‘Crucial Step’ Taken in HLB Bacterium Cultivation

Daniel CooperHLB Management, Research


Huanglongbing (HLB) is caused by the bacterium Candidatus Liberibacter asiaticus (CLas), which has been challenging to culture outside its host because of its intracellular nature and genome reduction. Due to these challenges, in-depth research on effective cultivation methods for CLas is essential to develop better control strategies.

Such in-depth research was conducted by a team from the U.S. Department of Agriculture Agricultural Research Service, the University of Florida and other institutions.

Research results were published in the journal Horticulture Research. The authors of the study are Desen Zheng, Cheryl M. Armstrong, Wei Yao, Bo Wu, Weiqi Luo, Charles Powell, Wayne Hunter, Feng Luo, Dean Gabriel and Yongping Duan.

The study focused on optimizing growth conditions for CLas in vitro, allowing for a significant increase in bacterial cells and maintaining their viability over extended periods. This breakthrough offers new avenues for studying CLas and developing targeted control measures against HLB.

The team optimized a semi-selective medium based on nutritional and antibiotic screening assays, achieving a 100- to 1,000-fold increase in CLas cell concentration. The bacteria remained viable for over 20 months and displayed limited growth in subcultures.

The study confirmed CLas growth through fluorescence in situ hybridization and gene expression analysis. Additionally, the research highlighted the importance of a helper bacterium, Stenotrophomonas maltophilia, in promoting CLas growth in vitro. The co-cultured CLas was successfully inoculated back into citrus seedlings via psyllid feeding, partially fulfilling Koch’s postulates and resulting in HLB symptoms.

“This is a crucial step toward understanding the biology of CLas and developing effective strategies to combat HLB,” said Duan. “Our ability to culture Las in vitro opens up new possibilities for research and testing potential antimicrobial treatments.”

The successful cultivation of CLas in vitro has significant implications for citrus disease management. It enables detailed study of the bacterium’s biology, interactions with its hosts, and the screening of antimicrobial compounds. This advancement brings researchers closer to developing targeted treatments for HLB, potentially mitigating the disease’s devastating impact on citrus.

Further research will focus on refining the culture method and exploring its applications in disease-control strategies.

Source: Chinese Academy of Sciences

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