Identification of Pectobacterium species isolated from the soft rot of tetecho (Neobuxbaumia tetetzo), a columnar cactus, and associated metagenomics

Neobuxbaumia tetetzo, commonly known as tetecho, is a columnar cactus endemic to Mexico. In the last 15 years, damage has been observed in young and adult plants of N. tetetzo, ranging from chlorotic spots with a wet appearance in early stages to tissue necrosis in advanced stages and finally the death of the plant; Pectobacterium brasiliense is the causal agent of the damages. Disease progression may be delayed or accelerated by the involvement of other bacteria, either pathogenic or endophytic, at the site of infection. Our goal was to confirm the presence of Pectobacterium brasiliense, in the soft rot of N. tetetzo and to determine the presence of other bacteria associated with the rot. We isolated three bacterial strains (A1, A3 and A8) from diseased tissue from three separate N. tetetzo plants, and compare them using biochemical and molecular techniques, such as whole-genome sequencing of strains A1 and A3. Phylogenetic analyzes confirmed that A1 corresponded to P. brasiliense, whereas A3 was more misimlar to P. polaris. Additionally, sequencing of 16S rRNA gene from metagenomic DNA isolated from healthy and diseased tissue of N. tetetzo indicated the presence of four operational taxonomic units (OTUs) at the order level, unique to the diseased tissue: Actinomycetales, Burkholderiales, Caulobacterales, and Sphingomonadales, with probable participation in the soft rot process.

An ultrasound absorbing inflorescence zone enhances echo-acoustic contrast of bat-pollinated cactus flowers

Flowering plants have evolved an extraordinary variety of signaling traits to attract and guide their pollinators. Most flowers rely on visual and chemical signals, but some bat-pollinated plants have evolved reflective surfaces to acoustically guide echolocating bats. All known echo-acoustic flower signals rely on the same basic acoustic principles of increased sonar reflectivity. Here we reveal a novel mechanism through which plants acoustically communicate with bats, a principle that relies on increased absorption of the area surrounding the target flower, thereby enhancing echo-acoustic contrast. In a bat-pollinated columnar cactus (Espostoa frutescens) from the Ecuadorian Andes we found a hairy inflorescence zone, a so called lateral cephalium. Flowers of this cactus solely emerge out of this hairy zone. We measured the ultrasound echoes of the hairy zones, the flowers and unspecialized column surfaces with a biomimetic sonar head and recorded echolocation calls of approaching bats. We found that the hairy inflorescence zones act as strong ultrasound absorber, attenuating the sound by −14 dB compared to other parts of the column. The absorption was highest around the echolocation call frequencies of approaching bats. Our results indicate that, instead of making flowers more reflective, plants can also evolve specific structures to attenuate the background echo, thereby enhancing the acoustic contrast with the target. Similar sound absorbing mechanisms may be found in other species that interact with bats across a wide range of ecological contexts.