A study on bio-diversity and antiplasmodial activity of rhizosphere soil samples from medicinal plants in Kolli Hills

Abstract Background Over the previous two decades, Plasmodium falciparum strains have become increasingly resistant to several medications. As a result, there is an urgent need to develop new therapeutic options. Taking this into account, we focused our research on screening microbial extracts from rhizosphere soil samples in specific regions, which increases the likelihood of discovering bacteria capable of producing antiplasmodial activity. Results In the current study, we aimed to isolate thirty-two different medicinal plant rhizosphere soil samples collected from Kolli Hills (January–December 2016). Isolation was performed on nutrient and starch casein agar medium by serial dilutions, and distinct colonies were chosen from each dilution. A total of two seventy-five bacterial isolates were isolated from the research plants and kept as pure cultures on nutrient agar. In which, maximum count of fourteen Gram-positive spore forming bacilli strains have been identified and further evaluated for morphological, cultural, and biochemical traits and significantly identified as Bacillus species. Further, promising anti-plasmodial action was demonstrated by B. megaterium bacterial extracts, with IC50 values of 24.65 µg/mL at 24 h and 7.82 µg/mL at 48 h. Bacillus mycoides showed good antiplasmodial activity with (IC50 P. falciparum 3D7: 23.52 μg/mL at 24 h and 22.88 μg/mL at 48 h, Bacillus flexus showed IC50 of 18.36 and 6.24 μg/mL and moderate antiplasmodial activity observed in Bacillus tequilensis. Poor antiplasmodial activity was found in Bacillus subtillis, Bacillus macerans, Bacillus pumilus and Bacillus larvey. Interestingly, 16S rRNA sequencing results confirmed that our bacterial species was Bacillus megaterium with 99% similarity observed with the accession number KX495303.1. Additionally, GC–MS analysis revealed effective anti-plasmodial bioactive compounds. Conclusions These findings show the potential of B. megaterium from Achyranthes aspera as a antiplasmodial agent. However, more research is needed to fully understand the bioactive compound of these strains and further studies are necessary to explore drug formulation and toxicity levels in the future.