Bacterial Endophytes of the Medicinal Herb Hygrophila spinosa T. Anders and Their Antimicrobial Activity.
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Date
2013-10
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Abstract
Aims: The ethnobotanical herb Hygrophila spinosa T. Anders (Acanthaceae) is native to
India and used in traditional ayurvedic medicines for its pharmacologically important
phytochemicals. This study aims to isolate and characterize the culturable bacterial
endophytes of H. spinosa and evaluate their antimicrobial properties.
Place and Duration of Study: The experiments were performed in the Department of
Botany, Serampore College, Serampore as well as in the Microbiology Laboratory,
Department of Botany, University of Calcutta, Kolkata during 2011 to 2012.
Methodology: Bacterial endophytes were isolated from healthy plant tissues following
surface sterilization and plating on nutrient agar, glycerol asparagine agar and tryptic soy
agar. They were characterized physio-biochemically following standard microbiological
and biochemical methods. The endophytes were screened for production of antimicrobial
compounds following cross-streak assay against test strains Bacillus subtilis, B. cereus,
Escherichia coli, Pseudomonas cepacia, Klebsiella pneumoniae and Staphylococcus
aureus on nutrient agar plates.
Results: Eleven phenotypically distinguishable bacterial endophytes were isolated from
surface sterilized leaf, stem and root tissues and Shannon Weaver diversity index clearly revealed more diverse (0.83) types of endophytes in leaves than in stem (0.48) and root
(0.41) tissues. Physio-biochemical features of the isolates clearly indicated distinct
variation in their sugar fermentation profiles along with NaCl tolerance. The endophytes
produced important enzymes like catalase, amylase, gelatinase, nitrate reductase and
lipase. The bacterial isolates belonged to the genera Bacillus, Paenibacillus,
Pseudomonas, Ralstonia, Staphylococcus, Micrococcus and Acidomonas. Antibiotic
sensitivity profile, however, have indicated that the isolates were mostly resistant to
amoxycillin and bacitracin, while they were highly susceptible to tetracycline followed by
neomycin and streptomycin. Interestingly, the bacterial endophytes of H. spinosa give a
definite stamp on their antimicrobial activity against E. coli and K. pneumoniae followed by
S. aureus. Two isolates, Paenibacillus HGS 202 and Acidomonas HGR 302 obtained from
stem and root segments respectively showed antimicrobial activity against B. subtilis, B.
cereus, E. coli, K. pneumoniae and S. aureus.
Conclusion: This study identified 11 bacterial endophytes harbored by the leaves, stem
and root of H. spinosa which demonstrated antibacterial activity against Gram-positive as
well as Gram-negative bacterial strains. Moreover these endophytic bacterial isolates
could be exploited as sources of antibacterial substances.
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Keywords
Hygrophila spinosa, endophytic bacteria, antibacterial activity, antibiotic sensitivity, enzyme profile, NaCl tolerance
Citation
Pal Arundhati, Paul A K. Bacterial Endophytes of the Medicinal Herb Hygrophila spinosa T. Anders and Their Antimicrobial Activity. British Journal of Pharmaceutical Research. 2013 Oct; 3(4): 795-806.