Azospirillum Genomes Reveal Transition of Bacteria from Aquatic to Terrestrial Environments

Abstract

Fossil records indicate that life appeared in marine environments ∼3.5 billion years ago (Gyr) and transitioned to terrestrial ecosystems nearly 2.5 Gyr. Sequence analysis suggests that “hydrobacteria” and “terrabacteria” might have diverged as early as 3 Gyr. Bacteria of the genus Azospirillum are associated with roots of terrestrial plants; however, virtually all their close relatives are aquatic. We obtained genome sequences of two Azospirillum species and analyzed their gene origins. While most Azospirillum house-keeping genes have orthologs in its close aquatic relatives, this lineage has obtained nearly half of its genome from terrestrial organisms. The majority of genes encoding functions critical for association with plants are among horizontally transferred genes. Our results show that transition of some aquatic bacteria to terrestrial habitats occurred much later than the suggested initial divergence of hydro- and terrabacterial clades. The birth of the genus Azospirillum approximately coincided with the emergence of vascular plants on land.

Potential of Bacterial Endophytes as Plant Growth Promoting Factors

“…[12] demonstrated that plant entry by the endophytic bacterium Enterobacter asburiae JM22 was assisted by ability of the bacterium to hydrolyze plant cell wall-bound cellulose. On the other hand, the bacterial species Herbaspirillum seropedicae, which lacks genes for degrading plant cell walls, is also a successful endophyte, confirming the existence of other strategies to penetrate plant tissues [42,43]. It not currently known whether there is any specific form of communication (other than chemotaxis) between endophytic bacteria and plants that is involved in the colonization of the internal tissues of plants, comparable to the mechanisms used by various Rhizobia spp.…”

Draft genome of Elstera litoralis, a freshwater epilithic biofilm associated bacterium from littoral zone of Lake Constance

“…The absence of any photosynthetic apparatus and genes of Calvin cycle was consistent with that of Azospirillum species in contrary to most of the other Rhodospirillaceae members (Wisniewski Dye et al, 2011;Baldani et al, 2014). As E. litoralis dwells in stone biofilms, prima ry production may not be necessary function, as these biofilms are mainly dominated by diatoms and algae that may provide organic car bon for heterotrophic community members.…”

“…it was sug gested that it might have diverged much later than the suggested Pre cambrian split of 'hydrobacteria' to 'terrabacteria'. Also, the separation of Azospirillum from their close aquatic relatives coincided with the emergence of vascular plants on land (Wisniewski Dye et al, 2011). Bacteria associated with stone biofilms such as E. litoralis, can also be also explored as a possible link for the transition from aquatic to terres trial habitats, as they are present physically on the borderline connecting land and water.…”

Analysis of Protease Effect on Biofilm Structure of Azospirillum Brasilense Strain Sp245 and Its Flagellation-Defective mmsB1 and fabG1 Mutants

“…Так, напри-мер, инактивация у бактерии A. brasilense Sp245 плазмидных генов, кодирующих гипотетические TAD пили, приводит к подавлению образования биопленок [9]. Сохранение полярного жгутика (Fla) на клетках A. brasilense Sp245, интегриро-ванных в зрелую биопленку, способствует под-держанию ее целостности и повышает ее устой-чивость в условиях гидродинамического сдвига [10].…”