Characteristics of bacteria in the forest soils under natural vegetation

Characteristics of the predominant bacteria isolated in November and May from the forest soils of both dry and wet types under natural vegetation were studied.

Although Gram-negative rods were the most abundant bacteria in both soil types and in both seasons, their contents were less and other bacteria especially spore-forming ones increased in May.

Among Gram-negative rods in the soil of the dry type in November, the most predominant was those with nonchromogenic rods motile with polar flagella which grew in a simple synthetic media containing glucose or p-hydroxybenzoate and ammonium as the sole carbon and nitrogen sources. In May, the ratio of the bacteria which require amino nitrogen or those with more chomplex nutritional requirement increased. In the soil of moderately wet type, the difference in kinds of bacteria between the two seasons was not so clear as that in the dry type.

Most of Bacillus species obtained in these soils were those requiring amino acids or other growth factors among which B. cereus was most abundant.