Rapid quasi-periodic oscillations in the relativistic jet of BL Lacertae

Blazars are active galactic nuclei (AGN) with relativistic jets whose non-thermal radiation is extremely variable on various timescales^1-3. This variability seems mostly random, although some quasi-periodic oscillations (QPOs), implying systematic processes, have been reported in blazars and other AGN. QPOs with timescales of days or hours are especially rare⁴ in AGN and their nature is highly debated, explained by emitting plasma moving helically inside the jet⁵, plasma instabilities^6,7 or orbital motion in an accretion disc^7,8. Here we report results of intense optical and γ-ray flux monitoring of BL Lacertae (BL Lac) during a dramatic outburst in 2020 (ref. ⁹). BL Lac, the prototype of a subclass of blazars¹⁰, is powered by a 1.7 × 10⁸ M_Sun (ref. ¹¹) black hole in an elliptical galaxy (distance = 313 megaparsecs (ref. ¹²)). Our observations show QPOs of optical flux and linear polarization, and γ-ray flux, with cycles as short as approximately 13 h during the highest state of the outburst. The QPO properties match the expectations of current-driven kink instabilities⁶ near a recollimation shock about 5 parsecs (pc) from the black hole in the wake of an apparent superluminal feature moving down the jet. Such a kink is apparent in a microwave Very Long Baseline Array (VLBA) image.

Blazar spectral variability as explained by a twisted inhomogeneous jet

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions-such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution-can explain snapshots of the spectral behaviour of blazars in many cases. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory.

[IDENTIFICATION OF CAUSATIVE AGENTS OF GLANDERS AND MELIOIDOSIS BASED ON PRINCIPLES OF POLYPHASE TAXONOMIC APPROACH]

AIM

Determine an optimal set of the most effective methods of identification and intraspecies typing ofcausative agents ofglanders and melioidosis. Materials andmethods. Bacteriologic, immunochemical, molecular-genetic methods were used.

RESULTS

A possibility to identify collection strains of pathogenic and closely related Burkholderia in semiautomatic systems is studied. Means of detection of informative variable genome segments ofthe specified microorganisms were developed, methods of their genetic typing were selected. Effectiveness of application of precipitating mAbs for differentiation of Burkholderia was established. Data on diagnostic possibilities of immunoglobulins fluorescing based on monoclonal antibodies of various etiotropic directionality for detection and identification of B. mallei and B. pseudomallei are generalized. Experimental series of amplification test-systems for identification of glanders and melioidosis causative agents in real-time PCR format are created.

CONCLUSION

A number of methods for identification and typing of glanders and melioidosis causative agents is proposed.

[GENOTYPING OF THE BURKHOLDERIA MALLEI STRAINS BASED ON DIFFERENT REGION ANALYSIS]

Development of the genotyping methods of glanders agent is urgent due to its high pathogenicity, lack of effective preventive measures and threat of the use of Burkholderia mallei as a biological weapon. In this work we proposed a scheme for the typing of the B. mallei strains based on different region analysis (DFR). The choice of variable loci differentially presented in various strains of glanders agents was performed by analyzing annotated whole-genome sequences of the B. mallei strains. Primers and fluorescence probes were designed for 9 selected loci. The amplification conditions for different regions were optimized in two variants: with electrophoretic detection and hybridization-fluorescence detection in the strip format. The possibility of applying the DFR analysis to genetic characterization of strains was assessed in 14 B. mallei strains. The genetic profiles of the studied B. mallei strains revealed that the developed DFR-typing scheme was characterized by high discrimination power (Hunter-Gaston index value was 0.92), reproducibility, rapidity, easy interpretation, and applicability for epidemiological surveillance of glanders.

[The comparative evalution of informativeness of immunologic and molecular genetic methods and means during stages of specific indication of melioidosis agent]

The reference-center of monitoring of agents of glanders and melioidosis carried out testing of reagents kits for diagnostic of agent of melioidosis and other close-related species of Burkholderiae in vitro. At the stage of specific identification of pathogenic Burkholderiae the diagnostic possibilities of commercial and experimental kits of reagents for express- and rapid analysis were evaluated. The criteria of evaluation of diagnostic value of kits of reagents were sensitivity, specificity and time of implementation of studies. The analysis with application of mono- and multi-locus amplification systems, including real-time polymerase chain reaction permitted during 5-6 hours to implement identification and differentiation of Burkholderia pseufomallei, B. thailandensis and B. cepacia.

[Molecular genetic analysis of Pseudomonas aeruginosa strains isolated from environment and patients in health care facilities]

AIM

Analysis of genetic heterogeneity of Pseudomonas aeruginosa strains isolated in and out of hospitals.

MATERIALS AND METHODS

To study the genetic diversity of 36 strains of P. aeruginosa plasmid analysis, random amplified polymorphic DNA (RAPD) technique as well as polymerase chain reaction for detection of virulence genes algD, lasB, toxA, plcH, plcN, exoS, nan1, and nan2.

RESULTS

Epidemically important strains were found in different ecological niches. It was shown that these virulence factors could play important roles in pathogenesis of infection.

CONCLUSION

RAPD technique was effective for analysis of P. aeruginosa isolates. Number of studied typing bands differed between related isolates for each random primer.

[The use of multilocus sequence typing (MLST) and randomly amplified polymorphic DNA (RAPD) for the differentiation between strains of Burkholderia mallei]

Burkholderia mallei is highly pathogenic microorganism for both humans and animals. In this work, the possibility of the use of the genotyping method for differentiation between strains of B. mallei was studied. A collection of 14 isolates of B. mallei was characterized using randomly amplified polymorphic DNA (RAPD) and multilocus sequence typing (MLST). RAPD was the best method used for detecting strain differences of B. mallei. It was suggested that this method would be an increasingly useful molecular epidemiological tool.

[Identification of the agents of coccidioidomycosis using polymerase chain reaction]

Two pairs of primers for diagnosis of coccidioidomycosis using the method of PCR were constructed. One pair was used for identification of the two species of Coccidioides (C. immitis and C. posadasil) on the basis of MBP-1 gene. The other pair was chosen on the basis of SOWgp82 gene, which encodes an immunodominant, spherule outer wall glycoprotein for detecting only C. posadasii. The used primers allowed the agents of coccidioidomycosis to be detected using PCR with high sensitivity and specificity. The effective method of isolation of fungus DNA from soil contaminated with arthroconidia of Coccidioides spp. was developed. It includes guanidinthiocyanate-phenol-chloroform deproteinization followed by DNA purification using nuclear sorption.