David Kothamasi | University of Delhi (original) (raw)

Papers by David Kothamasi

Journal of Environmental Management, Jan 31, 2024

Nature Biotechnology

Novel beneficial traits in agricultural microbes represent inventive steps of nature, but the ina... more Novel beneficial traits in agricultural microbes represent inventive steps of nature, but the inability of patent laws to reward nonhuman inventors has led to conflicts over microbial ownership rights and presents barriers to the sharing of benefits.

Mycorrhiza, Sep 3, 2021

We investigated the role of plant host and soil variables in determining arbuscular mycorrhizal f... more We investigated the role of plant host and soil variables in determining arbuscular mycorrhizal fungi (AMF) community composition in plant roots of two spatially separated mangrove estuaries on the rivers Aghanashini (14°30′30″N-74°22′44″E) and Gangavali (14°35′26″N-74°17′51″E) on the west coast of India. Both mangrove estuaries had similar plant species composition but differed in soil chemistries. We amplified a 550 bp portion of 18S small subunit (SSU) rDNA from mangrove plant roots and analysed it by restriction fragment length polymorphism (RFLP). Clones representing unique RFLP patterns were sequenced. A total of 736 clones were obtained from roots of seven and five plant species sampled at Aghnashini and Gangavali, respectively. AMF phylotype numbers in plant roots at Aghanashini (12) were higher than at Gangavali (9) indicating quantitative differences in the AMF community composition in plant roots at the two mangrove estuaries. Because both estuaries had similar plant species composition, the quantitative difference in AMF communities between the estuaries could be an attribute of the differences in rhizospheric chemistry between the two sites. Non-metric multidimensional scaling (NMDS) revealed overlap in the AMF communities of the two sites. Three and two AMF phylotypes had significant indicator value indices with specific hosts at Aghanashini and Gangavali respectively. Environmental vector fitting to NMDS ordination did not reveal a significant effect of any soil variable on AMF composition at the two sites. However, significant effects of both plant hosts and sites were observed on rhizospheric P. Our results indicate that root AMF community composition may be an outcome of plant response to rhizospheric variables. This suggests that plant identity may have a primary role in shaping AMF communities in mangroves.

Environmental Pollution, Jul 1, 2023

Soil contaminants threaten global food security by posing threats to food safety through food cha... more Soil contaminants threaten global food security by posing threats to food safety through food chain pollution. Fly ash is a potential agent of soil contamination that contains heavy metals and hazardous pollutants. However, being rich in macro-and micronutrients that have direct beneficial effects on plant growth, fly ash has been recommended as a low-cost soil ameliorant in agriculture in countries of the Global South. Arbuscular mycorrhizal fungi (AMF), ubiquitous in agricultural soils, enhance efficiency of plant nutrient uptake from soils but can equally increase uptake of toxic pollutants from fly ash ameliorated soils to edible crop tissues. We investigated AMF-mediated amplification of nutrient and heavy metal uptake from fly ash amended soils to shoots, roots and grains of barley. We used a microcosm-based experiment to analyse the impacts of fly ash amendments to soil in concentrations of 0 (control), 15, 30 or 50% respectively, on root colonization by AMF Rhizophagus irregularis and AMF-mediated transfer of N, P and heavy metals: Ni, Co, Pb and Cr to barley tissues. These concentrations of fly ash are equivalent to 0, 137, 275 and 458 t ha − 1 respectively, in soil. Root AMF colonization correlated negatively with fly ash concentration and was not detected at 50% fly ash amendment. Shoots, roots and grains of mycorrhizal barley grown with 15, 30 and 50% fly ash amendments had significantly higher concentrations of Ni, Co, Pb and Cr compared to the control and their respective non-mycorrhizal counterparts. Presence of heavy metals in barley plants grown with fly ash amended soil and their increased AMF-mediated translocation to edible grains may significantly enhance the volume of heavy metals entering the human food chain. We recommend careful assessment of manipulation of agricultural soils with fly ash as heavy metal accumulation in agricultural soils and human tissues may cause irreversible damage.

Journal of Basic Microbiology, Oct 23, 2019

Arbuscular mycorrhizal fungi (AMF) and plant growth–promoting rhizobacteria inhabit the plant rhi... more Arbuscular mycorrhizal fungi (AMF) and plant growth–promoting rhizobacteria inhabit the plant rhizosphere. Both functional groups can influence plant community structures, and interactions between them can vary from being synergistic to antagonistic. HCN‐producing Pseudomonas protegens CHA0 is a plant growth–promoting rhizobacterium. P. protegens CHA0 has been shown to weakly attach to AMF hyphae. Here, we analyze the effect of P. protegens CHA0 on the viability of intraradical AMF hyphae. Using pot experiments, we have grown mycorrhizal and nonmycorrhizal Sorghum vulgare var. M35 with P. protegens CHA0 or HCN– mutant P. protegens CHA77, which did not produce HCN. Mycorrhizal and nonmycorrhizal Sorghum grown without CHA0 or CHA77 served as the control. While metabolically active AMF was not detected in mycorrhizal plants grown with HCN+ CHA0, the percentage of root colonization of metabolically active AMF in plants grown with HCN– CHA77 was lower than in the control. Root phosphorus was highest in mycorrhizal plants grown with HCN+ CHA0, but root Fe was higher in plants grown with the bacterial strains. Our results indicate that HCN‐producing P. protegens can affect the viability of intraradical AMF.

Journal of Hazardous Materials

Distillery spent wash (DSW) from molasses-based distilleries is being used as a low-cost alternat... more Distillery spent wash (DSW) from molasses-based distilleries is being used as a low-cost alternative to chemical fertilizers in countries like India and Brazil. However, using DSW as a fertilizer substitute causes organic pollutant leaching, including melanoidins and caramel colourants that turn bodies of water dark brown. This study investigated the arbuscular mycorrhiza (AM) mediated degradation of organic pollutants in DSW. Mycorrhizal and non-mycorrhizal Sorghum bicolor were grown in microcosms for 16 weeks. The plants were fertilized with either raw DSW or Hoagland solution. Leachates draining from the microcosms after fertilization were collected three times in 30-day intervals. Each 30-day collection was preceded by two fertilizations. A gas chromatography-mass spectrometry comparative analyses of raw DSW with leachates of the third collection from mycorrhizal and non-mycorrhizal microcosms was made. Sixty-five and 42 complex organic compounds were detected in raw DSW and leachate collected from the non-mycorrhizal pots respectively.

The gharial (<i>Gavialis gangeticus</i>) is a critically endangered, long-snouted cro... more The gharial (<i>Gavialis gangeticus</i>) is a critically endangered, long-snouted crocodylian, endemic to the Indian sub-continent. Today, the species' distribution and numbers have reduced by >95% in all the large rivers where it was formerly abundant. Living upstream in a reservoir dammed in 1976, the Katerniaghat gharial population has continued to nest along the Girwa River, subject to seasonal flooding in recent decades. In 2010, a natural flood upstream in Nepal, resulted in a permanent reduction in the mainstream river flow. As a consequence, the formerly open sand banks and mid river islands have converted gradually to riverbanks with woody vegetation in years subsequent to the flood. Coincident with the increased vegetation growth, gharial nesting sites and nest numbers declined by >40% by 2018. In an attempt to reverse the observed decline in nesting, we intervened with vegetation removal (VR) in 2019 and sand addition (SA) in 2020, to augment availab...

Gharial (Gavialis gangeticus) is a critically endangered fresh water crocodile endemic to the Ind... more Gharial (Gavialis gangeticus) is a critically endangered fresh water crocodile endemic to the Indian subcontinent. The species has suffered > 95% decline in population and habitat size. A small population of gharials comprising of 50 breeding adults is resident in a 20 Km stretch of the River Girwa in Katerniaghat wildlife sanctuary, India. Gharials in this 20 Km stretch have been genetically isolated since 1976 by a barrage that functions as a barrier to gene flow. A captive rear and release program has been initiated since 1979 under Project Crocodile for restocking declining wild gharial populations. Thousands of gharial eggs were collected from gharial populations at Girwa and Chambal Rivers. Hatchlings from the collected eggs were captive reared at a common location in Kukrail Gharial Centre, India and released back to multiple gharial populations including the isolated population at Girwa. This restocking programme was not preceded by a genetic screening of captive animals ...

Ecological Solutions and Evidence, 2021

The gharial (Gavialis gangeticus) is a critically endangered, long‐snouted crocodilian, endemic t... more The gharial (Gavialis gangeticus) is a critically endangered, long‐snouted crocodilian, endemic to the Indian sub‐continent. Today, the species' distribution and numbers have reduced by more than 95% in all the large rivers where it was formerly abundant. Living upstream in a reservoir dammed in 1976, the Katerniaghat gharial population has continued to nest along the Girwa River, subject to seasonal flooding in recent decades. In 2010, a natural flood upstream in Nepal resulted in a permanent reduction in the mainstream river flow. As a consequence of reduced flow, the formerly open sand banks and mid‐river islands have converted gradually to riverbanks with woody vegetation. Coincident with the increased vegetation growth, gharial nesting sites and nest numbers declined by more than 40% by 2018. In an attempt to reverse the observed decline in nesting, we intervened with vegetation removal (VR) in 2019 and sand addition (SA) in 2020, to augment available nesting opportunities ...

Scientific Reports, 2021

The gharial (Gavialis gangeticusGmelin) is a fish-eating specialist crocodylian, endemic to south... more The gharial (Gavialis gangeticusGmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat adjacent to the Nepal border, within the Katerniaghat Wildlife Sanctuary (KWS), and nests along a 10 km riverbank of the Girwa River. A natural channel shift in the mainstream Karnali River (upstream in Nepal) has reduced seasonal flow in the Girwa stretch where gharials nest, coincident with a gradual loss of nest sites, which in turn was related to an overall shift to woody vegetation at these sites. To understand how these changes in riparian vegetation on riverbanks were related to gharial nesting, we sampled vegetation at these sites from 2017 to 2019, and derived an Enhanced Vegetation Index (EVI) from LANDSAT 8 satellite data to quantify riverside vegetation from 1988 through 2019. We found that sampled sites transitioned to woody cover, the n...

Conservation Genetics Resources, 2020

Microsatellite DNA is among the several molecular tools used for determining genetic variability ... more Microsatellite DNA is among the several molecular tools used for determining genetic variability and inbreeding depression in threatened populations. It has been used extensively for population genetics studies in conservation of crocodilians. Even though single nucleotide polymorphisms have higher precision compared to microsatellite DNA markers, microsatellites offer a cost advantage which is particularly important to researchers in the global south. Here, we review the role of microsatellite DNA as a conservation tool in crocodilians. Employing appropriate keywords in three online databases, we studied 78 publications, where microsatellite DNA had been used to study crocodilian species. We found that 504 species-specific markers were designed for 13, out of a total of 24 crocodilian taxa. Genus Crocodylus had the highest number of speciesspecific markers and was the most studied taxa using microsatellites. Moreover, microsatellite markers developed for C. porosus were successful in cross amplification of microsatellite markers in 19 other crocodilian species. Microsatellite based studies had highest focus on analyses of multiple populations of a single species. Based on our review of microsatellite based studies on populations of crocodilian species, we recommend that microsatellite DNA markers are an effective conservation tool that can provide critical information on population structures of threatened crocodilian species.

Journal of Basic Microbiology, 2019

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria inhabit the plant rhi... more Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria inhabit the plant rhizosphere. Both functional groups can influence plant community structures, and interactions between them can vary from being synergistic to antagonistic. HCN-producing Pseudomonas protegens CHA0 is a plant growth-promoting rhizobacterium. P. protegens CHA0 has been shown to weakly attach to AMF hyphae. Here, we analyze the effect of P. protegens CHA0 on the viability of intraradical AMF hyphae. Using pot experiments, we have grown mycorrhizal and nonmycorrhizal Sorghum vulgare var. M35 with P. protegens CHA0 or HCNmutant P. protegens CHA77, which did not produce HCN. Mycorrhizal and nonmycorrhizal Sorghum grown without CHA0 or CHA77 served as the control. While metabolically active AMF was not detected in mycorrhizal plants grown with HCN + CHA0, the percentage of root colonization of metabolically active AMF in plants grown with HCN-CHA77 was lower than in the control. Root phosphorus was highest in mycorrhizal plants grown with HCN + CHA0, but root Fe was higher in plants grown with the bacterial strains. Our results indicate that HCN-producing P. protegens can affect the viability of intraradical AMF.

Journal of Environmental Radioactivity, 2019

Ectomycorrhizal (EM) fungi form symbioses with dominant tree families in boreal, temperate and tr... more Ectomycorrhizal (EM) fungi form symbioses with dominant tree families in boreal, temperate and tropical ecosystems and are important drivers of ecosystem function. EM fungal hyphae extend over a large area making them susceptible to enhanced radiation levels from naturally occurring or anthropogenically originating radioisotopes in the rhizosphere. In this study, the in-vitro effects of ionizing radiation on the growth and biomass of EM fungi Suillus luteus, S. bovinus and Rhizopogon luteolus were investigated. EM fungal cultures were exposed to gamma radiation from a 137 Cs source for 137 h in darkness at 21°C at dose rates of 404, 108.5 and 54.9 mGy h −1 resulting in total absorbed doses of 55.21, 14.82 and 7.50 Gy respectively. Cultures grown in the dark at 21°C but not exposed to the 137 Cs source served as the control. Our results show that EM fungi vary in their sensitivity to ionizing radiation. EM fungi used in this study produced melanin and reactive oxygen species scavenging enzymes such as catalase and superoxide dismutase as a response to ionizing radiation.

Global change biology, Dec 14, 2017

Substantial amounts of nutrients are lost from soils through leaching. These losses can be enviro... more Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal (AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. T...

Fems Microbiology Letters, 2009

Mycorrhiza, 2015

Long-lived radionuclides such as (90)Sr and (137)Cs can be naturally or accidentally deposited in... more Long-lived radionuclides such as (90)Sr and (137)Cs can be naturally or accidentally deposited in the upper soil layers where they emit β/γ radiation. Previous studies have shown that arbuscular mycorrhizal fungi (AMF) can accumulate and transfer radionuclides from soil to plant, but there have been no studies on the direct impact of ionizing radiation on AMF. In this study, root organ cultures of the AMF Rhizophagus irregularis MUCL 41833 were exposed to 15.37, 30.35, and 113.03 Gy gamma radiation from a (137)Cs source. Exposed spores were subsequently inoculated to Plantago lanceolata seedlings in pots, and root colonization and P uptake evaluated. P. lanceolata seedlings inoculated with non-irradiated AMF spores or with spores irradiated with up to 30.35 Gy gamma radiation had similar levels of root colonization. Spores irradiated with 113.03 Gy gamma radiation failed to colonize P. lanceolata roots. P content of plants inoculated with non-irradiated spores or of plants inoculated with spores irradiated with up to 30.35 Gy gamma radiation was higher than in non-mycorrhizal plants or plants inoculated with spores irradiated with 113.03 Gy gamma radiation. These results demonstrate that spores of R. irregularis MUCL 41833 are tolerant to chronic ionizing radiation at high doses.

Mycorrhiza, 2014

Multiple species of arbuscular mycorrhizal fungi (AMF) can colonize roots of an individual plant ... more Multiple species of arbuscular mycorrhizal fungi (AMF) can colonize roots of an individual plant species but factors which determine the selection of a particular AMF species in a plant root are largely unknown. The present work analysed the effects of drought, flooding and optimal soil moisture (15-20 %) on AMF community composition and structure in Sorghum vulgare roots, using PCR-RFLP. Rhizophagus irregularis (isolate BEG 21), and rhizosphere soil (mixed inoculum) of Heteropogon contortus, a perennial C 4 grass, collected from the semi-arid Delhi ridge, were used as AMF inocula. Soil moisture functioned as an abiotic filter and affected AMF community assembly inside plant roots by regulating AMF colonization and phylotype diversity. Roots of plants in flooded soils had lowest AMF diversity whilst root AMF diversity was highest under the soil moisture regime of 15-20 %. Although plant biomass was not affected, root P uptake was significantly influenced by soil moisture. Plants colonized with R. irregularis or mixed AMF inoculum showed higher root P uptake than non-mycorrhizal plants in drought and control treatments. No differences in root P levels were found in the flooded treatment between plants colonized with R. irregularis and non-mycorrhizal plants, whilst under the same treatment, root P uptake was lower in plants colonized with mixed AMF inoculum than in non-mycorrhizal plants.