Biochar influence the production and release of exopolysaccharides on plant growth promoting bacteria
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Biochar is known as a multifunctional carbonaceous material mainly used in agrosystems. Little information is available on possible antagonistic, toxicological and negative effects of biochar on soil microorganisms. This work explored the effects of different doses of biochar produced from sugarcane bagasse and corn cob husk in the growth and development of plant growth promoting bacteria (Leocobacter sp. and Bacillus aryabhattai). Two types of low-dose solid culture media of biochar (0.4% w w-1) were tested: biochar directly inserted into the medium and another one elaborated with the biochars extractable water compounds. The growth results indicated a deleterious effect on the survival of the colonies when in direct contact with the extractable compounds in water of the biochars. On the other hand, the strains grown in solid medium supplemented with biochar (high and low-dose) had some outbreaks with colonies of bacteria, where there was also the formation of exopolysaccharide films. The production of exopolysaccharides by Bacillus sp. was characterized by infrared chemical mapping at the nanoscale (AFM NANO-IR). The information obtained indicated that the dosage and the type of biochar modified the morphology and topography of the biofilms, as well as the presence of chemical groups such as Amide I and II, lipids and proteins. This fact suggests that adaptation and survival of the bacterial species depend on their interaction path with the molecular structure of the biochar surface. Thus, the binding force, or even biochar colonization, can be influenced by the type of dominant molecule readily available on the surface of the biochar, where hydrophobic components, covalent bonds, van der Waals forces, anionic or cation exchange or even substitution of ion can act as chemical signals that induce specific responses in bacteria.