FIRST INSIGHTS INTO THE EPS-PRODUCTION ABILITY OF NATIVE ENTOMOPATHOGENIC FUNGI

DANILOVICH M; VALDEZ A; SAMMARITANO J; VAZQUEZ F; LECHNER B; FARIÑA JI; DELGADO OD

Buenos Aires

Congreso; II Workshop Polímeros Biodegradables y Biocompuestos y el III Workshop BIOPURFIL, Compuestos Poliuretanos de Base Bio con Rellenos Naturales; 2015

Bioeconomía Argentina

Microbial exopolysaccharides (EPS)s have a variety of beneficial functions such as gel formation, absorption, cohesion, emulsification, and film formation. Different types of EPSs have been examined up to date considering their potential use in medicine,as immuno-stimulators or anti-tumour agents, and as additives in cosmetics, foods and other industrial procedures . On the other hand, in pathogenic fungi, EPSs can participate in the infection mechanism. Synthesis of EPS by fungi can be affected bydifferent factors such as culture medium composition, agitation, aeration and further operative conditions. The aim of this work was to assess the ability of five entomopathogenic fungi isolated from nature to produce EPSs when cultured in threedifferent media, and to evaluate two different precipitating agents for EPS recovery. Five entomopathogenic fungi isolated in Argentina: Metharhiziumsp. isolates 381, 388, 409 and 413 (from San Juan), and Lecanicilliumsp. LY 72.14 (from Tucumán) wereevaluated. Isolates were grown in CZM agar (7 days at 25°C) and then transferred to fresh culture medium by cutting out 5 mycelium-covered agar plugs. For EPS production, cultures were grown in 250-mL Erlenmeyer flasks containing 50 mL of threedifferent liquid media: PMP modified supplemented with 4 g/L sucrose and 1 g/L corn steep liquor, MLP ((NH4)2SO4, 5g/L; glucose, 39 g/L) and MOPT (sucrose, 150 g/L; sodium nitrate, 2,25 g/L). The EPS production was tested after 7 days of cultivation at25°C and 200 rpm. To recover the EPSs, culture broths were centrifuged (9000 g, 20 min) and the resulting supernatant was mixed with 2 volumes of either ethanol 96° + 1 g/L CaCl2 , or isopropanol. Biomass and EPS were measured as dry weight.Residual sugars were determined by the 3,5-dinitro salicylic acid reaction .Most of the isolates showed greater mycelial growth in MOPT medium, reaching values from 11.25 to 15.47 g/L. For the majority of isolates, EPS production was higher in MOPT.Remarkably, for Metharhiziumsp. 413, EPS production reached a value of 7.30 g/L. This result suggested that osmotic stress associated to MOPT medium may stimulate EPS production by this fungus, as also found for other recognized EPS-producingfungi [2]. The EPS recovery process was more efficient with CaCl2-amended ethanol, leading to higher EPS amounts in comparison to the isopropanol precipitation. For example, in the case of the EPS produced by Metharhiziumsp. 388, the recovery byCaCl2-ethanol precipitation allowed to achieve 4.4 g EPS/L while isopropanol-based recovery led to a lower EPS amount (2.3 g/L). This differential behavior in the presence of different precipitating agents could suggest the polyelectrolytic character of theprecipitated polysaccharide, as previously described by García-Ochoa et al. for xanthan precipitation. Concerning sugar uptake, residual sugars were in some cases lower than expected, suggesting their consumption for cellular functions other than thoseexclusively related to EPS production.