Potential for phenol biodegradation in cloud waters

Phenol is toxic and can be found in many environments, in particular in the atmosphere due to its high volatility. It can be emitted directly from manufacturing processes or natural sources, and it can also result from benzene oxidation. Although phenol biodegradation by microorganisms has been studied in many environments, the cloud medium has not been investigated yet as the discovery of active microorganisms in cloud is rather recent. The main objective of this work was to evaluate the potential degradation of phenol by cloud microorganisms. Phenol concentrations were measured by GC-MS on two cloud samples collected at the PUY station (summit of Puy de Dôme, 1465 m a.s.l., France): they ranged from 0.15 to 0.21 µg L−1. The strategy for investigating its potential biodegradation involved a metatranscriptomic analysis and metabolic screening of bacterial strains from cloud water collected at the PUY station for phenol degradation capabilities (from the 145 tested strains, 33 were isolated for this work). Among prokaryotic messenger RNA-enriched metatranscriptomes obtained from three cloud water samples, which were different from those used for phenol quantification, we detected transcripts of genes coding for enzymes involved in phenol degradation (phenol monooxygenases and phenol hydroxylases) and its main degradation product, catechol (catechol 1,2-dioxygenases). These enzymes were likely from Gammaproteobacteria, a dominant class in clouds, more specifically the genera Acinetobacter and Pseudomonas. Bacterial isolates from cloud water samples (Pseudomonas spp., Rhodococcus spp., and strains from the Moraxellaceae family) were screened for their ability to degrade phenol: 93 % of the 145 strains tested were positive. These findings highlight the possibility of phenol degradation by microorganisms in clouds. Metatranscriptomic analysis suggested that phenol could be biodegraded in clouds, while 93 % of 145 bacterial strains isolated from clouds were able to degrade phenol.