Publications

4855

Abstract At the dawn of modern microbiology, Cohn observed abundant filamentous bacteria in drinking water wells that he named Crenothrix polyspora . Subsequent research has revealed the methanotrophic metabolism of Crenothrix bacteria and their disproportionately high activity in stratified lakes compared to unicellular strains, yet laboratory cultivation has proven elusive, leaving the ecophysiology of Crenothrix bacteria largely unknown. Here we report the isolation of two methanotroph strains of the “lacustrine Crenothrix” clade from an iron-rich wetland and reveal their highly unique cell biologies and potential ecological roles. Using physiological approaches, we demonstrate that the strains perform a microaerobic methane metabolism while growing distinct filaments having wide and directionally oriented connective structures. The strains further have broad genomic repertoires for addressing redox stress that we show are uniquely associated with lacustrine Crenothrix compared to related methanotrophs based on genome data. Aligning with laboratory observations, we identify lacustrine Crenothrix bacteria along potential redox gradients in the wetland at iron-rich snow sites, and we further detect such bacteria in diverse global ecosystems based on public metagenome searches. Together, our data strongly point to an ecophysiology of lacustrine Crenothrix bacteria that is tightly linked to redox stress, and we propose these bacteria may uniquely store or share metabolic intermediates via their filamentous lifestyle to thrive under such conditions. Our results provide a fresh view of the diversity, evolution, and ecology of aerobic methanotrophs, connecting over 150 years of microbiology research opening vast new opportunities to probe bacterial adaptations that drive global methane cycling under redox stress.

Pear decline (PD), associated with ‘Candidatus Phytoplasma pyri’, is a major disease of pear in Europe and the United States. Several psyllid species are involved in the tritrophic system of PD as vectors of phytoplasmas belonging to the 16SrX group. Four years after the first detection of PD in Sicily, an integrated approach was applied to investigate the epidemic in a major pear-growing area. Visual surveys and molecular analyses were conducted over two years in eight orchards. A total of 115 plant samples and 101 Cacopsylla spp. specimens selected from a total of 1,435 collected individuals were analysed, confirming ‘Ca. P. pyri’ in 69% of symptomatic plants and in 4.6% of C. pyri individuals. Multilocus sequence typing (MLST) revealed high genetic similarity among 16SrX isolates. Remote sensing analyses since 2018, combined with vector monitoring, confirmed the epidemic nature of PD and the persistence of a risk of further pathogen spread within the region, proving, inter alia, to be a valid method for identifying the syndrome even on a large scale.

ABSTRACT Citrus Huanglongbing (HLB), a devastating disease caused by the unculturable bacterium ‘ Candidatus Liberibacter asiaticus’ ( C Las), poses a severe threat to global citrus production. C Las secretes effectors to suppress host immune responses and facilitate its colonisation. Previously, the C Las effector SECP8 (CLIBASIA_05330) has been identified as an immune inhibitor. However, its molecular mechanisms on host immune suppression remain unclear. This study identifies the citrus transcription factor CsTCP15 as a target of SECP8. Transgenic citrus plants overexpressing CsTCP15 enhanced resistance to C Las, whereas CsTCP15 ‐RNAi interference plants became more susceptible, confirming its role as a positive immune regulator. Meanwhile, CsTCP15 was demonstrated to directly bind to cis ‐elements of salicylic acid (SA)‐responsive genes CsPR5 and CsWRKY22 , and overexpression of either gene strengthened citrus hairy roots' resistance against C Las. However, SECP8 directly interacts with CsTCP15 and inhibits its homodimerization. Concurrently, mSECP8 facilitates CsBRG3‐mediated degradation and further prevents the dimerization of CsTCP15. This two‐pronged interference eventually impairs the transcriptional activation of CsPR5 and CsWRKY22 , thereby compromising salicylic acid‐mediated immunity and promoting C Las infection. Our findings reveal a virulence strategy whereby a C Las effector manipulates a key host immune regulator to establish pathogenesis.

Abstract Model bacteria are fundamental for research, but knowledge about their ecology and evolution is often limited. Here, we establish an evolutionary and ecological context for the model organism Caulobacter crescentus —an alphaproteobacterium intensively studied for its dimorphic lifecycle. By analyzing the phylogenetic relatedness and genetic potential of hundreds of Caulobacterales species, we reveal substantial diversity regarding their environmental distribution, morphology, cell development, and metabolism. Our work provides insights into the evolutionary history of morphological features such as the cell curvature determinant crescentin and uncovers a striking case of convergent loss of traits for cellular dimorphism among close relatives of C. crescentus . Moreover, we find that genes for phototrophy are widespread across Caulobacterales and that the new genus Acaudatibacter , described here, includes the first reported Caulobacterales lineage with photoautotrophic potential. Our study advances our understanding of an environmentally widespread bacterial order and sheds light on the evolution of fundamental prokaryotic features.

ABSTRACT Candidatus Loosdrechtia sp. KJ is an anaerobic ammonium-oxidizing bacterium enriched from a bioreactor operated under alkaline conditions (pH 9.2 ± 0.4). We report its 3.39 Mb draft genome, containing 3,065 predicted coding sequences, 47 tRNA genes, and a single rrn operon.

From 2016, witches’ broom and stunting symptoms were observed in Lolium rigidum grown in some fruit tree nurseries in Faragheh (Abarkouh, Yazd province, Iran). Total DNAs were extracted from symptomatic and asymptomatic plants and assessed for phytoplasma presence using direct and nested PCR to detect the 16S ribosomal RNA gene. From all symptomatic L. rigidum plant samples, expected length PCR amplicons were obtained. RFLP analysis with informative restriction enzymes showed identical profiles in all the samples resulted positive, that were also consistent with those of one of the subgroups of the aster yellows phytoplasmas (16SrI). The 16S rRNA gene sequence of Faragheh L. rigidum bushy stunt strain was 100% identical to some ‘Candidatus Phytoplasma asteris’ related strains, and 99.12% similar to the reference ‘Ca. P. asteris’ strain. The virtual RFLP pattern was identical (similarity coefficient 1.00) to the pattern of phytoplasmas in subgroup 16SrI-F. This is the first report of occurrence and molecular identification of this phytoplasma strain in L. rigidum and indicates a potential phytoplasma reservoir for trees in fruit tree nurseries where insect vectors may be present. This phytoplasma strain has been reported in symptomatic stone fruits in Spain and in potato in Ecuador. Further research on the epidemiology of witches’ broom and stunting in L. rigidum is required to develop elimination the phytoplasma from areas surrounding agricultural crops and avoid the risks of epidemics.