Growth strategies of bacteria and yeast degraders of onion waste.

RINLAND ME; BALDINI M; GOMEZ MA

Villa Carlos Paz, Córdoba

Congreso; VI CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL; 2009

SAMIGE

Over 20,000 tonnes of onion waste (OW) are produced annually in Patagonian protected region in Argentina. Almost all of onion refuses are incinerated with significant amount of carbon dioxide released. In addition, the accumulation of wastes in growing areas and processing centers are a source of odour and pollution. Therefore, new products produced from worthless onions are strongly desired in order to allow both value additions and effective reuses of the onions. One option is to compost it and return it to the land as an organic fertilizer. In the present study we investigated microbial populations during the degradation of OW and examined ways to accelerate this process. We used microcosms (3 kg of waste) to evaluate different OW treatments to identify the optimum waste composition to achieve minimum composting time. We analyzed OW from different sites at different stages of the production process to obtain a wide diversity of degrading microorganisms. Total aerobic heterotrophs were quantified on Nutrient Agar and fungi and yeasts on Yeast Extract Glucose Chloramphenicol (YGC) Agar. Seventy-three colonies were randomly picked. Ability to use onion‟s nutrients was assessed by inoculating pure cultures (53 bacteria and 20 yeast cultures) into tubes with onion medium (1 g K2HPO4, 0,5 g MgSO4, 150 ml onion juice and 1 l distilled water). Each culture was also inoculated in Nutrient broth or YGC broth as control medium. One set of tubes was incubated at 28oC and the other at 4oC for 7 days, as degradation of onion crop residues has been observed in field conditions even at low temperatures. Microbial growth was assessed by absorbance at 620 nm. The OW decomposition may be achieved in two months if the pile is made with chopped bulbs. All samples had a large count of total aerobic heterotrophic bacteria (7,9 to 9,9 log10 CFU g-1), fungi and yeasts (4,6 to 8,6 log10 CFU g-1). Microorganisms showed different growth strategies. All microorganisms were able to develop in onion juice at 28oC and some bacteria grew better in onion juice than in control medium. Some bacteria and yeasts were also able to develop in onion juice at 4oC. In two cases (one bacteria and one yeast) growth pattern changed with temperature. They had greater turbidity in onion medium than in control medium at 28oC but the opposite occurred at 4oC. One gram of waste contains about 106 of these isolates. In conclusion, there is a large diversity of bacteria and yeasts which varied with location that are capable of degrading onions between 4 to 28oC.