Bacteria, Volume 2, Issue 2 (June 2023) – 2 articles

Phosphorus (P) is one of the most important elements required for crop production. The ideal soil pH for its absorption by plants is about 6.5, but in alkaline and acidic soils, most of the consumed P forms an insoluble complex with calcium, iron, and aluminum elements and its availability for absorption by the plant decreases. The supply of P needed by plants is mainly achieved through chemical fertilizers; however, in addition to the high price of these fertilizers, in the long run, their destructive effects will affect the soil and the environment. The use of cheap and abundant resources such as rock phosphate (RP) can be an alternative strategy for P chemical fertilizers, but the solubilization of P of this source has been a challenge for agricultural researchers. For this, physical and chemical treatments have been used, but the solution that has recently attracted the attention of the researchers is to use the potential of rhizobacteria to solubilize RP and supply P to plants by this method. These microorganisms, via. mechanisms such as proton secretion, organic and mineral acid production, siderophore production, etc., lead to the solubilization of RP, and by releasing its P, they improve the quantitative and qualitative performance of agricultural products. In this review, addressing the potential of rhizosphere microbes (with a focus on rhizobacteria) as an eco-friendly strategy for RP solubilization, along with physical and chemical solutions, has been attempted. Full article

Extremophilic microorganisms such as those that thrive in high-salt and high-alkaline environments are promising candidates for the recovery of useful biomaterials including polyhydroxyalkanoates (PHAs). PHAs are ideal alternatives to synthetic plastics because they are biodegradable, biocompatible, and environmentally friendly. This work was aimed at conducting a bioprospection of bacteria isolated from hypersaline-alkaliphilic lakes in Kenya for the potential production of PHAs. In the present study, 218 isolates were screened by Sudan Black B and Nile Red A staining. Of these isolates, 31 were positive for PHA production and were characterized using morphological, biochemical, and molecular methods. Through 16S rRNA sequencing, we found that the isolates belonged to the genera Arthrobacter spp., Bacillus spp., Exiguobacterium spp., Halomonas spp., Paracoccus spp., and Rhodobaca spp. Preliminary experiments revealed that Bacillus sp. JSM-1684023 isolated from Lake Magadi had the highest PHA accumulation ability, with an initial biomass-to-PHA conversion rate of 19.14% on a 2% glucose substrate. Under optimized fermentation conditions, MO22 had a maximum PHA concentration of 0.516 g/L from 1.99 g/L of cell dry weight and 25.9% PHA conversion, equivalent to a PHA yield of 0.02 g/g of biomass. The optimal PHA production media had an initial pH of 9.0, temperature of 35 °C, salinity of 3%, and an incubation period of 48 h with 2.5% sucrose and 0.1% peptone as carbon and nitrogen sources, respectively. This study suggests that bacteria isolated from hypersaline and alkaliphilic tropical lakes are promising candidates for the production of polyhydroxyalkanoates. Full article