Biology subjects

McBain, A. J.

Publications and source records attributed to McBain, A. J..

6 recordsLinked to original sources

bioRxiv2025

Keratinocyte Arginase1 Deficiency Impairs Healing and Antimicrobial Defence against Pseudomonas aeruginosa Infection

Wound infection is a major disruptor of wound healing. Keratinocytes, critical in repair and microbial responses, require the L-arginine hydrolysing enzyme arginase1, for effective healing. Wound pathogens such as Pseudomonas aeruginosa may also need L-arginine. We therefore investigated host-microbial interactions in the context of wound healing and L-arginine metabolism. Arginase-inhibited murine wounds challenged with P. aeruginosa, exhibited significantly delayed re-epithelialisation. This finding was recapitulated in vitro using P. aeruginosa-challenged, arginase1 deficient (shARG1) keratinocytes, associated with reduced epithelial proliferation and viability, and heightened inflammation. Whilst P. aeruginosa challenge promoted host metabolism of L-arginine, this was perturbed in wounded shARG1 keratinocytes. There was, however, heightened downstream polyamine metabolism in shARG1 cells when under P. aeruginosa challenge. Host keratinocyte arginase1 deficiency promoted bacterial growth in vitro, in line with a failure to upregulate the anti-microbial peptides, {beta}-defensins, in shARG1 scratches. This work demonstrates a pivotal role for keratinocyte arginase1 in wound infection. HIGHLIGHTSO_LIHost arginase is required for effective healing under P. aeruginosa challenge. C_LIO_LIP. aeruginosa enhances host keratinocyte L-arginine metabolism upon scratch. C_LIO_LIP. aeruginosa promotes polyamine metabolism in arginase1 deficient wounds in vitro. C_LIO_LIArginase1 is required for keratinocyte anti-microbial defence against P. aeruginosa. C_LI

microbiology↗

bioRxiv2025

Evolutionary potential of the Escherichia coli antimutator ΔnudJ is reduced via altered mutational spectrum

The rate of spontaneous mutation is a key factor in determining the capacity of a population to adapt to a novel environment, for example a bacterial population exposed to antibiotics. Genetic and environmental factors controlling the mutation rate commonly also cause shifts in the relative rates of different mutational classes, i.e. the spectrum of spontaneous mutations. When the mutational spectrum is altered, the relatively enriched and depleted mutations may differ in their fitness effects. Here we aim to explore how a reduced mutation rate and altered mutational spectrum can contribute to adaptation in Escherichia coli. We measure mutation rates across a set of Nudix hydrolase deletants, finding multiple strains with an antimutator phenotype. We focus on the antimutator {Delta}nudJ which can cause a 6-fold mutation rate reduction relative to the wildtype with an altered mutational spectrum. Not only does nudJ deletion reduce the probability of antibiotic resistance arising but, in the case of rifampicin, the accessible resistance mutations under this altered mutation spectrum have greater fitness costs. While this effect is, so far, specific to this drug, it opens up the possibility of reducing the likelihood of resistance mutations establishing through simultaneous modification of mutation rate and spectrum. The identification and characterisation of antimutator alleles such as {Delta}nudJ provides potential targets for antievolution drugs which could be applied during antibiotic treatment to inhibit NudJ activity. Such an approach could suppress spontaneous resistance evolution both through fewer resistance mutations and by limiting access to the fittest mutations.

evolutionary biology↗

bioRxiv2024

Spectral Characterization of a Blue Light-Emitting Micro-LED Platform and Microbial Chromophores for Therapeutic Applications in Skin Conditions

The therapeutic application of blue light (380 - 500nm) has garnered considerable attention in recent years as it offers a non-invasive approach for the management of prevalent skin conditions including acne vulgaris and atopic dermatitis. These conditions are often characterised by an imbalance in the microbial communities that colonise our skin, termed the skin microbiome. In conditions including acne vulgaris, blue light is thought to address this imbalance through the selective photoexcitation of microbial species expressing wavelength-specific chromophores, differentially affecting skin commensals and thus altering the relative species composition. However, the abundance and diversity of these chromophores across the skin microbiota remains poorly understood. Similarly, devices utilised for studies are often bulky and poorly characterised which if translated to therapy could result in reduced patient compliance. Here, we present a clinically viable micro-LED illumination platform with peak emission 450 nm (17 nm FWHM) and adjustable irradiance output to a maximum 0.55{+/-}0.01 W/cm2, dependent upon the concentration of titanium dioxide nanoparticles applied to an accompanying flexible light extraction substrate. Utilising spectrometry approaches, we characterised the abundance of prospective blue light chromophores across skin commensal bacteria isolated from healthy volunteers. Of the strains surveyed 62.5% exhibited absorption peaks within the blue light spectrum, evidencing expression of carotenoid pigments (18.8%, 420 - 483 nm; Micrococcus luteus, Kocuria spp.), porphyrins (12.5%, 402 - 413 nm; Cutibacterium spp.) and potential flavins (31.2%, 420 - 425 nm; Staphylococcus and Dermacoccus spp.). We also present evidence of the capacity of these species to diminish irradiance output when combined with the micro-LED platform and in turn how exposure to low-dose blue light causes shifts in observed absorbance spectra peaks. Collectively these findings highlight a crucial deficit in understanding how microbial chromophores might shape response to blue light and in turn evidence of a micro-LED illumination platform with potential for clinical applications.

microbiology↗

bioRxiv2023

Investigating the Association Between Nitrate Dosing and Nitrite Generation by the Human Oral Microbiota in Continuous Culture

The generation of nitrite by the oral microbiota is believed to contribute to healthy cardiovascular function, with oral nitrate reduction to nitrite associated with systemic blood pressure regulation. There is the potential to manipulate the composition or activities of the oral microbiota to a higher nitrate-reducing state through nitrate supplementation. The current study examined microbial community composition and enzymatic responses to nitrate supplementation in in sessile oral microbiota grown in continuous culture. Nitrate reductase activity and nitrite concentrations were not significantly different to tongue-derived inocula in model biofilms. These were generally dominated by Streptococcus spp., initially, and a single nitrate supplementation resulted in the increased relative abundance of the nitrate-reducing genera Veillonella, Neisseria and Proteus spp. Nitrite concentrations increased concomitantly and continued to increase throughout oral microbiota development. Continuous nitrate supplementation, over a 7-day period, was similarly associated with an elevated abundance of nitrate-reducing taxa and increased nitrite concentration in the perfusate. In experiments in which the models were established in continuous low or high nitrate environments, there was an initial elevation in nitrate reductase, and nitrite concentrations reached a relatively constant concentration over time similar to the acute nitrate challenge with a similar expansion of Veillonella and Neisseria. In summary, we have investigated nitrate metabolism in continuous culture oral biofilms, showing that nitrate addition increases nitrate reductase activity and nitrite concentrations in oral microbiota with the expansion of putatively NaR-producing taxa. ImportanceClinical evidence suggests that blood pressure regulation can be promoted by nitrite generated through the reduction of supplemental dietary nitrate by the oral microbiota. We have utilised oral microbiota models to investigate the mechanisms responsible, demonstrating that nitrate addition increases nitrate reductase activity and nitrite concentrations in oral microbiota with the expansion of nitrate-reducing taxa.

microbiology↗

bioRxiv2022

Consumption of the non-nutritive sweetener stevia for 12 weeks does not alter the composition of the gut microbiota

The use of non-nutritive sweeteners (NNS) as an alternative to caloric sugars has increased in recent years. Stevia is a NNS that has demonstrated beneficial effects on appetite and energy intake. However, the impact on the gut microbiome is not well understood. Therefore, we investigated how regular consumption of stevia, for up to 12 weeks, impacts upon the human gut microbiome. Healthy subjects with a normal body mass index participated in the study; the stevia group (n = 14) were asked to consume five drops of stevia, twice daily, compared against control participants (n = 13). Faecal samples collected before and after treatment were analysed by 16S sequencing. Stevia did not cause significant changes in the beta or alpha diversity when compared to the control groups. When relative abundances of taxa were investigated, no clear differences could be detected. Conversely, random forest analysis could correctly associate the gut microbiome with control and stevia groups with an average of 75% accuracy, suggesting that there are intrinsic patterns that could discriminate between control and stevia use. However, large-scale changes in the gut microbiome were not apparent in this study and therefore, our data suggest that stevia does not significantly impact the gut microbiome.

microbiology↗

bioRxiv2018

Opposing effects of population density and stress on Escherichia coli mutation rate

Evolution depends on mutations. For an individual genotype, the rate at which mutations arise is known to increase with various stressors (stress-induced mutagenesis - SIM) and decrease at high population density (density-associated mutation-rate plasticity - DAMP). We hypothesised that these two forms of mutation rate plasticity would have opposing effects across a nutrient gradient. Here we test this hypothesis, culturing Escherichia coli bacteria in increasingly rich media. We distinguish an increase in mutation rate with added nutrients through SIM (dependent on error-prone polymerases Pol IV and Pol V) and an opposing effect of DAMP (dependent on MutT, which removes oxidised G nucleotides). The combination of DAMP and SIM result in a mutation rate minimum at intermediate nutrient levels (which can support 7x108 cells ml-1). These findings demonstrate a strikingly close and nuanced relationship of ecological factors - stress and population density - with mutation, the fuel of all evolution.

evolutionary biology↗