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A supply and temperature fluctuation compensation technique is proposed to solve the gain fluctuation of the residual voltage dynamic amplifier used in pipeline analog-to-digital converter (ADC). Combining slave amplifier with the positive temperature coefficient (PTAT) voltage generation circuit, the gain of the amplifier under different temperature is calibrated adaptively without any complex hardware. At the same time, PTAT can also compensate the fluctuation voltage of power supply then the voltage gain of the amplifier is kept. The design is simulated with 40nm process, the voltage gain variation is less than 1.9% in -40℃~80℃ and 1.4% at the supply voltage range of 1.05V to 1.15V.

A digital adaptive mismatch calibration (DAMC) circuit is proposed to decrease the output jitter of phase-locked loop (PLL). After amplifying the phase error with a linear time amplifier (TA), the DAMC adopts a successive approximation pulse width calibration method to reduce the mismatch current of the charge pump. The PLL prototype is fabricated in a 40nm process, the static phase error of the proposed PLL can be reduced from 358 ps to 10 ps at a 50 MHz reference clock approximately, and the RMS jitter of the PLL output is reduced from 4.91 ps to 3.59 ps, and the extended DAMC area only occupies 1.3% of the whole PLL area.

In this paper, we propose a new kind of optomechanical metamaterial based on a planar ELC-type absorbing structure fabricated on the low-loss flexible substrate. The nonlinear coupling mechanism and nonlinear response phenomenon of the proposed optomechanical metamaterial driven by electromagnetic induced force are analyzed theoretically. The mechanical deformation/displacement and the mechanical resonance frequency shift of the metamaterial unit deposed on the flexible substrate are also numerically and experimentally demonstrated to reveal the coupling phenomenon of electromagnetic field and mechanical field. These results will help researchers to further understand the multi-physics interactions of optomechanical metamaterials and will promote the developments of new type of metasurface for high-efficiency dynamic electromagnetic wave controlling and formatting.

The problem of simultaneous localization and mapping (SLAM) has been extensively studied by using a variety of specialized sensors. In this paper, we show that the SLAM could be realized using a sensor-rich smartphone. We assume that an indoor pedestrian always carries a sounding smartphone and the pedestrian moves autonomously inside a room. At every step, the loudspeaker of the smartphone produces a chirp pulse (frequency band is in the upper of human hearing area), the microphone of this smartphone registers the echoes, and the inertial sensors record the accelerometer and gyroscope readings, then the position of the moving pedestrian and the geometry map of the room are done simultaneously. However, when in a rectangular room of regular shape, reconstructing the room geometry at each sound source position is quite redundant. To avoid this redundancy and improve the sound source localization performance, we address SLAM by Matrix Analysis-based geometry estimation, and then this information is applied to the real-time positioning requirements taking the advantage of multi-source information fusion concept. Finally, we show the effectiveness of the proposed SLAM method by experiments with real measured acoustic events, the result fully demonstrates that the proposed SLAM method could be easily implemented using the smartphone carried by the pedestrian.

Many biological species distinguish self from nonself by using different mechanisms. Higher animals recognize close kin via complex processes that often involve the five senses, cognition, and learning, whereas some microbes achieve self-recognition simply through the activity of a single genetic locus. Here we describe a single locus, traA, in myxobacteria that governs cell-cell recognition within natural populations. We found that traA is widespread across the order Myxococcales. TraA is highly polymorphic among diverse myxobacterial isolates, and such polymorphisms determine selectivity in self-recognition. Through bioinformatic and experimental analyses, we showed that traA governs many distinct recognition groups within Myxococcales. This report provides an example in which a single locus influences social recognition across a wide phylogenetic range of natural populations., Self-recognition underlies sociality in many group-living organisms. In bacteria, cells use various strategies to recognize kin to form social groups and, in some cases, to transition into multicellular life. One strategy relies on a single genetic locus that encodes a variable phenotypic tag (“greenbeard”) for recognizing other tag bearers. Previously, we discovered a polymorphic cell surface receptor called TraA that directs self-identification through homotypic interactions in the social bacterium Myxococcus xanthus. Recognition by TraA leads to cellular resource sharing in a process called outer membrane exchange (OME). A second gene in the traA operon, traB, is also required for OME but is not involved in recognition. Our prior studies of TraA identified only six recognition groups among closely related M. xanthus isolates. Here we hypothesize that the number of traA polymorphisms and, consequently, the diversity of recognition in wild isolates are much greater. To test this hypothesis, we expand the scope of TraA characterization to the order Myxococcales. From genomic sequences within the three suborders of Myxococcales, we identified 90 traA orthologs. Sequence analyses and functional characterization of traAB loci suggest that OME is well maintained among diverse myxobacterial taxonomic groups. Importantly, TraA orthologs are highly polymorphic within their variable domain, the region that confers selectivity in self-recognition. We experimentally defined 10 distinct recognition groups and, based on phylogenetic and experimental analyses, predicted >60 recognition groups among the 90 traA alleles. Taken together, our findings revealed a widespread greenbeard locus that mediates the diversity of self-recognition across the order Myxococcales.

Myxobacteria are social microbes that exhibit complex multicellular behaviors. By use of fluorescent reporters, we show that Myxococcus xanthus isolates produce long narrow filaments that are enclosed by the outer membrane (OM) and contain proteins. We show that these OM tube (OMT) structures are produced at surprisingly high levels when cells are placed in liquid medium or buffer without agitation. OMTs can be long and easily exceed multiple cell lengths. When viewed by transmission electron microscopy, their morphology varies between tubes and chain-like structures. Intermediate-like structures are also found, suggesting that OMTs may transition between these two morphotypes. In support of this, video epifluorescence microscopy found that OMTs in solution dynamically twist and jiggle. On hard surfaces, myxobacteria glide, and upon cell-cell contact, they can efficiently exchange their OM proteins and lipids by a TraAB-dependent mechanism. Although the structure of OMTs hints at a possible role as conduits for exchange, evidence is presented to the contrary. For example, abundant OMT production occurs in traA or traB mutants and when cells are grown in liquid medium, yet transfer cannot occur under these conditions. Thus, genetic and environmental conditions that promote OMT production are incongruent with OM exchange.

Summary Microbial biofilms represent heterogeneous populations of cells that form intimate contacts. Within these populations cells communicate, cooperate and compete. Myxobacteria are noted for their complex social interactions, including gliding motility and lipoprotein exchange. Here, we investigated cis protein sequence and cellular behaviour requirements for lipoprotein transfer between Myxococcus xanthus cells. Specifically, an outer membrane (OM) type II signal sequence (SS) fused to the heterologous mCherry fluorescent reporter resulted in OM localization. When donor cells harbouring SSOM–mCherry were mixed with GFP-labelled recipient cells they developed red fluorescence. Our results surprisingly showed that a type II SS for OM localization, but not inner membrane localization, was necessary and sufficient for rapid and efficient heterologous protein transfer. Importantly, transfer did not occur in liquid or on surfaces where cells were poorly aligned. We conclude that cell–cell contact and alignment is a critical step for lipoprotein exchange. We hypothesize that protein transfer facilitates cooperative myxobacteria behaviours.

The chemolithoautotroph Nitrosomonas europaea has two genes predicted to encode outer-membrane (OM) ferrioxamine transporters. Expression of the ferrioxamine uptake system required induction, as shown by the shorter lag phase in ferrioxamine-containing cultures when ferrioxamine-exposed cells were used as an inoculum. The two OM ferrioxamine siderophore transporters encoded by foxA(1) (NE1097) and foxA(2) (NE1088) were produced only in cells grown in Fe-limited ferrioxamine-containing medium. The inactivation of foxA(1), singly or in combination with foxA(2), prevented growth in Fe-limited medium containing excess desferrioxamine (DFX). The foxA(2)-disrupted single mutant grew poorly in the regular Fe-limited (0.2 microM) medium with 10 microM DFX, but grew well when the Fe level was raised to 1.0 microM with 10 microM DFX. For efficient acquisition of Fe-loaded ferrioxamine, N. europaea needs both ferrioxamine transporters FoxA(1) and FoxA(2). FoxA(1) probably regulates its own production, and it controls the production of FoxA(2) as well.

Tn 5 mutants of Sinorhizobium meliloti RMB7201 which swarmed 1.5 to 2.5 times faster than the parental strain in semisolid agar, moist sand, and viscous liquid were identified. These faster-swarming (FS) mutants outgrew the wild type 30- to 40-fold within 2 days in mixed swarm colonies. The FS mutants survived and grew as well as or better than the wild type under all of the circumstances tested, except in a soil matrix subjected to air drying. Exopolysaccharide (EPS) synthesis was reduced in each of the FS mutants when they were grown on defined succinate-nitrate medium, but the extent of reduction was different for each. It appears that FS behavior likely results from a modest, general derepression of motility involving an increased proportion of motile and flagellated cells and an increased average number of flagella per cell and increased average flagellar length. Spontaneous FS variants of RMB7201 were obtained at a frequency of about 1 per 10,000 to 20,000 cells by either enrichment from the periphery of swarm colonies or screening of colonies for reduced EPS synthesis on succinate-nitrate plates. The spontaneous FS variants and Tn 5 FS mutants were symbiotically effective and competitive in alfalfa nodulation. Reversion of FS variants to wild-type behavior was sporadic, indicating that reversion is affected by unidentified environmental factors. Based on phenotypic and molecular differences between individual FS variants and mutants, it appears that there may be multiple genetic configurations that result in FS behavior in RMB7201. The facile isolation of spontaneous FS variants of Escherichia coli and Pseudomonas aeruginosa indicates that switching to FS behavior may be fairly common among bacterial species. The substantial growth advantage of FS mutants and variants wherever nutrient gradients exist suggests that switching to FS forms may be an important behavioral adaptation in natural environments.

The changes in motility, chemotactic responsiveness, and flagellation of Rhizobium meliloti RMB7201, L5-30, and JJ1c10 were analyzed after transfer of the bacteria to buffer with no available C, N, or phosphate. Cells of these three strains remained viable for weeks after transfer to starvation buffer (SB) but lost all motility within just 8 to 72 h after transfer to SB. The rates of motility loss differed by severalfold among the strains. Each strain showed a transient, two- to sixfold increase in chemotactic responsiveness toward glutamine within a few hours after transfer to SB, even though motility dropped substantially during the same period. Strains L5-30 and JJ1c10 also showed increased responsiveness to the nonmetabolizable chemoattractant cycloleucine. Cycloleucine partially restored the motility of starving cells when added after transfer and prevented the loss of motility when included in the SB used for initial suspension of the cells. Thus, interactions between chemoattractants and their receptors appear to affect the regulation of motility in response to starvation independently of nutrient or energy source availability. Electron microscopic observations revealed that R. meliloti cells lost flagella and flagellar integrity during starvation, but not as fast, nor to such a great extent, as the cells lost motility. Even after prolonged starvation, when none of the cells were actively motile, about one-third to one-half of the initially flagellated cells retained some flagella. Inactivation of flagellar motors therefore appears to be a rapid and important response of R. meliloti to starvation conditions. Flagellar-motor inactivation was at least partially reversible by addition of either cycloleucine or glucose. During starvation, some cells appeared to retain normal flagellation, normal motor activity, or both for relatively long periods while other cells rapidly lost flagella, motor activity, or both, indicating that starvation-induced regulation of motility may proceed differently in various cell subpopulations.

Cell-cell recognition is a fundamental process that allows cells to coordinate multicellular behaviors. Some microbes, such as myxobacteria, build multicellular fruiting bodies from free-living cells. However, how bacterial cells recognize each other by contact is poorly understood. Here we show that myxobacteria engage in recognition through interactions between TraA cell surface receptors, which leads to the fusion and exchange of outer membrane (OM) components. OM exchange is shown to be selective among 17 environmental isolates, as exchange partners parsed into five major recognition groups. TraA is the determinant of molecular specificity because: (i) exchange partners correlated with sequence conservation within its polymorphic PA14-like domain and (ii) traA allele replacements predictably changed partner specificity. Swapping traA alleles also reprogrammed social interactions among strains, including the regulation of motility and conferred immunity from inter-strain killing. We suggest that TraA helps guide the transition of single cells into a coherent bacterial community, by a proposed mechanism that is analogous to mitochondrial fusion and fission cycling that mixes contents to establish a homogenous population. In evolutionary terms, traA functions as a rare greenbeard gene that recognizes others that bear the same allele to confer beneficial treatment., Author Summary How individual cells recognize each other to cooperate and assemble functional tissues is a fundamental question in biology. Although multicellularity is a trait that is typically associated with eukaryotes, certain groups of bacteria also exhibit complex multicellular behaviors, which are perhaps best exemplified by the myxobacteria. For example, in response to starvation myxobacteria will assemble fruiting bodies, wherein thousands of cells function as a coherent unit in development and cell differentiation. However, how myxobacteria, or for that matter other bacteria, recognize cooperating partnering cells through cell contact-dependent interactions is poorly understood. Here we describe a mechanism where myxobacteria distinguish sibling and cohort cells from other myxobacteria isolates. We show that molecular recognition is mediated by a cell surface receptor called TraA. Cell-cell specificity involves mutual recognition by partnering cells and is mediated by proposed homotypic TraA interactions. The specificity for recognition is determined by variable sequences found within traA alleles. Thus, simply swapping traA alleles between isolates predictably changes partner recognition. TraA-TraA recognition in turn leads to the fusion and exchange of outer membrane (OM) components between cells. We suggest that OM exchange allows the cells to communicate and become homogenous with respect to their OM proteome. We further suggest these interactions build a cohesive cell population that functions in multicellular processes.

Myxobacteria exhibit complex social traits during which large populations of cells coordinate their behaviors. An iconic example is their response to starvation: thousands of cells move by gliding motility to build a fruiting body in which vegetative cells differentiate into spores. Here we review mechanisms that the model species Myxococcus xanthus uses for cellecell interactions, with a focus on developmental signaling and social gliding motility. We also discuss a newly discovered cellecell interaction whereby myxobacteria exchange their outer membrane (OM) proteins and lipids. The mechanism of OM transfer requires physical contact between aligned cells on a hard surface and is apparently mediated by OM fusion. The TraA and TraB proteins are required in both donor and recipient cells for transfer, suggesting bidirectional exchange, and TraA is thought to serve as a cell surface adhesin. OM exchange results in phenotypic changes that can alter gliding motility and development and is proposed to represent a novel microbial interacting platform to coordinate multicellular activities. 2012 Published by Elsevier Masson SAS on behalf of Institut Pasteur.

Biofilms are dense microbial communities. Although widely distributed and medically important, how biofilm cells interact with one another is poorly understood. Recently, we described a novel process whereby myxobacterial biofilm cells exchange their outer membrane (OM) lipoproteins. For the first time we report here the identification of two host proteins, TraAB, required for transfer. These proteins are predicted to localize in the cell envelope; and TraA encodes a distant PA14 lectin-like domain, a cysteine-rich tandem repeat region, and a putative C-terminal protein sorting tag named MYXO-CTERM, while TraB encodes an OmpA-like domain. Importantly, TraAB are required in donors and recipients, suggesting bidirectional transfer. By use of a lipophilic fluorescent dye, we also discovered that OM lipids are exchanged. Similar to lipoproteins, dye transfer requires TraAB function, gliding motility and a structured biofilm. Importantly, OM exchange was found to regulate swarming and development behaviors, suggesting a new role in cell–cell communication. A working model proposes TraA is a cell surface receptor that mediates cell–cell adhesion for OM fusion, in which lipoproteins/lipids are transferred by lateral diffusion. We further hypothesize that cell contact–dependent exchange helps myxobacteria to coordinate their social behaviors., Author Summary All cells interact with their environment, including other cells, to elicit cellular responses. Cell–cell interactions between eukaryotic cells are widely appreciated as large multicellular organisms coordinate cell behaviors for tissue and organ functions. In bacteria cell–cell interactions are not widely appreciated, as these organisms are relatively simple and are often depicted as single-cell entities. However, over the past decade, the concept of bacteria living in microbial communities or biofilms has received broad acceptance as a major lifestyle. As biofilm cells are packed in tight physical contact, there is an opportunity for cell–cell signaling to provide spatial and physiological clues of neighboring cells to elicit cellular responses. Although much has been learned about diffusible signals through quorum sensing, little is known about cell contact–dependent signaling in bacteria. In this report we describe a new mechanism where bacterial cells within structured biofilms form contacts that allow cellular material to be exchanged. This exchange elicits phenotypic changes, including in cell movements and development. We hypothesize that OM exchange involves kin recognition that bestows social benefits to myxobacterial populations.

Myxobacteria are predatory and are prolific producers of secondary metabolites. Here, we tested a hypothesized role that secondary metabolite antibiotics function as weapons in predation. To test this, a Myxococcus xanthus Δta1 mutant, blocked in antibiotic TA (myxovirescin) production, was constructed. This TA − mutant was defective in producing a zone of inhibition (ZOI) against Escherichia coli . This shows that TA is the major M. xanthus -diffusible antibacterial agent against E. coli . Correspondingly, the TA − mutant was defective in E. coli killing. Separately, an engineered E. coli strain resistant to TA was shown to be resistant toward predation. Exogenous addition of spectinomycin, a bacteriostatic antibiotic, rescued the predation defect of the TA − mutant. In contrast, against Micrococcus luteus the TA − mutant exhibited no defect in ZOI or killing. Thus, TA plays a selective role on prey species. To extend these studies to other myxobacteria, the role of antibiotic corallopyronin production in predation was tested and also found to be required for Corallococcus coralloides killing on E. coli . Next, a role of TA production in myxobacterial fitness was assessed by measuring swarm expansion. Here, the TA − mutant had a specific swarm rate reduction on prey lawns, and thus reduced fitness, compared to an isogenic TA + strain. Based on these observations, we conclude that myxobacterial antibiotic production can function as a predatory weapon. To our knowledge, this is the first report to directly show a link between secondary metabolite production and predation.

The technique of weak small target detection and recognition has been the key technique of the electro-optical detecting system, many scholars are engaging the research of detection for weak and small targets. The effective detection for small targets in low SNR images is still a hot research field. Because infrared sensor is easily affected by atmosphere hot radiation, long distance and sensor noise, the detected targets in infrared images often present like small targets and drowned in noise. The basic problem inherent to extent the detection range is the detection of small, low observable, no obvious structural information in images and complicated background. In order to improve the detection ratio of weak small targets and decrease the false alarming ratio in the condition of complicated background, the paper presents the technology of pretreatment of infrared images and the technology of detection for weak small targets, mainly including the technology of Sobel edge algorithm and multi-degree and multi-orientation gradient. Based upon horizon-correlative characteristic of infrared images which were gotten by scanning, considering of the target properties in complicated background, an algorithm of weak and small target detection is presented. Because the images appear horizon-correlative characteristic, Sobel horizontal operator is adopted. By this algorithm, the background clutter was suppressed. Then an adaptive threshold was proposed to extract the precise location of small target. Incorporated with the two methods, a single frame weak and small target detection algorithm was built. Its high performance was then proved in a serial of experiments. In order to solve the detection problems of weak and small infrared targets under complicated background, a detection algorithm integrating with multi-degree and multi-orientation gradient fusion is proposed. Based on the principle of infrared radiation property of target, i.e., the gradient variations of pixel gray scale in horizontal and vertical directions, the algorithm handles the property of weak and small target into analysis of image singularity and detects targets by means of multi-degree gradient step length. Then the detected results show this method can remove most false targets. As a result, the algorithms have fulfilled the engineering demands for reliability and real-time property.

Quadrature amplitude modulation (QAM) is applied extensive in the fields of broadcasting and satellite communication for its high efficiency on power consumption and bandwidth using. The paper introduces a novel circuit which makes use of CORDIC algorithm to implement QAM modulator. The CORDIC module can complete ASK function as well as export two-way orthogonal signal synchronously .By using this character, we can implement high speed QAM modulator with single filter.

Summary Analysis of the structure and inventory of the genome of Nitrosomonas eutropha C91 revealed distinctive features that may explain the adaptation of N. eutropha-like bacteria to N-saturated ecosystems. Multiple gene-shuffling events are apparent, including mobilized and replicated transposition, as well as plasmid or phage integration events into the 2.66 Mbp chromosome and two plasmids (65 and 56 kbp) of N. eutropha C91. A 117 kbp genomic island encodes multiple genes for heavy metal resistance, including clusters for copper and mercury transport, which are absent from the genomes of other ammonia-oxidizing bacteria (AOB). Whereas the sequences of the two ammonia monooxygenase and three hydroxylamine oxidoreductase gene clusters in N. eutropha C91 are highly similar to those of Nitrosomonas europaea ATCC 19718, a break of synteny in the regions flanking these clusters in each genome is evident. Nitrosomonas eutropha C91 encodes four gene clusters for distinct classes of haem-copper oxidases, two of which are not found in other aerobic AOB. This diversity of terminal oxidases may explain the adaptation of N. eutropha to environments with variable O2 concentrations and/or high concentrations of nitrogen oxides. As with N. europaea, the N. eutropha genome lacks genes for urease metabolism, likely disadvantaging nitrosomonads in low-nitrogen or acidic ecosystems. Taken together, this analysis revealed significant genomic variation between N. eutropha C91 and other AOB, even the closely related N. europaea, and several distinctive properties of the N. eutropha genome that are supportive of niche specialization.

Resilient Packet Ring (RPR) is a new technology has just been standardized as IEEE 802.17 for Metropolitan Area Networks (MAN). RPR is significantly more efficient than other technologies especially other ring technologies . But the ring topology is not suit for "Star" pattern traffic which exiting widely in WAN. And when there are too many nodes on a ring, it will risk more time delay and less throughput per node. In this paper, we introduce a novel star-ring architecture and analyse its key technology such as physical topology, logical topology, data path and scalability . The analysis show that the star-ring architecture has advantage than ring and is not hard to implement.

Resilient Packet Ring (RPR) is a new technology has just been standardized as IEEE 802.17 for Metropolitan Area Networks (MAN). RPR can be regarded as a buffer (or register) insertion ring. Thus, the buffer size configuration is very important to the performance of RPR. Currently, it is lacked for its theoretic analysis. In this paper, we initiated RPR'S queue length into queuing theory and investigated their relations with throughput and number of nodes. The results are very close to those of engineering. It also turns out some new points such as queue length does not increase linearly with number of nodes as in our imagination.

The transcriptome of Nitrosomonas europaea was analyzed with whole-genome microarrays. Growing cells were compared to cells deprived of (NH4)2SO4 and Na2CO3. Hybridization signals were detected for 76% of the genes represented on the array under either or both conditions. Transcript levels for 68% of the genes were at least twofold higher in growing cells than in deprived cells, while only 0.42% of the genes were present at more than twofold higher levels in deprived cells. Transcript levels for the remaining 7% of the genes did not change significantly with the treatments. These trends were confirmed for selected genes by Northern hybridizations and quantitative RT-PCR. Compared to heterotrophic bacteria, N. europaea downregulates a greater proportion of its genes and fewer genes appear to be associated with the adaptation to starvation.

Nitrosomonas europaea, as an ammonia-oxidizing bacterium, has a high Fe requirement and has 90 genes dedicated to Fe acquisition. Under Fe-limiting conditions (0.2 microM Fe), N. europaea was able to assimilate up to 70% of the available Fe in the medium even though it is unable to produce siderophores. Addition of exogenous siderophores to Fe-limited medium increased growth (final cell mass). Fe-limited cells had lower heme and cellular Fe contents, reduced membrane layers, and lower NH3- and NH2OH-dependent O2 consumption activities than Fe-replete cells. Fe acquisition-related proteins, such as a number of TonB-dependent Fe-siderophore receptors for ferrichrome and enterobactin and diffusion protein OmpC, were expressed to higher levels under Fe limitation, providing biochemical evidence for adaptation of N. europaea to Fe-limited conditions.

Nitrosomonas europaeais an aerobic ammonia-oxidizing bacterium that participates in the C and N cycles.N. europaeautilizes CO2as its predominant carbon source, and is an obligate chemolithotroph, deriving all the reductant required for energy and biosynthesis from the oxidation of ammonia (NH3) to nitrite (). This bacterium fixes carbon via the Calvin–Benson–Bassham (CBB) cycle via a type I ribulose bisphosphate carboxylase/oxygenase (RubisCO). The RubisCO operon is composed of five genes,cbbLSQON. This gene organization is similar to that of the operon for ‘green-like’ type I RubisCOs in other organisms. ThecbbRgene encoding the putative regulatory protein for RubisCO transcription was identified upstream ofcbbL. This study showed that transcription ofcbbgenes was upregulated when the carbon source was limited, whileamo,haoand other energy-harvesting-related genes were downregulated.N. europaearesponds to carbon limitation by prioritizing resources towards key components for carbon assimilation. Unlike the situation foramogenes, NH3was not required for the transcription of thecbbgenes. All fivecbbgenes were only transcribed when an external energy source was provided. In actively growing cells, mRNAs from the five genes in the RubisCO operon were present at different levels, probably due to premature termination of transcription, rapid mRNA processing and mRNA degradation.