Loss of the Acetate Switch in Vibrio vulnificus Enhances Predation Defense against Tetrahymena pyriformis.

Vibrio vulnificus is an opportunistic human pathogen and autochthonous inhabitant of coastal marine environments, where the bacterium is under constant predation by heterotrophic protists or protozoans. As a result of this selection pressure, genetic variants with antipredation mechanisms are selected for and persist in the environment. Such natural variants may also be pathogenic to animal or human hosts, making it important to understand these defense mechanisms. To identify antipredator strategies, 13 V. vulnificus strains of different genotypes isolated from diverse environments were exposed to predation by the ciliated protozoan Tetrahymena pyriformis, and only strain ENV1 was resistant to predation. Further investigation of the cell-free supernatant showed that ENV1 acidifies the environment by the excretion of organic acids, which are toxic to T. pyriformis. As this predation resistance was dependent on the availability of iron, transcriptomes of V. vulnificus in iron-replete and iron-deplete conditions were compared. This analysis revealed that ENV1 ferments pyruvate and the resultant acetyl-CoA leads to acetate synthesis under aerobic conditions, a hallmark of overflow metabolism. The anaerobic respiration global regulator arcA was upregulated when iron was available. An ΔarcA deletion mutant of ENV1 accumulated less acetate and, importantly, was sensitive to grazing by T. pyriformis. Based on the transcriptome response and quantification of metabolites, we conclude that ENV1 has adapted to overflow metabolism and has lost a control switch that shifts metabolism from acetate excretion to acetate assimilation, enabling it to excrete acetate continuously. We show that overflow metabolism and the acetate switch contribute to prey-predator interactions. IMPORTANCE Bacteria in the environment, including Vibrio spp., interact with protozoan predators. To defend against predation, bacteria evolve antipredator mechanisms ranging from changing morphology, biofilm formation, and secretion of toxins or virulence factors. Some of these adaptations may result in strains that are pathogenic to humans. Therefore, it is important to study predator defense strategies of environmental bacteria. V. vulnificus thrives in coastal waters and infects humans. Very little is known about the defense mechanisms V. vulnificus expresses against predation. Here, we show that a V. vulnificus strain (ENV1) has rewired the central carbon metabolism, enabling the production of excess organic acid that is toxic to the protozoan predator T. pyriformis. This is a previously unknown mechanism of predation defense that protects against protozoan predators.

High rates of unprotected anal intercourse with regular and casual partners and associated risk factors in a sample of ethnic Malay men who have sex with men (MSM) in Penang, Malaysia.

OBJECTIVE: To assess the prevalence of unprotected anal intercourse (UAI) and its correlates among ethnic Malay men who have sex with men (MSM). METHODS: In 2010, a convenience sample of 350 MSM in Penang were recruited to participate in an anonymous, computerised survey with rapid HIV testing. Participants who were not of Malay ethnicity (n=44) or who did not report sex with another man in the previous 12 months (n=22) were excluded, resulting in 284 participants in the final analysis. Correlates of UAI were examined separately for regular and casual partnerships using bivariate and multivariate logistic regression. RESULTS: Four men (1.9%) tested HIV positive. In the past 12 months, 64.7% of participants had regular sexual partners, 77.1% had casual sexual partners and 41.9% had both. Most participants (83.1%) reported UAI, which was more common in regular partnerships. Over two-thirds of participants had never been tested for HIV. In multivariate analysis, agreement about sexual risk reduction practices was associated with a reduction in UAI with regular partners (adjusted OR (AOR)=0.14, 95% CI 0.05 to 0.40). Reporting difficulty in using condoms was associated with an increase in UAI with casual partners (AOR=9.07, 95% CI 3.35 to 24.5), and any exposure to HIV prevention was associated with a decrease in UAI with casual partners (AOR=0.22, 95% CI 0.09 to 0.54). CONCLUSIONS: Despite highly prevalent HIV risk behaviours, HIV seropositivity and prior HIV testing were low. Increasing sexual negotiation skills and access to HIV testing and other prevention services may improve future prevention efforts.

metaPR2 : A database of eukaryotic 18S rRNA metabarcodes with an emphasis on protists.

In recent years, metabarcoding has become the method of choice for investigating the composition and assembly of microbial eukaryotic communities. The number of environmental data sets published has increased very rapidly. Although unprocessed sequence files are often publicly available, processed data, in particular clustered sequences, are rarely available in a usable format. Clustered sequences are reported as operational taxonomic units (OTUs) with different similarity levels or more recently as amplicon sequence variants (ASVs). This hampers comparative studies between different environments and data sets, for example examining the biogeographical patterns of specific groups/species, as well analysing the genetic microdiversity within these groups. Here, we present a newly-assembled database of processed 18S rRNA metabarcodes that are annotated with the PR2 reference sequence database. This database, called metaPR2 , contains 41 data sets corresponding to more than 4000 samples and 90,000 ASVs. The database, which is accessible through both a web-based interface (https://shiny.metapr2.org) and an R package, should prove very useful to all researchers working on protist diversity in a variety of systems.