ABSTRACT
Cyanobacteria can cope with various environmental stressors, due to the excretion of exopolysaccharides (EPS). However, little is known about how the composition of these polymers may change according to water availability. This work aimed at characterizing the EPS of Phormidium ambiguum (Oscillatoriales; Oscillatoriaceae) and Leptolyngbya ohadii (Pseudanabaenales; Leptolyngbyaceae), when grown as biocrusts and biofilms, subject to water deprivation. The following EPS fractions were quantified and characterized: soluble (loosely bound, LB) and condensed (tightly bound, TB) for biocrusts, released (RPS), and sheathed in P. ambiguum and glycocalyx (G-EPS) in L. ohadii for biofilms. For both cyanobacteria upon water deprivation, glucose was the main monosaccharide present and the amount of TB-EPS resulted was significantly higher, confirming its importance in these soil-based formations. Different profiles of monosaccharides composing the EPSs were observed, as for example the higher concentration of deoxysugars observed in biocrusts compared to biofilms, demonstrating the plasticity of the cells to modify EPS composition as a response to different stresses. For both cyanobacteria, both in biofilms and biocrusts, water deprivation induced the production of simpler carbohydrates, with an increased dominance index of the composing monosaccharides. The results obtained are useful in understanding how these very relevant cyanobacterial species are sensitively modifying the EPS secreted when subject to water deprivation and could lead to consider them as suitable inoculants in degraded soils.
ABSTRACT
Chemical compounds are key to understand symbiotic interactions. In the leafcutter ant-microbe symbiosis a plethora of filamentous fungi continuously gain access the ant colonies through plant substrate collected by workers. Many filamentous fungi are considered transient in attine ant colonies, however, their real ecological role in this environment still remains unclear. A possible role of these microorganisms is the antagonism towards Leucoagaricus gongylophorus, the mutualistic fungus that serve as food for several leafcutter ant species. Here, we showed the antagonism of filamentous fungi isolated from different sources, and the negative impacts of their metabolites on the growth of the ant-fungal cultivar. Our results demonstrate that the chemical compounds produced by filamentous fungi can harm the mutualistic fungus of leafcutter ants.
