High-throughput identification of promoters and screening of highly active promoter-5'-UTR DNA region with different characteristics from Bacillus thuringiensis

Screening and Constructing a Library of Promoter-5'-UTR Complexes with Gradient Strength in Pediococcus acidilactici

The GRAS (generally recognized as safe) strain Pediococcus acidilactici is well known for its antibacterial and probiotic functions. Furthermore, as P. acidilactici has excellent high temperature and salt resistance, it is an ideal host for the production of food enzymes, food additives, and pharmaceuticals. In this regard, it is desirable and feasible to enhance the production of these products through the metabolic engineering of P. acidilactici. However, the rare gene expression elements greatly obstruct the development of engineering P. acidilactici. In this study, we screened and constructed a library of promoter-5'-UTR (PUTR) complexes in P. acidilactici DY15 for regulating gene expression at the transcription and translation levels. In the post-log phase, the mRNA and protein expression level ranges of the 90 screened native PUTRs were 0.059-2010% and 0.77-245%, respectively, of the P32 promoter. Besides, several PUTRs exhibited great expression stability under high temperature, salt, and ethanol stress. We analyzed the structure of PUTRs and obtained the conserved regions of the promoter and 5'-UTR. Based on the identified core regions of PUTRs, we constructed a panel of combinatorial PUTRs with higher and stable protein expression levels. The strongest combinatorial PUTR was 853% of the P32 promoter in the protein expression level. Finally, the obtained PUTRs were applied to optimize the expression level of aminotransferase and improve the phenyllactic acid (PLA) production in P. acidilactici DY15. The achieved yield was 950.6 mg/L, which was 79.2% higher than the wild-type strain. These results indicated that the obtained PUTRs with gradient strength had great potential for precisely regulating gene expression to achieve various goals in P. acidilactici.

Utilization of a strong promoter combined with the knockout of protease genes to improve the yield of Vip3Aa in Bacillus thuringiensis BMB171

BACKGROUND

Vip3Aa is an insecticidal protein secreted by some Bacillus thuringiensis strains during vegetative growth. It has excellent insecticidal activity, its mechanism of action is different from that of Cry protein, and it can delay the development of pest resistance. To date, Vip3Aa has been widely used in genetically modified Bt crops. However, the secretion of Vip3Aa by industrial production strains is usually very low. Moreover, most of the Vip3Aa in the medium is degraded by proteases, limiting its application as a biopesticide.

RESULTS

We report a novel constitutive strong promoter from B. thuringiensis, P_rsi , which directs the abundant expression of vip3Aa in B. thuringiensis BMB171. Furthermore, to reduce the degradation of Vip3Aa caused by proteases, we constructed B. thuringiensis mutants in which different protease genes were knocked out. We found that the degradation of Vip3Aa was greatly inhibited and its yield was significantly improved in a mutant that lacked all three protease genes.

CONCLUSION

Our results provide a new strategy to enhance the production of Vip3Aa in B. thuringiensis and have reference value for the research and development of novel bioinsecticides. © 2023 Society of Chemical Industry.

The RNA Chaperone Protein Hfq Regulates the Characteristic Sporulation and Insecticidal Activity of Bacillus thuringiensis

Bacillus thuringiensis (Bt) is one of the most widely used bio-insecticides at present. It can produce many virulence factors and insecticidal crystal proteins during growth and sporulation. Hfq, on the other hand, is a bacterial RNA chaperone that can regulate the function of different kinds of RNAs, thereby affecting various bacterial phenotypes. To further explore the physiological functions of Hfq in Bt, we took BMB171 as the starting strain, knocked out one, two, or three hfq genes in its genome in different combinations, and compared the phenotypic differences between the deletion mutant strains and the starting strain. We did observe significant changes in several phenotypes, including motility, biofilm formation, sporulation, and insecticidal activity against cotton bollworm, among others. Afterward, we found through transcriptome studies that when all hfq genes were deleted, 32.5% of the genes in Bt were differentially transcribed, with particular changes in the sporulation-related and virulence-related genes. The above data demonstrated that Hfq plays a pivotal role in Bt and can regulate its various physiological functions. Our study on the regulatory mechanism of Hfq in Bt, especially the mining of the regulatory network of its sporulation and insecticidal activity, could lay a theoretical foundation for the better utilization of Bt as an effective insecticide.

6S-1 RNA Contributes to Sporulation and Parasporal Crystal Formation in Bacillus thuringiensis

6S RNA is a kind of high-abundance non-coding RNA that globally regulates bacterial transcription by interacting with RNA polymerase holoenzyme. Through bioinformatics analysis, we found that there are two tandem 6S RNA-encoding genes in the genomes of Bacillus cereus group bacteria. Using Bacillus thuringiensis BMB171 as the starting strain, we have explored the physiological functions of 6S RNAs, and found that the genes ssrSA and ssrSB encoding 6S-1 and 6S-2 RNAs were located in the same operon and are co-transcribed as a precursor that might be processed by specific ribonucleases to form mature 6S-1 and 6S-2 RNAs. We also constructed two single-gene deletion mutant strains ΔssrSA and ΔssrSB and a double-gene deletion mutant strain ΔssrSAB by means of the markerless gene knockout method. Our data show that deletion of 6S-1 RNA inhibited the growth of B. thuringiensis in the stationary phase, leading to lysis of some bacterial cells. Furthermore, deletion of 6S-1 RNA also significantly reduced the spore number and parasporal crystal content. Our work reveals that B. thuringiensis 6S RNA played an important regulatory role in ensuring the sporulation and parasporal crystal formation.

Expression of ribosomal protection protein RppA is regulated by a ribosome-dependent ribo-regulator and two mistranslation products

Gene expression is tightly controlled by transcription factors and RNA regulatory elements, including trans-acting small RNAs, cis-regulatory riboswitches and ribosome-dependent ribo-regulators. In the present study, we demonstrated that a ribosome-dependent ribo-regulator and two mistranslation products co-regulate rppA (encoding a ribosomal protection protein) expression in Bacillus thuringiensis BMB171. The leader RNA of the rppA gene controls rppA expression via translation of leader ORF1 resident in its sequence. In the presence of chloramphenicol, a +1 frameshift product (ORF2) and a stop codon readthrough product (ORF3) of ORF1 emerged. ORF3 exerted a negative effect on rppA expression. By contrast, the ORF2 promoted rppA expression. The regulation mode identified in the present study will lead to a deeper understanding of bacterial gene expression.

Construction of a High-Expression System in Bacillus through Transcriptomic Profiling and Promoter Engineering

Bacillus subtilis is an ideal host for secretion and expression of foreign proteins. The promoter is one of the most important elements to facilitate the high-level production of recombinant protein. To expand the repertoire of strong promoters for biotechnological applications in Bacillus species, 14 highly transcribed genes based on transcriptome profiling of B. pumilus BA06 were selected and evaluated for their promoter strength in B. subtilis. Consequently, a strong promoter P₂₀₆₉ was obtained, which could drive the genes encoding alkaline protease (aprE) and green fluorescent protein (GFP) to express more efficiency by an increase of 3.65-fold and 18.40-fold in comparison with the control promoter (P_aprE), respectively. Further, promoter engineering was applied to P₂₀₆₉, leading to a mutation promoter (P_2069M) that could increase GFP expression by 3.67-fold over the wild-type promoter (P₂₀₆₉). Moreover, the IPTG-inducible expression systems were constructed using the lac operon based on the strong promoters of P₂₀₆₉ and P_2069M, which could work well both in B. subtilis and B. pumilus. In this study, highly efficient expression system for Bacillus was constructed based on transcriptome data and promoter engineering, which provide not only a new option for recombinant expression in B. subtilis, but also novel genetic tool for B. pumilus.

Unraveling the regulation of sophorolipid biosynthesis in Starmerella bombicola

Starmerella bombicola very efficiently produces the secondary metabolites sophorolipids (SLs). Their biosynthesis is not-growth associated and highly upregulated in the stationary phase. Despite high industrial and academic interest, the underlying regulation of SL biosynthesis remains unknown. In this paper, potential regulation of SL biosynthesis through the telomere positioning effect (TPE) was investigated, as the SL gene cluster is located adjacent to a telomere. An additional copy of this gene cluster was introduced elsewhere in the genome to investigate if this results in a decoy of regulation. Indeed, for the new strain, the onset of SL production was shifted to the exponential phase. This result was confirmed by RT-qPCR analysis. The TPE effect was further investigated by developing and applying a suitable reporter system for this non-conventional yeast, enabling non-biased comparison of gene expression between the subtelomeric CYP52M1- and the URA3 locus. This was done with a constitutive endogenous promotor (pGAPD) and one of the endogenous promotors of the SL biosynthetic gene cluster (pCYP52M1). A clear positioning effect was observed for both promotors with significantly higher GFP expression levels at the URA3 locus. No clear GFP upregulation was observed in the stationary phase for any of the new strains.

2-Methylcitrate cycle: a well-regulated controller of Bacillus sporulation

Bacillus thuringiensis is the most widely used eco-friendly biopesticide, containing two primary determinants of biocontrol, endospore and insecticidal crystal proteins (ICPs). The 2-methylcitrate cycle is a widespread carbon metabolic pathway playing a crucial role in channelling propionyl-CoA, but with poorly understood metabolic regulatory mechanisms. Here, we dissect the transcriptional regulation of the 2-methylcitrate cycle operon prpCDB and report its unprecedented role in controlling the sporulation process of B. thuringiensis. We found that the transcriptional activity of the prp operon encoding the three critical enzymes PrpC, PrpD, and PrpB in the 2-methylcitrate cycle was negatively regulated by the two global transcription factors CcpA and AbrB, while positively regulated by the LysR family regulator CcpC, which jointly account for the fact that the 2-methylcitrate cycle is specifically and highly active in the stationary phase of growth. We also found that the prpD mutant accumulated 2-methylcitrate, the intermediate metabolite of the 2-methylcitrate cycle, which delayed and inhibited sporulation at the early stage. Thus, our results not only revealed sophisticated transcriptional regulatory mechanisms for the metabolic 2-methylcitrate cycle but also identified 2-methylcitrate as a novel regulator of sporulation in B. thuringiensis.

A c-di-AMP riboswitch controlling kdpFABC operon transcription regulates the potassium transporter system in Bacillus thuringiensis

The intracellular K+ level in bacteria is strictly controlled by K+ uptake and efflux systems. Among these, KdpFABC is a high-affinity K+ transporter system that is generally activated by the KdpDE two-component system in response to K+ limitation stress. However, the regulatory mechanism remains obscure in bacteria lacking the kdpDE genes. Here we report that the transcription of a kdpFABC operon is distinctively regulated by a cyclic diadenylate monophosphate (c-di-AMP) riboswitch located at the 5'-untranslated region of kdp transcript, and binding of c-di-AMP to the riboswitch promotes its intrinsic termination that blocks the kdpFABC transcription. Further, the intracellular c-di-AMP concentration was found to decrease under the K+ limitation stress, leading to transcriptional read-through over the terminator to allow kdpFABC expression. This regulatory element is found predominantly in the Bacillus cereus group and correlate well with the K+ and c-di-AMP homeostasis that affects a variety of crucial cellular functions.

Transcriptome Landscape of Mycobacterium smegmatis

The non-pathogenic bacterium Mycobacterium smegmatis mc²155 has been widely used as a model organism in mycobacterial research, yet a detailed study about its transcription landscape remains to be established. Here we report the transcriptome, expression profiles and transcriptional structures through growth-phase-dependent RNA sequencing (RNA-seq) as well as other related experiments. We found: (1) 2,139 transcriptional start sites (TSSs) in the genome-wide scale, of which eight samples were randomly selected and further verified by 5′-RACE; (2) 2,233 independent monocistronic or polycistronic mRNAs in the transcriptome within the operon/sub-operon structures which are classified into five groups; (3) 47.50% (1016/2139) genes were transcribed into leaderless mRNAs, with the TSSs of 41.3% (883/2139) mRNAs overlapping with the first base of the annotated start codon. Initial amino acids of MSMEG_4921 and MSMEG_6422 proteins were identified by Edman degradation, indicating the presence of distinctive widespread leaderless features in M. smegmatis mc²155. (4) 150 genes with potentially wrong structural annotation, of which 124 proposed genes have been corrected; (5) eight highly active promoters, with their activities further determined by β-galactosidase assays. These data integrated the transcriptional landscape to genome information of model organism mc²155 and lay a solid foundation for further works in Mycobacterium.

Determination and optimization of a strong promoter element from Bacillus amyloliquefaciens by using a promoter probe vector

OBJECTIVE

To construct a promoter probe vector, pBE-bgaB, to screen strong promoters from Bacillus amyloliquefaciens.

RESULTS

266 colonies containing active promoter elements from the genomic DNA of B. amyloliquefaciens were identified. Among these, promoter P41 exhibited the strongest β-Gal activity in Escherichia coli and B. amyloliquefaciens. Sequence analysis showed that promoter P41 contained P _ykuN , a ykuN gene encoding flavodoxin. Optimization of the ribosome-binding site from P41 to P₃₈₂ improved β-Gal activity by ~ 200%.

CONCLUSION

A new strong promoter for protein expression and genetic engineering of Bacillus species.

Bicistronic expression strategy for high-level expression of recombinant proteins in Corynebacterium glutamicum

Directly using the promoter associated with 5'-untranslated region of a high-protein-abundance gene from the genome may cause low expression activity of an expression system. A bicistronic expression part containing the short 5' coding sequence of the source gene and an embedded Shine-Dalgarno sequence can cause higher expression levels of the recombinant gene in a bicistronic cassette. Here, we evaluated two methods to construct expression parts and exploited genomic sequence sources to provide specific functional sequences to complete the expression system. The architecture of the bicistronic part increased the expression levels of target genes and performed more reliably than conventional expression parts with the same promoter and 5' untranslated region. For Corynebacterium glutamicum, the strongest bicistronic part, HP-BEP4, was obtained from a heterologous sequence source, leading to a 2.24-fold increase in the expression level of fluorescent protein over constitutively expressed pXMJ19 or the production of more than 100 mg/L single-chain variable fragment (scFv). It could meet the needs of overexpressing key genes in C. glutamicum.

Bottleneck in secretion of α-amylase in Bacillus subtilis

Amylase plays an important role in biotechnology industries, and Gram-positive bacterium Bacillus subtilis is a major host to produce heterogeneous α-amylases. However, the secretion stress limits the high yield of α-amylase in B. subtilis although huge efforts have been made to address this secretion bottleneck. In this question-oriented review, every effort is made to answer the following questions, which look simple but are long-standing, through reviewing of literature: (1) Does α-amylase need a specific and dedicated chaperone? (2) What signal sequence does CsaA recognize? (3) Does CsaA require ATP for its operation? (4) Does an unfolded α-amylase is less soluble than a folded one? (5) Does α-amylase aggregate before transporting through Sec secretion system? (6) Is α-amylase sufficient stable to prevent itself from misfolding? (7) Does α-amylase need more disulfide bonds to be stabilized? (8) Which secretion system does PrsA pass through? (9) Is PrsA ATP-dependent? (10) Is PrsA reused after folding of α-amylase? (11) What is the fate of PrsA? (12) Is trigger factor (TF) ATP-dependent? The literature review suggests that not only the most of those questions are still open to answers but also it is necessary to calculate ATP budget in order to better understand how B. subtilis uses its energy for production and secretion.

Relative Strengths and Regulation of Different Promoter-Associated Sequences for Various blaSHV Genes and Their Relationships to β-Lactam Resistance

AIMS

This work investigated the relative strengths of different blaSHV promoter-associated sequences and their regulation function in blaSHV expression and β-lactam resistance.

METHODS

Recombinant plasmids with the promoter-associated sequences (P-W, P-S, P-IS, and P-WPD), tac promoter, and combined fragments of promoter and blaSHV were separately constructed and transformed into Escherichia coli DH5α. The relative strengths of the promoters indicated by the intensities of green fluorescent protein and the mRNA expression levels of blaSHV were compared. The minimum inhibitory concentration and extended spectrum β-lactamase phenotypes were evaluated.

RESULTS

The relative strengths were ranked as P-tac > P-WPD > P-IS > P-S > P-W. The mRNA expression and β-lactam resistance levels of the different promoter-associated sequence groups were generally consistent with the strength rank, but the extent of gfp and blaSHV mRNA levels varied significantly in each group. The β-lactam resistance levels were inconsistent with the strength rank in certain blaSHV groups. In relation to the different promoter-associated sequences, blaSHV-ESBLs displayed significantly different change modes of β-lactam resistance compared with blaSHV-non-ESBLs.

CONCLUSION

The mRNA expression and β-lactam resistance of the blaSHV showed consistencies and inconsistencies with the strengths of the promoter-associated sequences. The mechanisms accounting for these discrepancies need further investigation.

Identification of strong promoters based on the transcriptome of Bacillus licheniformis

OBJECTIVES

To expand the repertoire of strong promoters for high level expression of proteins based on the transcriptome of Bacillus licheniformis.

RESULTS

The transcriptome of B. licheniformis ATCC14580 grown to the early stationary phase was analyzed and the top 10 highly expressed genes/operons out of the 3959 genes and 1249 operons identified were chosen for study promoter activity. Using beta-galactosidase gene as a reporter, the candidate promoter pBL9 exhibited the strongest activity which was comparable to that of the widely used strong promoter p43. Furthermore, the pro-transglutaminase from Streptomyces mobaraensis (pro-MTG) was expressed under the control of promoter pBL9 and the activity of pro-MTG reached 82 U/ml after 36 h, which is 23% higher than that of promoter p43 (66.8 U/ml).

CONCLUSION

In our analyses of the transcriptome of B. licheniformis, we have identified a strong promoter pBL9, which could be adapted for high level expression of proteins in the host Bacillus subtilis.

Cyclic di-GMP contributes to adaption and virulence of Bacillus thuringiensis through a riboswitch-regulated collagen adhesion protein

Cyclic di-GMP is a ubiquitous second messenger that regulates diverse cellular processes in bacteria by binding to various protein or riboswitch effectors. In Bacillus thuringiensis BMB171, a c-di-GMP riboswitch termed Bc2 RNA resides in the 5'-untranslated region (5'-UTR) of an mRNA that encodes a collagen adhesion protein (Cap). The expression of cap was strongly repressed in parent strain BMB171 because of the presence of Bc2 RNA but was significantly promoted in the Bc2 RNA markerless deletion mutant. Bc2 RNA acts as a genetic "on" switch, which forms an anti-terminator structure to promote cap read-through transcription upon c-di-GMP binding. As a result, cap transcription was de-repressed under high c-di-GMP levels. Therefore, Bc2 RNA regulates cap expression using a repression/de-repression model. Bc2 RNA-regulated Cap was also found to be tightly associated with motility, aggregation, exopolysaccharide secretion, biofilm formation, and virulence of B. thuringiensis BMB171 against its host insect Helicoverpa armigera.

Promoter Screening from Bacillus subtilis in Various Conditions Hunting for Synthetic Biology and Industrial Applications

The use of Bacillus subtilis in synthetic biology and metabolic engineering is highly desirable to take advantage of the unique metabolic pathways present in this organism. To do this, an evaluation of B. subtilis’ intrinsic biological parts is required to determine the best strategies to accurately regulate metabolic circuits and expression of target proteins. The strengths of promoter candidates were evaluated by measuring relative fluorescence units of a green fluorescent protein reporter, integrated into B. subtilis’ chromosome. A total of 84 predicted promoter sequences located upstream of different classes of proteins including heat shock proteins, cell-envelope proteins, and proteins resistant against toxic metals (based on similarity) and other kinds of genes were tested. The expression levels measured ranged from 0.0023 to 4.53-fold of the activity of the well-characterized strong promoter P43. No significant shifts were observed when strains, carrying different promoter candidates, were cultured at high temperature or in media with ethanol, but some strains showed increased activity when cultured under high osmotic pressure. Randomly selected promoter candidates were tested and found to activate transcription of thermostable β-galactosidase (bgaB) at a similar level, implying the ability of these sequences to function as promoter elements in multiple genetic contexts. In addition, selected promoters elevated the final production of both cytoplasmic bgaB and secreted protein α-amylase to about fourfold and twofold, respectively. The generated data allows a deeper understanding of B. subtilis’ metabolism and will facilitate future work to develop this organism for synthetic biology.

Characterization of a natural triple-tandem c-di-GMP riboswitch and application of the riboswitch-based dual-fluorescence reporter

c-di-GMP riboswitches are structured RNAs located in the 5'-untranslated regions (5'-UTRs) of mRNAs that regulate expression of downstream genes in response to changing concentrations of the second messenger c-di-GMP. We discovered three complete c-di-GMP riboswitches (Bc3, Bc4 and Bc5 RNA) with similar structures, which are arranged in tandem to constitute a triple-tandem (Bc3-5 RNA) riboswitch in the 5'-UTR of the cspABCDE mRNA in Bacillus thuringiensis subsp. chinensis CT-43. Our results showed that this natural triple-tandem riboswitch controlled the expression of the reporter gene more stringently and digitally than the double-tandem or single riboswitch. A sandwich-like dual-fluorescence reporter was further constructed by fusing the Bc3-5 RNA gene between the two fluorescence protein genes amcyan and turborfp. This reporter strain was found to exhibit detectable fluorescence color changes under bright field in response to intracellular c-di-GMP level altered by induced expression of diguanylate cyclase (DGC) PleD. Using this system, two putative membrane-bound DGCs from B. thuringiensis and Xanthomonas oryzae were verified to be functional by replacing pleD with the corresponding DGC genes. This report represented the first native triple-tandem riboswitch that was applied to serve as a riboswitch-based dual-fluorescence reporter for the efficient and convenient verification of putative DGC activity in vivo.

Identification of a highly efficient stationary phase promoter in Bacillus subtilis

A promoter that enabled high-level expression of the target gene during the stationary phase in the absence of an inducer would facilitate the efficient production of heterogeneous proteins at a low cost. In this study, a genome-scale microarray-based approach was employed to identify promoters that induced high-level expression of the target genes in Bacillus subtilis from the late log phase to the stationary phase without an inducer. Eleven candidate promoters were selected based on B. subtilis microarray data and the quantitative PCR analysis. Among the selected promoters, Pylb exhibited the highest activity with the reporter bgaB during the stationary phase. Compared with P43 (a commonly used constitutive promoter), promoter Pylb could express two reporter genes (egfp and mApple), and the expression levels of EGFP and RFP were 7.8- and 11.3-fold higher than that of P43, respectively. This finding was verified by overexpression of the genes encoding pullulanase and organophosphorus hydrolase, the activities of which were 7.4- and 2.3-fold higher, respectively, when driven by Pylb compared with P43. Therefore, our results suggest that the Pylb promoter could be used to overexpress target genes without an inducer; this method could facilitate the identification and evaluation of attractive promoters in the genome.

Functional analysis of the sporulation-specific diadenylate cyclase CdaS in Bacillus thuringiensis

Cyclic di-AMP (c-di-AMP) is a recently discovered bacterial secondary messenger molecule, which is associated with various physiological functions. In the genus Bacillus, the intracellular level and turnover of c-di-AMP are mainly regulated by three diadenylate cyclases (DACs), including DisA, CdaA and CdaS, and two c-di-AMP-specific phosphodiesterases (GdpP and PgpH). In this study, we demonstrated that CdaS protein from B. thuringiensis is a hexameric DAC protein that can convert ATP or ADP to c-di-AMP in vitro and the N-terminal YojJ domain is essential for the DAC activity. Based on the markerless gene knock-out method, we demonstrated that the transcription of cdaS was initiated by the sporulation-specific sigma factor σ(H) and the deletion of cdaS significantly delayed sporulation and parasporal crystal formation. These findings contrast with similar experiments conducted using B. subtilis, wherein transcription of its cdaS was initiated by the sigma factor σ(G). Deletion of all the three DAC genes from a single strain was unsuccessful, suggesting that c-di-AMP is an indispensable molecule in B. thuringiensis. Phylogenetic analysis indicated increased diversity of CdaS in the B. cereus and B. subtilis Bacillus subgroups. In summary, this study identifies important aspects in the regulation of c-di-AMP in the genus Bacillus.

Enhanced production of l-sorbose in an industrial Gluconobacter oxydans strain by identification of a strong promoter based on proteomics analysis

Gluconobacter oxydans is capable of rapidly incomplete oxidation of many sugars and alcohols, which means the strain has great potential for industrial purposes. Strong promoters are one of the essential factors that can improve strain performance by overexpression of specific genes. In this study, a pipeline for screening strong promoters by proteomics analysis was established. Based on the procedure, a new strong promoter designated as PB932_2000 was identified in G. oxydans WSH-003. The promoter region was characterized based on known genome sequence information using BPROM. The strength of PB932_2000 was further assessed by analysis of enhanced green fluorescent protein (egfp) expression and comparison with egfp expression by two commonly used strong promoters, PE. coli_tufB and PG. oxydans_tufB. Both quantitative real-time PCR and fluorescence intensities for egfp gene expression showed that PB932_2000 promoter is stronger than the other two. Overexpression of d-sorbitol dehydrogenase (sldh) by PB932_2000 in G. oxydans WSH-003 enhanced the titer and productivity of l-sorbose synthesis from d-sorbitol by 12.0 % and 33.3 %, respectively. These results showed that proteomics analysis is an efficient way to identify strong promoters. The isolated promoter PB932_2000 could further facilitate the metabolic engineering of G. oxydans.

Plasmids are vectors for redundant chromosomal genes in the Bacillus cereus group

Background

Prokaryotic plasmids have played significant roles in the evolution of bacterial genomes and have a great impact on the metabolic functions of the host cell. Many bacterial strains contain multiple plasmids, but the relationships between bacterial plasmids and chromosomes are unclear. We focused on plasmids from the Bacillus cereus group because most strains contain several plasmids.

Results

We collected the genome sequences of 104 plasmids and 20 chromosomes from B. cereus group strains, and we studied the relationships between plasmids and chromosomes by focusing on the pan-genomes of these plasmids and chromosomes. In terms of basic features (base composition and codon usage), the genes on plasmids were more similar to the chromosomal variable genes (distributed genes and unique genes) than to the chromosomal core genes. Although all the functional categories of the chromosomal genes were exhibited by the plasmid genes, the proportions of each category differed between these two gene sets. The 598 gene families shared between chromosomes and plasmids displayed a uniform distribution between the two groups. A phylogenetic analysis of the shared genes, including the chromosomal core gene set, indicated that gene exchange events between plasmids and chromosomes occurred frequently during the evolutionary histories of the strains and species in this group. Moreover, the shared genes between plasmids and chromosomes usually had different promoter and terminator sequences, suggesting that they are regulated by different elements at the transcriptional level.

Conclusions

We speculate that for the entire B. cereus group, adaptive genes are preserved on both plasmids and chromosomes; however, in a single cell, homologous genes on plasmids and the chromosome are controlled by different regulators to reduce the burden of maintaining redundant genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-014-1206-5) contains supplementary material, which is available to authorized users.

Overlapping genes: a window on gene evolvability

Background

The forces underlying genome architecture and organization are still only poorly understood in detail. Overlapping genes (genes partially or entirely overlapping) represent a genomic feature that is shared widely across biological organisms ranging from viruses to multi-cellular organisms. In bacteria, a third of the annotated genes are involved in an overlap. Despite the widespread nature of this arrangement, its evolutionary origins and biological ramifications have so far eluded explanation.

Results

Here we present a comparative approach using information from 699 bacterial genomes that sheds light on the evolutionary dynamics of overlapping genes. We show that these structures exhibit high levels of plasticity.

Conclusions

We propose a simple model allowing us to explain the observed properties of overlapping genes based on the importance of initiation and termination of transcriptional and translational processes. We believe that taking into account the processes leading to the expression of protein-coding genes hold the key to the understanding of overlapping genes structures.