The future of taxonomy

Unaddressed non-energy use in the chemical industry can undermine fossil fuels phase-out

Around 13% of fossil fuels globally are used for non-combustion purposes. Fossil fuel processing plants, such as petroleum refineries, exhibit interdependent material and energy system dynamics, making the transition away from fossil fuels in energy systems more challenging without addressing the non-energy outputs. This study explores the future role of fossil fuels for non-energy purposes in climate-stringent scenarios with restrictions on alternative feedstock availability, focusing on the primary chemicals sector. Using a global integrated assessment model with detailed refining and primary chemicals sectors, findings across various scenarios reveal that up to 62% of total feedstock use in the chemical sector could be provided by alternative sources by 2050. This would require significant scale-up in biomass utilisation and carbon capture technologies. Annual CO2 emissions from the chemical sector could be reduced to as low as -1Gt CO2 by the same year if carbon storage in non-recycled and non-incinerated bioplastics is accounted for.

A microbial identification framework for risk assessment

Micro-organisms are increasingly used in a variety of products for commercial uses, including cleaning products. Such microbial-based cleaning products (MBCP) are represented as a more environmentally-friendly alternative to chemically based cleaning products. The identity of the micro-organisms formulated into these products is often considered confidential business information and is not revealed or it is only partly revealed (i.e., identification to the genus, not to the species). That paucity of information complicates the evaluation of the risk associated with their use. The accurate taxonomic identification of those micro-organisms is important so that a suitable risk assessment of the products can be conducted. To alleviate difficulties associated with adequate identification of micro-organisms in MBCP and other products containing micro-organisms, a microbial identification framework for risk assessment (MIFRA) has been elaborated. It serves to provide guidance on a polyphasic tiered approach, combining the data obtained from the use of various methods (i.e., polyphasic approach) combined with the sequential selection of the methods (i.e., tiered) to achieve a satisfactory identity of the micro-organism to an acceptable taxonomic level. The MIFRA is suitable in various risk assessment contexts for micro-organisms used in any commercial product.

Identification of distinctive molecular traits that are characteristic of the phylum "Deinococcus-Thermus" and distinguish its main constituent groups

The phylum "Deinococcus-Thermus" contains two heavily researched groups of extremophilic bacteria: the highly radioresistant order Deinococcales and the thermophilic order Thermales. Very few characteristics are known that are uniquely shared by members of the phylum "Deinococcus-Thermus". Comprehensive phylogenetic and comparative analyses of >65 "Deinococcus-Thermus" genomes reported here have identified numerous molecular signatures in the forms of conserved signature insertions/deletions (CSIs) and conserved signature proteins (CSPs), which provide distinguishing characteristics of the phylum "Deinococcus-Thermus" and its main groups. We have identified 58 unique CSIs and 155 unique CSPs that delineate different phylogenetic groups within the phylum. Of these identified traits, 24 CSIs and 29 CSPs are characteristic of the phylum "Deinococcus-Thermus" and they provide novel and reliable means to circumscribe/describe this phylum. An additional 3 CSIs and 3 CSPs are characteristic of the order Deinococcales, and 6 CSIs and 51 CSPs are characteristic of the order Thermales. The remaining 25 CSIs and 72 CSPs identified in this study are distinctive traits of genus level groups within the phylum "Deinococcus-Thermus". The molecular characteristics identified in this work provide novel and independent support for the common ancestry of the members of the phylum "Deinococcus-Thermus" and provide a new means to distinguish the main constituent clades of the phylum. Additionally, the CSIs and CSPs identified in this work may play a role in the unique extremophilic adaptations of the members of this phylum and further functional analyses of these characteristics could provide novel biochemical insights into the unique adaptations found within the phylum "Deinococcus-Thermus".

Impact of genomics on the understanding of microbial evolution and classification: the importance of Darwin's views on classification

Analyses of genome sequences, by some approaches, suggest that the widespread occurrence of horizontal gene transfers (HGTs) in prokaryotes disguises their evolutionary relationships and have led to questioning of the Darwinian model of evolution for prokaryotes. These inferences are critically examined in the light of comparative genome analysis, characteristic synapomorphies, phylogenetic trees and Darwin's views on examining evolutionary relationships. Genome sequences are enabling discovery of numerous molecular markers (synapomorphies) such as conserved signature indels (CSIs) and conserved signature proteins (CSPs), which are distinctive characteristics of different prokaryotic taxa. Based on these molecular markers, exhibiting high degree of specificity and predictive ability, numerous prokaryotic taxa of different ranks, currently identified based on the 16S rRNA gene trees, can now be reliably demarcated in molecular terms. Within all studied groups, multiple CSIs and CSPs have been identified for successive nested clades providing reliable information regarding their hierarchical relationships and these inferences are not affected by HGTs. These results strongly support Darwin's views on evolution and classification and supplement the current phylogenetic framework based on 16S rRNA in important respects. The identified molecular markers provide important means for developing novel diagnostics, therapeutics and for functional studies providing important insights regarding prokaryotic taxa.

Genome-based taxonomic framework for the class Negativicutes: division of the class Negativicutes into the orders Selenomonadales emend., Acidaminococcales ord. nov. and Veillonellales ord. nov

The class Negativicutes is currently divided into one order and two families on the basis of 16S rRNA gene sequence phylogenies. We report here comprehensive comparative genomic analyses of the sequenced members of the class Negativicutes to demarcate its different evolutionary groups in molecular terms, independently of phylogenetic trees. Our comparative genomic analyses have identified 14 conserved signature indels (CSIs) and 48 conserved signature proteins (CSPs) that either are specific for the entire class or differentiate four main groups within the class. Two CSIs and nine CSPs are shared uniquely by all or most members of the class Negativicutes, distinguishing this class from all other sequenced members of the phylum Firmicutes. Four other CSIs and six CSPs were specific characteristics of the family Acidaminococcaceae, two CSIs and four CSPs were uniquely present in the family Veillonellaceae, six CSIs and eight CSPs were found only in Selenomonas and related genera, and 17 CSPs were identified uniquely in Sporomusa and related genera. Four additional CSPs support a pairing of the groups containing the genera Selenomonas and Sporomusa. We also report detailed phylogenetic analyses for the Negativicutes based on core protein sequences and 16S rRNA gene sequences, which strongly support the four main groups identified by CSIs and by CSPs. Based on the results from different lines of investigation, we propose a division of the class Negativicutes into an emended order Selenomonadales containing the new families Selenomonadaceae fam. nov. and Sporomusaceae fam. nov. and two new orders, Acidaminococcales ord. nov. and Veillonellales ord. nov., respectively containing the families Acidaminococcaceae and Veillonellaceae.

Community genomic analyses constrain the distribution of metabolic traits across the Chloroflexi phylum and indicate roles in sediment carbon cycling

BACKGROUND

Sediments are massive reservoirs of carbon compounds and host a large fraction of microbial life. Microorganisms within terrestrial aquifer sediments control buried organic carbon turnover, degrade organic contaminants, and impact drinking water quality. Recent 16S rRNA gene profiling indicates that members of the bacterial phylum Chloroflexi are common in sediment. Only the role of the class Dehalococcoidia, which degrade halogenated solvents, is well understood. Genomic sampling is available for only six of the approximate 30 Chloroflexi classes, so little is known about the phylogenetic distribution of reductive dehalogenation or about the broader metabolic characteristics of Chloroflexi in sediment.

RESULTS

We used metagenomics to directly evaluate the metabolic potential and diversity of Chloroflexi in aquifer sediments. We sampled genomic sequence from 86 Chloroflexi representing 15 distinct lineages, including members of eight classes previously characterized only by 16S rRNA sequences. Unlike in the Dehalococcoidia, genes for organohalide respiration are rare within the Chloroflexi genomes sampled here. Near-complete genomes were reconstructed for three Chloroflexi. One, a member of an unsequenced lineage in the Anaerolinea, is an aerobe with the potential for respiring diverse carbon compounds. The others represent two genomically unsampled classes sibling to the Dehalococcoidia, and are anaerobes likely involved in sugar and plant-derived-compound degradation to acetate. Both fix CO2 via the Wood-Ljungdahl pathway, a pathway not previously documented in Chloroflexi. The genomes each encode unique traits apparently acquired from Archaea, including mechanisms of motility and ATP synthesis.

CONCLUSIONS

Chloroflexi in the aquifer sediments are abundant and highly diverse. Genomic analyses provide new evolutionary boundaries for obligate organohalide respiration. We expand the potential roles of Chloroflexi in sediment carbon cycling beyond organohalide respiration to include respiration of sugars, fermentation, CO2 fixation, and acetogenesis with ATP formation by substrate-level phosphorylation.