Yeasts can accumulate heavy metals and grow in acidic media. In the present study, it was shown that Candida yeasts in an aqueous solution accumulate single Cu(II) and Ni(II) cations. The effect of heavy metal ions on the specific growth rate of biomasses and the uptake of metal ions during the growth phase was investigated in a batch system. Bioaccumulation efficiency decreased with increasing metal ion concentrations at constant sucrose concentrations. Both the specific growth rate and the biomass concentration were more inhibited in the bioaccumulation media containing Ni(II) ions singly as compared with the bioaccumulation media containing Cu(II) ions singly. The maximum specific growth rate and the saturation constant of yeasts were examined with a double-reciprocal form of Monod equation. Metal uptake performance decreased from 81.68% to 46.28% with increasing Ni(II) concentration from 25 mg/L to 250 mg/L for Candida lipolytica. Candida biomasses may be an alternative way of removal of heavy metals from wastewaters and may constitute a sample to produce new biomass. The study showed that Candida yeasts can be used as economical biomass due to their metal resistance and efficient production.Özet: Mayalar, asidik ortamda büyüyebilir ve ağır metalleri biriktirebilir. Bu çalışma, Candida türü mayaların sulu çözeltilerden tekli Cu(II) ve Ni(II) katyonlarını biriktirdiğini göstermiştir. Ağır metal iyonlarının, biyokütlelerin spesifik büyüme hızı ve büyüme periyodu boyunca metal iyonlarını giderimi üzerindeki etkisi, bir kesikli sistemde araştırılmıştır. Sabit sakaroz derişiminde, metal iyonu derişimi arttıkça, biyobirikim verimi azalmıştır. Hem spesifik büyüme hızı hem de biyokütle konsantrasyonu, tek başına Cu(II) iyonları içeren biyoakümülasyon ortamına kıyasla Ni(II) iyonları içeren biyoakümülasyon ortamında daha fazla inhibe edilmiştir. Mayaların maksimum özgül büyüme hızı ve doygunluk sabiti, Monod denkleminin çift-karşılıklı formu ile incelenmiştir. Candida lipolytica'nın metal giderim performansı Ni(II) derişiminin 25 mg/L'den 250 mg/L'ye çıkmasıyla % 81,68'den % 46,28'e düşmüştür. Candida biyokütleleri, ağır metallerin atık sulardan gideriminde alternatif bir yol olabilir ve yeni biyokütle üretimi için bir örnek oluşturabilir. Bu çalışma, Candida mayalarının, metal direnci ve verimli üretimleri nedeniyle ekonomik biyokütle olarak kullanılabileceğini göstermektedir.

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In this study, microorganism growth and bioaccumulation of Cu(II) and Ni(II) ions by Candida yeasts was tested as a function of sucrose, and metal ion concentration in metal-free and metal media. The growth of the yeasts and bioaccumulation of heavy metals was studied under laboratory conditions in the batch system. The optimum pH value for maximum growth and Cu(II) and Ni(II) bioaccumulation was obtained as 4.0 for the yeasts at 10 g/L constant sucrose concentration. The maximum specific growth rate and microorganism concentration increased with increasing sucrose concentration up to 20 g/L for Candida yeasts. It was observed that the metal uptake capacity of yeasts was increased with increasing initial metal concentrations in the range of 25-250 mg/L for Cu(II) and Ni(II) ions. Although Cu(II) and Ni(II) ions caused an inhibition effect on the growth of the yeasts, Candida lipolytica showed the highest specific growth rate and metal uptake capacity among the other yeasts. It was found that the inhibition effect of the Ni(II) ion was higher than Cu(II) ion on all the yeast. Monod equation was used to study the inhibition kinetics of bioaccumulation of Cu(II) and Ni(II). It was observed that saturation constant (Ks) increased with increasing the initial Cu (II) and Ni (II) ion concentrations whereas maximum specific growth rates (µmax) decreased.