Halotolerant bacterial biofilms for desalination and water treatment: a pilot study.

Salinity has a significant impact on the water quality and crop yield. Physical desalination techniques were once thought to be expensive and time-consuming. Among biological techniques, halotolerant bacteria were thought to be the fastest and most effective way to reduce the salt content in brackish saltwater water. In the current study, halotolerant bacterial biofilms were used to desalinate saline water on abiotic substrates (such as sand, pebbles, glass beads, and plastic beads), and studied subsequently for the effects on Zea mays germination. Briefly, salt samples (SLT7 and SLT8) from the Khewra site in Punjab, Pakistan, as well as seawater and sea sand samples (USW1, USW3, USW6, DSW1, DSW4, SS1, and SS3) from Karachi, Sindh, Pakistan's Arabian Sea, were collected. Halotolerant bacteria were isolated and characterized. Crystal violet ring assays and capsule staining were used to estimate extracellular polymeric substance (EPS) and biofilm development, respectively. All halotolerant bacterial strains were spore formers and produced EPS and formed biofilms well. 16S rRNA gene sequencing of the best halotolerant bacteria, USW6, showed the closest (100%) similarity to Bacillus aerius strain G-07 (a novel species) (accession number ON202984). A pilot-scale experiment for desalinating the artificial water (supplemented with 1 M NaCl) using biofilm adhered abiotic beads showed declined level of NaCl from 1 M to 0.00003 M after 15 days in treated water. Also, Zea mays germination was observed in the plants using treated water compared to no growth in the non-treated saline water. Estimations of chlorophyll, total soluble sugar, and protein revealed that plants cultivated using elute collected from a desalinated pilot scale setup contained less chlorophyll (i.e., 5.994 and 116.76). Likewise, plants grown with elute had a total soluble protein and sugar content of 1.45 mg/ml and 1.3 mg/ml, respectively. Overall, in treated water plants, a minor drop in chlorophyll content, a slight increase in total soluble sugar content, and a slight increase in protein content were noted. The study concluded that biofilm-treated desalt water has the potential to significantly reduce the effects of droughts, soil salinization, and economic and environmental issues associated with agricultural drainage. The results specified the application of halotolerant bacteria biofilms (Bacillus aerius, a novel species, USW6) for water desalination to overcome the problem of water scarcity caused by global warming and the increased salinity.

Assessment of heavy metals in different organs of cattle egrets (Bubulcus ibis) from a rural and urban environment in Pakistan.

The study was conducted to evaluate the concentration of essential elements (Cu, Fe, Mn, Ni, Se, Zn, and B) and non-essential elements (Cd, Pb, Hg, Cr, As, and Ni) in muscle, liver, bone, and intestine of matured cattle egret (Bubulcus ibis). Sampling was carried out at two sites of Lahore, Pakistan-Havalian Karbath (site I) and Mehmood Booti (site II)-over a period of 1 month in the winter season. Metal analyses of samples were carried out using inductively coupled plasma mass spectroscopy (ICPMS). The trend of essential elements in liver and intestine of site I was noticed as Fe > Zn > Cu > B > Mn > Se > Ni and almost same for bone and muscle as Fe > Zn > B > Mn > Cu > Se > Ni. It was noticed that Cu was less deposited in bone and muscle tissues compared to liver and intestine from site I. The deposition of essential elements in liver and intestine from site II was noticed as Fe > Zn > Cu > Mn > B > Se > Ni. Similar trend was found for bone and muscle: Fe > Zn > B > Mn > Cu > Se > Ni with great deposition of B than Cu compared to liver and intestine. The findings of the present study revealed almost similar trend for essential elements deposition at both sites. However, a random trend was observed for deposition of non-essential elements (Ag, As, Ba, Cd, Cr, Hg, Pb) in organs from both sites. Moreover, data showed higher levels of non-essential elements accumulation (particularly As, Ba, and Pb) in the body tissues/organs of cattle egret in an urban area (site II) as compared to rural area (site I) of Lahore. Furthermore, non-essential elements were more in intestine, bone, and muscles from site II showing more exposure to some non-essential elements at urban site due to human and natural activities. However, higher concentration of non-essential elements in liver from site I as compared to other organs not only reflect the land exposure to plant growth promoting fertilizers and sewage water for irrigation purpose but also better detoxification abilities of the rural birds. The study gave a new insight to inform contamination levels in the rural and urban sites. Future implications of this study need remediation strategies to clean environment requisite for avian species.

Bacterial exopolysaccharide and biofilm formation stimulate chickpea growth and soil aggregation under salt stress

To compensate for stress imposed by salinity, biofilm formation and exopolysaccharide production are significant strategies of salt tolerant bacteria to assist metabolism. We hypothesized that two previously isolated salt-tolerant strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) have an ability to improve plant growth, These strains can form biofilm and accumulate exopolysacharides at increasing salt stress. These results showed that bacteria might be involved in developing microbial communities under salt stress and helpful in colonizing of bacterial strains to plant roots and soil particles. Eventually, it can add to the plant growth and soil structure. We investigated the comparative effect of exopolysacharide and biofilm formation in two bacterial strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) in response to varying salt stress. We found that biofilm formation and exopolysaccharide accumulation increased at higher salinity. To check the effect of bacterial inoculation on the plant (Cicer arietinum Var. CM-98) growth and soil aggregation, pot experiment was conducted by growing seedlings under salt stress. Inoculation of both strains increased plant growth at elevated salt stress. Weight of soil aggregates attached with roots and present in soil were added at higher salt concentrations compared to untreated controls. Soil aggregation was higher at plant roots under salinity. These results suggest the feasibility of using above strains in improving plant growth and soil fertility under salinity.

Biofilm formation in moderately halophilic bacteria is influenced by varying salinity levels.

Bacteria in a biofilm have a co-dependent lifestyle resulting in a harmonized and complex coordination of the bacterial cells within an exopolysaccharide (EPS) matrix. We hypothesized that biofilm formation and EPS production in salt-tolerant bacteria are helpful for plant growth improvement in saline soil, but that they are influenced differently. To investigate this hypothesis, we tested the effect of different salinity levels on the biofilm formation of the bacterial strains PAa6 (Halomonas meridiana), HT2 (Kushneria indalinina) and ST2 (Halomonas aquamarina) on different abiotic and biotic surfaces. Maximum biofilm formation was established at 1 M salt concentration. However, EPS production was maximal at 0-1 M NaCl stress. We also studied the effect of salt stress on EPS produced by the bacterial strains and confirmed the presence of EPS on Cicer arietinum var. CM 98 roots and in soil at different salinity levels, using Alcian blue staining. Overall, the strain PAa6 was more effective in biofilm formation and EPS production. Under saline and non-saline conditions, this strain also colonized the plant roots more efficiently as compared to the other two strains. We conclude that the strain PAa6 has the potential of biofilm formation and EPS production at different salinity levels. The presence of EPS in the biofilm helped the bacterial strains to better colonize the roots.

Bacterial exopolysaccharide and biofilm formation stimulate chickpea growth and soil aggregation under salt stress.

To compensate for stress imposed by salinity, biofilm formation and exopolysaccharide production are significant strategies of salt tolerant bacteria to assist metabolism. We hypothesized that two previously isolated salt-tolerant strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) have an ability to improve plant growth, These strains can form biofilm and accumulate exopolysacharides at increasing salt stress. These results showed that bacteria might be involved in developing microbial communities under salt stress and helpful in colonizing of bacterial strains to plant roots and soil particles. Eventually, it can add to the plant growth and soil structure. We investigated the comparative effect of exopolysacharide and biofilm formation in two bacterial strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) in response to varying salt stress. We found that biofilm formation and exopolysaccharide accumulation increased at higher salinity. To check the effect of bacterial inoculation on the plant (Cicer arietinum Var. CM-98) growth and soil aggregation, pot experiment was conducted by growing seedlings under salt stress. Inoculation of both strains increased plant growth at elevated salt stress. Weight of soil aggregates attached with roots and present in soil were added at higher salt concentrations compared to untreated controls. Soil aggregation was higher at plant roots under salinity. These results suggest the feasibility of using above strains in improving plant growth and soil fertility under salinity.