Sugarcane bagasse (SB), as a major by-product of sugarcane, is one of the most abundant organic matter and characterized by cheap and easily available carbon source in Hainan Island, China. The objective of this study was to isolate tropical cellulolytic bacteria from Hainan Island and demonstrate their prospects of utilization of SB as a low-cost carbon source to greatly reduce the cost of aquaculture. A total of 97 cellulolytic marine bacteria were isolated, of which, 58 cellulolytic marine bacteria displayed the hydrolysis capacity (HC) of more than 1, while 28 cellulolytic marine bacteria displayed more than 2. Of the 28 tropical cellulolytic bacterial strains with HC more than 2, Microbulbifer sp. CFW-C18 and Vibrio sp. MW-M19 exhibited excellent SB decomposition in a small-scale laboratory simulation of shrimp aquaculture, up to 75.31 and 74.35%, respectively, and both of them were safe for shrimps. Meanwhile, both of CFW-C18 and MW-M19 besides displaying low multiple antibiotic resistance (MAR) index, also increased the C/N ratio (CFW-C18: C/N ratio of 14.34; MW-M19: C/N ratio of 14.75) of the small-scale laboratory simulation of shrimp aquaculture by decreasing the nitrogen content after a supplement of SB for 15 days. More importantly, CFW-C18 and MW-M19 displayed a relatively low MAR index, 0.47 and 0.1, respectively, especially MW-M19, with the lowest MAR index (0.1), which was resistant to only three antibiotics, streptomycin, amikacin, and levofloxacin, indicating that this strain was safe and non-drug resistance for further use. Overall, tropical cellulolytic bacteria isolated from Hainan Island, especially CFW-C18 and MW-M19, will provide the proficient candidates as probiotics for further construction of the recirculating aquaculture system based on the supplement of low-cost external carbon source—SB.

Background: In aquaculture system, it is essential to adjust the inherent disadvantage of C/N ratio by adding a lot of additional carbon sources, such as sugarcane molasses, organic acids, and organic acid salts, which will greatly increase the cost of shrimp aquaculture. Herein, we aimed to isolate cellulolytic marine bacteria to hydrolyze sugarcane bagasse (SB) for reducing the cost of addition of external carbon sources in industrial Litopenaeus vannamei aquaculture.Results: A total of 97 cellulolytic marine bacterial strains belonged to 6 genera were isolated from 2,585 indigenous bacteria, indicating that seagrass bed can be used as an important place for screening the cellulolytic bacteria. The hydrolysis capacity (HC) of 58 cellulolytic marine bacterial strains was ranged from 1.1–4.0. MW-M5 displayed the largest HC value, followed by MW-M10 and MW-M14. The cellulase contents of 30 strains were more than 3 U/g in the supernatant of fermentation broth after 24 h, which was significantly higher than that of commercial cellulose. 26 cellulolytic marine bacteria with HC greater than 2 were safe for L. vannamei. MW-M19 with the lowest multiple antibiotic resistance index, 0.1, had a highest SB enzyme activity, 4.14 U/mL. The SB decomposition rates of CFW-C18 and MW-M15 were up to about 63.81% and 48.57% after fifteen days, respectively. Conclusions: These results provide valuable information for further construction of a shrimp aquaculture system based on low-cost external carbon sources using cellulolytic bacteria, and even for other biotechnological applications.