| Summary: | Remediation of chromium contaminated soils is commonly conducted
physical and chemical treatments. Both are characterized by environment
unfriendly, costly, and rise to secondary impacts. Alternative technique that is
cheaper and lead to sustainable is the use of biological agents, termed as
bioremediation. The right one in bioremediation is utilization of potential
symbiosis between plants (which naturally has ability in adsorption of metal) and
rhizobacteria, known as rhizoremediation. The aims of this research were to
obtain isolates of rhizobacteria which can increase chromium uptake by plants,
studying the effectiveness of the rhizobacteria in increasing chromium uptake by
plants, and the mechanisms of chromium hexavalent transformation.
Isolation rhizobacteria was conducted by pouring the rhizospheric soils
of plants that grow well in chromium contaminated soils in Soil Extract Agar
medium, followed by streak plating method to purify the isolates on Luria Bertani
medium. Rhizobacteria isolates were selected by bioassay method on Corn plants
(Zea maysL.), and identification of the isolates were carried morphologically,
physiologically, and molecularly by 16S rDNA sequencing. Study about the
effectiveness of Rhizobacteriain increasing chromium uptake by plant was
conducted by bioassays on Jute (Boehmerianivea L. Gaud) for getting chromium
high accumulation in shoots, and green mustard (Brassica rapa var.
Parachinensis L.) for getting chromium high accumulation inroots,cultivated on
growing media of sterile Grumusol and Regosol soils supplemented by manure
and compost. Observations of this bioassay include dry weight and the content
levels of chromium in the roots, and shoots. Study about the mechanism of Cr(VI)
transformation was carried out by exposing chromium Cr(VI) to rhizobacteria
isolates in the form of growing cells, resting cells, and their supernatant within
several hours incubation, then the residual Cr(VI) and the pH value of the medium
were measured. These treatment products were applied in bioassays on maize,
and then measuring chromium uptake by plants.
Isolation resulted 39 rhizobacterial isolates (I1 - I39). Based on the first
bioassay on maize, chosen 7 isolates which were influencing chromium
absorption by plant, 5 isolates (I26, I30, I37, I38 and I13) inclined to influence
chromium accumulation in root and 2 isolates (I3 and I20) in shoot. These 7
isolates were identified and coninued examine. The result of the identification,
Isolate I3was identified as genus Rhizobium sp., and isolates I13 , I20 , I26, I30, I37,
and I38 were identified as genus Agrobacterium sp. Based on the bioassay on jute,
Isolate I3 and combination of isolate I3+compost in grumusol and regosol, efective
in increasing plant dry weight and root + shoot chromium uptake
(phytostabilization and phytoextraction) 2 times. Based the bioassay on Indian
mustard, combination of Isolat I37+manure in grumusol efective in increasing
plant dry weight and root, and plant chromium uptake (phytostabilition) 2 times,
while ini regosol increasing plant dry weight, root, shoot and plant chromium
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uptake (phytostabilition and phytoextraction) 4 times. Indian mustard as the
hyperaccumulator, could be decreased the shoot chromium uptake and increased
the root uptake. In the mechanism of Cr(VI) transformation, rhizobacteria
produced metabolites especially chromate reductase enzyme and organic acids,
which chromate reductase enzyme would reduce Cr(VI) become Cr(III) and
organic acids as the electron donor.
Keywords: Chromium, Rhizobacteria, Chromium uptake, Jute (Boehmeria nivea L.
Gaud), Green Mustard (Brassica rapa var. parachinensis L.).
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