R.K. Nadella*, M.
Vaiyapuri,???????????? A.B. Kusunur, T.C. Joseph,??????????? L.K. Velayudhan
and???????????????????????? M.P. Mothadaka
MFB Division, ICAR-Central Institute of
Cochin-682 029, India
Author Email :
Aim: Isolation and
characterization of Halothiobacillus sp. from the shrimp aquaculture
farm soil and their sulphur oxidation ability and utilization of H2S in
Methodology: Starkeys mineral
salt medium was used to screen autotrophic sulphur oxidizing bacteria. For
the qualitative screening, bacterial isolates were inoculated in mineral salt
medium containing bromo phenol blue indicator to monitor change in pH. The
isolates were studied further for their sulphate ion production, sulphur
oxidase enzyme production and utilization of Na2S. Identification
was carried out by conventional biochemical and molecular methods.
Results: Fifty isolates
showed distinct sulphur oxidizing ability on the mineral salt medium. The pH
reduction test revealed that out of fifty isolates six could efficiently
reduce the pH of the medium to 3.0 from an initial pH of 7 within 96 hr of
incubation at 30oC. Maximum sulphate ion (12.65 mg ml-1) and
sulphur oxidase enzyme (16.64 mM sulphate hr-1 ml-1)
was produced by a bacterial isolate, Halothiobacillus sp. strain rk3.
All the six isolates efficiently utilized Na2S in in-vitro conditions.
Conventional and molecular identification (16S rRNA sequence analysis)
revealed that the sulphur oxidizing bacterial isolates belonged to
Halothiobacillus spp. Furthermore, sequencing similarity calculation showed
an average nucleotide identity (ANI) values higher than 99% which suggests
that the isolates were not genetically different.
Interpretation: The present
investigation revealed the presence of Halothiobacillus sp. as natural
microflora of farm soils in shrimp aquaculture.
Key words: Aquaculture, Halothiobacillus, Sulphur oxidizing
bacteria, Sulphur oxidase, Sulphate ion
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