Response of planktonic microbial assemblages to disturbance in an urban sub-tropical estuary.

Microbes are sensitive indicators of estuarine processes because they respond rapidly to dynamic disturbance events. As most of the world's population lives in urban areas and climate change-related disturbance events are becoming more frequent, estuaries bounded by cities are experiencing increasing stressors, at the same time that their ecosystem services are required more than ever. Here, using a multidisciplinary approach, we determined the response of planktonic microbial assemblages in response to seasonality and a rainfall disturbance in an urban estuary bounded by Australia's largest city, Sydney.

Elevated c-di-GMP Levels and Expression of the Type III Secretion System Promote Corneal Infection by Pseudomonas aeruginosa.

Pseudomonas aeruginosa is generally believed to establish biofilm-associated infections under the regulation of the secondary messenger c-di-GMP. To evaluate P. aeruginosa biofilm physiology during ocular infections, comparative transcriptomic analysis was performed on wild-type P.

The biofilm matrix scaffold of Pseudomonas aeruginosa contains G-quadruplex extracellular DNA structures.

Extracellular DNA, or eDNA, is recognised as a critical biofilm component; however, it is not understood how it forms networked matrix structures. Here, we isolate eDNA from static-culture Pseudomonas aeruginosa biofilms using ionic liquids to preserve its biophysical signatures of fluid viscoelasticity and the temperature dependency of DNA transitions. We describe a loss of eDNA network structure as resulting from a change in nucleic acid conformation, and propose that its ability to form viscoelastic structures is key to its role in building biofilm matrices.

Whole genome sequencing (WGS) fails to detect antimicrobial resistance (AMR) from heteroresistant subpopulation of Salmonella enterica.

Due to rapidly falling costs, whole genome sequencing (WGS) is becoming an essential tool in the surveillance of antimicrobial resistance (AMR) in Salmonella enterica. Although there have been many recent works evaluating the accuracy of WGS in predicting AMR from a large number of Salmonella isolates, little attention has been devoted to deciphering the underlying causes of disagreement between the WGS genotype and experimentally determined AMR phenotype. This study analyzed the genomes of six S.

Evaluation of sxtA and rDNA qPCR assays through monitoring of an inshore bloom of Alexandrium catenella Group 1.

Alexandrium catenella (formerly A. tamarense Group 1, or A. fundyense) is the leading cause of Paralytic Shellfish Poisoning in North and South America, Europe, Africa, Australia and Asia.

Transcriptomic investigation into polyketide toxin synthesis in Ostreopsis (Dinophyceae) species.

In marine ecosystems, dinoflagellates can become highly abundant and even dominant at times, despite their comparatively slow growth. Their ecological success may be related to their production of complex toxic polyketide compounds. Ostreopsis species produce potent palytoxin-like compounds (PLTX), which are associated with human skin and eye irritations, and illnesses through the consumption of contaminated seafood.

Glutathione Activates Type III Secretion System Through Vfr in .

Glutathione (GSH) is the most abundant antioxidant in all living organisms. Previously, we have shown that a deletion mutant in the glutathione synthetase gene (Δ) decreases the expression of type III secretion system (T3SS) genes of . However, the mechanism remains elusive.

Accessory genome of the multi-drug resistant ocular isolate of Pseudomonas aeruginosa PA34.

Bacteria can acquire an accessory genome through the horizontal transfer of genetic elements from non-parental lineages. This leads to rapid genetic evolution allowing traits such as antibiotic resistance and virulence to spread through bacterial communities. The study of complete genomes of bacterial strains helps to understand the genomic traits associated with virulence and antibiotic resistance.

Comparative genomics of clinical strains of Pseudomonas aeruginosa strains isolated from different geographic sites.

The large and complex genome of Pseudomonas aeruginosa, which consists of significant portions (up to 20%) of transferable genetic elements contributes to the rapid development of antibiotic resistance. The whole genome sequences of 22 strains isolated from eye and cystic fibrosis patients in Australia and India between 1992 and 2007 were used to compare genomic divergence and phylogenetic relationships as well as genes for antibiotic resistance and virulence factors. Analysis of the pangenome indicated a large variation in the size of accessory genome amongst 22 stains and the size of the accessory genome correlated with number of genomic islands, insertion sequences and prophages.

Association between possession of ExoU and antibiotic resistance in Pseudomonas aeruginosa.

Virulent strains of Pseudomonas aeruginosa are often associated with an acquired cytotoxic protein, exoenzyme U (ExoU) that rapidly destroys the cell membranes of host cells by its phospholipase activity. Strains possessing the exoU gene are predominant in eye infections and are more resistant to antibiotics. Thus, it is essential to understand treatment options for these strains.

Stress Resistance Development and Genome-Wide Transcriptional Response of Escherichia coli O157:H7 Adapted to Sublethal Thymol, Carvacrol, and -Cinnamaldehyde.

Thymol, carvacrol, and -cinnamaldehyde are essential oil (EO) compounds with broad-spectrum antimicrobial activities against foodborne pathogens, including O157:H7. However, little is known regarding direct resistance and cross-resistance development in O157:H7 after adaptation to sublethal levels of these compounds, and information is scarce on microbial adaptive responses at a molecular level. The present study demonstrated that O157:H7 was able to grow in the presence of sublethal thymol (1/2T), carvacrol (1/2C), or -cinnamaldehyde (1/2TC), displaying an extended lag phase duration and a lower maximum growth rate.

Characterization of a novel multidrug resistance plasmid pSGB23 isolated from subspecies enterica serovar Saintpaul.

Background: subspecies enterica serovar Saintpaul (. Saintpaul) is an important gut pathogen which causes salmonellosis worldwide. Although intestinal salmonellosis is usually self-limiting, it can be life-threatening in children, the elderlies and immunocompromised patients.

Reduced Intracellular c-di-GMP Content Increases Expression of Quorum Sensing-Regulated Genes in .

Cyclic-di-GMP (c-di-GMP) is an intracellular secondary messenger which controls the biofilm life cycle in many bacterial species. High intracellular c-di-GMP content enhances biofilm formation via the reduction of motility and production of biofilm matrix, while low c-di-GMP content in biofilm cells leads to increased motility and biofilm dispersal. While the effect of high c-di-GMP levels on bacterial lifestyles is well studied, the physiology of cells at low c-di-GMP levels remains unclear.

Metagenomic and metatranscriptomic analysis of saliva reveals disease-associated microbiota in patients with periodontitis and dental caries.

The taxonomic composition of the salivary microbiota has been reported to differentiate between oral health and disease. However, information on bacterial activity and gene expression of the salivary microbiota is limited. The purpose of this study was to perform metagenomic and metatranscriptomic characterization of the salivary microbiota and test the hypothesis that salivary microbial presence and activity could be an indicator of the oral health status.

Qualitative and quantitative assessment of the presence of ciguatoxin, P-CTX-1B, in Spanish Mackerel () from waters in New South Wales (Australia).

Ciguatera Fish Poisoning (CFP) is a tropical disease caused by the consumption of fish contaminated with ciguatoxins (CTXs). Currently, the only feasible prevention methods for CFP are to avoid the consumption of fish of certain species from some regions, avoid larger fish of certain species, or avoid all fish caught from specific regions. Here, we quantified levels of P-CTX-1B in Spanish Mackerel (), which is the main fish species that causes CFP in New South Wales and Queensland, Australia, using LC-MS detection against a toxin standard.

Both modular and single-domain Type I polyketide synthases are expressed in the brevetoxin-producing dinoflagellate, Karenia brevis (Dinophyceae).

Dinoflagellates are prolific producers of polyketide compounds, many of which are potent toxins with adverse impacts on human and marine animal health. To identify polyketide synthase (PKS) genes in the brevetoxin-producing dinoflagellate, Karenia brevis, we assembled a transcriptome from 595 million Illumina reads, sampled under different growth conditions. The assembly included 125,687 transcripts greater than 300 nt in length, with over half having >100× coverage.

The rapid evolution of in ventilator-associated pneumonia patients leads to attenuated virulence.

is an opportunistic pathogen that causes severe airway infections in humans. These infections are usually difficult to treat and associated with high mortality rates. While colonizing the human airways, could accumulate genetic mutations that often lead to its better adaptability to the host environment.

A new species of Gambierdiscus (Dinophyceae) from the south-west Pacific: Gambierdiscus honu sp. nov.

Two isolates of a new tropical, epiphytic dinoflagellate species, Gambierdiscus honu sp. nov., were obtained from macroalgae sampled in Rarotonga, Cook Islands, and from North Meyer Island, Kermadec Islands.

Predation by Bdellovibrio bacteriovorus significantly reduces viability and alters the microbial community composition of activated sludge flocs and granules.

We recently isolated and characterised a predatory Bdellovibrio bacteriovorus strain from activated sludge (Ulu Pandan Water Reclamation Plant, Singapore), and this strain, B. bacteriovorus UP, was able to prey upon a broad spectrum of bacterial isolates from the activated sludge when grown as planktonic cells or as biofilms. Here, we have tested the effect of Bdellovibrio predation on floccular and granular sludge to determine if the spatial organisation, loosely or tightly aggregated communities, was protective from predation.

Role of Modular Polyketide Synthases in the Production of Polyether Ladder Compounds in Ciguatoxin-Producing Gambierdiscus polynesiensis and G. excentricus (Dinophyceae).

Gambierdiscus, a benthic dinoflagellate, produces ciguatoxins that cause the human illness Ciguatera. Ciguatoxins are polyether ladder compounds that have a polyketide origin, indicating that polyketide synthases (PKS) are involved in their production. We sequenced transcriptomes of Gambierdiscus excentricus and Gambierdiscus polynesiensis and found 264 contigs encoding single domain ketoacyl synthases (KS; G.

A new Gambierdiscus species (Dinophyceae) from Rarotonga, Cook Islands: Gambierdiscus cheloniae sp. nov.

Ciguatera fish poisoning (CFP) has been reported for many years in Rarotonga, Cook Islands, and has had the world's highest reported incidence of this illness for the last 20 years. Following intensive sampling to understand the distribution of the causative organisms of CFP, an undescribed Gambierdiscus species was isolated from the Rarotongan lagoon. Gambierdiscus cheloniae sp.

Evolutionary distinctiveness of fatty acid and polyketide synthesis in eukaryotes.

Fatty acids, which are essential cell membrane constituents and fuel storage molecules, are thought to share a common evolutionary origin with polyketide toxins in eukaryotes. While fatty acids are primary metabolic products, polyketide toxins are secondary metabolites that are involved in ecologically relevant processes, such as chemical defence, and produce the adverse effects of harmful algal blooms. Selection pressures on such compounds may be different, resulting in differing evolutionary histories.