Bacterial isolates from a number of different soils were screened by growth observation and microscopic examination for Arthrobacter spp. Incidence of arthrobacter in the total population varied, but averaged around 15% in the soils investigated. One hundred and thirty arthrobacter isolates were tested for their ability to utilize aromatic hydrocarbons as their sole carbon source. Seventy-seven percent of these organisms were able to grow on at least two aromatic substrates and many were capable of growth on a wide range of these compounds. Nutritional studies indicated that arthrobacter with simple requirements were able to utilize the greatest number of aromatic hydrocarbons as their sole carbon source. The ability of the arthrobacter to metabolize aromatic compounds is discussed in terms of their possible role in the formation and turnover of residual soil organic matter.
The reduction of 2,3,5-triphenyltetrazolium chloride to triphenylformazan has been used to estimate the dehydrogenase activity of the soil microflora in situ. Preliminary investigations suggest that the formation of the formazan may be used as an index of endogenous respiration in soil since a significant correlation has been obtained between dehydrogenase activity and the oxygen uptake of a number of different untreated soils. A direct relationship also was observed between formazan formation and the respiration of a soil sampled at intervals after the application of fresh plant material. In a survey of a number of field soils no relationship was found between dehydrogenase activity and bacterial numbers; however, the two parameters were parallel during the decomposition of flax residues added to one of the soils.
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