Triclosan changes community composition and selects for specific bacterial taxa in marine periphyton biofilms in low nanomolar concentrations

An Overview of the Impact of Pharmaceuticals on Aquatic Microbial Communities

Pharmaceuticals are present as pollutants in several ecosystems worldwide. Despite the reduced concentrations at which they are detected, their negative impact on natural biota constitutes a global concern. The consequences of pharmaceuticals' presence in water sources and food have been evaluated with a higher detail for human health. However, although most of the pharmaceuticals detected in the environment had not been designed to act against microorganisms, it is of utmost importance to understand their impact on the environmental native microbiota. Microbial communities can suffer serious consequences from the presence of pharmaceuticals as pollutants in the environment, which may directly impact public health and ecosystem equilibrium. Among this class of pollutants, the ones that have been studied in more detail are antibiotics. This work aims to provide an overview of the impacts of different pharmaceuticals on environmental biofilms, more specifically in biofilms from aquatic ecosystems and engineered water systems. The alterations caused in the biofilm function and characteristics, as well as bacteria antimicrobial tolerance and consequently the associated risks for public health, are also reviewed. Despite the information already available on this topic, the need for additional data urges the assessment of emerging pollutants on microbial communities and the potential public health impacts.

Triclosan Promotes Conjugative Transfer of Antibiotic Resistance Genes to Opportunistic Pathogens in Environmental Microbiome

Although triclosan, as a widely used antiseptic chemical, is known to promote the transmission of antibiotic resistance to diverse hosts in pure culture, it is still unclear whether and how triclosan could affect the transmission of broad-host-range plasmids among complex microbial communities. Here, bacterial culturing, fluorescence-based cell sorting, and high-throughput 16S rRNA gene amplicon sequencing were combined to investigate contributions of triclosan on the transfer rate and range of an IncP-type plasmid from a proteobacterial donor to an activated sludge microbiome. Our results demonstrate that triclosan significantly enhances the conjugative transfer of the RP4 plasmid among activated sludge communities at environmentally relevant concentrations. High-throughput 16S rRNA gene sequencing on sorted transconjugants demonstrates that triclosan not only promoted the intergenera transfer but also the intragenera transfer of the RP4 plasmid among activated sludge communities. Moreover, triclosan mediated the transfer of the RP4 plasmid to opportunistic human pathogens, for example, Legionella spp. The mechanism of triclosan-mediated conjugative transfer is primarily associated with excessive oxidative stress, followed by increased membrane permeability and provoked SOS response. Our findings offer insights into the impacts of triclosan on the dissemination of antibiotic resistance in the aquatic environmental microbiome.

Distinct Temporal Succession of Bacterial Communities in Early Marine Biofilms in a Portuguese Atlantic Port

Marine biofilms are known to influence the corrosion of metal surfaces in the marine environment. Despite some recent research, the succession of bacterial communities colonizing artificial surfaces remains uncharacterized in some temporal settings. More specifically, it is not fully known if bacterial colonizers of artificial surfaces are similar or distinct in the different seasons of the year. In particular the study of early biofilms, in which the bacterial cells communities first adhere to artificial surfaces, are crucial for the development of the subsequent biofilm communities. In this work, we used amplicon-based NGS (next-generation sequencing) and universal 16S rRNA bacterial primers to characterize the early biofilm bacterial communities growing on 316 L stainless steel surfaces in a Northern Portugal port. Sampling spanned 30-day periods in two distinct seasons (spring and winter). Biofilm communities growing in steel surfaces covered with an anti-corrosion paint and planktonic communities from the same location were also characterized. Our results demonstrated that distinct temporal patterns were observed in the sampled seasons. Specifically, a significantly higher abundance of Gammaproteobacteria and Mollicutes was found on the first days of biofilm growth in spring (day 1 to day 4) and a higher abundance of Alphaproteobacteria during the same days of biofilm growth in winter. In the last sampled day (day 30), the spring biofilms significantly shifted toward a dominance of photoautotrophic groups (mostly diatoms) and were also colonized by some macrofouling communities, something not observed during the winter sampling. Our results revealed that bacterial composition in the biofilms was particularly affected by the sampled day of the specific season, more so than the overall effect of the season or overall sampling day of both seasons. Additionally, the application of a non-fouling-release anti-corrosion paint in the steel plates resulted in a significantly lower diversity compared with plates without paint, but this was only observed during spring. We suggest that temporal succession of marine biofilm communities should be taken in consideration for future antifouling/anti-biofilm applications.