. Protein activity analysis demonstrated that RecA1, but not RecA2, catalyzed DNA strand exchange (DSE) and LexA autocleavage in vitro. Transcriptomic analysis indicated that RecA2 has evolved mainly to regulate gene expression for cellular transportation and antioxidation. This is the first report of functional divergence of duplicated bacterial recA genes. The results highlight the evolutionary strategy of M. xanthus cells for DNA HR and genome sophistication.

Insights into the persistence and phenotypic effects of the endogenous and cryptic plasmid pMF1 in its host strain Myxococcus fulvus 124B02.

Many endogenous plasmids carry no noticeable benefits for their bacterial hosts, and the persistence of these 'cryptic plasmids' and their functional impacts are mostly unclear. In this study, we investigated these uncertainties using the social bacterium Myxococcus fulvus 124B02 and its endogenous plasmid pMF1. pMF1 possesses diverse genes that originated from myxobacteria, suggesting a longstanding co-existence of the plasmid with various myxobacterial species. The curing of pMF1 from 124B02 had almost no phenotypic effects on the host. Laboratory evolution experiments showed that the 124B02 strain retained pMF1 when subcultured on dead Escherichia coli cells but lost pMF1 when subcultured on living E. coli cells or on casitone medium; these results indicated that the persistence of pMF1 in 124B02 was environment-dependent. Curing pMF1 caused the mutant to lose the ability to predate and develop fruiting bodies more quickly than the pMF1-containing strain after they were subcultured on dead E. coli cells, which indicated that the presence of pMF1 in M. fulvus 124B02 has some long-term effects on its host. The results provide some new insights into the persistence and impacts of cryptic plasmids in their natural bacterial cells.