Isolation and screening of cellulose and organic matter degrading bacteria from aquaculture ponds for improving water quality in aquaculture

Abstract

Aquaculture is one of the agroindustrial activities that has the highest growth rate in last decades and provides undeniable benefits for humanity such as providing food, generating jobs as well as contributing to economic development. However, intensive aquaculture also is one of the most criticized activities because of their environmental impacts, in which feed is the main source of waste and is responsible for most of the environmental impacts of aquaculture. Besides high concentration of organic and inorganic wastes from uneaten feed and excreta of aquaculture animals, amount of insoluble fiber (e.g., cellulose, hemicellulose, lignin) in aquaculture water is significant due to the majority of aquaculture feed is plant-based feed and contain a high amount of fiber. The polluted aquaculture water results in not only increase of environmental treatment cost but also outbreaks of aquaculture animal diseases. Improving water quality and reducing the accumulation of pollutants in aquaculture crops are therefore constant concerns. In this study, we isolated and screened cellulose and organic matter degrading bacteria from aquaculture ponds for producing probiotics which can improve aquaculture water quality and feed digestibility of aquaculture animals. From sediment and water samples collected at fish ponds in Phu Vang district, Thua Thien Hue provine, we isolated 215 bacterial strains, of which 25 isolates exhibited at least one of cellulolytic, amylolytic and proteolytic activities. Particularly, the strain Bacillus sp. W12 produced enzymes that are capable of degrading both cellulose and organic matters (cellulase, protease and amylase). The optimum conditions for enzyme production by Bacillus sp. W12 were obtained at pH 7, temperature 30°C, 72 h of incubation and 0.4% of NaCl. Activity of the enzymes reached the highest activity at pH 6-8 and temperature 30 - 40°C. The present study showed the strain Bacillus sp. W12 as a potential probiotic candidate for degrading cellulose and organic substrates in aquaculture water as well as improving feed digestibility of aquaculture animals.