Use of metabolic and molecular methods for the identification of a Bacillus strain isolated from paper affected by foxing.

Foxing of paper is a deterioration phenomenon occurring in the form of brown-yellowish spots, the abiotic and/or biotic causes of which are not yet completely understood. Nevertheless, microbiological infection has been recognized that may contribute to paper damage and therefore it becomes important to know the taxonomic position and the degradative activity of the potential infectious biological agents which mostly are fungi, but also bacteria and yeasts. A cellulolytic bacterial strain isolated from a foxed paper sample exhibited morphological and physiological characteristics of the Bacillus genus. To study its taxonomic position, different identification methods were used: the Biolog system, the direct amplified polymorphic DNA-polymerase chain reaction analysis (DAPD-PCR) and the partial sequencing of the 16S rDNA gene. Biolog system and partial sequencing of 16S rDNA gene assigned the strain to the Paenibacillus polymyxa species. DAPD-PCR analysis indicated a high similarity with Bacillus circulans, by comparing the isolated strain with some closely related Bacillus species.

Influence of substrate composition and flow rate on growth of Azospirillum brasilense Cd in a co-culture with 3 sorghum rhizobacteria.

The ability of Azospirillum brasilense Cd to colonize the niche occupied by 3 bacterial strains previously isolated from sorghum rhizosphere was studied by means of the Biolog system. The isolates were identified by different methods as strains belonging to Pseudomonas putida, Stenotrophomonas maltophilia, and Klebsiella terrigena species. Several C sources, also chosen among the constituents of sorghum root exudates, were used to evaluate the metabolic profiles of Azospirillum and the sorghum rhizobacteria. Azospirillum brasilense Cd exploited the same class of C compounds as the sorghum rhizobacteria and overlapped in their niche requirements. Since structure and functioning of a microbial community are largely affected by the flow rate of nutrient supply, the competitive behavior of A. brasilense Cd was studied in a chemostat mixed culture under C-limited conditions using disodium succinate as C source. Only at high growth rates, i.e., when the C source was highly supplied, A. brasilense Cd appeared to be a good competitor and it became the dominant species, whereas at low growth rates, it was outnumbered by the other species. However, the coexistence of all the strains was always maintained, thus suggesting that interactions other than competition or a potential cross-feeding might occur within the mixed culture.