posted on 2016-12-31, 00:00authored byTekle
Tafese Fida, Silvia K. Moreno-Forero, Philip Breugelmans, Hermann J. Heipieper, Wilfred F. M. Röling, Dirk Springael
Soil bioaugmentation involves the
inoculation of pollutant-degrading
bacteria to accelerate pollutant degradation. Often the inoculum shows
a dramatic decrease in Colony Forming Units (CFU) upon soil inoculation
but this behavior is not well-understood. In this study, the physiology
and transcriptomic response of a GFP tagged variant of Novosphingobium sp. LH128 was examined after inoculation into phenanthrene spiked
soil. Four hours after inoculation, strain LH128-GFP showed about
99% reduction in CFU while microscopic counts of GFP-expressing cells
were identical to the expected initial cell density, indicating that
the reduction in CFU number is explained by cells entering into a
Viable But Non-Culturable (VBNC)-like state and not by cell death.
Transcriptome analysis showed a remarkably higher expression of phenanthrene
degradation genes 4 h after inoculation, compared to the inoculum
suspension concomitant with an increased expression of genes involved
in stress response. This indicates that the cells were active in phenanthrene
degradation while experiencing stress. Between 4 h and 10 days, CFU
numbers increased to numbers comparable to the inoculated cell density.
Our results suggest that strain LH128-GFP enters a VBNC-like state
upon inoculation into soil but is metabolically active and that VBNC
cells should be taken into account in evaluating bioaugmentation approaches.