Comparison of CcrM-dependent methylation in Caulobacter crescentus and Brucella abortus by nanopore sequencing.

Bacteria rely on DNA methylation for restriction-modification systems and epigenetic control of gene expression. Here, we use direct detection of methylated bases by nanopore sequencing to monitor global DNA methylation in Alphaproteobacteria, where use of this technique has not yet been reported. One representative of this order, Caulobacter crescentus, relies on DNA methylation to control cell cycle progression, but it is unclear whether other members of this order, such as Brucella abortus, depend on the same systems. We addressed these questions by first measuring CcrM-dependent DNA methylation in Caulobacter and showing excellent correlation between nanopore-based detection and previously published results. We then directly measure the impact of Lon-mediated CcrM degradation on the epigenome, verifying that loss of Lon results in pervasive methylation. We also show that the AlkB demethylase has no global impact on DNA methylation during normal growth. Next, we report on the global DNA methylation in B. abortus for the first time and find that CcrM-dependent methylation is reliant on Lon but impacts the two chromosomes differently. Finally, we explore the impact of the MucR transcription factor, known to compete with CcrM methylation, on the Brucella methylome and share the results with a publicly available visualization package. Our work demonstrates the utility of nanopore-based sequencing for epigenome measurements in Alphaproteobacteria and reveals new features of CcrM-dependent methylation in a zoonotic pathogen.IMPORTANCEDNA methylation plays an important role in bacteria, maintaining genome integrity and regulating gene expression. We used nanopore sequencing to directly measure methylated bases in Caulobacter crescentus and Brucella abortus. In Caulobacter, we showed that stabilization of the CcrM methyltransferase upon loss of the Lon protease results in prolific methylation and discovered that the putative methylase AlkB is unlikely to have a global physiological effect. We measured genome-wide methylation in Brucella for the first time, revealing a similar role for CcrM in cell-cycle methylation but a more complex regulation by the Lon protease than in Caulobacter. Finally, we show how the virulence factor MucR impacts DNA methylation patterns in Brucella.

Increased Brucella abortus asRNA_0067 expression under intraphagocytic stressors is associated with enhanced virB2 transcription.

Intracellular pathogens like Brucella face challenges during the intraphagocytic adaptation phase, where the modulation of gene expression plays an essential role in taking advantage of stressors to persist inside the host cell. This study aims to explore the expression of antisense virB2 RNA strand and related genes under intracellular simulation media. Sense and antisense virB2 RNA strands increased expression when nutrient deprivation and acidification were higher, being starvation more determinative. Meanwhile, bspB, one of the T4SS effector genes, exhibited the highest expression during the exposition to pH 4.5 and nutrient abundance. Based on RNA-seq analysis and RACE data, we constructed a regional map depicting the 5' and 3' ends of virB2 and the cis-encoded asRNA_0067. Without affecting the CDS or a possible autonomous RBS, we generate the deletion mutant ΔasRNA_0067, significantly reducing virB2 mRNA expression and survival rate. These results suggest that the antisense asRNA_0067 expression is promoted under exposure to the intraphagocytic adaptation phase stressors, and its deletion is associated with a lower transcription of the virB2 gene. Our findings illuminate the significance of these RNA strands in modulating the survival strategy of Brucella within the host and emphasize the role of nutrient deprivation in gene expression.

Structure-function analysis of the cyclic ß-1,2-glucan synthase from Agrobacterium tumefaciens.

The synthesis of complex sugars is a key aspect of microbial biology. Cyclic ß-1,2-glucan (CßG) is a circular polysaccharide critical for host interactions of many bacteria, including major pathogens of humans (Brucella) and plants (Agrobacterium). CßG is produced by the cyclic glucan synthase (Cgs), a multi-domain membrane protein. So far, its structure as well as the mechanism underlining the synthesis have not been clarified. Here we use cryo-electron microscopy (cryo-EM) and functional approaches to study Cgs from A. tumefaciens. We determine the structure of this complex protein machinery and clarify key aspects of CßG synthesis, revealing a distinct mechanism that uses a tyrosine-linked oligosaccharide intermediate in cycles of polymerization and processing of the glucan chain. Our research opens possibilities for combating pathogens that rely on polysaccharide virulence factors and may lead to synthetic biology approaches for producing complex cyclic sugars.

Getting to the point: unipolar growth of Hyphomicrobiales.

The governing principles and suites of genes for lateral elongation or incorporation of new cell wall material along the length of a rod-shaped cell are well described. In contrast, relatively little is known about unipolar elongation or incorporation of peptidoglycan at one end of the rod. Recent work in three related model systems of unipolar growth (Agrobacterium tumefaciens, Brucella abortus, and Sinorhizobium meliloti) has clearly established that unipolar growth in the Hyphomicrobiales order relies on a set of genes distinct from the canonical elongasome. Polar incorporation of envelope components relies on homologous proteins shared by the Hyphomicrobiales, reviewed here. Ongoing and future work will reveal how unipolar growth is integrated into the alphaproteobacterial cell cycle and coordinated with other processes such as chromosome segregation and cell division.

Multiplicación de Brucella abortus y producción de óxido nítrico en dos líneas celulares de macrófagos de distinto origen / Multiplication of Brucella abortus and production of nitric oxide in two macrophage cell lines of different origin

Brucella abortus es una bacteria que causa abortos e infertilidad en el ganado y fiebre ondulante en el hombre. Se multiplica en el citoplasma celular evadiendo los mecanismos de muerte intracelular. El óxido nítrico (NO) es importante en la regulación de la respuesta inmune. En el presente trabajo estudiamos la habilidad de tres cepas de B. abortus para sobrevivir intracelularmente en dos líneas celulares de macrófagos. La multiplicación de bacterias en ambas líneas celulares fue determinada a distintos tiempos en número de UFC/ml, también fue observada al microscopio de campo claro y de fluorescencia utilizando Giemsa y naranja de acridina, respectivamente. La tinción de ambas líneas celulares inoculadas con B. abortus mostró un resultado concordante con el encontrado en la determinación del número de UFC. Fue confirmada la presencia de B. abortus por microscopía electrónica. Para medir la producción de NO se utilizó el reactivo de Griess. La multiplicación de la cepa rugosa RB51 disminuyó en ambas líneas celulares y los niveles de NO fueron mayores en células inoculadas con dicha cepa que cuando fueron inoculadas con las cepas lisas (S19 y 2308). Estos resultados sugieren que probablemente la ausencia de cadena O en el lipopolisacárido afecta el crecimiento intracelular de B. abortus.

Brucella abortus is a bacterium which causes abortions and infertility in cattle and undulant fever in humans. It multiplies intracellularly, evading the mechanisms of cellular death. Nitric oxide (NO) is important in the regulation of the immune response. In the present work, we studied the ability of three B. abortus strains to survive intracellularly in two macrophage cell lines. The bacterial multiplication in both cell lines was determined at two different times in UFC/ ml units. Moreover the inoculated cells were also observed under light-field and fluorescence microscopy stained with Giemsa and acridine orange, respectively. The stain of both cellular lines showed similar results with respect to the UFC/ml determination. The presence of B. abortus was confirmed by electronic microscopy. In both macrophage cell lines inoculated with RB51, the multiplication diminished and the level of NO was higher, compared with cells inoculated with smooth strains (S19 and 2308). These results suggest that the absence of O-chain of LPS probably has affects the intracellular growth of B. abortus.

Tipificación molecular de Brucella abortus cepa 19 y su aplicación al control de biológicos / Molecular characterization of Brucella abortus strain 19 and its application for controlling biologics

Brucella abortus es el agente etiológico de la brucelosis bovina. La cepa 19, utilizada en la elaboración de vacunas, puede ser identificada a través de una deleción en la región eri asociada con la sensibilidad al eritritol. Se optimizó un ensayo de PCR para caracterizar específicamente esta cepa. El método que describimos es un procedimiento rápido para identificar B. abortus y simultáneamente diferenciar la cepa 19 de otras cepas de B. abortus biovar 1. Hemos aplicado este ensayo para la detección de la cepa 19 en vacunas contra la brucelosis bovina elaboradas en Argentina. Los resultados indican que este método podría ser útil para el seguimiento de las cepas madres y semillas utilizadas en la producción industrial de esta vacuna. Esta metodología también contribuiría a la reducción del riesgo de la infección adquirida en el laboratorio y podría aplicarse como prueba de rutina para confirmar la presencia de B. abortus en vacunas no relacionadas.

Brucella abortus is the etiological agent of bovine brucellosis. The strain 19 used in vaccine elaboration can be identified through a deletion in the eri region associated with its susceptibility to erythritol. We optimized a PCR assay for specific characterization of this strain. The method described here is a rapid procedure that enables identification of B. abortus, and simultaneous differentiation of the strain 19 from other B. abortus biovar 1 strains. We applied the assay to detect the strain 19 in vaccines against B. abortus produced in Argentina. The results show this method could be used to follow vaccine seed cultures of this strain. The methodology could also contribute to reduce the risk of a laboratory-acquired infection and could be of great help as a routine test for confirmation of B. abortus in non related vaccines.