Isolation and characterization of Candida tropicalis B: a promising yeast strain for biodegradation of petroleum oil in marine environments

Abstract

The increasing interest in environmental protection laws has compelled companies to regulate the disposal of waste organic materials. Despite efforts to explore alternative energy sources, the world remains heavily dependent on crude petroleum oil and its derivatives. The expansion of the petroleum industry has significant implications for human and environmental well-being. Bioremediation, employing living microorganisms, presents a promising approach to mitigate the harmful effects of organic hydrocarbons derived from petroleum. This study aimed to isolate and purify local yeast strains from oil-contaminated marine water samples capable of aerobically degrading crude petroleum oils and utilizing them as sole carbon and energy sources. One yeast strain (isolate B) identified as Candida tropicalis demonstrated high potential for biodegrading petroleum oil in seawater. Physiological characterization revealed the strain's ability to thrive across a wide pH range (4-11) with optimal growth at pH 4, as well as tolerate salt concentrations ranging from 1 to 12%. The presence of glucose and yeast extract in the growth medium significantly enhanced the strain's biomass formation and biodegradation capacity. Scanning electron microscopy indicated that the yeast cell diameter varied based on the medium composition, further emphasizing the importance of organic nitrogenous sources for initial growth. Furthermore, the yeast strain exhibited remarkable capabilities in degrading various aliphatic and aromatic hydrocarbons, with a notable preference for naphthalene and phenol at 500 and 1000 mg/l, naphthalene removal reached 97.4% and 98.6%, and phenol removal reached 79.48% and 52.79%, respectively. Optimization experiments using multi-factorial sequential designs highlighted the influential role of oil concentration on the bioremediation efficiency of Candida tropicalis strain B. Moreover, immobilized yeast cells on thin wood chips demonstrated enhanced crude oil degradation compared to thick wood chips, likely due to increased surface area for cell attachment. These findings contribute to our understanding of the potential of Candida tropicalis for petroleum oil bioremediation in marine environments, paving the way for sustainable approaches to address oil pollution.

Keywords: Candida tropicalis; Immobilization; Oil biodegradation; Statistical experimental design.

Fig. 1

A Growth of isolate B at different pHs. B Growth of the isolate B at different NaCl concentrations

Fig. 2

Morphology of isolate B cells grown on different media as shown by scanning electron microscopy (SEM). (M2, M5 and M6 are described in materials and methods)

Fig. 3

A Growth of C. tropicalis on different hydrocarbons; each was examined at the concentrations 500 and 1000 mg/l, B The degradation effect of C. tropicalis on different hydrocarbons; each was examined at the concentrations 500 and 1000 mg/l

Fig. 4

A Growth of C. tropicalis on different concentrations of naphthalene, B The degradation efficiency (%) of C. tropicalis on different concentrations of naphthalene

Fig. 5

A Growth of C. tropicalis on different concentrations of naphthalene, B The degradation efficiency (%) of C. tropicalis on different concentrations of naphthalene

Fig. 6

Effect of different culture factors on petroleum oil removal by C. tropicalis strain B in according to the results of the Plackett–Burman experiment

Fig. 7

The response surface of oil consumption by C. tropicalis strain B as a function of a D-Glucose and oil, b oil and pH, c D-Glucose and pH in the culture environment. Triangular symbols represent the actual measured response data points

Fig. 8

Thick wood chips (A) and thin wood chips (B)

Fig. 9

Oil consumption by yeast cells immobilized on thick and thin wood chips at different incubation times

Fig. 10

Scanning electron micrograph (SEM) showing adsorbed yeast on wood chips units. arrows indicate the focused unit. B1: X300; B2: X500; B3: X1500; B4: X2200

Fig. 11

Photomicrograph (SEM) of wood chips surface with crude oil as a negative control. C1 X300; C2 X1500