Growth of 'Candidatus Liberibacter asiaticus' in a host-free microbial culture is associated with microbial community composition.

'Candidatus Liberibacter asiaticus' ('Ca. L. asiaticus'), the suspected causative agent of citrus greening disease, is one of many phloem-restricted plant pathogens that have not been isolated and grown in an axenic culture. In this study, infected Asian citrus psyllids were used to prepare a host-free source of 'Ca. L. asiaticus'. Host-free mixed microbial cultures of 'Ca. L. asiaticus' were grown in the presence of various antibiotic treatments to alter the composition of the microbial communities. Our hypothesis was that the presence of selected antibiotics would enhance or reduce the presence of 'Ca. L. asiaticus' in a host-free culture composed of a mixed bacterial population through changes in the microbial community structure. We determined how 'Ca. L. asiaticus' growth changed with the various treatments. Treatment with vancomycin (50 µg/mL), streptomycin (0.02 µg/mL), or polymyxin B (4 µg/mL) was associated with an increased abundance of 'Ca. L. asiaticus' of 7.35 ±â€¯0.27, 5.56 ±â€¯0.15, or 4.54 ±â€¯0.83 fold, respectively, compared to untreated mixed microbial cultures, while treatment with 100 µg/mL vancomycin; 0.5, 1, or 2 µg/mL streptomycin; or 0.5 µg/mL of polymyxin B was associated with reduced growth. In addition, the growth of 'Ca. L. asiaticus' was associated with the microbial community composition of the mixed microbial cultures. A positive relationship between the presence of the Pseudomonadaceae family and 'Ca. L. asiaticus' growth was observed, while the presence of 'Ca. L. asiaticus' was below the detection limit in cultures that displayed high abundances of Bacillus cereus. Our findings offer strategies for developing effective axenic culture conditions and suggest that enrichment of the Bacillaceae family could serve as a paratransgenic approach to controlling citrus greening disease.

Physiochemical changes mediated by "Candidatus Liberibacter asiaticus" in Asian citrus psyllids.

Plant pathogenic bacteria interact with their insect host(s)/vector(s) at the cellular and molecular levels. This interaction may alter the physiology of their insect vector, which may also promote the growth and transmission of the bacterium. Here we studied the effect of "Candidatus Liberibacter asiaticus" ("Ca. L. asiaticus") on physiochemical conditions within its insect vector, the Asian citrus psyllid (ACP), and whether these changes were beneficial for the pathogen. The local microenvironments inside ACPs were quantified using microelectrodes. The average hemolymph pH was significantly higher in infected ACPs (8.13 ± 0.21) than in "Ca. L. asiaticus"-free ACPs (7.29 ± 0.15). The average hemolymph oxygen tension was higher in "Ca. L. asiaticus"-free ACPs than in infected ACPs (67.13% ± 2.11% vs. 35.61% ± 1.26%). Oxygen tension reduction and pH increase were accompanied by "Ca. L. asiaticus" infection. Thus, oxygen tension of the hemolymph is an indicator of infection status, with pH affected by the severity of the infection.

The infection of its insect vector by bacterial plant pathogen "Candidatus Liberibacter solanacearum" is associated with altered vector physiology.

Many bacterial and viral plant pathogens are transmitted by insect vectors, and pathogen-mediated alterations of plant physiology often influence insect vector behavior and fitness. It remains largely unknown for most plant pathogens whether, and how, they might directly alter the physiology of their insect vectors in ways that promote pathogen transmission. Here we examined whether the presence of "Candidatus Liberibacter solanacearum" ("Ca. L. solanacearum"), an obligate bacterial pathogen of plants and of its psyllid vector alters the physiochemical environment within its insect vector, the potato psyllid (Bactericera cockerelli). Microelectrodes were used to measure the local pH and oxygen tension within the abdomen of "Ca. L. solanacearum"-free psyllids and those infected with "Ca. L. solanacearum". The hemolymph of infected psyllids had higher pH at 9.09 ± 0.12, compared to "Ca. L. solanacearum"-free psyllids (8.32 ± 0.11) and a lower oxygen tension of 33.99% vs. 67.83%, respectively. The physicochemical conditions inside "Ca. L. solanacearum"-free and -infected psyllids body differed significantly with the infected psyllids having a higher hemolymph pH and lower oxygen tension than "Ca. L. solanacearum"-free psyllids. Notably, the bacterial titer increased under conditions of higher pH and lower oxygen tension values. This suggests that the vector's physiology is altered by the presence of the pathogen, potentially, resulting in a more conducive environment for "Ca. L. solanacearum" survival and subsequent transmission.

Cross-Linked Protein Nanofilter with Antibacterial Properties for Multifunctional Air Filtration.

Development of high-performance nanomaterials with not only strong ability to trap the pollutants but also good structure stability under varying environmental conditions is a critical need for air-filtration applications. However, it has been very challenging for a filtering material to simultaneously realize multifunctional air filtration and good environmental stability. Here, based on our previous studies on protein-based nanofilters, we report a cross-linked protein nanofabric to address this challenging issue. It is found that cross-linked protein nanofabrics can significantly improve the structure stability against different moisture levels and temperatures, while maintaining the multifunctional filtration performance. Moreover, it is demonstrated that the cross-linked protein nanomaterials also possess antibacterial properties, such as Shewanella oneidensis bacteria, further improving the environmental stability. The effects of cross-linking with different loadings of cross-linking agent on the structure stability and filtration performance are further investigated at different humidity levels and temperatures. This study provides a cost-effective solution for advanced "green" nanomaterials with excellent performance in both filtration functions and structure stability under varying environment.