A Short Communication-Isolation and characterization of <i>Bacillus thuringiensis</i> from coastal intertidal brackish sediments and from farmlands in Machakos District Kenya

Abstract

Bacillus thuringiensis (Bt) delta endotoxins represent the most successful use of biological control agents targeting crop pests to date.  Studies  have  shown  that  Bt  produces  a  wider  range  of  toxins  targeting  a  variety  of  unrelated  pests  than  was  initially documented. This further  increases  the prospects  for  its wider use as a microbial biopesticide.  In  this view  the study sought  to isolate  and  characterize  native  Bt  from  two  different  ecological  regions;  Kenya  coastal  intertidal  brackish  sediments  and farmlands  in Machakos  district. Twenty  eight Bt  isolates were  isolated  and  identified. Distinctions  between  the  isolates were based on their morphological appearances, presence of parasporal inclusions and biochemical characteristics. Results for staining tests revealed  that the isolates were Gram positive, rod shaped cells, with  the spores  terminally  located. The cells from the two ecological regions did not have significant variation in average size. The rods had length ranging between 2.0 μm and 3.0 μm on average while the width was approximately 1 μm on average. Parasporal inclusions had varied shapes (i.e. bipyramidal, circular, squared,  oval  and  rhomboid). Both  biochemical  tests  (Proskauer  (VP)  test  and  catalase  test) were  positive. Average  optimum temperature range for growth was between 28°C and 35°C while the optimal pH growth range was between 5.5 and 7.5. Both the morphological and biochemical results provided evidence that the isolates were different forms of Bacillus thuringiensis. Out of the fifty six soil and sediment samples, 28 samples  (50%) yielded Bacillus  thuringiensis. 53.6% of  the  isolates were recovered from  samples  from  farms  in Machakos  district  and  46.4% from  the intertidal  brackish  sediments  from  the Gazi  coastal mangroves of Kenya. This shows that Bt is also present in soils which are under constant cultivation and those lying fallow within the intertidal brackish sediments.

Key Words: Intertidal Brackish Sediments; Bacillus thuringiensis; Characterization; δ-crystal.