Studies on Bioflocculant Production by Pseudoalteromonas sp. NUM8, a Marine Bacteria Isolated from the Circulating Seawater

A bioflocculant producing potential bacteria was isolated from the circulating seawater of bio-filter using streak plate methods. The bacteria was identified through biochemical characteristics, partial 16S ribosomal ribonucleic acids (rRNA), nucleotide sequencing, and BLAST analysis of the gene sequence that showed the bacteria have 99% similarity to Pseudoalteromonas sp. and deposited in GenBank as Pseudoalteromonas sp. NUM8 with accession number JX435820. Influences of time course assay, carbon sources, nitrogen sources, inoculum size, as well as initial pH on the bacteria producing extracellular bioflocculant activity were investigated. The results showed that the strain optimal production period of microbial bioflocculant was at 72 h (flocculating activity of 94.5%), then dropped slowly. The bacteria optimally produced the bioflocculant when 1.0% sucrose and 0.5% sodium nitrate were used as sole sources of carbon and nitrogen with flocculating activities of 92.8% and 93.8% respectively. Also, the bacteria produced the bioflocculant optimally when initial pH of the medium was 5.0 (flocculating activity 93.2%), and when Ca²⁺ was used as cation (flocculating activity 93.4%). The culture condition of inoculum size of 3% (v/v) was optimal flocculant production (flocculating activity 94.4%). Composition analyses indicated the bioflocculant to be principally a glycoprotein made up of about 34.3% protein and 63.4% total carbohydrate.