Ribosomal RNA Cistron Similarities among Hyphomicrobium Species and Several other Hyphal, Budding Bacteria

Abstract

Relationships among hyphomicrobia and similar strains were determined by DNA/rRNA hybrid thermal stability expressed as Tm(e) values and depicted in a dendrogram. The rRNA cistron similarities observed indicated that the genus Hyphomicrobium is rather heterogeneous. At least five groups of hyphomicrobia could be differentiated with only distant relationships to each other. The first group contains strains of Hyphomicrobium facilis , the second group consists of the type strains of Hyphomicrobium vulgare and Hyphomicrobium aestuarii , and the third group contains the type strain of Hyphomicrobium hollandicum and an isolate from polluted water of Long Island Sound. The last two groups are represented by only one strain each: IFAM 1460 and the rosette-forming Hyphomicrobium zavarzinii . These five groups are as distantly related to each other as they are to the type strain of Pedomicrobium ferrugineum . The moderately halophilic and thermophilic bacterium Dichotomicrobium strain IFAM 954 was even more distant from the other budding, hyphal bacteria. Low Tm(e) values of around 50°C were shown by hybrids of hyphomicrobia with the Hyphomonas strains and with strain IFAM 1315 (group “T”) and IFAM 1415; these bacteria are not considered to be closely related to the hyphomicrobia.