Leptothrix ochracea
Species of bacterium
From Wikipedia, the free encyclopedia
Leptothrix ochracea is a neutrophilic aerobic rod-shaped, Gram-negative bacterium that can oxidize iron. This bacterium is commonly found in iron-rich freshwater streams, wetlands, ponds, and the rhizosphere.[2] L. ochracea are typically identified by the thick orange fluffy mats they form out of iron biominerals including ferrihydrite, goethite, and lepidocrocite.[3] It frequently coexists with another iron oxidizing bacteria Gallionella ferruginea, with G. ferruginea dominating iron mats in the spring and L. ochracea making up the majority of iron mats during the rest of the year.[4]
| Leptothrix ochracea | |
|---|---|
Scientific classification  | |
| Domain: | Bacteria |
| Kingdom: | Pseudomonadati |
| Phylum: | Pseudomonadota |
| Class: | Betaproteobacteria |
| Order: | Burkholderiales |
| Genus: | Leptothrix |
| Species: | L. ochracea |
| Binomial name | |
| Leptothrix ochracea Kützing 1843, species.[1] | |
Morphology and sheath function
L. ochracea is a Gram-negative, rod-shaped bacterium that occurs in cell chains in sheaths, among many empty sheaths. The sheaths, believed to prevent iron accumulation in the cells, are made of iron oxyhydroxide minerals. The sheaths are typically thin and 1-2 microns wide with a rough surface.[5] The mineral structures may protect the bacteria from predation and act as a holdfast or anchor point allowing the bacteria to attach to a surface. Another consideration is that the excretion of the minerals may allow the bacteria to break up complex organic compounds as a food source.[6]
Phylogeny and Genome Statistics
The bacterium is not in isolation. Sequence size of the metagenome-assembled genomes ranged from 2.59 to 3.04 Mb. The GC content was found to be about 60%. In the SILVA database, L. ochracea was misidentified as the genus Paucibacter based on 16S rRNA sequencing.[2] It is closely related to other Leptothrix sp. including L. cholodnii with 96% homology, as well as the genus Sphaerotilus, based on single cell genomics.[5]
Metabolism and genomic potential
The possession of canonical iron oxidase genes including cyc2 and mtoA support the idea that it is an iron oxidizer, and Fe(II) is necessary for its energy and growth.[2] The possession of two iron oxidases could enable it to use different phases of iron; in Gallionellaceae Sideroxydans lithotrophicus ES-1, mtoA is upregulated in the presence of solid Fe(II) in the form of smectite clay.[7] L. ochracea possesses a multicopper oxidase (MCO) called mofA. While MCOs help other bacteria oxidize iron or manganese, it is unknown how mofA is utilized by L. ochracea. Oxygen respiration genes mean it is an aerobe. It uses atmospheric oxygen for the oxidation of Fe(II) to Fe(III). The presence of RuBisCO indicates the ability to fix carbon but it also possesses genes involved with organic carbon utilization. Sox genes indicate the potential for sulfur oxidation. It also possesses genes for nitrate reduction and ammonia and urea assimilation. Since its genome suggests it can utilize organic and inorganic electron donors and carbon sources, L. ochracea is likely a mixotrophic iron oxidizer.[2]
Significance
These mats support many other species by providing habitat in its physical structure, allowing nutrient cycling, making L. ochracea a keystone species in its environment. The sheaths have the ability to sorb metals, meaning they may be useful in contaminant removal systems.[6] Additionally, biominerals are studied in order to create synthetic materials.[8]
