Evidence for Ecological Flexibility in the Cosmopolitan Genus Curtobacterium

Abstract

Assigning ecological roles to bacterial taxa remains imperative to understanding how microbial communities will respond to changing environmental conditions. Here we analyze the genus Curtobacterium, as it was found to be the most abundant taxon in a leaf litter community in southern California. Traditional characterization of this taxon predominantly associates it as the causal pathogen in the agricultural crops of dry beans. Therefore, we sought to investigate whether the abundance of this genus was because of its role as a plant pathogen or another ecological role. By collating >24,000 16S rRNA sequences with 120 genomes across the Microbacteriaceae family, we show that Curtobacterium has a global distribution with a predominant presence in soil ecosystems. Moreover, this genus harbors a high diversity of genomic potential for the degradation of carbohydrates, specifically with regards to structural polysaccharides. We conclude that Curtobacterium may be responsible for the degradation of organic matter within litter communities.

Emergence of soil bacterial ecotypes along a climate gradient

“…Whether an isolate is representative of its broader taxon will depend on the particular trait of interest (McLaren and Callahan, 2018), as different traits vary in the degree to which they are phylogenetically conserved (Martiny et al, 2013). Many traits are conserved across all Curtobacterium diversity including those contributing to its dominance as a leaf litter bacterium (Chase et al, 2016). For instance, all strains in this study shared the ability to degrade polymeric carbohydrates common in leaf litter, cellulose and xylan, and, relative to other genera in the Microbacteriaceae family, Curtobacterium has a high genomic potential for carbohydrate degradation (as assessed by the total number of GH-CBM genes; Chase et al, 2016).…”

“…Many traits are conserved across all Curtobacterium diversity including those contributing to its dominance as a leaf litter bacterium (Chase et al, 2016). For instance, all strains in this study shared the ability to degrade polymeric carbohydrates common in leaf litter, cellulose and xylan, and, relative to other genera in the Microbacteriaceae family, Curtobacterium has a high genomic potential for carbohydrate degradation (as assessed by the total number of GH-CBM genes; Chase et al, 2016). Additionally, the taxon generally appears to prefer relatively dry surface soil conditions (Lennon et al, 2012) as the relative abundance of Curtobacterium as a whole tends to increase in drier seasons (Chase et al, 2017).…”

“…GH and CBM genes and their targeted substrate were identified according to the Pfam identifiers as stated in Chase et al . (). Total GH and CBM gene composition profiles for each genome were normalized and used to construct a Euclidean distance matrix for producing an ordination plot.…”

“…We ground the litter in a sterile coffee grinder and vortexed 0.2 g of homogenized litter in 5 ml of 0.9% saline (NaCl) solution for 5 min. Samples were serially diluted and plated on grassland leaf litter leachate media (Chase et al, 2016). Colonies were visually screened for phenotypic characteristics ascribed to Curtobacterium (Evtushenko and Takeuchi, 2006), streaked on Luria Broth (LB) media agar plates, transferred three times and stored in glycerol solution at −80 C. We identified each cultured isolate by PCR amplification and Sanger sequencing of a 1500 bp region of the 16S rRNA region.…”

“…Here, we sought to determine whether soil bacterialike marine bacteriaform distinct ecotypes that are differentially distributed. To test this idea, we focused on the widespread soil taxon Curtobacterium (Chase et al, 2016). In a southern California grassland, Curtobacterium is highly abundant in leaf litter, the top layer of soil, suggesting a potential functional role in plant decomposition, and therefore, the carbon cycle (Matulich et al, 2015).…”