Sanjib Kumar Manna

Ecological significance and phosphorus release potential of phosphate solubilizing bacteria in freshwater ecosystems

Phosphorus (P) is a limiting nutrient in some freshwater ecosystems. Phosphate solubilizing bacteria (PSB) are candidates for enhancing P availability in rhizoplane, but their P release potential in freshwater environments needs further evaluations. This study conducted in floodplain wetlands correlated PSB abundance, decline in sediment pH, and natural mobilization of sediment Ca–P. PSB were abundantly present in floodplain wetland waters, sediments, and in river and ponds, showing low to moderate Ca–P solubilization activity; PSB from Churni River and Bhomra wetland sediments had comparatively higher activity than those from other environments. In laboratory sediment microcosms, PSB were effective in enhancing available P concentration in interstitial water indicating their P release potential. However, P-fractionation of incubated sediments showed only a short-term decline in Ca–P by PSB, suggesting that Ca–P might not be their sole or preferred metabolic target. Despite low to moderate activity in culture medium, high population density and efficacy in P release in sediment suggest significant role of PSB in P cycling in freshwater environments.

Arsenic in freshwater ecosystems of the Bengal delta: status, sources and seasonal variability

The study aimed to examine the contamination status of arsenic (As) in excavated small water bodies, commonly known as ponds – the integral part of daily life in the arsenic-affected rural areas of West Bengal, India in comparison to the unaffected areas. The ponds of the contaminated area had higher levels of As: water 2–174 µg L−1 (mean 31 ± 2 µg L−1) and sediment 1.3–37.3 mg kg−1 (mean 10.3 ± 0.4 mg kg−1), than those from the unaffected area: water 1–8 µg L−1 (mean 4 ± 0 µg L−1) and sediment 1.4–5.3 mg kg−1 (mean 3.0 ± 0.1 mg kg−1). A moderate positive correlation was observed between the water and sediment arsenic content of the ponds of the arsenic-affected region (r = 0.688, n = 277, p < 0.0001). Contaminated ground water, either as direct input or through agricultural washings, was found to be the major contributor of arsenic pollution to these ecosystems. Seasonal variations were not prominent. This study emphasized the beneficial role of using the studied ecosystems over the highly contaminated ground water for various livelihood activities in the Gangetic delta region.

Isolation, Identification and Efficacy of Inorganic Phosphate-Solubilizing Bacteria from Oxbow Lakes of West Bengal, India

Microbial mobilization of sediment calcium-bound P constitutes an important process of P cycling in aquatic environments. The present study was conducted to identify the bacterial community responsible for inorganic phosphate solubilization in tropical oxbow lakes. Fifty eight phosphate-solubilizing bacteria were isolated from bottom soil, water, and fish gut and examined for solubilization of tricalcium phosphate. Results revealed aquatic PSB to be low-to-moderately capable in P solubilization (mean: 33.5 mg P L−1; range: 6.3–68.8 mg P L−1), and bacteria from wetland sediment and water were more effective than those from fish gut. The PSB were identified to belong to diverse genera, viz. Bacillus, Brevibacillus, Enterobacter, Agrobacterium, Pseudomonas, Acinetobacter, Microbacterium, Curtobacterium, Stenotrophomonas and Novosphingobium. The findings help in understanding the microbial role in inorganic P solubilization and identifying important P solubilizers in freshwater environments.

Sediment phosphorus forms and levels in two tropical floodplain wetlands

Inorganic phosphorus is one of the critical nutrients determining trophic state and freshwater productivity. Sediment may act as a sink or source of phosphorus to the overlying water depending on its pH, redox state, various forms of phosphorus present, etc. To examine potential sorption or mobilization of sediment phosphorus in floodplain wetlands, the amount and distribution of phosphorus fractions were evaluated using a sequential chemical extraction procedure. Exceedingly high levels of total phosphorus (mean: 6040 ± 344, 5470 ± 363 mg kg−1), consisting largely of organic and refractory fraction (70 – 98%), followed by calcium-phosphorus (mean: 584 ± 31.3, 143 ± 8.42 mg kg−1) and iron-phosphorus (mean: 108 ± 10.1, 91.0 ± 7.68 mg kg−1) were recorded respectively in Bhomra and Akaipur wetlands of West Bengal, India. The inorganic phosphorus, comprising the loosely sorbed phosphorus and all the mineral bound forms contributed only about 6–14% to the total phosphorus indicating their less significance in phosphorus sorption or desorption in these tropical wetlands. Although the loosely sorbed phosphorus was in moderate level (2.69 ± 0.69, 1.54 ± 0.53 mg kg−1), water dissolved phosphorus was recorded at higher concentrations (mean: 0.16 ± 0.02 mg l−1 in Akaipur and 1.08 ± 0.12 mg l−1 in Bhomra). However, the higher level of water available phosphorus was not reflected in plankton production since the dominance of weeds suppresses their growth. This study recorded large accumulation of organic matter and nutrients in the form of detritus in these wetlands which may be channelized for fish production through stocking of suitable detritivorous fishes and/or reducing macrophyte coverage that would give space and nutrients for phytoplankton growth.

Draft Genome Sequence of the Aquatic Phosphorus-Solubilizing and -Mineralizing Bacterium Bacillus sp. Strain CPSM8.

ABSTRACT Bacillus sp. strain CPSM8 is an efficient solubilizer and mineralizer of phosphorus. Here, we present the 4.39-Mb draft genome sequence of the strain, providing insight into the phosphorus-releasing genes related to productivity in aquatic habitats.

Significant Arsenic Reduction by Pond Sediment Microflora in the Arsenic-Affected Bengal Delta

ABSTRACT Biogeochemical reduction and mobilization of sediment-bound arsenic have triggered widespread groundwater arsenic contamination and public health emergency in Bengal Delta. The present study examines arsenic reduction ability of pond sediment microbiota and their diversity from arsenic-affected villages. Arsenic reduction ability of pond sediment microbiota and individual bacterial isolates were studied in sediment microcosm and in culture medium. Arsenic-reducing strains were identified from 16S rDNA sequences. Pond sediment microflora caused profuse arsenic reduction under anoxic and partial anoxic conditions, and under the influence of labile organic matter. Prominent arsenic-reducing strains were identified as Chryseobacterium sp., Pseudomonas sp., Acinetobacter sp., and Comamonas aquatica. The presence of partial-to-true anoxic conditions, typical of pond ecosystems in this region and labile organic matter, as well as organic manure applications in ponds for aquaculture, strongly favored arsenic reduction by sediment microflora. The Bengal Delta plain is bestowed with thousands of aquaculture ponds and floodplain wetlands which might act as important sites for microbial reduction and mobilization of arsenic to the groundwater hydrologic system in the region.