Biology subjects

Van, T. T. H.

Publications and source records attributed to Van, T. T. H..

4 recordsLinked to original sources

bioRxiv2020

Cloning and functional expression of a food-grade circular bacteriocin, plantacyclin B21AG, in probiotic Lactobacillus plantarum WCFS1

There is an increasing consumer demand for minimally processed, preservative free and microbiologically safe food. These factors, combined with risks of antibiotic resistance, have led to interest in bacteriocins produced by lactic acid bacteria (LAB) as natural food preservatives and as protein therapeutics. We previously reported the discovery of plantacyclin B21AG, a novel circular bacteriocin produced by Lactobacillus plantarum B21. Here, we describe the cloning and functional expression of the bacteriocin gene cluster in the probiotic Lactobacillus plantarum WCFS1. Genome sequencing demonstrated that the bacteriocin is encoded on a 20 kb native plasmid, designated as pB21AG01. Seven open reading frames (ORFs) putatively involved in bacteriocin production, secretion and immunity were cloned into an E. coli/Lactobacillus shuttle vector, pTRKH2. The resulting plasmid, pCycB21, was transformed into L. plantarum WCFS1. The cell free supernatants (CFS) of both B21 and WCFS1 (pCycB21) showed an antimicrobial activity of 800 AU/mL when tested against the WCFS1 (pTRKH2) indicator strain, indicating functional expression of plantacyclin B21AG. Real-time PCR analysis revealed that the relative copy number of pB21AG01 was 7.60 {+/-} 0.79 in L. plantarum B21 whilst pCycB21 and pTRKH2 was 0.51 {+/-} 0.05 and 25.19 {+/-} 2.68 copies, respectively in WCFS1. This indicates that the bacteriocin gene cluster is located on a highly stable, low copy number plasmid pB21AG01 in L. plantarum B21. Inclusion of the native promoter for the bacteriocin operon from pB21AG01 may result in similar inhibitory zones observed in both wild type and recombinant hosts despite the low copy number of pCycB21.

microbiology↗

bioRxiv2020

Discovery and characterisation of novel circular bacteriocin plantacyclin B21AG from Lactobacillus plantarum B21

Lactobacillus plantarum B21 isolated from Vietnamese sausage (nem chua) has previously displayed broad antimicrobial activity against gram positive bacteria including foodborne pathogens Listeria monocytogenes and Clostridium perfringens. This study successfully identified the antimicrobial agent as plantacyclin B21AG, a 5668 Da circular bacteriocin demonstrating high thermostability, resistance to a wide range of pH, proteolytic resistance and temporal stability. We report a reverse genetics approach used to identify and characterise plantacyclin B21AG. The bacteriocin was purified from culture supernatant by a short process consisting of concentration, n-butanol extraction and cation exchange chromatography. A de novo peptide sequencing using LC-MS/MS techniques identified two putative peptide fragments which were mapped to the genome of Lactobacillus plantarum B21. This revealed an ORF corresponding to a putative circular bacteriocin with a 33-amino acid leader peptide and 58-amino acid mature peptide found on native plasmid pB21AG01. The corresponding gene cluster, consisted of seven genes associated with post-translational circularisation, immunity and secretion. The robust nature of plantacyclin B21AG, its antimicrobial activity and associated machinery for cyclisation make it an interesting biotechnological target for further development, and application as a food-safe antimicrobial.

biochemistry↗

bioRxiv2019

Oregano powder reduces Streptococcus and increases SCFA concentration in a mixed bacterial culture assay of chicken.

Food borne illnesses have a world-wide economic impact and industries are continuously developing technologies to reduce the spread of disease caused by microorganisms. Antimicrobial growth promoters (AGPs) have been used to decrease microbiological infections in animals and their potential transfer to humans. In recent years there has been a global trend to remove AGPs from animal feed in an attempt to reduce the spread of antimicrobial resistant genes into the human population. Phytobiotics, such as oregano powder, are one of the potential replacements for AGPs due to their well-established antimicrobial components. 16S rRNA gene amplicons were used to determine the effect of oregano powder (1% w/v) on the microbiota of mixed bacterial cell cultures, which were obtained from the ceca of traditionally grown meat chickens (broilers). Oregano powder had a mild effect on the microbial cell cultures increasing Enterococcus faecium, rearranging ratios of members in the genus Lactobacillus and significantly reducing the genus Streptococcus (p=1.6e-3). Beneficial short chain fatty acids (SCFA), acetic and butyric acid, were also significantly increased in oregano powder supplemented cultures. These results suggest that oregano powder at a concentration of 1 % (w/v) may have beneficial influences on mixed microbial communities and SCFA production.

microbiology↗

bioRxiv2018

An intermittent hypercaloric diet alters gut microbiota, prefrontal cortical gene expression and social behaviours in rats

Excessive consumption of high fat and high sugar (HFHS) diets are known to alter reward processing and aspects of behaviour, and change microbiota profiles. Studies in gnotobiotic mice also provide evidence that gut microorganisms influence social behaviour. To further investigate these interactions, the impact of intermittent access to a HFHS diet on social behaviour, gene expression and microbiota composition was examined. Rats were permitted intermittent daily access (2h / day) to a palatable HFHS diet for 28 days across the adolescent period. Social interaction, social memory and novel object recognition were assessed during this period. Following testing, RT-PCR was conducted on hippocampal and prefrontal cortex (PFC) samples. 16S ribosomal RNA amplicon sequencing was used for identification and relative quantification of bacterial taxa. Reduced social interaction behaviours, and impaired social memory and novel object recognition were observed in HFHS diet rats. Reduced levels of monoamine oxidase A (Maoa), catechol-O-methyltransferase (Comt) and brain derived neurotrophic factor (Bdnf) mRNA were observed in the PFC of HFHS diet rats. The relative abundance of a number of specific taxa differed significantly between the two diet groups, in particular, Lachnospiraceae and Ruminoccoceae bacteria, which also predicted social behaviours, novel object recognition performance and Maoa expression. This is the first study to show that limited daily access to HFHS diet alters social behaviour and cognition in rats. Furthermore, behavioural changes are associated with alterations to cortical gene expression of enzymes involved in monoamine synthesis and neuroplasticity, and microbiota profiles predicted diet-induced changes to behaviour and gene expression.

neuroscience↗