Biology subjects

Bulach, D.

Publications and source records attributed to Bulach, D..

5 recordsLinked to original sources

bioRxiv2024

Enteropathogenic Providencia alcalifaciens: A subgroup of P. alcalifaciens that causes diarrhea.

Even though Providencia alcalifaciens is considered as a normal flora of the large intestine, there are reports of it causing diarrhea. In a previous study, a strain, 2939/90 obtained as a pure stool culture from a dead diarrheal patient was shown to cause invasion and actin condensation in mammalian cells, and diarrhea in a rabbit model. In a subsequent study, four TnphoA mutants of 2939/90 produced negligible invasion and actin condensation in mammalian cells. In the present study, the parent strain was sequenced by short-read and long-read sequencing, and the mutants by short read sequencing. In all four mutants, a TnphoA insertion was detected in the type three secretion system (T3SS) locus present on the largest of four plasmids (p2939_90_1) and not in a seemingly independent, functional T3SS locus on the chromosome. A survey of 52 genomes of P. alcalifaciens available in the public database identified the chromosomal T3SS locus in all strains, including both P. alcalifaciens genomic clades that we have classified as (group A) and (group B); a highly related gene layout and gene synteny flanking the locus suggested that these chromosomal loci are orthologous. There is a low sequence similarity between the chromosomal and plasmid-borne T3SS; a survey of plasmid T3SS showed its presence in only 21 of 52 genomes and mostly in group A genomes. Group A included several isolates from an outbreak of haemorrhagic diarrhea in dogs. Using prediction software (EffectiveDB), we detected several known and unknown effectors flanking the plasmid T3SS locus. The observation that TnphoA insertion only in the plasmid T3SS locus affected the invasion phenotype suggested that this locus is critical for causation of diarrhea. This leads us to conclude that a subgroup of P. alcalifaciens that possesses this plasmid-borne T3SS locus (in the case of strain, 2939/90) can cause diarrheal disease. We name this subgroup as enteropathogenic P. alcalifaciens (EPA). EPA should be included in future studies of etiology of diarrhea. A unique sequence that may be present in the T3SS locus in the plasmid may be investigated as a marker in a simple molecular test for diagnosis of EPA.

microbiology↗

bioRxiv2020

Development of a free radical scavenging probiotic to mitigate coral bleaching

Corals are colonized by symbiotic microorganisms that exert a profound influence on the animals health. One noted symbiont is a single-celled alga (from the family Symbiodiniaceae), which provides the coral with most of its fixed carbon. During thermal stress, hyperactivity of photosynthesis results in a toxic accumulation of reactive oxygen species (ROS). If not scavenged by the antioxidant network, ROS may trigger a signaling cascade ending with the coral host and algal symbiont disassociating; this process is known as bleaching. Our goal was to construct a probiotic comprised of host-associated bacteria able to neutralize free radicals such as ROS. Using the coral model, the anemone Exaiptasia diaphana, and pure bacterial cultures isolated from the model animal, we identified six strains with high free radical scavenging ability belonging to the families Alteromonadaceae, Rhodobacteraceae, Flavobacteriaceae, and Micrococcaceae. In parallel, we established a "negative" probiotic consisting of genetically related strains with poor free radical scavenging capacities. From their whole genome sequences, we explored genes of interest that may contribute to their potential beneficial roles, which may help facilitate the therapeutic application of a bacterial probiotic. In particular, the occurrence of key pathways that are known to influence ROS in each of the strains has been inferred from the genomes sequences and are reported here. IMPORTANCECoral bleaching is tightly linked to the production of reactive oxygen species (ROS), which accumulates to a toxic level in algae-harboring host cells leading to coral-algal dissociation. Interventions targeting ROS accumulation, such as the application of exogenous antioxidants, have shown promise for maintaining the coral-algal partnership. With the feasibility of administering antioxidants directly to corals being low, we aim to develop a probiotic to neutralize toxic ROS during a thermal stress event. This probiotic can be tested with corals or a coral model to assess its efficacy in improving coral resistance to environmental stress.

bioengineering↗

bioRxiv2020

Temporal transcriptome profiling of Microchloropsis gaditana CCMP526 under hyper-saline conditions

Microalgae can tolerate a wide range of environmental conditions and have been exploited for their lipid and carbohydrate accumulating properties. The utility of this process could be further enhanced through understanding the critical gene regulatory networks that govern the acclimatization process. Advancements in systems biology and sequencing tools now enable us to obtain a genome-wide overview of gene expression under particular conditions of interest. Under salinity stress, Microchloropsis gaditana CCMP526, a commercially important alga has been previously reported to accumulate carbohydrate and lipid. To understand the mechanism of acclimatization, here we report a temporal transcriptomic analysis of M. gaditana under two different salinity levels (55 and 100 PSU). The short term (0, 1 and 6 h) and long term (24 and 72 h) responses of the salt-induced transcript pool were used to identify salinity-inducible genes using correspondence analysis. The transcript abundance of genes involved in triacylglycerol biosynthesis, membrane lipid modification, carbon assimilation and shunting, and osmolyte biosynthesis indicated that M. gaditana employs a two-stage acclimatization strategy during hypersaline conditions.

microbiology↗

bioRxiv2020

A Data-Independent-Acquisition-based proteomic approach towards understanding the acclimation strategy of Microchloropsis gaditana CCMP526 in hypersaline conditions

Salinity is one of the significant factors that affect growth and cellular metabolism, including photosynthesis and lipid accumulation, in microalgae and higher plants. Microchloropsis gaditana CCMP526 can acclimatize to different salinity levels by accumulating compatible solutes, carbohydrates, and lipids as an energy storage molecule. We used proteomics to understand the molecular basis for acclimation of M. gaditana to increased salinity levels (55 and 100 PSU (Practical Salinity Unit). Correspondence analysis (CA) was used for the identification of salinity-responsive proteins (SRPs). The highest number of altered proteins was observed in 100 PSU. Gene Ontology (GO) enrichment analysis revealed a separate path of acclimation for cells exposed to 55 and 100 PSU. Osmolyte and lipid biosynthesis was up-regulated in high saline conditions. However, concomitantly lipid oxidation pathways were also up-regulated at high saline conditions, providing acetyl-CoA for energy metabolism through the TCA cycle. Carbon fixation and photosynthesis were tightly regulated, while chlorophyll biosynthesis was affected under high salinity conditions. Importantly, temporal proteome analysis of salinity-challenged M. gaditana revealed vital salinity-responsive proteins which could be used for strain engineering for improved salinity resistance.

plant biology↗

bioRxiv2018

The changing landscape of VREfm in Victoria, Australia: a state-wide genomic snapshot

Vancomycin-resistant Enterococcus faecium (VREfm) represent a major source of nosocomial infection worldwide. In Australia, the vanB genotype is dominant; however there has been a recent increase in the predominantly plasmid-encoded vanA genotype, prompting investigation into the genomic epidemiology of VREfm in this context.\n\nMaterials and MethodsA cross-sectional study of VREfm in Victoria, Australia (Nov.10th - Dec.9th, 2015). A total of 321 VREfm isolates (from 286 patients) were collected and whole-genome sequenced with Illumina NextSeq. Single nucleotide polymorphisms (SNPs) were used to assess relatedness. Multi-locus sequence types (STs), and genes associated with resistance and virulence were identified. The vanA-harbouring plasmid from an isolate from each ST was assembled using long-read data.\n\nResultsvanA-VREfm comprised 17.8% of isolates. ST203, ST80 and a pstS(-) clade, ST1421, predominated (30.5%, 30.5% and 37.2% of vanA-VREfm, respectively). Most vanB-VREfm were ST796 (77.7%). vanA-VREfm isolates were closely-related within hospitals vs. between them (core SNPs 10 [interquartile range 1-357] vs. 356 [179-416] respectively), suggesting discrete introductions of vanA-VREfm, with subsequent intra-hospital transmission. In contrast, vanB-VREfm had similar core SNP distributions within vs. between hospitals, due to widespread dissemination of ST796. Overall, vanA-harbouring plasmids differed across STs, and with exception of ST78 and ST796, Tn1546 transposons also varied.\n\nConclusionsvanA-VREfm in Victoria is associated with multiple STs, and is not solely mediated by a single shared plasmid/Tn1546 transposon; clonal transmission appears to play an important role, predominantly within, rather than between, hospitals. In contrast, vanB-VREfm appears to be well-established and widespread across Victorian healthcare institutions.

genomics↗