4. Conclusions
The five autochthonous strains present at least one tolerance/
resistance mechanism because all of them are able to grow
and develop in the presence of Cr(VI).The maximum decreases in
Cr(VI) concentration were produced by K. oxytoca P2 (74.32%) in
pure cultures and the combination K. ornithinolytica 1P, P. veronii 2E
(72.88%) in mixed cultures. The performance of these two microorganisms
is better in mixed than in the individual cultures (65.01%
for K. ornithinolytica 1P, and 44.47% for P. veronii 2E) showing a
synergetic effect together (72.88%).
The nucleic acid studies show that the only two microorganisms
which are able to grow together in all the stages are the two last
mentioned but it could not be established yet a correlation between
this fact and the best percentage Cr(VI) disappearance found.All the
strains showed a good Cr(VI) biotransformation efficiency but to
decrease the final metal values in the treated effluents a combination
of techniques must be used. In order to achieve this goal,
further studies using pure and the best mixed cultures, in growing
or non-growing conditions, combined with flocculation steps,
should be developed.