Ecology

Disease caused by the bacterial pathogen “Candidatus Liberibacter solanacearum” (Lso) represents a serious threat to solanaceous crop production. Insecticide applications to control the psyllid vector, Bactericera cockerelli Šulc (Hemiptera: Triozidae) has led to the emergence of resistance in psyllids populations. Efforts to select natural resistant cultivars have been marginally successful and have been complicated by the presence of distinct Lso haplotypes (LsoA, LsoB) differing in symptoms severity on potato and tomato. A potentially promising management tool is to boost host resistance to the pathogen and/or the insect vector by promoting mycorrhization. Here we tested the hypothesis that mycorrhizal fungi can mitigate the effect of Lso infection on tomato plants. The presence of mycorrhizal fungi substantially delayed and reduced the incidence of Lso-induced symptoms on tomato as compared to non-mycorrhized plants. However, PCR with specific Lso primers revealed that mycorrhization did not prevent Lso transmission or translocation to newly formed leaves. Mycorrhization significantly reduced oviposition by psyllids harboring LsoA and survival of nymphs from these eggs. However, mycorrhization had no effect on oviposition by psyllids harboring LsoB or the survival of nymphs from parents harboring LsoB. These findings indicate the use of mycorrhizal fungi is a promising strategy for the mitigation of disease caused by both LsoA and LsoB and warrants additional field testing.

Liberibacter crescens is a bacterium that is closely related to plant pathogens that have caused billions of dollars in crop losses in recent years. Particularly devastating are citrus losses due to citrus greening disease, also known as Huanglongbing, which is caused by “ Candidatus Liberibacter asiaticus” and carried by the Asian citrus psyllid. L. crescens is the only close relative of “ Ca . Liberibacter asiaticus” that can currently be grown in culture, and it therefore serves as an important model organism for the growth, genetic manipulation, and biological control of the pathogenic species. Here, we show that one of the greatest limitations to L. crescens growth is the sharp increase in alkaline conditions it produces as a consequence of consumption of its preferred nutrient source. In addition to new information about L. crescens growth and metabolism, we provide new guidelines for culture conditions that improve the survival and yield of L. crescens .

For Thaumarchaeota , the ratio of their glycerol dialkyl glycerol tetraether (GDGT) lipids depends on growth temperature, a premise that forms the basis of the widely applied TEX 86 paleotemperature proxy. A thorough understanding of which GDGTs are produced by which Thaumarchaeota and what the effect of temperature is on their GDGT composition is essential for constraining the TEX 86 proxy. “ Ca . Nitrosotenuis uzonensis” is a moderately thermophilic thaumarchaeote enriched from a thermal spring, setting it apart in its environmental niche from the other marine mesophilic members of its order. Indeed, we found that the GDGT composition of “ Ca . Nitrosotenuis uzonensis” cultures was distinct from those of other members of its order and was more similar to those of other thermophilic, terrestrial Thaumarchaeota . This suggests that while phylogeny has a strong influence on GDGT distribution, the environmental niche that a thaumarchaeote inhabits also shapes its GDGT composition.

Abstract Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), transmits Candidatus Liberibacter asiaticus (Las), the bacterial pathogen putatively responsible for citrus huanglongbing. Multiple studies have shown psyllids acquire Las more frequently, and are more likely to inoculate susceptible plants, when they acquire Las as nymphs. Understanding the transmission of Las to nymphs is critical to the Las lifecycle. The objective of this study was to determine the transmission Las by female D. citri to their offspring. Two transmission pathways were quantified: horizontal transmission (acquisition of Las via feeding at the oviposition site) and vertical transmission (transovarial). Eggs of individual, infected females were transferred to an uninfected seedling to assess vertical transmission. In a second experiment, horizontal transmission was evaluated by replacing eggs laid by infected females with uninfected nymphs. Nymphs exposed to Las via horizontal transmission of the oviposition site were more likely to acquire Las than from vertical transmission. Las deposited in flush by an infected adult female feeding during oviposition was sufficient for infecting nymphs. Combined results of both experiments suggest that vertical transmission allows Las to spread in low amounts even when infected plant hosts are not available and that inoculation of the oviposition site provides a source of Las to developing nymphs via the plant phloem. These data support the hypothesis that transmission through infected plant material via maternal inoculation is a primary pathway of Las transmission between vector and host.

As one group of the most important functional phosphorus removal organisms, “ Candidatus Accumulibacter,” affiliated with the Rhodocyclus group of the Betaproteobacteria , is a widely recognized and studied PAO in the field of biological wastewater treatment. The morphotypes and population structure of clade-level “ Candidatus Accumulibacter” were studied through novel FISH-staining-flow cytometry, which involved denitrifying phosphorus removal (DPR) achieving carbon and energy savings and simultaneous removal of N and P, thus inferring the different denitrifying phosphorus removal abilities of these clades. Additionally, based on this method, in situ quantification for specific polyphosphate-accumulating organisms (PAOs) enables a more efficient process and more accurate result. The establishment of FISH-staining-flow cytometry makes cell sorting of clade-level noncultivated organisms available.

“ Ca. Nitrotoga” is a NOB of high environmental relevance, but physiological data exist for only a few representatives. Initially, it was detected in specialized niches of low temperature and low nitrite concentrations, but later on, its ubiquitous distribution revealed its critical role for N removal in engineered systems like WWTPs. In this study, we analyzed the competition between Nitrotoga and Nitrospira in bioreactors and identified conditions where the K strategist Ns. defluvii was almost replaced by Nitrotoga sp. BS. We show that the pH value is an important factor that regulates the composition of the nitrite-oxidizing enrichment with a dominance of Nitrotoga sp. BS versus Ns. defluvii at a neutral pH of 7.4 in combination with a temperature of 17°C. The physiological diversity of novel Nitrotoga cultures improves our knowledge about niche differentiation of NOB with regard to functional nitrification under suboptimal conditions.