Identification and characterization of Lysobacter capsici strain PG4: a new plant health-promoting rhizobacterium.

A Gram-negative bacterial isolate, named PG4, was recovered from the rhizosphere of a tobacco plant (Nicotiana tabacum cv. Burley) and was identified as Lysobacter capsici based on the sequencing and phylogenetic analysis of 16S rRNA and characteristics in the Biolog Identification System. Strain PG4 showed chitinase and protease activity and was able to inhibit the growth of a broad range of phytopathogenic fungi. Growth of Gram-negative bacteria was not affected by PG4, but it was active against some Gram-positive bacteria such as Bacillus subtilis, Lysteria monocytogenes and Rhodococcus fascians. Fe3+ availability positively influenced PG4 antagonism towards the latter group of bacteria, even though siderophore production was not detected. Seed bacterization reduced the number of the resulting tomato seedlings infected by Fusarium oxysporum f. sp. lycopersici, F. oxysporum f. sp. radicis-lycopersici and Rhizoctonia solani. In greenhouse trials strain PG4 drastically reduced the incidence of tomato crown and root rot and led to a marked increase in plant fresh weight.