Louise Weaver

The landscape of antimicrobial resistance (AMR) is changing across the animal, human and environmental ecosphere, with both climate change and AMR recognised as leading threats to human health. In this viewpoint, we argue that climate change is likely to reshape the conditions under which AMR emerges, persists and spreads, with important implications for how risks are understood and managed in Aotearoa New Zealand (ANZ). These risks arise because climate‐related exposures interact with existing vulnerabilities and adaptive capacity across human, animal and environmental systems. Addressing AMR under climate change requires long‐term, transdisciplinary planning that integrates surveillance, infrastructure resilience, emissions reduction and protection of human, animal and environmental systems. We highlight the need for a One Health lens to understand transmission pathways across human, animal and environmental systems, situated within a broader Planetary Health perspective that recognises AMR as part of interconnected challenges of climate change, including pollution and biodiversity loss. Therefore, embedding AMR within climate adaptation health planning is essential to strengthen resilience and reduce future public and environmental health risks.

Antimicrobial resistance (AMR) is recognised as a significant global health threat, yet research, surveillance and intervention strategies remain largely focused on clinical and veterinary settings, with limited attention to environmental reservoirs and transmission pathways. Growing global evidence, including from Aotearoa New Zealand (NZ), points to a clear link between dominant sources of AMR entering the environment (such as wastewater) and its dissemination in receiving environments. Once in these environments, a wide range of microorganisms, both environmental and introduced, interact in complex ways, with their associated resistomes contributing to potential human exposure pathways. However, clear attribution of environmental AMR contributions to human (and animal) health outcomes remains limited and represents a critical next step for research and surveillance. This viewpoint highlights global and regional evidence on environmental contributions to AMR transmission and dissemination, with emphasis on co‐selective pressures including antibiotics, heavy metals, biocides and plastics that promote resistance selection, persistence and horizontal gene transfer. We identify key gaps in NZ, notably the lack of integrated, cross‐sector monitoring, robust attribution approaches and quantitative assessment of risks to human health. We conclude that effective mitigation requires integrated cross‐sector frameworks linking environmental surveillance, genomic data, microbial source attribution and quantitative risk assessment to inform targeted, risk‐based interventions. These interventions need to be based on a deeper understanding of the interactions between environmental reservoirs, co‐selective pressures and the key drivers and pathways of AMR, including broader environmental influences such as co‐contaminants and climate change.

Woodchip denitrifying bioreactors (WDBs) are passive environmental treatment technologies used to reduce nitrate pollution in agricultural drainage water and wastewater, but their capacity to attenuate microbial contaminants under field conditions remains poorly studied. This limits their use as multi-functional water pollution control systems. In this study, we evaluated microbial removal and transport in an operational WDB using a controlled tracer experiment with known microbial inputs. Serving as bacterial, viral and protozoan models, Escherichia coli (E. coli), MS2 bacteriophage, and a Cryptosporidium surrogate (glycoprotein-coated microspheres) were dosed into a 75 m-long WDB treating agricultural drainage water at a flow rate of 3.2 L/s and hydraulic retention time of 16 h. Water samples were collected along the WDB over a 28 h period. Microbial tracer peak concentrations decreased exponentially with distance. Spatial removal rates were 0.153 log/m for the Cryptosporidium surrogate, 0.044 log/m for E. coli, and 0.028 log/m for MS2, consistent with particle-size-dependent attenuation. Removal rates were an order of magnitude lower than those reported for WDBs with longer residence times, smaller woodchips, and warmer temperatures. These findings show that WDBs operated under nitrate-optimised field conditions provide limited pathogen-model removal. If WDBs are intended to deliver microbial-risk reduction as a treatment co-benefit, process design should consider lower flow rates, longer hydraulic residence times, and/or smaller media to increase contact, attachment and filtration opportunities.

The ecological impacts of plastics and their additives on marine microbiota remain unclear. We applied prokaryotic 16S rRNA gene and fungal ITS2 region amplicon sequencing, alongside shotgun metagenomic sequencing, to identify compositional and functional changes in microbial communities on marine plastic. Five common plastics, both non‐aged and artificially aged, were submerged in Auckland Harbour, Aotearoa‐New Zealand. Biofilms on linear low‐density polyethylene (LLDPE), nylon‐6 (PA), polyethylene terephthalate (PET), polylactic acid (PLA), oxo‐biodegradable LLDPE (OXO) and glass were sampled over 12 months. The taxonomy and functional potential of biofilm communities differed from surrounding seawater communities and varied with biofilm age. Younger biofilms were more diverse, with Proteobacteria, unknown fungi and unclassified Metazoa dominating prokaryotic, fungal and eukaryotic communities, respectively. Taxa related to previously reported plastic‐degraders were found in very low abundance across all substrates. Plastic type and UV‐ageing did not significantly shape biofilm communities over a year. Although some genes differed in relative abundance due to UV‐ageing, overall functional profiles remained consistent across plastics. Genes conferring reported plastic‐degrading traits were present regardless of plastic type, UV‐ageing and biofilm age. Nevertheless, nylon hydrolases were notably associated with PA, suggesting marine plastic impacts may be restricted to taxa or functions involved in its degradation.

Free-living amoebae (FLA) are common in both natural and engineered freshwater ecosystems. They play important roles in biofilm control and contaminant removal through the predation of bacteria and other taxa. Bacterial predation by FLA is also thought to contribute to pathogen dispersal and infectious disease transmission in freshwater environments via the egestion of viable bacteria. Despite their importance in shaping freshwater microbial communities, the diversity and function of FLA in many freshwater ecosystems are poorly understood. In this study, we isolated and characterized FLA from two groundwater sites in Canterbury, New Zealand using microbiological, microscopic, and molecular techniques. Different methods for groundwater FLA isolation and enrichment were trialed and optimized. The ability of these isolated FLA to predate on human pathogen Legionella pneumophila was assessed. FLA were identified by 18S metagenomic amplicon sequencing. Our study showed that Acanthamoeba spp. (including A. polyphaga) and Vermamoeba veriformis were the main FLA species present in both groundwater sites examined. While most of the isolated FLA co-existed with L. pneumophila, the FLA populations in the L. pneumophila co-culture experiments predominantly consisted of A. polyphaga, Acanthamoeba spp., Naegleria spp., V. vermiformis, Paravahlkampfia spp., and Echinamoeba spp. These observations suggest that FLA may have the potential to act as reservoirs for L. pneumophila in Canterbury, New Zealand groundwater systems and could be introduced into the local drinking water infrastructure, where they may promote the survival, multiplication, and dissemination of Legionella. This research addresses an important gap in our understanding of FLA-mediated pathogen dispersal in freshwater ecosystems.

Plastic pollution in the terrestrial environment is emerging as another significant human-made threat to ecosystem function and health. Plastic contamination can range from the macro- to the nanoscale, and environmental impacts are evident at each level. Although significant knowledge gaps remain regarding the interactions between the natural environment and nano- and microplastics (NMPs), there is an increasing body of evidence concerning detrimental effects on a wide range of taxa. The surface properties of NMPs lead to the adsorption of heavy metals, endocrine-disrupting chemicals, antibiotics and other persistent organic pollutants, which, therefore, can result in their co-migration in the terrestrial environment. Although airborne and dietary transmission routes of NMPs have been observed, their effects on human health are still not fully understood, which is of concern to the scientific community. This state-of-the-art review paper firstly examines available evidence for, and knowledge of, various sources of NMP contamination to the terrestrial environment. Attention then focuses on (a) the biological processes from the source to soils and plants, (b) potential impacts of NMPs on soil and subsurface ecosystems, (c) trophic interactions and function and (d) implications for environmental and human health. This paper concludes by identifying knowledge gaps and presents recommendations on prioritised research needs.

Groundwater is a vital ecosystem of the global water cycle, hosting unique biodiversity and providing essential services to societies. Despite being the largest unfrozen freshwater resource, in a period of depletion by extraction and pollution, groundwater environments have been repeatedly overlooked in global biodiversity conservation agendas. Disregarding the importance of groundwater as an ecosystem ignores its critical role in preserving surface biomes. To foster timely global conservation of groundwater, we propose elevating the concept of keystone species into the realm of ecosystems, claiming groundwater as a keystone ecosystem that influences the integrity of many dependent ecosystems. Our global analysis shows that over half of land surface areas (52.6%) has a medium‐to‐high interaction with groundwater, reaching up to 74.9% when deserts and high mountains are excluded. We postulate that the intrinsic transboundary features of groundwater are critical for shifting perspectives towards more holistic approaches in aquatic ecology and beyond. Furthermore, we propose eight key themes to develop a science‐policy integrated groundwater conservation agenda. Given ecosystems above and below the ground intersect at many levels, considering groundwater as an essential component of planetary health is pivotal to reduce biodiversity loss and buffer against climate change.