Abstract
Poly-lactic acid (PLA) is increasingly used as a biodegradable alternative to traditional petroleum-based plastics. In this study, we identify a novel agricultural soil isolate of Bacillus pumilus (B12) that is capable of degrading high molecular weight PLA films. This degradation can be detected on a short timescale, with significant degradation detected within 48-h by the release of L-lactate monomers, allowing for a rapid identification ideal for experimental variation. The validity of using L-lactate as a proxy for degradation of PLA films is corroborated by loss of rigidity and appearance of fractures in PLA films, as measured by atomic force microscopy and scanning electron microscopy (SEM), respectively. Furthermore, we have observed a dose-dependent decrease in PLA degradation in response to an amino acid/nucleotide supplement mix that is driven mainly by the nucleotide base adenine. In addition, amendments of the media with specific carbon sources increase the rate of PLA degradation, while phosphate and potassium additions decrease the rate of PLA degradation by B. pumilus B12. These results suggest B. pumilus B12 is adapting its enzymatic expression based on environmental conditions and that these conditions can be used to study the regulation of this process. Together, this work lays a foundation for studying the bacterial degradation of biodegradable plastics.
Highlights
The crisis of plastic pollution in the environment has led to an increased adoption of biodegradable polymers in the commercial plastic industry
Poly-lactic acid films of 10 mg/mL were created in 96-well plate formats and serially diluted concentrations of Proteinase K were added to each well in minimal salt media (MSM)
The measurement of poly-lactic acid (PLA) degradation has historically relied on techniques that are either time consuming or expensive to perform when running experiments with many variables
Summary
The crisis of plastic pollution in the environment has led to an increased adoption of biodegradable polymers in the commercial plastic industry. Biodegradable polymers are considered a more ecologically friendly alternative to conventional plastic polymers due to a limited accumulation in the environment (Emadian et al, 2017) Some of these biodegradable polymers, such as polyhydroxyalkanoate (PHA) and polylactic acid (PLA), are derived from renewable biomass (Madkour et al, 2013; Singhvi and Gokhale, 2013), while other biodegradable polymers are synthesized from fossil fuel feed stocks (e.g., PBAT and PCL). Most previous research monitoring biodegradation has focused on the production of CO2 as an indicator of cellular respiration and loss of film mass as a gauge for polymer degradation (Ahn et al, 2011; Arrieta et al, 2014; Mihai et al, 2014) This practice tends to be performed over the course of weeks to months and does not lend itself to rapid identification of novel microbial isolates, quick detection of enzymes capable of PLA degradation, or speedy categorization of microbial adaptation through changes in gene expression
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