FACTORS AFFECTING THE SURVIVAL OF A FLAVOBACTERIUM SPECIES IN NON-PLANTED AND RHIZOSPHERE SOIL

Factors affecting the survival of a Gram-negative soil Flavobacterium sp. (P25) were investigated in small-scale laboratory microcosms. Two terms for expressing P25 persistence are used: survival-describing the number of P25 reisolated from soil at a certain time point; and survi val rate-expressed as the time in days taken for a 90% (t90), 99% (t99 ) or 99.9% (t99.9) decline in numbers of P25. Survival rates of P25 in creased in rhizosphere as opposed to bulk soil and were increased furt her by applying the inoculum directly to the planted seedling (t99 = 2 1 d) rather than homogenizing it through the soil prior to planting (t 99 = 10.5 d). Survival was increased by using greater inoculum densiti es, for example following inoculation at 1.1 x 10(9) P25 g-1 soil, num bers surviving at day 40 were 12.5-fold greater than that achieved wit h 1.1 x 10(4) P25 g-1. In addition, survival rates of P25 were increas ed by applying the inoculant to soil at moisture holding capacities (M HC) between 40 and 50% (t99.9 = 12.2 d) in comparison to either wetter (e.g. 100% MHC, t99.9 = 3.5 d) or drier (e.g. 10% MHC, t99.9 = 1 d) s oils. Carbon amendments (i.e. galactose, maltose, sorbitol) significan tly increased survival of P25 in non-planted soil throughout the 35 d study whereas in rhizosphere soil an increase was only recorded for th e first 14 d.