Plant-associated bacteria fulfill important functions for plant growth and health. However, our knowledge about the impact of bacterial treatments on the host's microbiome and physiology is limited. The present study was conducted to assess the impact of bacterial inoculants on the microbiome of chamomile plants Chamomilla recutita (L.) Rauschert grown in a field under organic management in Egypt. Chamomile seedlings were inoculated with three indigenous Gram-positive strains (Streptomyces subrutilus Wbn2-11, Bacillus subtilis Co1-6, Paenibacillus polymyxa Mc5Re-14) from Egypt and three European Gram-negative strains (Pseudomonas fluorescens L13-6-12, Stenotrophomonas rhizophila P69, Serratia plymuthica 3Re4-18) already known for their beneficial plant-microbe interaction. Molecular fingerprints of 16S rRNA gene as well as real-time PCR analyses did not show statistically significant differences for all applied bacterial antagonists compared to the control. In contrast, a pyrosequencing analysis of the 16S rRNA gene libraries revealed significant differences in the community structure of bacteria between the treatments. These differences could be clearly shown by a shift within the community structure and corresponding beta-diversity indices. Moreover, B. subtilis Co1-6 and P. polymyxa Mc5Re-14 showed an enhancement of the bioactive secondary metabolite apigenin-7-O-glucoside. This indicates a possible new function of bacterial inoculants: to interact with the plant microbiome as well as to influence the plant metabolome.

Heavy metal pollution has become one of the most serious environmental problems today. Biological methods such as biosorption or bioaccumulation strategies for the removal of metals ions may provide an attractive alternative to existing technologies. Microorganisms, as heavy metal bioadsorbents, offer a new alternative for removal of toxic or valuable metals in water. Saccharomyces cerevisiae has received increasing attention due to its unique nature and capacity for metal sorption. It is one of the most promising biosorbents capable of removing metal ions from aqueous solution. Manganese occurs naturally in many surface water and groundwater sources and in soils that may erode into this water. Eleven S. cerevisiae yeast strains in alive and dead forms were screened for biosorption and bioaccumulation of manganese from artificial aqueous solution. S. cerevisiae F-25 in alive form was found to be highly biosorbent for Mn +2 and biosorbed 22.5 mg Mn +2 /gm yeast biomass. Optimization of environmental conditions reveals that optimum concentrations for maximum Mn 2+ biosorption by S. cerevisiae F-25 in alive form were 4.8 mg Mn 2+ /l after 30 min at pH 7, agitation 150 rpm and yeast biomass concentration 0.1 gm/l at 30°C. Competition of Mn +2 with other heavy metals shows that Mn +2 in control sample without, any other heavy metals added in solution at 4.8 mg/l of the biosorbed Mn +2 was 41.3 mg/g biomass. Addition of other heavy metals affects the percent of biosorbed Mn +2 . ª 2015 Production and hosting by Elsevier B.V. on behalf of Housing and Building National Research Center. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).

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