Bacterial Community Shift in Two Sectors of a Tannery Plant and its Cr (VI) Removing Potential

The bacterial community, analyzed by both 16S rRNA gene-based clone library and cultivation methods, changed in two different sectors of a tannery plant. Ten different bacterial phyla were detected through the clone library. The bacterial community of the tanning waste consisted of Gammaproteobacteria (34.8%), Bacteroidetes (20.9%), Betaproteobacteria (12.8%), Alphaproteobacteria (7.0%), Firmicutes (7.0%), Deinococcus-Thermus (7%), Planctomycetes (4.7%), Verrucomicrobia (2.3%), Epsilonproteobacteria (1.2%), Spirochaetes (1.2%), and that of the settling tank sludge consisted of Firmicutes (38.8%), Betaproteobacteria (27.1%), Gammaproteobacteria (11.8%), Bacteroidetes (9.4%), Alphaproteobacteria (4.7%), Deltaproteobacteria (3.5%), Actinobacteria (2.4%), Synergistes (1.2%). The tanning waste accommodated higher biodiversity than the downstream primary settling tank did. Cultivation conditions seriously influenced the culturability and isolation of bacterial strains: different levels of nutrients and Cr (VI) and temperatures resulted in isolation of different bacterial strains, which showed different removal of Cr (VI) (from 1.2% to 99.1%). In addition, supplementation of nutritious LB medium enhanced the Cr (VI) culturability of bacterial isolates. Several bacteria detected as operational taxonomy units (OTUs) by culture-independent analysis were isolated, yet many OTUs did not have their relative isolates. Among the isolates, Pseudochrobactrum, Shewanella, Marinobacter, Microbacterium, Psychrobacter and Agrococcus strains showed considerable Cr (VI) removal efficiencies and good potentials for Cr (VI) pollution treatment.