Biology subjects

Stratford, M.

Publications and source records attributed to Stratford, M..

3 recordsLinked to original sources

bioRxiv2026

Contraction type dependence of serial sarcomere addition following resistance training

Longitudinal muscle growth occurs through the addition of sarcomeres in series, a process termed serial sarcomerogenesis. To investigate contraction mode dependence of sarcomerogenesis in Sprague-Dawley rats (n=36, 14 to18 weeks, ~468g), we compared the effects of isometric, eccentric, and concentric training (4 to 6 weeks; 3 times/week) on morphological and mechanical adaptations of the plantar flexors. Isometric training was performed at a joint angle corresponding to the plateau nearing the descending limb of the force length relationship, eccentric contractions began at a shorter muscle length and lengthened to this same joint position, and concentric contractions started at this lengthened position but then actively shortened. Owing to the rapid regulation of serial sarcomere number the 4-and 6-week timepoints were collapsed. While force output increased across all training modes (+16%; p<0.05), longitudinal muscle growth was regulated by contraction type. Both isometric and eccentric training were highly effective at increasing serial sarcomere number when optimal loading conditions (high forces at longer lengths) are provided (+7-9%; p<0.05). Concentric training, even when initiated at long lengths with high forces was not an effective stimulus for longitudinal remodelling (+2%; p>0.05). Therefore, these findings identify the mechanical loading environment associated with isometric and eccentric training as a key driver of serial sarcomerogenesis.

physiology↗

bioRxiv2020

The preservative sorbic acid targets respiration, explaining the resistance of fermentative spoilage-yeast species

A small number (10-20) of yeast species cause major spoilage in foods. Spoilage yeasts of soft drinks are resistant to preservatives like sorbic acid and they are highly fermentative, generating large amounts of carbon dioxide gas. Conversely, many yeast species derive energy from respiration only and most of these are sorbic acid-sensitive, so prevented from causing spoilage. This led us to hypothesize that sorbic acid may specifically inhibit respiration. Tests with respiro-fermentative yeasts showed that sorbic acid was more inhibitory to both Saccharomyces cerevisiae and Zygosaccharomyces bailii during respiration (of glycerol) compared with fermentation (of glucose). The respiration-only species Rhodotorula glutinis was equally sensitive when growing on either carbon source, suggesting that ability to ferment glucose specifically enables sorbic acid-resistant growth. Sorbic acid inhibited the respiration process more strongly than fermentation. We present a dataset supporting a correlation between the level of fermentation and sorbic acid resistance across 191 yeast species. Other weak acids, C2 - C8, inhibited respiration in accordance with their partition coefficients, suggesting that effects on mitochondrial respiration were related to membrane localization rather than cytosolic acidification. Supporting this, we present evidence that sorbic acid causes production of reactive oxygen species, the formation of petite (mitochondria-defective) cells, and Fe-S cluster defects. This work rationalises why yeasts that can grow in sorbic acid-preserved foods tend to be fermentative in nature. This may inform more-targeted approaches for tackling these spoilage organisms, particularly as the industry migrates to lower-sugar drinks, which could favour respiration over fermentation in many spoilage yeasts. IMPORTANCESpoilage by yeasts and moulds is a major contributor to food and drink waste, which undermines food security. Weak acid preservatives like sorbic acid help to stop spoilage but some yeasts, commonly associated with spoilage, are resistant to sorbic acid. Different yeasts generate energy for growth by the processes of respiration and/or fermentation. Here we show that sorbic acid targets the process of respiration, so fermenting yeasts are more resistant. Fermentative yeasts are also those usually found in spoilage incidents. This insight helps to explain the spoilage of sorbic acid-preserved foods by yeasts and can inform new strategies for effective control. This is timely as sugar content of products like soft drinks is being lowered, which may favour respiration over fermentation in key spoilage yeasts.

microbiology↗

bioRxiv2019

Weak Acid Sensitive A, a novel transcription factor required for regulation of weak-acid resistance and spore-spore heterogeneity in Aspergillus niger

Propionic, sorbic and benzoic acids are organic weak acids that are widely used as food preservatives, where they play a critical role in preventing microbial growth. In this study, we uncovered new mechanisms of weak acid resistance in moulds. By screening a library of 401 transcription-factor deletion strains in Aspergillus fumigatus for sorbic acid hypersensitivity, a previously uncharacterised transcription factor was identified, and named as WarA (Weak Acid Resistance A). The orthologous gene in the spoilage mould Aspergillus niger was identified and deleted. WarA was required for resistance to a range of weak acids, including sorbic, propionic and benzoic acids. A transcriptomic analysis was performed to characterise genes regulated by WarA during sorbic acid treatment in A. niger. Several genes were significantly upregulated in the wild type compared with a {Delta}warA mutant, including genes encoding putative weak acid detoxification enzymes and transporter proteins. Among these was An14g03570, a putative ABC-type transporter which we found to be required for weak acid resistance in A. niger. We also show that An14g03570 is a functional homologue of the Saccharomyces cerevisiae protein Pdr12p, and therefore named as PdrA. Lastly, resistance to sorbic acid was found to be highly heterogeneous within genetically-uniform populations of ungerminated A. niger conidia, and we demonstrate that pdrA is a determinant of this heteroresistance. This study has identified novel mechanisms of weak acid resistance in A. niger which could help to inform and improve future food spoilage prevention strategies.\n\nIMPORTANCEWeak acids are widely used as food preservatives, as they are very effective at preventing growth of most species of bacteria and fungi. However, some species of moulds can survive and grow in the concentrations of weak acid employed in food and drink products, thereby causing spoilage with resultant risks for food security and health. Current knowledge of weak acid resistance mechanisms in these fungi is limited, especially in comparison to that in yeasts. We characterised gene functions in the spoilage mould species Aspergillus niger which are important for survival and growth in the presence of weak acid preservatives. Such identification of weak acid resistance mechanisms in spoilage moulds will help to design new strategies to reduce food spoilage in the future.

microbiology↗