Study into biodegradation of cocamidopropyl betaine, an amphoteric surfactant, by Pseudomonas bacteria and activated sludge

The paper examines the biodegradation rate of cocamidopropyl betaine by bacteria of the genus Pseudomonas and activated sludge. The following microorganisms were taken as destructor strains: Pseudomonas fluorescens TR (VKPM B-4881), Pseudomonas putida TP-19 (B-6582), Pseudomonas stutzeri T (B-4904), Pseudomonas putida TSh-18 (B-2950), Pseudomonas putida TO (B-3959), Pseudomonas mendocina 2S (B-4710), Pseudomonas oleovorans TF4-1L (B-8621) and activated sludge obtained at activated sludge reactors of a Kuzbass plant. Biooxidation of surfactant samples was carried out in 250 cm3 glass flasks, placed into an incubator shaker, at a constant temperature of 30ºС for pure cultures and 18ºС for activated sludge. The destructor strain should reduce the surfactant concentration to safe values within a minimum time interval. Pseudomonas stutzeri T (B-4904) and Pseudomonas fluorescens TR (B-4881) strains provided the shortest half-life of the surfactant under study – 2.5 and 2.6 days, respectively. For Pseudomonas putida TO (B-3959), Pseudomonas putida TSh-18 (B-2950) and Pseudomonas oleovorans TF4-1L (B-8621) strains, these values amounted to 3.0, 4.5 and 4.9 days, respectively. The maximum half-life of the surfactant under study was demonstrated by Pseudomonas mendocina 2S (B-4710) and Pseudomonas putida TP-19 (B-6582) microorganisms – 5.5 and 6.0 days, respectively. The maximum biodegradation of the surfactant was observed under its exposure to the biocenosis of microorganisms. Over 14 days, the concentration of cocamidopropyl betaine decreased to 0.27% of its initial concentration. The efficiency of Pseudomonas bacteria as destructors of surfactants was demonstrated. Bacteria of this genus exhibit a shorter generation time and a higher rate of biomass growth when compared to other strains and a shorter period of adaptation to surfactants when compared to activated sludge. Capable of reducing surfactant concentrations to safe values in a minimum time interval, Pseudomonas strains can be used as an effective agent in the development of technologies for wastewater purification from amphoteric surfactants.

Filling in the Gaps in Metformin Biodegradation: A New Enzyme and a Metabolic Pathway for Guanylurea

The widely prescribed pharmaceutical metformin and its main metabolite guanylurea are currently two of the most common contaminants in surface and wastewater. Guanylurea often accumulates and is poorly, if at all, biodegraded in wastewater treatment plants. This study describes Pseudomonas mendocina strain GU isolated from a municipal wastewater treatment plant using guanylurea as its sole nitrogen source. The genome was sequenced with 36-fold coverage and mined to identify guanylurea degradation genes. The gene encoding the enzyme initiating guanylurea metabolism was expressed, the enzyme purified and characterized. Guanylurea hydrolase, a newly described enzyme, was shown to transform guanylurea to one equivalent of ammonia and guanidine. Guanidine also supports growth as a sole nitrogen source. Cell yields from growth on limiting concentrations of guanylurea revealed that metabolism releases all four nitrogen atoms. Genes encoding complete metabolic transformation were identified bioinformatically, defining the pathway as follows: guanylurea to guanidine to carboxyguanidine to allophanate to ammonia and carbon dioxide. The first enzyme, guanylurea hydrolase, is a member of the isochorismatase-like hydrolase protein family that includes biuret hydrolase and triuret hydrolase. Although homologs, the three enzymes show distinct substrate specificities. Pairwise sequence comparisons and the use of sequence similarity networks allowed fine structure discrimination between the three homologous enzymes and provided insights into the evolutionary origins of guanylurea hydrolase. IMPORTANCE Metformin is a pharmaceutical most prescribed for type 2 diabetes and is now being examined for potential benefits to COVID-19 patients. People taking the drug pass it largely unchanged and it subsequently enters wastewater treatment plants. Metformin has been known to be metabolized to guanylurea. The levels of guanylurea often exceed that of metformin, leading to the former being considered a “dead end” metabolite. Metformin and guanylurea are water pollutants of emerging concern as they persist to reach non-target aquatic life and humans, the latter if it remains in treated water. The present study has identified a Pseudomonas mendocina strain that completely degrades guanylurea. The genome was sequenced and the genes involved in guanylurea metabolism were identified in three widely separated genomic regions. This knowledge advances the idea that guanylurea is not a dead end product and will allow for bioinformatic identification of the relevant genes in wastewater treatment plant microbiomes and other environments subjected to metagenomic sequencing.

Whole Genome Analysis of Environmental Pseudomonas mendocina Strains: Virulence Mechanisms and Phylogeny

Pseudomonas mendocina is an environmental bacterium, rarely isolated in clinical specimens, although it has been described as producing endocarditis and sepsis. Little is known about its genome. Whole genome sequencing can be used to learn about the phylogeny, evolution, or pathogenicity of these isolates. Thus, the aim of this study was to analyze the resistome, virulome, and phylogenetic relationship of two P. mendocina strains, Ps542 and Ps799, isolated from a healthy Anas platyrhynchos fecal sample and a lettuce, respectively. Among all of the small number of P.mendocina genomes available in the National Center for Biotechnology Information (NCBI) repository, both strains were placed within one of two well-defined phylogenetic clusters. Both P. mendocina strains lacked antimicrobial resistance genes, but the Ps799 genome showed a MOBP3 family relaxase. Nevertheless, this study revealed that P. mendocina possesses an important number of virulence factors, including a leukotoxin, flagella, pili, and the Type 2 and Type 6 Secretion Systems, that could be responsible for their pathogenesis. More phenotypical and in vivo studies are needed to deepen the association with human infections and the potential P. mendocina pathogenicity.