Leptospirosis is a worldwide re-emerging zoonosis with a high incidence in Oceania and Asia. This environmentally transmitted infectious disease is responsible for over 1 million human cases and 60,000 deaths annually. It is caused by aerobic, gram-negative, virulent bacteria of the genus Leptospira. Pathogenic leptospires can either cause acute infection with severe organ damage, or they can infect mammals asymptomatically by evading the immune system and persisting in the renal tubules. Asymptomatic chronic carriers of pathogenic Leptospira, such as rodents, can shed the bacteria in their urine throughout their lives. Once in the soil, pathogenic bacteria can survive for several weeks and may even be able to multiply. Biofilm formation is a survival mechanism to cope with stress and a dominant bacterial lifestyle in the environment. Biofilms are organised multicellular bacterial aggregates embedded in a three-dimensional self-produced matrix that favours persistence and survival. Within the genus Leptospira, both saprophytes and pathogenic species are able to form a biofilm in vitro, and detection of Leptospira in environmental biofilms has also been reported. We characterised the transcriptomic changes within a mature biofilm of Leptospira interrogans and, together with other stress data, identified a specific operon that was up-regulated 30-fold.
The three genes of this operon, csor, copZ and copA, are described to be involved in copper detoxification. Although copper was present in the culture medium used, we hypothesised that its concentration of 1.2µM was not sufficient to induce the transcriptomic responses observed. To verify these hypotheses, we performed copper stress at 500µM to assess the transcriptomic regulation of the target genes of interest. In addition, now that we have a good understanding of the data set, we would also like to carry out a transcriptome in a late biofilm produced in a copper-free culture medium.
