Publications

4368

Abstract Presence of glycogen granules in anaerobic ammonium-oxidizing (anammox) bacteria has been reported so far. However, very little is known about their glycogen metabolism and the exact roles. Here, we studied the glycogen metabolism in “Ca. Brocadia sinica” growing in continuous retentostat cultures with bicarbonate as a carbon source. The effect of the culture growth phase was investigated. During the growing phase, intracellular glycogen content increased up to 32.6 mg-glucose (g-biomass dry wt)−1 while the specific growth rate and ATP/ADP ratio decreased. The accumulated glycogen begun to decrease at the onset of entering the near-zero growth phase and was consumed rapidly when substrates were depleted. This clearly indicates that glycogen was synthesized and utilized as an energy storage. The proteomic analysis revealed that “Ca. B. sinica” synthesized glycogen via three known glycogen biosynthesis pathways and simultaneously degraded during the progress of active anammox, implying that glycogen is being continuously recycled. When cells were starved, a part of stored glycogen was converted to trehalose, a potential stress protectant. This suggests that glycogen serves at least as a primary carbon source of trehalose synthesis for survival. This study provides the first physiological evidence of glycogen metabolism in anammox bacteria and its significance in survival under natural substrate-limited habitat.

In 2019, citrus production in Florida declined by more than 70%, mostly because of Huanglongbing (HLB), which is caused by the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas). Thermotherapy for HLB-affected trees was proposed as a short-term management solution to maintain field productivity. It was hypothesized that thermotherapy could eliminate HLB from affected branches; therefore, the study objectives were to show which time–temperature combinations eliminated CLas from woody tissues. Hardening, rounded Valencia twigs collected from HLB-affected field trees were treated in a steam chamber at different time–temperature combinations (50°C for 60 s; 55°C for 0, 30, 60, 90, and 120 s; 60°C for 30 s; and an untreated control). Three independent repetitions of 13 branches per treatment were grafted onto healthy rootstocks and tested to detect CLas after 6, 9, and 12 months. For the RNA-based CLas viability assay, three branches per treatment were treated and bark samples were peeled for RNA extraction and subsequent gene expression analyses. During the grafting study, at 12 months after grafting, a very low frequency of trees grafted with twigs treated at 55°C for 90 s and 55°C for 120 s had detectable CLas DNA. In the few individuals with CLas, titers were significantly lower (P ≤ 0.0001) and could have been remnants of degrading DNA. Additionally, there was a significant decrease (P ≤ 0.0001) in CLas 16S rRNA expression at 55°C for 90 s, 55°C for 120 s, and 60°C for 30 s (3.4-fold change, 3.4-fold change, and 2.3-fold change, respectively) in samples 5 days after treatment. Heat injury, not total CLas kill, could explain the limited changes in transcriptional activity; however, failed recovery and eventual death of CLas resulted in no CLas detection in most of the grafted trees treated with the highest temperatures or longest durations.

Abstract“Huanglongbing” (HLB) is one of the most devastating diseases of citrus orchards worldwide. Samples from 183 citrus plants of different cultivars and rootstock/cultivar combinations, showing HLB symptoms in three Caribbean countries (Cuba, Jamaica, and Guadeloupe-France), were collected to verify the possible co-infection of ‘Candidatus Phytoplasma’ and ‘Candidatus Liberibacter’ species. The 64% of the samples resulted positive to the ‘Ca. L. asiaticus’ and the 27% to diverse ‘Ca. Phytoplasma’-related species, moreover about the 14% of the samples infected with ‘Ca. Liberibacter’ were also found positive to phytoplasmas, indicating the presence of mixed infection especially in the orchards located in Cuba. Moreover, in one of the samples from Jamaica mixed phytoplasma infection was detected. Moreover the detection of only phytoplasmas in 11 symptomatic citrus samples collected from Cuba and Guadeloupe without ‘Ca. Liberibacter’ detection, confirmed that the symptomatology cannot be the sole criterium to discriminate between the presence of the two pathogens, and molecular detection is necessary to identify single or mixed infections. Diaphorina citri insects collected from Cuba and Guadeloupe resulted infected with ‘Ca. L. asiaticus’ confirming its active role in the dissemination of the pathogen. Only one insect of the Cicadidae family, collected in Guadeloupe, was found positive for phytoplasma presence. Considering that the phytoplasmas belonging to some ‘Candidatus species’ were detected in the three countries in different citrus varieties, a relevant role as phytoplasma reservoir can be attribute to citrus orchards.

Abstract Candidatus Liberibacter solanacearum (Lso) is a phloem-limited, Gram-negative, unculturable bacterium that is primarily spread by psyllid insect vectors. It is considered very invasive due to its ability to be transported primarily in infective psyllids (Munyaneza et al., 2007a; 2010a,b; 2012a,b; Munyaneza, 2012; Alfaro-Fernandez et al., 2012a,b). It has been shown that Lso distribution in the Americas, New Zealand and Europe follows the distribution of its known psyllid vectors (Munyaneza, 2010; 2012).In New Zealand, where Lso was introduced along with Bactericera cockerelli, supposedly from Western USA in early 2000s, the bacterium had already spread to both North and South Island by the time it was first documented in 2006 (Gill, 2006). It is clear that introduction of the psyllid vectors of Lso into new regions is likely to result in the rapid spread of this bacterium. Lso and several of its vectors are already on several alert lists, including the EPPO A1 Regulated Quarantine Plant Pests.

AbstractThe Candidate Phyla Radiation (CPR) constitutes a large group of mostly uncultured bacterial lineages with small cell sizes and limited biosynthetic capabilities. They are thought to be symbionts of other organisms, but the nature of this symbiosis has been ascertained only for cultured Saccharibacteria, which are epibiotic parasites of other bacteria. Here, we study the biology and the genome of Vampirococcus lugosii, which becomes the first described species of Vampirococcus, a genus of epibiotic bacteria morphologically identified decades ago. Vampirococcus belongs to the CPR phylum Absconditabacteria. It feeds on anoxygenic photosynthetic gammaproteobacteria, fully absorbing their cytoplasmic content. The cells divide epibiotically, forming multicellular stalks whose apical cells can reach new hosts. The genome is small (1.3 Mbp) and highly reduced in biosynthetic metabolism genes, but is enriched in genes possibly related to a fibrous cell surface likely involved in interactions with the host. Gene loss has been continuous during the evolution of Absconditabacteria, and generally most CPR bacteria, but this has been compensated by gene acquisition by horizontal gene transfer and de novo evolution. Our findings support parasitism as a widespread lifestyle of CPR bacteria, which probably contribute to the control of bacterial populations in diverse ecosystems.