User:TaylorLHildenbrand/sandbox

Primary: Taylor Hildenbrand

Collaborators: AJ Beach and Stephanie Stamp

Bio 409

27 November 2017

= Mollicutes-related/ mycoplasma related endobacteria (MRE) =

Introduction
Mollicutes-related endobacteria or mycoplasma-related endobacteria (MRE) and canditatus Glomeribacter gigasporarum    , are obligate to fungi endobacteria found in cytoplasm of all major lineages of arbuscular mycorrhizal fungi (AMF), Glomeromycota       and Endogone, Mucoromycotina. Canditatus Glomeribacter gigasporarum are gram negative rod shape bacteria, MRE are coccoid in shape taxa yet to be fully understood. This association can be traced back using phylogenetic evidence to over 400 million years ago. Their true function is unknown, many researchers have recently concluded that the bacterial genomes resemble those of antagonists to the AMF host. In continually growing human populations, the knowledge of this relationship may contribute to better utilizing sustainable agriculture. It is possible to aid in plant growth and survival to better produce for large populations via the symbionts it interacts with, instead of polluting our soils with costly fertilizers.

Ancient Relationship
In early research, MRE are referred to as Mollicutes-related endobacteria due to evidence of relatedness to Mollicutes. Their family is now referred to as Mycoplasmataceae members of which have a homogeneous cell wall and contain minimal genomes with probable metabolic dependence on the host. These endobacteria are not host specific, every major lineage of AMF is known to carry this symbiont from generation from generation likely since the Paleozoic. The occurrence of bacteria inside the cytoplasm of fungi that are inside the cell of a plant is quite remarkable. As technology advanced and allowed us to examine microscopic relationships at the cellular level, our discoveries of in depth intertwined relationships of species continues to become more complicated.

Simple Genomes
Their unique genomes code for proteins involved with protein-protein interactions with the eukaryotic host as well as small ubiquitin-like modifier (SUMO) genes horizontally transmitted from fungal hosts. They are most commonly vertically transmitted, from one host to another. Despite this, MRE have high intra-species variability. This was seen when comparing 16s ribosomal sequences. Not only is there genetic variability as a whole, but even within a single individual fungal host. The endobacteria is found to be an ultra-fast evolving microbe, which is contributed to by living in the cytoplasm. This environment is different from that of their free-living relatives, resulting in different evolutionary pressures.

One dilemma these endobacteria are expected to face is Muller’s ratchet. MRE have been able to persevere for so long by maintaining particular genetic tools for genetic plasticity and frequent recombination to avoid ultimate demise as a small vertically transmitted population. One class of genetic variation worth maintaining are simple sequence repeats (SSRs) or Microsatellite that contribute to high intra-species variability. In order to keep genetic plasticity and aid chromosome structure, MRE genomes have a high number of XerC/D genes and high AT richness. XerC/D genes allow for inversions and the insertion or excision of gene cassettes. MRE have many tools in their genetic tool belt, which include several DNA recombination systems and mobile genetic elements (MGE). Even if their genomes are quite minimal when it comes to metabolic pathways, there are important pressures for MRE to maintain a high degree of genetic variability in order to survive.

Endobacteria as antagonist?
After analyzing what is retained in their plastic and dynamic genome, it is likely that the endobacteria are antagonists of their host. MRE genetic variance would be important if a host began to choose against a genotype, and ever-changing phenotype would keep the host behind the loop of excluding the endobacteria.

Conclusion
While maintaining the bare minimum for cell maintenance retaining genes for recombination and plasticity are an apparent factor in the pressures on the endobacteria. The genome of MRE have lost a great deal over time, but they are also so successful by constantly changing and keeping genetic diversity abundant despite being a vertically transmitted endobacteria.