Xanthobacteraceae

The family Xanthobacteraceae is quite diverse. Some cells are polymorphic. It contains a Gram-negative type cell wall and major respiratory quinone is consist of ubiquinone Q-10. Cells contain refractile (phosphate) and lipid bodies and it is evenly distributed in the cells. As cells contain polyphosphate granules, sometimes Gram reaction gives false positive results. Most chemolithoautotrophic strains need H_2, O₂ and CO₂ in mineral media.[4] Chemoorganoheterotrophic strains use methanol, ethanol, n-propanol, n-butanol, and different organic acid as carbon source. Some genera show the ability to fix N₂ under decreased O₂ pressure.[4]

On average the chromosomes are 4.77–5.37 Mbp in length. In Azorhizobium caulinodans, Starkeya novella, and X. autotrophicus, there are 4417–4847 predicted genes presents in the genome. A 316-kb plasmid containing 308 genes present in X. autotrophicus Py2 strains.[5]

Members of the genus can be found in freshwater, wet soil that contains decaying organic materials and in the sediments.[3]^: 1–25 Rice paddies, soils environments, freshwater habitats such as ponds, creeks and lakes contain Ancylobacter aquaticus. Study showed that there is a relationship between the watershed urbanization and the alteration of bacterial community composition. Xanthobacteraceae consistently showed decreased abundance on increasing watershed urbanization.[6]

There are three known phages that can infect Xanthobacter autotrophicus strain GZ29.[7] There are two lytic phages named CA1 and CA2. Both have head of 61-68 nm in diameter. CA1 has a 98-100 nm tails while the length of tail for CA2 is 166-175 nm. The third phage called CA3 is lysogenic in nature and contain head of 37-43 nm and a tail of 43-50 nm in length. CA3 also contains a small DNA molecule of 3.3 kDa.[4]

Most of the strains can grow chemolithoautotrophically in the mineral media in the presence of H_2, O₂ and CO₂. Other strains can grow chemoorganoheterotrophically on methanol, ethanol, propanol, n-butanol and organic acids. Temperature for optimal growth varies from 25–42 °C.[4] Generally, they can grow at pH 6.5-8 with optimum growth at pH 7.5. Some strains decrease the pH of the medium during growth. Therefore, addition of buffer is recommended to maintain the optimal growth.[3] Cultures can be maintained for 10 months at 2-5 °C in liquid medium and for up to 15 months in sealed agar slants. At -20 °C, the culture can be stored for 3 years in the presence of 60% (v/v) glycerol. Lyophilization is recommended for long term storage.[4][3]

There is no known pathogenic strain found in the Xanthobacteraceae.  Some species of genus Azorhizobium are associated with plant such as Sesbania and some other leguminous plants that live in symbiosis.[4] Some species of Xanthobacteraceae are sensitive to penicillin, novobiocin and polymyxin B. X. autotrophicus and X. flavus  are resistant to erythromycin and bacitracin.[3]

Xanthobacteraceae species such as X. viscosus and X. aminoxidans are found in the activated sludge of water treatment plant indicating that they may play an important role in the degradation of organic compound in the pollutant environment.[4] Recent study reveals that Xanthobacter species have some interesting biotechnological applications. Industrial activity releases some toxic compound such as polycyclic aromatic compounds (PAHs). Some bacteria in this family can degrade the toxic compound into CO₂ and water. Toxic aromatic hydrocarbon such as naphthalene can be used as the sole carbon source for newly isolated Xanthobacteraceae strain Starkeya sp. strain N1B for bacterial cellulose production.[6] This bacterial produce cellulosic biofilm using toxic compound such as naphthalene Christal. Therefore, proper knowledge about the family Xanthobacteraceae might be very useful in microbial biotechnological and environmental science.

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN).[1] The phylogeny is based on whole-genome analysis.[8]