Why we should care about culturing the Huanglongbing associated bacterium ‘Candidatus Liberibacter asiaticus’: the importance of terms and interpretations

Author(s): Merfa, Marcus Vinicius; De La Fuente, Leonardo | Abstract: Having bacteria grown in pure culture has been the foundation of bacteriology, by allowing a wide range of microbiological studies towards understanding the functionality of a specific bacterium. However, most bacteria have not been axenically cultured to date, thus hindering the understanding of their role in the context of their host or environment. One of these unculturable bacteria are the recently emergent plant pathogens ‘Candidatus Liberibacter spp.’. This group is comprised by dynamic psyllid-vectored, phloem-limited plant pathogens and endophytes that harm a wide range of economically important crops worldwide. ‘Candidatus Liberibacter asiaticus’ (CLas) is associated with Huanglongbing (HLB) in most of the main citrus-producing areas globally, a disease causing severe economic damages. Although the establishment of axenic cultures of CLas remains a major scientific challenge, many research groups have devoted efforts to culture this bacterium to aid in elucidating its virulence mechanism and contribute towards effective HLB management. This led to the development of innovative systems to culture and grow CLas, however different authors have approached the concepts of bacterial culture and axenic culture in different manners, leading to confusion in the terminology used. In this review, we provide the scientific definitions of important terms in bacteriology, while critically reviewing the contribution of each of these important CLas culturing studies.