Variability in cadmium tolerance of closely related isolates originating from dairy processing environments.

UNLABELLED

Increased tolerance to cadmium in has been suggested to contribute to their persistence in natural and food production environments. This study investigated the phenotypic cadmium response of strains with efflux pump (variants 1-4) and related strains with . Growth of variant strains ( = 5) in 0 µM-120 µM cadmium salts (CdCl, CdSO) in Mueller-Hinton broth (MHB) was evaluated. Additionally, 88 . strains from dairy processing facilities were exposed to 43.8 µM CdCl in MHB, and their lag phase duration (LPD) was measured. Strains with through showed similar growth trends in the presence of cadmium, while the variant (Scott A) had the highest CdCl minimum inhibitory concentration (175 µM). Growth varied between the two salts, with CdSO significantly increasing LPD ( < 0.05) compared to CdCl. In 43.8 µM CdCl, strains displayed LPDs ranging from 0.99 ± 0.14 h to 6.44 ± 0.08 h, with no clear genomic differences explaining this variability. Strains without did not grow at 43.8 µM CdCl but exhibited low tolerance (10.9 µM CdCl), potentially due to non-specific soft metal ATPases (626 aa; 737 aa) and soft metal resistance proteins encoded by genes (289 aa; 291 aa; 303 aa) within their chromosomes. These findings enhance our understanding of cadmium tolerance and underscore the need for further research to explore the genetic and physiological factors underlying these trends.

IMPORTANCE

Mobile genetic elements in contribute to its survival in natural and food processing environments. This study focused on how different genetic variants of the efflux pump gene and group of closely related strains respond to cadmium exposure. When exposed to two cadmium salts, cadmium chloride and cadmium sulfate, we observed varying growth patterns, with a significantly longer lag phase in cadmium sulfate compared to cadmium chloride. Strains with to had similar growth trends, whereas a strain with the variant had the highest minimum inhibitory concentration value. Among 88 strains from dairy processing facilities, significant phenotypic differences were observed despite core genome similarities, indicating other underlying genetic and physiological factors contribute to cadmium tolerance. Since cadmium tolerance studies in are limited, with rare phenotypic comparisons between closely related strains, our study makes an important observation and contribution to understanding of tolerance to cadmium by providing phenotypic comparisons between numerous strains within the same clonal group (<16 single nucleotide polymorphisms).