Microbiology

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    Screening and characterisation of yeast species for citric acid production using glycerol and agro-waste
    (The Nigerian Society for Microbiology (NSM), 2025) Afolabi, F. T.; Adeoye, A. E.
    The present study was aimed to isolate and screen yeast species for the production of citric acid using glycerol and agro-waste. Fruit samples (orange, lime, lemon and pineapple) were collected from Bodija market in Ibadan. The samples were subjected to microbiological and physicochemical analyses. A total of 43 yeast isolates were recovered from the fruit and 17 isolates had the potential to produce citric acid after screening. Yeast isolates were identified as: Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2. The best incubation period for citric acid production by Candida tropicalis PiB10 was 120 hours (18.02 g/l), highest citric acid production (33.53 g/l) at pH 5.0, maximum citric acid production (20.84 g/l) was at 30°C, Glucose was the best carbon source, yielding 18.00 g/l of citric acid. Yeast extract was the best nitrogen source with citric acid production of 19.20 g/l and the highest production of 19.58 g/l at 200 rpm from glycerol. Meyerozyma guilliermondii LeB1 showed the highest citric acid production at 120 hours of incubation, yielding 17.02 g/l. The best pH was 5.5, yielding 35.90 g/l of citric acid. The best temperature was 30°C, with a production of 15.80 g/l, Glucose was also the preferred carbon source for this isolate, with a production of 20.13 g/l. Yeast extract was the best nitrogen source for Pichia guilliermondii LeB1, yielding 18.85 g/l. At 200 rpm from glycerol, the highest production was 22.37 g/l. This study demonstrated that Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2 yielded high amount of citric acid using glycerol and agro-industrial wastes as substrates.
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    Isolation and screening of phytase-producing fungi for phytase production by solid state fermentation using agro wastes
    (Plovdiv University Press, 2025) Afolabi, F. T.; Atunwa S. O.
    Phytases are phosphatase enzymes that catalyze the hydrolysis of phytic acid and its salts. This study aimed to isolate and screen for phytase-producing fungi from cereals, fruits, palm kernel cake and soil samples by solid state fermentation. Isolation and identification was done using standard methods. The fungal isolates were screened for phytase production using phytase screening medium (PSM) agar. The isolates with the highest and consistent zone of hydrolysis were used. Eighty seven (87) fungal isolates were obtained while eighteen showed consistent zone of hydrolysis. These were screened to five (5) isolates: Aspergillus niger PKruw7, Aspergillus awamori Pkruw5, Aspergillus flavus PBDJ7, Aspergillus niger MOJ5b and Penicillium chrysogenum OBDJ1.They were used for solid state fermentation using rice bran, soy bean and wheat bran for phytase production. The optimized conditions for phytase production were: 40ºC temperature, 5.5 pH, 1% w/w fructose and 0.5% w/w yeast extract by both Aspergillus niger PKruw7 and Aspergillus flavus PBDJ7, 40ºC, 4.5 pH, 1% w/w fructose and 0.5% w/w NH4NO3: Aspergillus awamori Pkruw5, 25ºC, 6.5 pH, 1% w/w fructose and 0.5% w/w NH4NO3: Aspergillus niger MOJ5b and 40ºC, 4.5 pH, 1% w/w sucrose and 0.5% w/w (NH4) 2SO4: Penicillium chrysogenum OBDJ1with incubation period of 120 hours optimal for all the isolates. Maximum phytase production from optimized culture conditions include; incubation period of 5 days, temperature of 40°C, pH of 4.5 to 6.5, fructose (1% w/w), yeast extract and ammonium nitrate (0.5% w/w). Phytase can be applied in animal feed to enhance digestibility and nutrient availability.
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    Comparative study of bioethanol production and reducing sugar yields from cassava peels using fungi
    (Bulgarian Society for Microbilogist, 2020) Afolabi, F. T.; Ayodele E. O.
    This study compared the yields of bioethanol from the fermentation of pretreated cassava peels using yeasts isolated from palm wine, and a pretreatment method with methanol + acid before solid-state fermentation of cassava peels using Trichoderma reesei for 5 days optimally yielded 1.78 g/mL of reducing sugar. The hydrolysate was fermented for bioethanol production using Saccharomyces cerevisiae and Candida tropicalis. S. cerevisiae performed optimally at 30oC, pH 4.5, and produced ethanol with a concentration of about 40.72 g/L, while C. tropicalis produced 29.90 g/L of ethanol concentration at 35oC, and pH 5. Both yeast isolates took the same fermentation time of 96 h. In conclusion, cassava peels are agricultural waste that is a degradable material suitable to produce simple reducing sugars, which can be fermented by yeast to produce bioethanol. The yield of ethanol was higher for S. cerevisiae than C. tropicalis.
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    Screening of yeasts obtained from different fermented foods for their ability to produce pectinase
    (Joanna Bródka, Poland, 2020) Afolabi, F. T.; Shitta Y. O.
    In the present study, Citrus pectin was used for the production of pectinase enzyme by yeast isolates using submerged fermentation. Fifty yeasts were isolated from different fermented foods and screened for their producing ability. Candida sp. OG2 and Candida tropicalis strain AUMC 10275 were the yeast isolates with the best potential of pectinase production. Fermentation parameters such as incubation period, pH, temperature, carbon and nitrogen source were optimized under submerged fermentation. The optimal conditions for pectinase production were found to be incubation time 48 hours, pH 6.0 and temperature 40°C. Citrus pectin best induced the production of pectinase while yeast extract/peptone (1:1) was the best source of nitrogen. Pectinase produced by Candida tropicalis strain AUMC 10275 was purified at 4.00 folds with a specific activity of 63.99 U/ml. The yeasts obtained from fermented foods have the ability to produce pectinase enzyme under optimized conditions and can be used for industrial purposes.
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    Tolerance of yeast to formic acid during ethanol fermentation
    (Bulgarian Society for Microbilogist, 2019) Afolabi, F. T.; Oduokpaha, G. E.; Onilude, A. A.
    This study was carried out to investigate the tolerance of yeasts isolated from some Nigerian traditional fermented foods to formic acid during laboratory-scale fermentation of ethanol. A total of 27 yeast strains were isolated from burukutu, ogi, kunu and palm wine. The yeasts were screened for formic acid tolerance using spot plate technique on two culture media. One strain was selected based on its ability to tolerate up to 15 mM concentration of formic acid on Yeast Extract Peptone Dextrose Agar and was further identified as Candida tropicalis strain IFM 63517. C. tropicalis was used for fermentation of ethanol with varying concentrations of formic acid, ethanol and residual glucose concentrations which were monitored at intervals. The total viable cell count was determined using plate count technique. The highest ethanol yield of 8.36% (v/v) with a residual glucose concentration of 0.33 g/L was obtained from 0 mM formic acid (control fermentation vessel) with a total viable cell count of 8.7x109 cfu/ml, while the lowest ethanol yield of 8.00% (v/v) with a residual glucose concentration of 0.14g/L was obtained from 15 mM concentration of formic acid with a total viable cell count of 6.1x109 cfu/ml. The yeast strain used in this work exhibited a high ethanol yield despite the presence of an inhibitory compound (formic acid) when comparing the ethanol yield at its tolerance threshold (15 mM of formic acid) to the control fermentation vessel without formic acid.
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    Fermentation conditions and process optimization of citric acid production by yeasts
    (Conscientia Beam, 2018) Afolabi, F. T.; Adeyemo, S. M.; Balogun, H. O.
    The aim of this study was to isolate and screen citric acid producing yeasts using low cost substrates. Thirty three yeast isolates were obtained from pineapple, plantain and sugar cane waste and identified as; Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida tropicalis, Pichia guilliiermondii, Debaromyces sp., Candida parapsilosis, Candida rugosa, and Candida krusei. Candida tropicalis had zone of clearance of 49±2.1 mm in diameter, Pichia guilliermondii had 40±1.2mm. Saccharomyces cerevisiae produced citric acid with glucose with 105.0 mg/l. C. tropicalis yielded 132.2 mg/l with sodium nitrate. S. cerevisiae and C. tropicalis produced citric acid at pH 6 with 23.70mg/l and 23.80mg/l. P. gulliermondii at pH 4 produced 23.00mg/l. The temperature of 30°C favoured S. cerevisiae and C. tropicalis yielding 40.80mg/l and 39.80 mg/l. After extraction, the yield of the citric acid was 4.231g, 3g of which was recrystallized to yield 2.16g of pure citric acid resulting into 72% recovery. The result indicated that pineapple wastes, plantain wastes and sugarcane cane are potential sources of yeasts that can be used for the production of citric acid.
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    Antibiotic resistance patterns of bacterial isolates obtained from catfish and tilapia fish types consumed in Ibadan.
    (Valahia University Press, 2018) Afolabi, F. T.; Fabunmi, F. K.
    This study was carried out to identify antibiotic resistant bacteria isolated from Catfish (Clarias gariepinus) and Tilapia (Oreochromis sp.) fish types at Eleyele, University of Ibadan fish farm and Asejire all within Ibadan metropolis. Antibiotic susceptibility testing was carried out on Ninety (90) of the previously isolated bacterial isolates using the agar gel diffusion technique. Antibiotics used were Gentamycin, Ofloxacin, Nitrofurantoin, Ampicillin, Augmentin, Amoxicillin, Ceftazidime, Cefuroxime, Ciprofloxacin, Ceftriaxone, Erythromycin, Amikacin and Ticarcillin. Various level of multi drug resistance was observed among the isolates. The bacterial population identified from this study includes; Staphylococcus aureus, Salmonella sp., Shigella sp., Pseudomonas aeruginosa, Klebsiella pneumonia, Klebsiella oxytoca, Klebsiella ozaenae, Acinetobacter baumanii, Proteus vulgaris, Escherichia coli, Enterobacter aerogenes, Citrobacter freundii and Moraxella catarrhalis. Twelve (12) of the isolates were further subjected to plasmid profile analysis in which, plasmids of different sizes were found for 10 of the isolates. It was observed that only one Shigella sp., out of the Five (5) isolates had lost the plasmids and became responsible to the earlier resistant antibiotics while the other four isolates Klebsiella pneumoniae, Moraxella catarrhalis, Staphylococcus aureus maintained their resistance to the antibiotics. The spread of multidrug resistance pathogens has constituted a major impediment to the control of infectious diseases, and since this study has shown that fish samples could be a reservoir of bacteria carrying R-plasmids as well as genes responsible for resistance, therefore, the indiscriminate use of antibiotics should be discouraged and also national regulations on the use of antibacterial should be introduced and enforced.
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    Isolation and characterization of ethanol-tolerant yeasts from decaying oranges for the production of bioethanol
    (Institute of Ecology and Environmental Studies, Faculty of Science, Obafemi Awolowo University (OAU), Ile-Ife, Osun State, Nigeria., 2017) Adeyemo, S. M.; Afolabi, F. T.; Awojobi, K. O.; Ojo, O. O.
    Decaying orange fruits are readily available agricultural waste in Nigeria, yet they seem to be underutilized as potential growth medium for local yeasts strains, despite their rich carbohydrate content that can support yeast growth. The ability of different strains of yeasts to grow on orange biomass and its utilization as raw material for the production of bio-ethanol was investigated in this study. Five replicate samples of decaying oranges were collected at different time intervals from dump sites at five different local markets in Ile-Ife from which different species of yeasts were isolated. Standard biochemical tests were conducted to identify and confirm their identities. Fermentation of orange juice was done with the yeast strains singly and in combination at 30°C for seven days and parameters essential for ethanol production such as titratable acidity, pH, specific gravity, Brix and Ethanol tolerance and content were determined following Association of Official Analytical Chemist procedures. Data were analysed using ANOVA at p=0.05. A total of thirty yeast isolates were isolated and identified as Saccharomyces cerevisiae, Schizosaccharomyces japanicus, Candida valida, Candida fructus, Candida krusei, Kluyveromyces africanus and Rhodotorula gramis. Abundant production of bioethanol was derived from S. cerevisiae, C. fructus and C. valida (C. fructus and C. valida were used singly while C. fructus and Saccharomyces were combined in the ratio 1:1). The highest alcohol value (7.65%) was derived from the mixed strain (Candida fructus and Saccharomyces cerevisiae) and the lowest value of alcohol (6.98%) from a single culture of Candida fructus. Decaying oranges, its juice and its biomass could be used to produce bio-ethanol which is of a good quality. The method is effective and efficient with high yield eco-friendly ethanol. The fruit waste which provides readily available and cheap substrates for industrial use and at the same time solves the problem of environmental pollution that the decaying oranges cause if not disposed appropriately.
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    Screening and characterisation of yeast species for citric acid production using glycerol and agro-waste
    (The Nigerian Society for Microbiology (NSM), 2025) Afolabi, F. T.; Adeoye, A. E.
    The present study was aimed to isolate and screen yeast species for the production of citric acid using glycerol and agro-waste. Fruit samples (orange, lime, lemon and pineapple) were collected from Bodija market in Ibadan. The samples were subjected to microbiological and physicochemical analyses. A total of 43 yeast isolates were recovered from the fruit and 17 isolates had the potential to produce citric acid after screening. Yeast isolates were identified as: Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2. The best incubation period for citric acid production by Candida tropicalis PiB10 was 120 hours (18.02 g/l), highest citric acid production (33.53 g/l) at pH 5.0, maximum citric acid production (20.84 g/l) was at 30°C, Glucose was the best carbon source, yielding 18.00 g/l of citric acid. Yeast extract was the best nitrogen source with citric acid production of 19.20 g/l and the highest production of 19.58 g/l at 200 rpm from glycerol. Meyerozyma guilliermondii LeB1 showed the highest citric acid production at 120 hours of incubation, yielding 17.02 g/l. The best pH was 5.5, yielding 35.90 g/l of citric acid. The best temperature was 30°C, with a production of 15.80 g/l, Glucose was also the preferred carbon source for this isolate, with a production of 20.13 g/l. Yeast extract was the best nitrogen source for Pichia guilliermondii LeB1, yielding 18.85 g/l. At 200 rpm from glycerol, the highest production was 22.37 g/l. This study demonstrated that Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2 yielded high amount of citric acid using glycerol and agro-industrial wastes as substrates.
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    Isolation and screening of phytase-producing fungi for phytase production by solid state fermentation using agro wastes
    (Plovdiv University Press, 2025) Afolabi, F. T.; Atunwa S. O.
    Phytases are phosphatase enzymes that catalyze the hydrolysis of phytic acid and its salts. This study aimed to isolate and screen for phytase-producing fungi from cereals, fruits, palm kernel cake and soil samples by solid state fermentation. Isolation and identification was done using standard methods. The fungal isolates were screened for phytase production using phytase screening medium (PSM) agar. The isolates with the highest and consistent zone of hydrolysis were used. Eighty seven (87) fungal isolates were obtained while eighteen showed consistent zone of hydrolysis. These were screened to five (5) isolates: Aspergillus niger PKruw7, Aspergillus awamori Pkruw5, Aspergillus flavus PBDJ7, Aspergillus niger MOJ5b and Penicillium chrysogenum OBDJ1.They were used for solid state fermentation using rice bran, soy bean and wheat bran for phytase production. The optimized conditions for phytase production were: 40ºC temperature, 5.5 pH, 1% w/w fructose and 0.5% w/w yeast extract by both Aspergillus niger PKruw7 and Aspergillus flavus PBDJ7, 40ºC, 4.5 pH, 1% w/w fructose and 0.5% w/w NH4NO3: Aspergillus awamori Pkruw5, 25ºC, 6.5 pH, 1% w/w fructose and 0.5% w/w NH4NO3: Aspergillus niger MOJ5b and 40ºC, 4.5 pH, 1% w/w sucrose and 0.5% w/w (NH4) 2SO4: Penicillium chrysogenum OBDJ1with incubation period of 120 hours optimal for all the isolates. Maximum phytase production from optimized culture conditions include; incubation period of 5 days, temperature of 40°C, pH of 4.5 to 6.5, fructose (1% w/w), yeast extract and ammonium nitrate (0.5% w/w). Phytase can be applied in animal feed to enhance digestibility and nutrient availability.