Reclamation of chromium-contaminated soil by native Cr(VI)-reducing and PHA-accumulating Bacillus aryabhattai CTSI-07.

Reclamation of chromium-contaminated soil by bacteria is a big confront concerning to soil health restoration, food safety, and environmental protection. Herein, the chromium-resistant Bacillus aryabhattai CTSI-07 (MG757377) showed resistance to 1000 and 300 ppm of Cr(VI) in nutrient rich Luria Bertani (LB) and nutrient-deficient sucrose low phosphate (SLP) medium, respectively. It reduced 96.7% of Cr(VI) from contaminated soil in the presence of 100 ppm of Mg within 96 h under optimized conditions. Furthermore, Cr(VI) reduction by the bacteria was validated by Fourier transform infrared spectroscopic (FTIR) and X-ray diffraction (XRD) analysis. Besides Cr(VI) reduction, the bacterial strain also showed plant growth promoting traits like N2 fixation and indole acetic acid (IAA) production. On the other hand, transmission electron microscopy (TEM) imaging confirmed polyhydroxyalkanoates' (PHAs) granule accumulation and 0.5 g/l of PHAs was extracted from bacterial cell using SLP medium. Infra-red (IR) spectra and proton nuclear magnetic resonance (1H NMR) chemical shift patterns established the PHAs as polyhydroxybutyrate (PHB). Melting (Tm) and thermal degradation (Td) temperature of the PHB were 169 °C and 275 °C, respectively, as evident from thermogravimetry differential thermal analysis (TG-DTA). Atomic force microscopic (AFM) imaging depicted that the PHB film surface was rough and regular. Furthermore, the multi-metal-resistant, plant growth-promoting, and PHB-producing bacteria could reduce 99.82% of Cr(VI) from contaminated soil within 120 days in pot culture. Thus, it can be used for long-term reclamation of chromium-contaminated soil to restore soil health, provide food safety, and environmental protection.

PHAs production by facultative anaerobic bacteria Bacillus cereus FM5 through submerged and solid-state fermentation under anoxic condition.

PHAs (polyhydroxyalkanoates) are the bio-polyester synthesized by different aerobic and anaerobic bacteria as energy storage granule. However, its synthesis by anaerobes or facultative anaerobes is an imperative part of their physiology via assimilating broad range of substrates than aerobes. Thus, three Gram positive facultative anaerobic PHAs producers viz., Enterococcus sp. FM3, Actinomyces sp. CM4 and Bacillus sp. FM5 were selected. Among them, Bacillus sp. FM5 showed higher cell biomass production in MSM (mineral salt medium) comprised of glucose & peptone as carbon & nitrogen source at pH 9, temperature 37 °C, inoculum 10% and incubation period 72 h. Under optimized condition, Bacillus sp. FM5 produced 0.89 and 1.5 g l-1 of PHAs through submerged and solid-state fermentation in anoxic condition. In-silico analysis confirmed the facultative anaerobic PHAs producing bacteria as Bacillus cereus FM5. IR spectra of PHAs illustrated a strong absorption peak at 1718.50 cm-1 representing carbonyl ester (C=O) functional group of PHB (polyhydroxybutyrate), belonging to the family PHAs. It is the first report demonstrating PHAs production by Bacillus cereus FM5 in anoxic condition through different bioprocess technology, which may pave the way in the arena of further biopolymer research.