Husbandry conditions of spotted ratfish (Hydrolagus colliei, Chimaeriformes) in aquaria for successful embryonic development and long-term survival of juveniles.

The spotted ratfish Hydrolagus colliei is the most common holocephalan species exhibited in aquaria worldwide for introducing deep-sea environments and raising awareness of their conservation. However, little is known about the biology of H. colliei. Current practices in aquaria allow long-term survival of sexually mature H. colliei specimens; however, this species struggles to complete a reproductive cycle in captivity mostly because embryos do not reach the hatchling stage. The aquarists of Planet Ocean Montpellier (POM, France) have bred H. colliei for 15 years and recorded parameters suitable for this species' successful embryonic and post-embryonic development. POM aquarists now regularly record egg-laying events of H. colliei and use four tanks to incubate eggs and raise neonates, late hatchlings, early and intermediate juveniles, subadults, and sexually mature specimens. In this work we provide the first long-term biometric data on H. colliei from the hatchling to the subadult stage. We also report the biotic and abiotic parameters sufficient to breed H. colliei in aquaria. We finally describe the methods used to facilitate individual monitoring of specimens along the ontogeny and several pathologies identified in this species, their putative causes, and the corresponding treatments. This work highlights the importance of ex situ research and points to the valuable outcomes of collaborative efforts between aquaria and academia in deciphering the biology of species whose study in the wild remains challenging.

Biofilms as protective cocoons against biocides: from bacterial adaptation to One Health issues.

Bacteria in the food chain mostly live in communities associated with surfaces known as biofilms, which confer specific survival and adaptive abilities. In such communities, the bacteria mostly exhibit higher tolerance to external stress, and their recurrent exposure along the food chain to biocides used during cleaning and disinfection procedures raises concern about the adaptation routes they develop, both at single-cell and communal levels. In recent years, an increasing number of research subjects have focused on understanding the specific features of biofilms that enable bacterial populations to adapt to biocide exposure within a 'protective cocoon'. The first part of this review concentrates on the diversity of adaptive strategies, including structural modulation of these biofilms, physiological response or the acquisition of genetic resistance. The second part discusses the possible side effects of biofilm adaptation to biocides on antimicrobial cross-resistance, virulence and colonization features from a One Health perspective.

Polyhexamethylene biguanide promotes adaptive cross-resistance to gentamicin in Escherichia coli biofilms.

Antimicrobial resistance is a critical public health issue that requires a thorough understanding of the factors that influence the selection and spread of antibiotic-resistant bacteria. Biocides, which are widely used in cleaning and disinfection procedures in a variety of settings, may contribute to this resistance by inducing similar defense mechanisms in bacteria against both biocides and antibiotics. However, the strategies used by bacteria to adapt and develop cross-resistance remain poorly understood, particularly within biofilms -a widespread bacterial habitat that significantly influences bacterial tolerance and adaptive strategies. Using a combination of adaptive laboratory evolution experiments, genomic and RT-qPCR analyses, and biofilm structural characterization using confocal microscopy, we investigated in this study how Escherichia coli biofilms adapted after 28 days of exposure to three biocidal active substances and the effects on cross-resistance to antibiotics. Interestingly, polyhexamethylene biguanide (PHMB) exposure led to an increase of gentamicin resistance (GenR) phenotypes in biofilms formed by most of the seven E. coli strains tested. Nevertheless, most variants that emerged under biocidal conditions did not retain the GenR phenotype after removal of antimicrobial stress, suggesting a transient adaptation (adaptive resistance). The whole genome sequencing of variants with stable GenR phenotypes revealed recurrent mutations in genes associated with cellular respiration, including cytochrome oxidase (cydA, cyoC) and ATP synthase (atpG). RT-qPCR analysis revealed an induction of gene expression associated with biofilm matrix production (especially curli synthesis), stress responses, active and passive transport and cell respiration during PHMB exposure, providing insight into potential physiological responses associated with adaptive crossresistance. In addition, confocal laser scanning microscopy (CLSM) observations demonstrated a global effect of PHMB on biofilm architectures and compositions formed by most E. coli strains, with the appearance of dense cellular clusters after a 24h-exposure. In conclusion, our results showed that the PHMB exposure stimulated the emergence of an adaptive cross-resistance to gentamicin in biofilms, likely induced through the activation of physiological responses and biofilm structural modulations altering gradients and microenvironmental conditions in the biological edifice.