Biology subjects

Rossi, M.

Publications and source records attributed to Rossi, M..

5 recordsLinked to original sources

bioRxiv2018

The ULK1-FBXW5-SEC23B nexus controls autophagy

In response to nutrient deprivation, the cell needs to mobilize an extensive amount of membrane to form and grow the autophagosome, allowing the progression of autophagy. By providing membranes and a source for LC3 lipidation, COPII (Coat Protein Complex II) localizes to the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC) and promotes autophagosome biogenesis. However, the molecular mechanisms that, in response to starvation, divert COPII from the secretory pathway to the autophagic pathway are largely unknown. Here, we show that the F-box protein FBXW5 targets SEC23B, a component of COPII, for proteasomal degradation and that this event limits the autophagic flux in the presence of nutrients. In response to starvation, ULK1 phosphorylates SEC23B on Serine 186, preventing the interaction of SEC23B with FBXW5 and, therefore, inhibiting its degradation. Phosphorylated and stabilized SEC23B associates with SEC24A and SEC24B, but not SEC24C and SEC24D, and they re-localize to the ERGIC, promoting autophagic flux. Induction of autophagy and localization of both SEC23B and SEC24B to the ERGIC in response to nutrient deprivation are significantly reduced in SEC23B(S186A) knock-in cells. We propose that, in the presence of nutrients, FBXW5 limits COPII-mediated autophagosome biogenesis. Inhibition of this event by ULK1 ensures efficient execution of the autophagic cascade in response to nutrient starvation.

cell biology↗

bioRxiv2018

Rapid Identification of Stable Clusters in Bacterial Populations Using the Adjusted Wallace Coefficient

Whole-genome sequencing (WGS) of microbial pathogens has become an essential part of modern epidemiological investigations. Although WGS data can be analyzed using a number of different approaches, such as traditional phylogenetic methods, a critical requirement for global systems for pathogen surveillance is the development of approaches for transforming sequence data into WGS-based subtypes, which creates a nomenclature that describes their higher-order relationships to one another. To this end, subtype similarity thresholds are needed to define clusters of subtypes representing lineages of interest. WGS-based subtyping presents a challenge since both the addition of novel genome sequences and small adjustments in similarity thresholds can have a dramatic impact on cluster composition and stability. We present the Neighbourhood Adjusted Wallace Coefficient (nAWC), a method for evaluating cluster stability based on computing cluster concordance between neighbouring similarity thresholds. The nAWC can be used to identify areas in in which distance thresholds produce robust clusters. Using datasets from Salmonella enterica and Campylobacter jejuni, representing strongly and weakly clonal bacterial species respectively, we show that clusters generated using such thresholds are both stable and reflect basic units in their overall population structure. Our results suggest that the nAWC could be useful for defining robust clusters compatible with nomenclatures for global WGS-based surveillance networks, which require stable clusters to be defined that both harness the discriminatory power of WGS data while allowing for long-term tracking of strains of interest.

genomics↗

bioRxiv2018

Genetics behind the biosynthesis of nonulosonic acid containing lipooligosaccharides in Campylobacter coli

Campylobacter jejuni and Campylobacter coli are the most common cause of bacterial gastroenteritis in the world. Ganglioside mimicry by C. jejuni lipooligosaccharide (LOS) is the triggering factor of Guillain-Barre syndrome (GBS), an acute polyneuropathy. Sialyltransferases from the glycosyltransferase (GT) family 42 are essential for the expression of ganglioside mimics in C. jejuni. Recently, two novel GT-42 genes, cstIV and cstV, have been identified in C. coli. Despite being present in [~]11% of currently available C. coli genomes, the biological role of cstIV and cstV is unknown. In the present study, mutation studies in two strains expressing either cstIV or cstV were performed and mass spectrometry was used to investigate differences in the chemical composition of LOS. Attempts were made to identify donor and acceptor molecules using in vitro activity tests with recombinant GT-42 enzymes. Here, we show that CstIV and CstV are involved in C. coli LOS biosynthesis. In particular, cstV is associated with LOS sialylation, while cstIV is linked to the addition of a diacetylated nonulosonic acid residue.\n\nIMPORTANCEDespite being a major foodborne pathogen, Campylobacter coli glycobiology has been largely neglected. The genetic makeup of the C. coli lipooligosaccharide biosynthesis locus was largely unknown until recently. C. coli harbour a large set of genes associated to lipooligosaccharide biosynthesis, including several putative glycosyltransferases involved in the synthesis of sialylated lipooligosaccharide in Campylobacter jejuni. In the present study, C. coli was found to express lipooligosaccharide structures containing sialic acid and other nonulosonate acids. These findings have a strong impact in understanding C. coli ecology, host-pathogen interaction, and pathogenesis.

microbiology↗

bioRxiv2017

Origin, evolution, and distribution of the molecular machinery for biosynthesis of sialylated lipooligosaccharide structures in Campylobacter coli

Campylobacter jejuni and Campylobacter coli are the most common cause of bacterial gastroenteritis worldwide. Additionally, C. jejuni is the most common bacterial etiological agent in the autoimmune Guillain-Barre syndrome (GBS). Ganglioside mimicry by C. jejuni lipooligosaccharide (LOS) is the triggering factor of the disease. LOS-associated genes involved in the synthesis (neuABC) and transfer of sialic acid (sialyltranferases) are essential in C. jejuni to synthesize ganglioside-like LOS. Therefore these genes have been identified as GBS markers. So far, scarce genetic evidence supports C. coli as a GBS causative agent despite being isolated from GBS patients. Here we show that genes putatively involved in sialic acid transfer are widely distributed in the C. coli population. Evidence found herein suggests that a small group of C. coli strains are very likely to express ganglioside mimics, implying that C. coli can potentially trigger GBS. C. coli also presents a larger repertoire of sialyltransferases than C. jejuni and loss of functions of some those LOS-associated genes has happened during adaptation to agriculture niche. Nevertheless, the activity of these sialyltransferases and their role in shaping C. coli population is yet to be explored.

microbiology↗

bioRxiv2017

chewBBACA: A complete suite for gene-by-gene schema creation and strain identification

Gene-by-gene approaches are becoming increasingly popular in bacterial genomic epidemiology and outbreak detection. However, there is a lack of open-source scalable software for schema definition and allele calling for these methodologies. The chewBBACA suite was designed to assist users in the creation and evaluation of novel whole-genome or core-genome gene-by-gene typing schemas and subsequent allele calling in bacterial strains of interest. The software can run in a laptop or in high performance clusters making it useful for both small laboratories and large reference centers. ChewBBACA is available at https://github.com/B-UMMI/chewBBACA or as a docker image at https://hub.docker.com/r/ummidock/chewbbaca/.\n\nDATA SUMMARYO_LIAssembled genomes used for the tutorial were downloaded from NCBI in August 2016 by selecting those submitted as Streptococcus agalactiae taxon or sub-taxa. All the assemblies have been deposited as a zip file in FigShare (https://figshare.com/s/9cbe1d422805db54cd52), where a file with the original ftp link for each NCBI directory is also available.\nC_LIO_LICode for the chewBBACA suite is available at https://github.com/B-UMMI/chewBBACA while the tutorial example is found at https://github.com/B-UMMI/chewBBACA_tutorial.\nC_LI\n\nI/We confirm all supporting data, code and protocols have been provided within the article or through supplementary data files. {boxtimes}\n\nIMPACT STATEMENTThe chewBBACA software offers a computational solution for the creation, evaluation and use of whole genome (wg) and core genome (cg) multilocus sequence typing (MLST) schemas. It allows researchers to develop wg/cgMLST schemes for any bacterial species from a set of genomes of interest. The alleles identified by chewBBACA correspond to potential coding sequences, possibly offering insights into the correspondence between the genetic variability identified and phenotypic variability. The software performs allele calling in a matter of seconds to minutes per strain in a laptop but is easily scalable for the analysis of large datasets of hundreds of thousands of strains using multiprocessing options. The chewBBACA software thus provides an efficient and freely available open source solution for gene-by-gene methods. Moreover, the ability to perform these tasks locally is desirable when the submission of raw data to a central repository or web services is hindered by data protection policies or ethical or legal concerns.

bioinformatics↗