Survival of inoculated Bacillus cereus spores and vegetative cells in non-planted and rhizosphere soil

The survival of vegetative cells and spores of an antibiotic-resistant Bacillus cereus (B11) inoculant was similar in wheat rhizosphere soil and non-planted soil over a period of 21 d. Reliable ways of producing either spore or vegetative single cell inocula were developed. When applied to give densities ranging from 1 × 102 to 1 × 107 g−1 soil, B11 spores survived for at least 21 d at levels similar to those introduced but numbers of vegetative cells decreased by 1–2 orders of magnitude within the first 48 h and the extent of decrease was proportionately greater at low inoculum density. There was no significant difference after 21 d between total counts (vegetative cells + spores) or spore counts in either the rhizosphere or non-planted soil, regardless of whether the inoculant was composed of vegetative or spore cells. There was no difference between the changing spore-to-vegetative cell ratio within total cell counts between rhizosphere and non-planted soil. Inoculating soil with a mixture of Bacillus B11 (2 × 107 g−1), Flavobacterium P25 (3 × 108 g−1) and Arthrobacter A109 (2 × 108 g−1) increased the survival of P25 and A109 but decreased the survival of B11 in both non-planted and rhizosphere soil compared with each bacterium inoculated alone. For example, at day 21 in rhizosphere soil there were 1 × 106 g−1 A109 (single inoculant) and 1 × 107 g−1 A109 (mixed inoculum) and in non-planted soil 1 × 105 g−1 (single) and 1 × 107 g−1 (mixed). Thus, neither the survival nor the physiological state of Bacillus B11 was affected by the presence of developing wheat roots but survival was negatively affected by the presence of other inoculants.