Root-surface colonization of black mangrove seedlings by Azospirillum halopraeferens and Azospirillum brusilense in seawater

Inoculation of axenic black mangrove seedlings in seawater for 8 days with either the terrestrial halotolerant plant growth-promoting bacterium Azospi rillum halopraeferens or with Azospirillum brasilense produced heavy coloni zation of the root surface. The colonization pattern was different for the two strains. A. halopraeferens yielded mainly single cells embedded in a th ick sheath, whereas A. brasilense produced primarily microaggregates. A. br asilense cells were anchored to the root surfaces and to themselves by a ne twork of fibrillar material. Both bacterial strains survived in seawater (a pproximately 10(4) colony forming units per ml) for more than 30 days, for 70 days in saline water (A. brasilense) and colonized mangrove roots at a v ery high population density. A. halopraeferens was a better root surface co lonizer, whereas the A. brasilense population was greater in the entire roo t. This work is the initial stage of studies designed to assess the feasibi lity of using terrestrial plant growth-promoting bacteria for the inoculati on of marine plants. (C) 1999 Federation of European Microbiological Societ ies. Published by Elsevier Science B.V. All rights reserved.