No Endospore Formation Confirmed in Members of the Phylum Proteobacteria

Abstract

Endospore formation is used by members of the phylum Firmicutes to withstand extreme environmental conditions. Several recent studies have proposed endospore formation in species outside of Firmicutes, particularly in Rhodobacter johrii and Serratia marcescens, members of the phylum Proteobacteria. Here, we aimed to investigate endospore formation in these two species by using advanced imaging and analytical approaches. Examination of the phase-bright structures observed in R. johrii and S. marcescens using cryo-electron tomography failed to identify endospores or stages of endospore formation. We determined that the phase-bright objects in R. johrii cells were triacylglycerol storage granules and those in S. marcescens were aggregates of cellular debris. In addition, R. johrii and S. marcescens containing phase-bright objects do not possess phenotypic and genetic features of endospores, including enhanced resistance to heat, presence of dipicolinic acid, or the presence of many of the genes associated with endospore formation. Our results support the hypothesis that endospore formation is restricted to the phylum Firmicutes.Importance: Bacterial endospore formation is an important process that allows the formation of dormant life forms called spores. As such, organisms able to sporulate can survive harsh environmental conditions for hundreds of years. Here, we follow up on previous claims that two members of Proteobacteria, Serratia marcescens and Rhodobacter johrii, are able to form spores. We conclude that those claims were incorrect and show that the putative spores in R. johrii and S. marcescens are storage granules and cellular debris, respectively. This study concludes that endospore formation is still unique to the phylum Firmicutes.

Characterization of the Bacterial Microbiome in Natural Populations of Barley Stem Gall Midge, Mayetiola hordei, in Morocco

“…They mainly rely on fermentation because they cannot grow in the presence of oxygen. Some members of Negativicutes are known by their ability to ferment lactate, as in the case of Veillonella , the genus that was present in our results, while other Gram-negative members can produce endospores [ 102 , 103 ]. At the genus level, Pseudomonas exhibited the highest relative abundances in Abda, Doukkala, and Rabat; this bacterial genus is known from a wide range of habitats and hosts and exhibits remarkable metabolic diversity [ 104 , 105 ].…”

Brassica seed meal fumigation restores beneficial bacterial communities by enriching taxa with high resistance and resilience

“…The superior resistance of Firmicutes to fumigation may be attributed to its special physiological characteristics. Firmicutes resist adverse environmental conditions including heat, radiation, and chemicals by employing the survival strategy of forming endospores (Beskrovnaya et al 2021;Filippidou et al 2016; Mandic-Mulec and Prosser 2011), which are considered the most resistant cellular structures (Abecasis et al 2013). In addition, Firmicutes use other strategies such as exogenous DNA uptake, chemotaxis, motility, bio lm formation, and functional diversi cation to adapt to extreme environmental conditions (Mandic-Mulec and Prosser 2011).…”

Extensive inheritance of gut microbial communities in a superorganismal termite

“…(B) The microbiome vertically transmitted to offspring colonies shares a strong taxonomic signal across pedigrees that implies consistency in inheritance at the population level. However, in contrast to the ASV-level, the identity of bacterial genera Systematic Bacteriology, 2010;Beskrovnaya et al, 2021;Jumas-Bilak & Marchandin, 2014). In line with this assertion, Firmicutes were predicted not to be inherited, potentially because aerobic respiration and endospore formation allow environmental acquisition (Bergey's Manual of Systematic Bacteriology, 2012).…”