FTIR spectroscopic study of biofilms formed by the rhizobacterium Azospirillum brasilense Sp245 and its mutant Azospirillum brasilense Sp245.1610

Abstract

Biofilms are spatially and metabolically structured communities of microorganisms, representing a mode of their existence which is ubiquitous in nature, with cells localised within an extracellular biopolymeric matrix, attached to each other, at an interface. For plant-growth-promoting rhizobacteria (PGPR), the formation of biofilms is of special importance due to their primary localisation at the surface of plant root systems. In this work, FTIR spectroscopy was used, for the first time for bacteria of the genus Azospirillum, to comparatively study 6-day-mature biofilms formed on the surface of ZnSe discs by the rhizobacterium Azospirillum brasilense Sp245 and its mutant A. brasilense Sp245.1610. The mutant strain, having an Omegon Km insertion in the gene of lipid metabolism fabG1 on the plasmid AZOBR_p1, as compared to the wild-type strain Sp245 (see http://dx.doi.org/10.1134/S1022795413110112), had previously been shown to possess alterations in the synthesis of fatty acids, as well as in the amount of biomass and relative content of lipopolysaccharide antigens in mature biofilms formed at a hydrophilic or hydrophobic surface (see http://dx.doi.org/10.1134/S002626171602017X). The 6-day biofilm of the wild-type strain A. brasilense Sp245 was found to contain moderate amounts of poly-3-hydroxybutyrate (PHB, a reserve biopolyester) featured by its typical bands (e.g., the ester carbonyl stretching mode at 1732 cm−1), while its mutant strain showed a diminished PHB content in the biofilm (the observed differences were also confirmed by analysing the second derivatives of the FTIR spectra). Thus it may be assumed that in this mutant strain, PHB synthesis is also affected which, in turn, can affect the formation and stability of biofilms.