High-throughput metal susceptibility testing of microbial biofilms

Area of Science:

• Microbiology
• Environmental Science
• Toxicology

Background:

• Microbial biofilms are ubiquitous and often coexist with environmental metal cations and oxyanions.
• Limited research exists on biofilm resistance mechanisms against toxic metals.
• This study addresses the need for standardized methods to assess metal susceptibility in biofilms.

Purpose of the Study:

• To develop and validate a high-throughput method for testing metal susceptibility in both biofilm and planktonic microbial cultures.
• To compare the metal tolerance of different microbial strains and growth conditions.
• To investigate the influence of exposure time and growth medium on metal susceptibility.

Main Methods:

• Utilized a batch culture technique with the MBEC assay, compatible with 96-well microtiter plates.
• Implemented a two-part, metal-specific neutralization protocol to minimize residual metal toxicity.
• Calibrated assays for comparative analysis of different organisms and investigated effects of exposure time and media composition.

Main Results:

• Generated 96 statistically equivalent biofilms per device, enabling comparative and combinatorial experiments.
• Demonstrated that biofilms can be significantly more resistant to metals than planktonic cells (e.g., up to 133 times more tolerant to tellurite).
• Showed that metal tolerance in E. coli JM109 biofilms and planktonic cells is dependent on exposure time.

Conclusions:

• The developed method provides accurate and reproducible comparisons of metal susceptibility between planktonic cells and biofilms.
• Facilitated direct comparisons of metal resistance capabilities across different microbial strains.
• Emphasized the critical role of exposure time as a variable in bacterial metal susceptibility testing.