| dc.description.abstract | The term alkaliphiles defines microorganisms that grow optimally at pH values above 9, often
between 10 and 12, but are unable to grow or grow slowly at the near neutral pH value of 6.5.
Consequently, their extremozymes such as amylases also have high catalytic efficiency and
stability at an alkaline pH range of pH9- 11. These alkaline active amylases have potential
applications for hydolysing starch under high pH conditions in the starch-based industries and
also as ingredients in enzyme-based detergents. Potential application of alkaliphilic amylases has
led to their bioprospecting from the microorganisms found thriving in naturally occurring
alkaline environments such as soda lakes found along the East African Rift valley.
In this study, five alkaliphilic bacteria designated Bacilus sp. LBW 213, Bacilus sp LBW 2.719,
Bacilus sp LBW 33, Bacilus sp LBW 35 and Bacilus sp LBW 313 previously isolated from Lake
Bogoria, a soda lake found in the east African Rift Valley in Kenya were screened for the
production of alkaline-tolerant amylases. The five Bacilli sp were grown on solid Horikoshi
medium pH (10.5) for 72 h, after which the plates were flooded with Gram’s iodine solution in
order to identify amylase-producers. All 5 bacteria exhibited extracellular starch hydrolysing
activities, as depicted by the presence of clearance zones or ‘halos’ around their colonies after
staining with Gram’s iodine solution. The ratios of the diameter of halos to that of colonies were
then used as a semi-quantitative method for classifying the bacteria. Bacillus sp. LBW 33 and
LBW 35 were considered as excellent producers while the rest were very good producers. Based
on this analysis, all the bacteria were considered for further experiments.
The five Bacilli sp. from Lake Bogoria in the presence of soluble starch were cultivated in liquid
broth at 37oC, 100rpm in a shaker incubator for up to 48h, during which samples were withdrawn
after every 12h to determine the cell growth by measuring their optical density at 600nm in order
to generate characteristic bacterial growth curves. During each withdrawal, cells were harvested
by centrifugation and the cell free culture supernatants used as crude enzyme source for
extracellular amylase assay using a glucose standard. All the bacteria exhibited both growth and
α-amylase enzyme production.
During the cultivation, all five bacteria exhibited a general growth profile, reaching optimal
growth at 24 h with maximum OD at 600nm of 4.370(Bacillus sp.LBW 213), 4.670 (Bacillus sp.
27 19), 5.206(Bacillus sp.LBW 33), 6.10(Bacillus sp.LBW 35) and 6.310(Bacillus sp.LBW 313).
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There was a general increase in α-amylase production by most of the bacteria, reaching optimum
levels during late exponential phases of bacterial growth (24 h) for most of the bacteria except
for Bacillus sp.LBW313, during cell death phase (36 h). Therefore, in this study the range of
enzymatic activity for all the five bacteria was 5.5 x 10-3 – 38 x 10-3U/ml. Although production
levels by the bacteria were low compared to those of other alkaliphilic bacteria studied, Bacillus
sp. LBW 33 was the most promising candidate for enzyme production (highest producer), thus
making it ideal for further studies. | en_US |
| dc.description.department | a
Department of Psychiatry, University of Nairobi, ; bDepartment of Mental Health, School of Medicine,
Moi University, Eldoret, Kenya | |
