Practice question

Pseudomonas putida strains such as KT2440 certified HV1 safety, mt-2 and F1 embody archetypal aerobic degraders of monoaromatic and polycyclic aromatic hydrocarbons due to extraordinary metabolic versatility conferred by large genome 6.2 megabases encoding more than 80 oxygenases and multiple catabolic plasmids including TOL plasmid pWW0 carrying upper pathway xylCMABN converting toluene and xylene to benzoate via xylene monooxygenase multicomponent system and meta-cleavage lower pathway xylXYZLTEGFJKIH, and NAH7 plasmid encoding naphthalene dioxygenase nahAc. Enzymatic repertoire includes toluene dioxygenase todC1C2BA introducing dioxygen to form cis-dihydrodiols, catechol 2,3-dioxygenase xylE catalyzing extradiol ring fission producing yellow 2-hydroxymuconic semialdehyde, and central tricarboxylic acid cycle integration. Chemotaxis genes che regulate flagellar movement toward aromatic gradients increasing bioavailability. Strain thrives in contaminated soils at densities 10^6 per gram, grows on benzene, toluene, ethylbenzene and xylene as sole carbon sources with generation time 2 to 3 hours. Unlike Escherichia coli lacking oxygenase repertoire, Lactobacillus focusing on sugar fermentation, Streptococcus pathogenic without catabolic plasmids, P. putida evolved in polluted niches possessing regulatory networks XylR and TodST responding to aromatic inducers, enabling rapid mineralization to CO2 with high specific affinity.