Outer-membrane vesicles (OMVs) produced by Helicobacter pylori deliver bacterial components to host cells, provide a mechanism for stabilization of secreted components and may allow the bacteria to exert ‘long-range’ effects in the gastric niche, promoting persistence. In addition to their well-characterized host cell interactions, membrane vesicles improve stress survival in other bacterial species, and are constitutively produced by both pathogenic and non-pathogenic bacteria. We aimed to determine whether OMVs could improve H. pylori survival of a range of stressors. The effects of purified OMVs on the resistance of H. pylori to a range of environmental and antimicrobial stresses were determined using growth curves and survival assays. Addition of purified OMVs to H. pylori cultures provided dose-dependent protection against hydrogen peroxide-mediated killing. Supplementation with OMVs also partially protected H. pylori against the bactericidal effects of the antibiotics clarithromycin and levofloxacin, but not against amoxicillin nor metronidazole. Addition of purified OMVs allowed H. pylori to grow in the presence of inhibitory concentrations of the antimicrobial peptide LL-37. In the presence of 50 µg OMVs ml⁻¹, significantly enhanced H. pylori growth was observed at higher LL-37 concentrations compared with lower LL-37 concentrations, suggesting that OMV–LL-37 interactions might facilitate release of growth-promoting nutrients. Taken together, these data indicate that production of membrane vesicles could help H. pylori to survive exposure to antibiotics and host antimicrobial defences during infection.

Plant-produced isoprene (2-methyl-1,3-butadiene) represents a significant portion of global volatile organic compound production, equaled only by methane. A metabolic pathway for the degradation of isoprene was first described for the Gram-positive bacterium Rhodococcus sp. AD45, and an alternative model organism has yet to be characterised. Here, we report the characterisation of a novel Gram-negative isoprene-degrading bacterium, Variovorax sp. WS11. Isoprene metabolism in this bacterium involves a plasmid-encoded iso metabolic gene cluster which differs from that found in Rhodococcus sp. AD45 in terms of organisation and regulation. Expression of iso metabolic genes is significantly upregulated by both isoprene and epoxyisoprene. The enzyme responsible for the initial oxidation of isoprene, isoprene monooxygenase, oxidises a wide range of alkene substrates in a manner which is strongly influenced by the presence of alkyl side-chains and differs from other well-characterised soluble diiron monooxygenases according to its response to alkyne inhibitors. This study presents Variovorax sp. WS11 as both a comparative and contrasting model organism for the study of isoprene metabolism in bacteria, aiding our understanding of the conservation of this biochemical pathway across diverse ecological niches.

Antimicrobial resistance (AMR) in soil is an ancient phenomenon with widespread spatial presence in terrestrial ecosystems. However, the natural processes shaping the temporal dissemination of AMR in soils are not well understood. We aimed to determine whether, how, and why AMR varies with soil age in recently deglaciated pioneer and developing Arctic soils using a space-for-time approach. Specifically, we assess how the magnitude and spread of AMR changes with soil development stages, including antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and antibiotic-resistant bacteria (ARB). We showed that ARGs, MGEs, and ARB are present, and exhibit a non-uniform distribution in the developing soils. Their abundance generally increases with soil age but at different rates overall and across different glacier forefields. Our analyses suggest a strong positive relationship between soil age and ARGs and ARB, which we attribute to increased competition between microbes in older soils. We also observed a strong negative relationship between soil age and ARG diversity mediated by soil organic matter – suggesting facilitation due to the alleviation of nutrient limitation. These contrasting results suggest that both competition and facilitation can regulate AMR spread through time in the Arctic, but competition might be the stronger determinant of AMR spread.

Bacteria that inhabit soils and the leaves of trees partially mitigate the release of the abundant volatile organic compound, isoprene (2‐methyl‐1,3‐butadiene). While the initial steps of isoprene metabolism were identified in Rhodococcus sp. AD45 two decades ago, the isoprene metabolic pathway still remains largely undefined. Limited understanding of the functions of isoG , isoJ and aldH and uncertainty in the route of isoprene‐derived carbon into central metabolism have hindered our understanding of isoprene metabolism. These previously uncharacterised iso genes are essential in Variovorax sp. WS11, determined by targeted mutagenesis. Using combined ‘omics‐based approaches, we propose the complete isoprene metabolic pathway. Isoprene is converted to propionyl‐CoA, which is assimilated by the chromosomally encoded methylmalonyl‐CoA pathway, requiring biotin and vitamin B12, with the plasmid‐encoded methylcitrate pathway potentially providing robustness against limitations in these vitamins. Key components of this pathway were induced by both isoprene and its initial oxidation product, epoxyisoprene, the principal inducer of isoprene metabolism in both Variovorax sp. WS11 and Rhodococcus sp. AD45. Analysis of the genomes of distinct isoprene‐degrading bacteria indicated that all of the genetic components of the methylcitrate and methylmalonyl‐CoA pathways are not always present in isoprene degraders, although incorporation of isoprene‐derived carbon via propionyl‐CoA and acetyl‐CoA is universally indicated.

Isoprene (2‐methyl‐1,3‐butadiene) is emitted to the atmosphere each year in sufficient quantities to rival methane (>500 Tg C yr ⁻¹ ), primarily due to emission by trees and other plants. Chemical reactions of isoprene with other atmospheric compounds, such as hydroxyl radicals and inorganic nitrogen species (NO _x ), have implications for global warming and local air quality, respectively. For many years, it has been estimated that soil‐dwelling bacteria consume a significant amount of isoprene (~20 Tg C yr ⁻¹ ), but the mechanisms underlying the biological sink for isoprene have been poorly understood. Studies have indicated or confirmed the ability of diverse bacterial genera to degrade isoprene, whether by the canonical iso ‐type isoprene degradation pathway or through other less well‐characterized mechanisms. Here, we review current knowledge of isoprene metabolism and highlight key areas for further research. In particular, examples of isoprene‐degraders that do not utilize the isoprene monooxygenase have been identified in recent years. This has fascinating implications both for the mechanism of isoprene uptake by bacteria, and also for the ecology of isoprene‐degraders in the environments.

Isoprene is a climate-active gas, largely produced by trees, which is released from the biosphere in amounts equivalent to those of methane and all other volatile organic compounds combined. Bacteria found in many environments, including soils and on the surface of leaves of isoprene-producing trees, can grow on isoprene and thus may represent a significant biological sink for this globally significant volatile compound and remove isoprene before it escapes to the atmosphere, thus reducing its potency as a climate-active gas.