Isolation and identification of starch-degrading bacteria from starch processing industry

Abstract

Cassava starch wastewater and sludge that discarded from the cassava starch processing industries contain high amount of starch and organic materials which causes environmental pollution. Starch-degrading bacteria that isolated from starch wastes are believed to have higher rate of starch degradation and production of - amylase. The aim of this study was to isolate starch-degrading bacteria from the cassava wastewater and sludge. The isolation was done by serial dilution. Total 17 bacterial isolates were isolated from the collected samples. Among the 17 isolates, one isolate from sludge showed amylolytic activity. The isolate is a Gram-positive bacteria with long rod-shaped under microscopic identification. Cassava wastewater was utilized as substrate in batch fermentation to study the hydrogen production, the growth kinetics, the rate of starch utilisation and the production of reducing sugars of the isolate. There was no hydrogen production from the isolate. The specific growth rate in cassava wastewater medium was 0.04876 h-1. The doubling time and number of cell generation were 14.21 hour and 1.69 respectively. The isolate consumed about 88% of starch at the end of the fermentation. The maximum amylase activity and reducing sugars of the isolate were 41.34 U/mL and 3.207 mg/mL. 16S rRNA gene sequencing and phylogenetic analysis indicated that the isolate is in the same clade as Bacillus cereus. The isolate was designated Bacillus sp. CS9 and the partial 16S rRNA sequence has been deposited into the GenBank with nucleotide accession number MF138129.