Dynamics of species in a co-culture under selective pressure of ampicillin.

Haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacteria belonging to the genus are highly abundant in microbial communities found in soda lakes and dominant in full-scale bioreactors removing sulfide from industrial waste gases. Despite certain soda lakes being remote and unaffected by anthropogenic activities, haloalkaliphilic microorganisms, including strains, possess various antibiotic resistance genes. In this study, we investigated the impact of the antibiotic ampicillin on a co-culture of two species ARh2 and AL2, both experimentally and through analysis of antibiotic resistance. Cell growth dynamics were monitored over time at increasing ampicillin concentrations using rep- and qPCR. Within ten days after the addition of ampicillin, the co-culture transitioned from a ARh2-dominated to a stable AL2-dominated culture. This shift was attributed to AL2 displaying a lower susceptibility to ampicillin, making it more competitive. These results emphasize the potential implications of antibiotic pressure on microbial communities, where a resistant species can outcompete a stable co-culture. This study presents the first evidence of such dynamics in haloalkaliphilic chemolithoautotrophs. By understanding the antibiotic resistance and the competitive dynamics of haloalkaliphilic bacteria like , we can gain insights into their behaviour and stress response.