Brazilian Ironstone Plant Communities as Reservoirs of Culturable Bacteria With Diverse Biotechnological Potential

Abstract

Extensive mineral extractivism in the Brazilian Iron Quadrangle (IQ) region has destroyed large areas of land, decimating plant species, and their associated microbiota. Very little is known about the microbiota of the region; hence, cultivable bacteria associated with plants of its soils were investigated for their biotechnological potential. Samples were collected from nine plant species and six soils, and 65 cultivable bacterial isolates were obtained. These represent predominantly gram-positive bacilli (70%) capable of producing amylases (55%), proteases (63%), cellulases (47%), indole acetic acid (IAA) (46%), siderophores (26%), and to solubilize phosphate (9%). In addition, 65% of these were resistant to ampicillin, 100% were sensitive to tetracycline, and 97% were tolerant to high arsenic concentrations. Three isolates were studied further: the isolate FOB3 (Rosenbergiella sp.) produced high concentrations of IAA in vitro in the absence of tryptophan – shown by the significant improvement in plant germination and growth rate where the isolate was present. For isolates C25 (Acinetobacter sp.) and FG3 (Serratia sp.), plasmids were purified and inserted into Escherichia coli cells where they modified the physiological profile of the transformed strains. The E. coli::pFG3B strain showed the highest capacity for biofilm production, as well as an increase in the replication rate, arsenic tolerance and catalase activity. Moreover, this strain increased DNA integrity in the presence of arsenic, compared to the wild-type strain. These results help to explain the importance of bacteria in maintaining plant survival in ferruginous, rocky soils, acting as plant growth promoters, and to highlight the biotechnological potential of these bacteria.IMPORTANCE The Iron Quadrangle region is responsible for ∼60% of all Brazilian iron production and, at the same time, is responsible for housing a wide diversity of landscapes, and consequently, a series of endemic plant species and dozens of rare species – all of which have been poorly studied. Studies exploring the microbiota associated with these plant species are limited and in the face of the continuous pressure of extractive action, some species along with their microbiota are being decimated. To understand the potential of this microbiota, we discovered that cultivable bacterial isolates obtained from plants in the ferruginous rocky soil of the Iron Quadrangle region have diverse biotechnological potential, revealing a genetic ancestry still unknown.

Serratia liquefaciens FG3 isolated from a metallophyte plant sheds light on the evolution and mechanisms of adaptive traits in extreme environments

“…Considering this potential for generation of GSH, it was possible to verify that SlFG3 also has a broad repertoire of genes related to oxidative metabolism. Our experimental assays showed that S1FG3 was able to multiply even under oxidizing stress conditions This may be associated with the previously described DNA modification events, but also with a high capacity to detoxify this compound, as observed previously 10 .…”

“…We also found a copy of arsR (transcriptional regulator), arsB (efflux pump), and two copies of arsC (arsenate reductase) related to arsenic resistance, which validate the results previously described by Caneschi, et al . 10 that experimentally shown that SlFG3 is able to high concentrations of this metalloid.…”

“…Some of these corroborate the results empirically shown by Caneschi, et al . 10 in preliminary work regarding the ability of SlFG3 to tolerate high concentrations of arsenic in culture medium. However, it was in terms of iron metabolism that SlFG3 stands out.…”

“…Recently, we investigated 9 the biotechnological potential of a bacterial strain provisionally identified as S. liquefaciens , isolated from a plant flower ( Stachytarpheta glabra Cham. ), in the ferruginous rupestrian fields of the Iron Quadrangle (IQ) region of Minas Gerais State, in Brazil 10 , at an altitude of 1,400 m. The IQ displays extreme environmental conditions for microbial communities, including a harsh soil rich in metals, especially iron, manganese, and arsenic, poor in nitrogen, phosphate, and organic matter, and suffering high UV ray incidence, with temperatures ranging from 70 °C during the day to 4 °C at night 11 . Despite these adverse conditions, the surviving plants are highly adapted, presenting a high degree of endemism 11 and biodiversity 12 , characterizing the region as an important conservation hotspot 13 .…”

“…The S. liquefaciens strain, which we named S. liquefaciens SlFG3, was shown to possess some remarkable characteristics, such as the capability of producing siderophores, exhibiting resistance to ampicillin and arsenic, and presenting high bacterial turnover rates. Molecular analysis allowed the identification of two plasmids associated with this bacterium, pFG3A and pFG3B, the latter responsible for conferring resistance to ampicillin, reducing the production of reactive oxygen species, elevating catalase activity, reducing DNA degradation and increasing bacterial turnover in transformed E. coli 10 .…”