Production of Aspergillus section Flavi biocontrol agent, Kluyveromyces spp. L16 using different growth media

MONTEMARANI, A.; NESCI, A; ETCHEVERRY, M.

Mendoza

Conferencia; MYCORED ARGENTINA ISM 2011 Conference, Strategies to reduce the impact of mycotoxins in Latin Amrica in a global context; 2011

MYCORED ARGENTINA

Fungal deterioration of stored seeds and grains is a problem in the Argentina storage system. Harvested grains can be colonized by several species of Aspergillus, which can cause spoilage and mycotoxin production. Control strategies are necessary to minimize the contamination in maize. Yeasts seem to be promising biocontrol agents and may be a good alternative to chemical fungicides for post-harvest protection of grains. Previous studies showed that Kluyveromyces spp. significantly reduced Aspergillus Section Flavi count and aflatoxin B1 level in maize meal extract agar and maize grain in vitro. Formulation of a biopesticide, is necessary to optimize the efficacy, stability, safety and ease of application of the product. Mass production is an important aspect in the commercial development of a biocontrol product. Commercial production requires low cost and high cells densities, and optimization of nutritional and environmental conditions. The aims of this study were to compare the viability and biomass production of the strain L16 of Kluyveromyces spp. in different growth media. The yeast grown in 100 mL of six different media: (1) MSB [molasses (20 gL-1) + soy powder (10 gL-1)]; (2) MYE [molasses (20 gL-1) + yeast extract (1,2 gL-1)]; (3) NYDB 50% [nutrient broth (4 gL-1) + dextrose (5 gL-1) + yeast extract (2,5 gL-1)]; (4) NYDB 75% [nutrient broth (6 gL-1) + dextrose (7,5 gL-1) + yeast extract (3,75 gL-1)]; (5) GYP [glucose (10 gL-1) + yeast extract (5 gL-1) + peptone (10 gL-1)] and (6) YMB [peptone (5 gL-1) + glucose (10 gL-1) + yeast extract (3 gL-1) + malt extract (3 gL-1)]. Media water activities were modified to 0.99, 0.97 and 0.95 aw using glucose. Each treatment was inoculated with 1.104 cells ml-1 of fresh cultures of Kluyveromyces spp. that was grown initially in mealt extract broth. Conical flasks were incubated on a rotary shaker (140 rpm) at 30°C. The growth in each treatment was determined spectrometrically to 620 nm and cell viability was estimated using the surface-plated method. This study has demonstrated that Kluyveromyces spp. L16 showed good viability in the six culture media in all water activities assayed. The highest constant growth rate was observed in NYDB 75% and YMC media at 0.99 (k=0.37 and 0.35 h-1) and 0.97 aw (k= 0.29 and 0.3 h-1 respectively). In these media, yeast achieved the lowest duplication time (g= 1.88 h and 1.94 h respectively). The results obtained show that the use of NYDB 75% and YMC media supported a rapid growth rate and high biomass production. Further investigations are needed to optimizing the formulation process of biocontrol agents against Aspergillus section Flavi in storage maize ecosystem.