Characterization and functional analysis of clpB gene from Acidovorax avenae subsp. avenae RS‐1

Abstract

The type VI secretion system (T6SS) has been reported to be highly associated with various cellular activities in strain RS‐1 of Acidovorax avenae subsp. avenae (Aaa), the pathogen of bacterial brown stripe of rice. However, the role of the clpB gene that presents in the T6SS gene cluster in Aaa pathogenicity has not been clarified. The aim of the current study was to characterize the function of clpB and to investigate its contribution to bacterial pathogenesis using insertional deletion mutation and complementation approaches. The results indicated that mutation of clpB significantly affected bacterial growth, virulence, exopolysaccharide (EPS) production, biofilm formation and expression of 13 other T6SS genes of Aaa RS‐1. The reduction of virulence may be also partially due to the change in EPS composition, which was characterized by the Fourier transform infrared (FTIR) spectra. Furthermore, analysis of protein homology modelling showed that the structure of ClpB is different from those of the other T6SS components. In addition, structural difference was observed between ClpB and Type IV pili (TFP) as well as Type IV pilus biogenesis proteins (PilP), whose functions are similar to ClpB. Taken together, this study demonstrated that the clpB gene plays a key role in Aaa bacterial virulence.

Halotolerant bacteria belonging to operational group Bacillus amyloliquefaciens in biocontrol of the rice brown stripe pathogen Acidovorax oryzae

“…The inhibitory effect of culture filtrates on bacterial growth may be, at least partially, attributed to the inhibition of virulence determinants such as swimming motility and biofilm formation, which has been found to be very closely associated with the virulence of Ao strains RS-1 and RS-2 in our previous studies Zhang et al 2017). Indeed, swimming motility has been thought to play a role in the initial steps of infection, mediated by chemo taxis and attachment through flagella (Josenhans and Suerbaum 2002;Liu et al 2012), while biofilms have been proposed to be involved in the virulence of plant pathogenic bacteria by increasing the potential of the bacteria to survive in deleterious conditions and poor nutrient availability (Mansfield et al 2012;Bogino et al 2013).…”

“…; Zhang et al . ). However, the harmful effect of Ao strains on seedlings height was attenuated by these antagonistic halotolerant bacteria.…”

“…; Zhang et al . ). Indeed, swimming motility has been thought to play a role in the initial steps of infection, mediated by chemo taxis and attachment through flagella (Josenhans and Suerbaum ; Liu et al .…”

“…In agreement with previous studies, our study indicated that the 15 halotolerant bacterial isolates, in particular, isolates K5-3 and PPB6 exhibited strong in vitro and in vivo antibacterial activities against both high virulent strain RS-1 and weak virulent RS-2 of Ao. The in vivo inhibitory effect of halotolerant bacterial isolates on this pathogen was determined based on the height of rice seedlings, which has been found to be high closely associated with the virulence of Ao in our previous studies Masum et al 2017;Zhang et al 2017).…”

“…S2, rice seedlings inoculated with Ao strains RS-1 and RS-2 were shorter with an average plant height of 2Á22 and 3Á01 cm, respectively, compared to the corresponding negative control (ddH2O) with an average plant height of 6Á20 cm. Obviously, this rice pathogen have a harmful effect on seedlings height, which has been used for evaluating the virulence of Ao in our previous studies Zhang et al 2017). However, the harmful effect of Ao strains on seedlings height was attenuated by these antagonistic halotolerant bacteria.…”