PAH-degradation by Paenibacillus spp. and description of Paenibacillus naphthalenovorans sp. nov., a naphthalene-degrading bacterium from the rhizosphere of salt marsh plants

Bacteria belonging to the genus Paenibacillus were isolated by enrichment from petroleum-hydrocarbon-contaminated sediment and salt marsh rhizosphere using either naphthalene or phenanthrene as the sole carbon source, and were characterized using phenotypic, morphological and molecular techniques. The isolates were grouped by their colony morphologies and polyaromatic hydrocarbon-degradation patterns. Phenanthrene-degrading isolates produced mottled colonies on solid media and were identified as P. validus by fatty acid methyl ester and 16S rRNA gene sequence analyses. In contrast, the naphthalene-degrading isolates with mucoid colony morphology were distantly related to Paenibacillus validus, according to fatty acid methyl ester and 16S rRNA gene sequence analyses. The predominant fatty acids of the mucoid isolates were 15:0 anteiso, 16:1ω11c, 16:0 and 17:0 anteiso, constituting, on average, 50.5, 12.0, 11.2 and 6.5% of the total, respectively. The G+C contents of their DNA ranged from 47 to 52 mol%. The 16S rDNA sequence analysis revealed the highest (≤94%) similarity to P. validus. In addition, phylogenetic analyses based on 16S rDNA sequences showed that the mucoid isolates formed a distinct cluster within Paenibacillus. DNA-DNA hybridization experiments showed only a 6% DNA similarity between the type strain of P. validus and mucoid strain PR-N1. On the basis of the morphological, phenotypic and molecular data, the naphthalene-degrading isolates merit classification as a new Paenibacillus species, for which the name Paenibacillus naphthalenovorans sp. nov. is proposed, with PR-N1^T (= ATCC BAA-206^T = DSM 14203^T) as the type strain.