sulfonate desulfurization, sulfate esters, mycorrhizal fungi, plant–microbe interactions, asf gene cluster, sulfatases, mycorrhizosphere
Plant growth is highly dependent on bacteria, saprophytic, and
mycorrhizal fungi which facilitate the cycling and mobilization of
nutrients. Over 95% of the sulfur (S) in soil is present in an organic
form. Sulfate-esters and sulfonates, the major forms of organo-S in
soils, arise through deposition of biological material and are
transformed through subsequent humification. Fungi and bacteria release S
from sulfate-esters using sulfatases, however, release of S from
sulfonates is catalyzed by a bacterial multi-component mono-oxygenase
system. The asfA gene is used as a key marker in this desulfonation process to study sulfonatase activity in soil bacteria identified as Variovorax, Polaromonas, Acidovorax, and Rhodococcus.
The rhizosphere is regarded as a hot spot for microbial activity and
recent studies indicate that this is also the case for the
mycorrhizosphere where bacteria may attach to the fungal hyphae capable
of mobilizing organo-S. While current evidence is not showing sulfatase
and sulfonatase activity in arbuscular mycorrhiza, their effect on the
expression of plant host sulfate transporters is documented. A revision
of the role of bacteria, fungi and the interactions between soil
bacteria and mycorrhiza in plant S supply was conducted.