The polysaccharides degrading mechanisms of two soil bacterial isolates

TOPALIAN, JULIANA; ONTAÑON ORNELLA M.; NAVAS, LAURA; VALACCO, MARIA PIA; CAMPOS ELEONORA

Mendoza

Congreso; Congreso SAIB 2022; 2022

SAIB

The production of efficient enzymatic extracts for deconstruction of the structural polysaccharides thatmake up the plant cell wall, cellulose and hemicellulose, is an important process for the valorization ofresidual biomass. Paenibacillus xylanivorans A59 and Cellulomonas sp. B6 are bacterial strains withcapacity for degrading polysaccharides, isolated from the soil of pristine environments. Underappropriate culture conditions, both strains can secrete different carbohydrate active enzymes(CAZymes).In this work, we studied the extracellular enzymatic activity and the exo-proteome of P. xylanivorans A59and Cellulomonas sp. B6 strains when grown on different carbon sources, including sugar cane residue(SCR) and wheat bran (WB), as well as sucrose (SAC) as negative control. Both strains presented mainlyextracellular xylanase activity when cultured on SCR or WB, determined as xylose equivalents of reducingsugars. The highest activity was achieved by culture on SCR for P. xylanivorans (11.06 IU/mL, 72 h) and onWB for Cellulomonas sp. B6 (3.06 IU/mL, 48 h). In all cases, cellulose degrading activity was low. By massspectrometry analysis of the culture supernatants (E) we identified the main enzymes responsible for theobserved activity. P. xylanivorans secreted 97 proteins when grown on SCR (E-SCR) from which 17corresponded to CAZymes: 15 glycoside hydrolases (GHs), 1 with auxiliary activity (AA) and 1 pectate lyase(PL). In the case of Cellulomonas sp. B6, 195 proteins were identified in E-WB, from which 37 were CAZymes:28 GHs, 1 AA, 2 glycosltransferases (GTs), 3 carbohydrate esterases (CEs) and 2 carbohydrate-bindingproteins (CBMs). While in P. xylanivorans the most abundant CAZyme was a GH10 β-xylanase, inCellulomonas sp. B6 several enzymes presented a similar high abundance, including endo- and exoglucanases, xylanases and debranching enzymes. In both cases, extracellular components of ABC sugartransport systems were identified, which could be involved in the transport of mono- and smalloligosaccharides into the cell.Most CAZymes were encoded in distant regions of the genome, with few exceptions. A common featurewas the presence of coding sequences for sugar transporters (mainly ABC family) and transcriptionalregulators along with genes encoding CAZymes. In summary, both bacteria can secrete GHs withdifferent relative abundance when cultured in lignocellulosic substrates, though the number and type ofenzymes varied. Cellulomonas sp. B6 secretes a garter number of proteins and a more diverse repertoryof CAZymes. Nevertheless, P. xylanivorans culture supernatant has higher xylanase activity, mainly due toa single GH10 xylanase. These results allowed us to build a model for polysaccharide utilization of eachbacterium.