L. Molina et al., Survival of Pseudomonas putida KT2440 in soil and in the rhizosphere of plants under greenhouse and environmental conditions, SOIL BIOL B, 32(3), 2000, pp. 315-321
Pseudomonas putida KT2440 is a root colonizer of potential interest for the
rhizoremediation of pollutants and the biological control of pests, The sh
ort- and long-term survival of this strain, as well as the possible effects
of its introduction on different populations of indigenous soil bacteria,
were tested in soil under greenhouse and field conditions. The greenhouse s
tudies showed that inoculated P. putida KT2440 was able to establish itself
after 3 d in nonvegetated soils at a density of 8 +/- 2 x 10(3) CFU g(-1)
soil. The introduction of this strain had no significant effect on the numb
er of several soil bacteria including those that were resistant to tetracyc
line; those that utilized p-hydroxyphenylacetic acid as the sole C-source,
and total fluorescent pseudomonads, In four independent field assays in non
planted soils. the numbers of P, putida KT2440 decreased during 50 d from a
n initial density of 1 x 10(6) CFU g(-1) soil to approximately 2 +/- 1 x 10
(2) CFU g(-1) soil. Thereafter, the number of cells was below detection lim
its (i.e. < 10(2) CFU g(-1) soil), although they were still present because
they could be recovered using selective enrichment from the soil for up to
200 d after the beginning of the experiment. This suggested that P. putida
was maintained at a low cell density long after inoculation. In contrast,
when P. putida KT2440 was introduced in the soil as a coating of corn (Zea
mays) or broad bean (Vicia faba) seeds, the bacteria established at high ce
ll densities in the rhizosphere (10(4)-10(5) CFU g(-1) soil in corn; 10(6)-
10(7) CFU g(-1) soil in broad beans) during the growth of the crops over 12
to 16 weeks. The numbers of P. putida in the bulk soil after 2 weeks were
1 to 2 orders of magnitude below those in the rhizosphere. During the field
assays, the population of p-hydroxyphenylacetic acid users was also monito
red in the rhizosphere and the bulk soil. No significant seasonal variation
s were found. (C) 2000 Elsevier Science Ltd. All rights reserved.