Comparative studies on Synthesis of Protease and Bioconversion of Cr+6 to Cr+3 by Bioleaching technique using Isolated Microbial consortia in Lab scale Batch experiment

A Nath, R Chowdhury, C Bhattacharjee

Abstract


Presence of heavy metal like hexavalent chromium
and high biological and chemical oxygen demands (BOD and
COD) due to presence of animal flesh, skin etc. in the tannery
effluent cause threat to the environment. Bacillus sp. (JUCHE2),
Micrococcus sp (JUCHE3) and Micrococcus sp (JUCHE4) isolated
from tannery waste, were used in a comparative study on
synthesis of protease and bioconversion of Cr+6 to Cr+3 by
bioleaching technique. The isolated microbial consortia could
tolerate high metal concentration and hostile environmental
conditions with respect to temperature and pH. It was observed
that among three types of bacterial growth media, namely, Nutrient
broth, Soyabean Casein Digest Medium and Luria broth,
bacterial growth was maximum at Casein Digest Medium and
laboratory scale batch experiments were performed in Soyabean
Casein Digest medium at 100 ppm chromium concentration at
aerobic conditions. Growth characteristics such as maximum
specific growth rate (u, max), Monod Constant (ks), synthesis
of protease, bioconversion of Cr+6 to C+3 by bioleaching
technique, utilization of substrates, namely, carbohydrate and
protein were measured at different time intervals in bacterial
growth media. For Bacillus sp. (JUCHE2) optimum values of
pH, temperature and agitation speed were found to be 7.0, 37 oC
and 100 rpm, respectively and those for both Micrococcus sp
(JUCHE3) and Micrococcus sp (JUCHE4) were observed to
be 6.0, 30 oC and 100 rpm, respectively. It was observed that
among three types of microbial consortia growth of Bacillus sp.
(JUCHE2) was very high compared to other microbial consortia
and followed Monod type model. Protease synthesis was strongly
associated with microbial growth whereas bioconversion of heavy
metals was not associated with microbial growth. Maximum
protease activities were notified after 30 hour incubation of
microbial culture and protease was characterized with respect
to optimum pH, temperature and enzyme kinetics. Reduction of
BOD and COD in form of reduction of proteins by synthesized
proteolytic enzymes and bioconversion of Cr+6 to Cr+3 by
bioleaching technique utilizing the isolated strains could be highly
effective for the treatment of tannery waste.

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