Abstract Biological flocculants are advantageous due to their biodegradability and safety to living beings. In this work, four bacterial strains, isolated from sugarcane cropped soil (Bacillus megaterium LBPMA-APFSG3Isox and B. toyonensis LBPMA-ACOPR1.Isox) and sludge of an agroindustrial effluent (B. pumilus LBPMA-BLD07 and B. thuringiensis LBPMA-EFIII), were studied. It was found that all of them secreted bioflocculants, at 37 ± 1 °C, with no pH changes over time and the flocculant activity increased during the time course of incubation. These results stimulated the optimization of the culture conditions to improve flocculation rates, such as the pH, nitrogen sources and carbon. For B. toyonensis LBPMA-ACOPR1.Isox and B. thuringiensis LBPMA-EFIII, the best pH for the bioflocculant production was 5.0. Sucrose and maltose were the best sources of carbon, while urea was the preferred source of nitrogen for two of the tested isolates (B. pumilus LBPMA-BLD07 and B. toyonensis LBPMA-ACOPR1.Isox), followed by (NH4)2SO4 (B. megaterium LBPMA-APFSG3Isox) and peptone (B. thuringiensis LBPMA-EFIII). The FTIR-ATR spectra of each extracted material responsible for the flocculant activities of the strains displayed carboxyl, hydroxyl and methoxy functional groups characteristic of polysaccharides.

Polyhydroxyalkanoates (PHAs) are fully biodegradable biopolyesters produced by many prokaryotes and accumulated as insoluble cytoplasmatic inclusions. The detection of these intracellular granule is usually provided using lipofilic azodyes, which are not specific. Another way to screen PHA-producing bacteria is through culture-independent molecular techniques such Polymerase Chain Reaction (PCR), and the search for new PHA-producer strains is essential to reduce the cost at industrial level. The application of these both methods is desirable. In the present study, 24 bacteria isolated from soil of the Atlantic forest in Maceió (AL, Brazil) and from agri-industrial sludge (Coruripe-AL, Brazil) were studied regarding to their capacity of growing in mineral salt medium, as indicative of PHA synthesis. All strains were submitted to biochemical characterization, whilst PCR has proved that isolates BMA-05, BMA-10, BMA-13 and BDL-07 has the gene phaC, which encodes a PHA synthase, the key for PHA synthesis. The amplification and sequencing of their 16S r-DNA region was able to identify these bacteria respectively as Pseudomonas fluorescens, Enterobacter aerogenes, Klebsiella oxytoca and Bacillus pumilus. The same minimal medium supplement with peptone demonstrated to induce growing of those strains.