Deciphering Microbial Community Dynamics Associated With Post-Harvest Sugar Loss Of Sugarcane

Sugarcane is the most important crop for sugar and ethanol production.Sucrose loss due to cane deterioration caused by the delay progressing of harvested cane is a severe problem in the sugar industry.Few studies have been done to evaluate the microbial community associated with sugar decline in harvested canes.The study was aimed to examine the relationships between the pH and sugar content decline and fungal community in the stalk of sugarcane by microbial metagenomics combined with physiological,biochemical and microbiological methods.Experiments simulating the process between harvest and milling were performed.After storing 12 hours at 20℃,30℃ and 40℃,the sucrose loss rate in cane powder were 40.3%、51.2% and 12.4%,respectively.And the pH value rapidly decreased from 5.8 to 4.0、3.6 and 3.7,respectively.After 36 hours,the sucrose content dropped to zero.At temperature of 20℃,30℃ and 40℃,the sucrose content in end portions(5 cm from the cut)of the stalk segment(30 cm)decreased by 27.7%,23.9% and 29.9% in 2 days,and 28.4%,31.9% and 52.5%in 5 days,respectively.pH of the stem segment decreased from 5.6 to 4.0 in 10 days.The sucrose decline in the internal region of the stalk segment was relatively slower,decreased by 8.5% after 10 days at 30℃.High temperature promoted cane deterioration and storing time contributed the most for sugar loss.Microbial community was characterized by 16 S rDNA and ITS sequencing.In the stalk powder experiment,the diversity of microbial community decreased significantly with the increase of temperature between 20～40℃,and increase of storage time.The dominant species in samples changed from Wickerhamomyces.anomalus before storing(20℃)to Kazachstania.humilis(30℃,12 hours)and Saccharomyces.cerevisiae(40℃,12 hours).In the segmented stalk experiments at 30℃ and 40℃,the microbial diversity in the end and internal regions decreased sharply with time,and the core microorganisms associated with the deterioration process included 7 bacterial genera(Lactobacillus,Acetobacter,Pantoea,Enterobacter,Gluconobacter,Weissella and Leuconostoc)and 7 fungal genera(Aspergillus,Wickerhamomyces,Candida,Trichoderma,Hanseniaspora,Cladosporium and Kazachstania).A total of 255 bacterial strains and 404 fungal strains were isolated from sugarcane stalks by the plate culture method.Comparing with the high-throughput sequencing results,only 20%(at genus level)of the microbes could be successfully isolated and cultured.This study demonstrated that microorganisms were closely related to the decrease of pH value and sucrose content in stalks after harvest,and the impact was influenced significantly by temperature and time of storage.The results could also serve as a reference for the scheduling of harvest of sugarcane.