Abstract
Acidobacteria have been described as one of the most abundant and ubiquitous bacterial phyla in soil. However, factors contributing to this ecological success are not well elucidated mainly due to difficulties in bacterial isolation. Acidobacteria may be able to survive for long periods in soil due to protection provided by secreted extracellular polymeric substances that include exopolysaccharides (EPSs). Here we present the first study to characterize EPSs derived from two strains of Acidobacteria from subdivision 1 belonging to Granulicella sp. EPS are unique heteropolysaccharides containing mannose, glucose, galactose and xylose as major components, and are modified with carboxyl and methoxyl functional groups that we characterized by Fourier transform infrared (FTIR) spectroscopy. Both EPS compounds we identified can efficiently emulsify various oils (sunflower seed, diesel, and liquid paraffin) and hydrocarbons (toluene and hexane). Moreover, the emulsions are more thermostable over time than those of commercialized xanthan. Acidobacterial EPS can now be explored as a source of biopolymers that may be attractive and valuable for industrial applications due to their natural origin, sustainability, biodegradability and low toxicity.
Highlights
Acidobacteria is a very abundant and ubiquitous bacterial phylum in natural ecosystems[1,2,3,4]
In light of the major absence of published reports on acidobacterial EPS, the aim of the present study was to gain insights into the physicochemical nature of EPS polymers produced by two genetically closely related Acidobacteria strains belonging to Granulicella sp., which genomes are not sequenced
Cellulose, gellan and alginate are exclusively produced by Azotobacter vinelandii during the exponential growth phase, curdlan by Alcaligenes faecalis during the deceleration growth phase, xanthan by Xanthomonas campestris during the exponential and stationary phases[25,26], and EPSs are produced by Alteromonas macleodii from the end of the exponential phase through the stationary phase[27]
Summary
Acidobacteria is a very abundant and ubiquitous bacterial phylum in natural ecosystems[1,2,3,4]. The ability to synthesize EPS has been previously reported for some members of the Acidobacteria phylum These reports include genome mining studies[11], description of cultured Acidobacteria species[12,13] and their interactions with plants[14]. The potential importance of EPS in soil is great - it may be involved in the formation of soil matrix, serve to sequester water and nutrition, and be involved in bacterial cell-surface adherence and soil aggregate formation[12]. These hypotheses have not yet been confirmed by functional studies and such functions may overlap with general biological and ecological functions that are protective in nature for Acidobacteria. The broad spectrum of applications for EPSs range from human health, to food and fodder production, to chemical industry and environmental technologies (e.g. bioremediation and phytoremediation)
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