Abstract:
A Gram negative aerobic flagellated bacterium with fungal growth inhibitory
properties was isolated from a culture of Trichoderma harzianum. According to
its cultural characteristics and biochemical properties it was identified as a strain
of Alcaligenes (aeca/is Castellani and Chalmers.
Antisera prepared in Balbc mice injected with live and heat-killed bacterial cells
gave strong reactions with the homologous immunogen and with ATCC 15554,
the type strain of A. taeca/is, but not with Escherichia coli or Enterobacter
aerogens in immunoprecipitation and dot immunobinding assays.
Growth of Botrytis cinerea Pers. and several other fungi was significantly
affected when co-cultured with A. taeca/is on solid media. Its detrimental effect
on germination and growth of B. cinerea has been found to be associated with
antifungal substances produced by the bacterium and released into the growth
medium.
A biotest for the antibiotic substances, based on their inhibitory effect on
germination of B. cinerea conidia, was developed. This biotest was used to study
the properties of these substances, the conditions in which they are produced,
and to monitor the steps of their separation during extraction procedures.
It has been found that at least two substances could be involved in the
antagonistic interaction. One of these is a basic volatile substance and has been
identified as ammonia. The other substance is a nonvolatile, dialysable, heat
stable, polar compound released into the growth medium.
After separation of growth medium samples by Sephadex G-10 column
chromatography a single peak with a molecular weight below 700 Daltons
exhibited inhibitory activity. From its behaviour in electrophoretic separation in
agarose gels it seems that this is a neutral or slightly positively charged.
