- Volume 128, Issue 3, 1982

When the Arrhenius equation is applied to microbial growth rates, a temperature characteristic (μA) represents the activation energy. While these μA values describe the energetics favouring growth, there is still no convincing evidence from empirical data to support the idea of a widely applicable relationship between μA values and optimal growth temperatures, which may serve as a basis for the classification of psychrophiles, psychrotrophs, mesophiles and thermophiles. The μA values for the exponential growth rates of 16 psychrophilic and psychrotrophic bacterial strains, including 9 from the literature, varied from 3 to 33 (kcal mol−1). A plot of μA versus growth temperature optimum deviated considerably from empirical equations reported recently ( Mohr & Krawiec, 1980 ) for a different selection of strains. Moreover, Arrhenius profiles with two distinct slopes at suboptimal temperatures were not restricted to bacteria with growth temperature optima higher than 37 °C, as had been suggested in that report. A psychrotrophic strain of Cytophaga johnsonae with a growth temperature optimum of 23–25 °C was characterized by two different temperature characteristics. Furthermore, in the upper range of suboptimal temperatures (11–24 °C), temperature characteristics (μA1) were also affected by temperature acclimation of the inoculum.

One hundred and thirty actinomycetes representing 19 genera and 50 species were compared in a numerical phenetic survey using 108 unit characters. Data were examined using the simple matching (SSM ), Jaccard (SJ ) and pattern (Dp ) coefficients and clustering was achieved using both the single and unweighted pair group average algorithms. Cluster composition was barely affected by the statistics used or by test error, estimated at 2·1%. Over 80% of the strains were assigned to 21 clusters containing between two and 25 organisms. Most of the clusters were distinct and homogeneous though two were divided into subclusters. Some of the clusters and subclusters were equated with the established taxa Actinomadura madurae, Actinomadura pelletieri, Dermatophilus congolensis, Geodermatophilus obscurus, Microbispora spp., Micromonospora spp., Micropolyspora brevicatena, Micropolyspora faeni, Nocardia spp., Nocardiopsis (Actinomadura) dassonvillei, Planobispora spp., Planomonospora spp., Saccharomonospora viridis, Streptomyces somaliensis, Thermoactinomyces candidus, Thermoactinomyces dichotomica, Thermoactinomyces sacchari, Thermoactinomyces vulgaris and ‘Thermomonospora fusca’. The numerical data, together with results from previous chemical and genetical studies, provide sufficient evidence for the transfer of Micropolyspora brevicatea to Nocardia as Nocardia brevicatena comb. nov.

One hundred and fifty pink-pigmented facultatively methylotrophic bacteria (PPFMs) of the ‘Pseudomonas extorquens’ type, 28 other facultative methylotrophs and 16 non-methylo-trophic marker strains of the genera Pseudomonas, Alcaligenes, Mycoplana and Microcyclus were compared in a numerical phenetic study using 140 unit characters. Data were analysed using the simple matching (SSM ) and Jaccard (SJ ) coefficients and single, complete and average linkage algorithms. Cluster composition was largely the same with each similarity coefficient and linkage method. Four major and seven minor clusters containing 187 of the 194 strains were defined above the 80% similarity level. The non-pink methylotrophs were recovered in two major, four minor and two single-membered clusters. One of the major clusters could be equated with Microcyclus aquaticus but strains in the other were not identified. Strains in two of the minor clusters were identified as Pseudomonas species but members of the other two minor and one of the single-strain clusters were not positively identified. They had pseudomonad properties but were not closely associated with any marker strains. The other single-membered methylotroph cluster was thought to be a cytophaga or flexibacter. The remaining minor and single-membered clusters contained only marker strains. All the PPFMs were recovered in the two remaining major clusters which were closely related to each other but not to the rest of the organisms studied. The generic assignment of the PPFMs is discussed and the suggestion is made that the genus Methylobacterium may be the most appropriate place for them, despite their apparent inability to utilize methane.