Dutta, K. | bioRxiv Science

bioRxiv2019

Enhanced biodegradation of naphthalene by Pseudomonas sp. consortium immobilized in calcium alginate beads

Polycyclic aromatic hydrocarbons (PAHs) belong to a large group of organic pollutant which considers as a potential health hazard to living beings. Herein, naphthalene biodegradation potential by free and immobilized Pseudomonas putida strain KD10 and Pseudomonas sp. consortium were studied. Additionally, naphthalene 1, 2-dioxygenase (nahAc) was sequenced and analyzed, which reveals two altered amino acid residues. However, the altered amino acid residues are not present in the vicinity of the active site. The gas-phase binding free energy ({Delta}GLondon) of the mutant variant of naphthalene 1, 2-dioxygenase was -7.10 kcal mol-1 which closely resembles the wild type variant. Naphthalene biodegradation rate by Pseudomonas putida strain KD10 was 79.12 mg L-1 day-1 and it was significantly elevated up to 123 mg L-1 day-1 by the immobilized Pseudomonas sp. consortium. The half-life (t1/2) for naphthalene biodegradation was 3.1 days with the inhibition constant (ki), substrate saturation constant (ks) and maximum specific degradation rate constant (qmax) of 1268 mg L-1, 395.5 mg L-1 and 0.65 h-1, respectively, for the Pseudomonas putida strain KD10. However, the t1/2 value was significantly reduced to 2 days along with ki, ks and qmaxvalues of 1475 mg L-1, 298.8 mg L-1 and 0.71 h-1, respectively, by the immobilized Pseudomonas sp. consortium. The GC-MS data suggest that KD10 might follow D-gluconic acid mediated meta-cleavage pathway of catechol biodegradation. It is concluded that naphthalene biodegradation performance by immobilized Pseudomonas sp. consortium was superior to free or immobilized Pseudomonas putida KD10. Microbial consortium immobilization could be a useful tool for water quality management and environmental remediation.\n\nHighlightsO_LISuperior naphthalene biodegradation by Pseudomonas sp. consortium immobilized in calcium alginate beads.\nC_LIO_LIA common mutation prone amino acid stretch inside chain A of naphthalene 1, 2-dioxygenase has been identified.\nC_LIO_LIA new naphthalene biodegradation pathway by Pseudomonas putida strain KD10 has been proposed.\nC_LI

microbiology↗

bioRxiv2019

Adaptive efficient coding of correlated acoustic properties

Natural sounds such as vocalizations often have co-varying acoustic attributes where one acoustic feature can be predicted from another, resulting in redundancy in neural coding. It has been proposed that sensory systems are able to detect such covariation and adapt to reduce redundancy, leading to more efficient neural coding. Results of recent psychoacoustic studies suggest that, following passive exposure to sounds in which temporal and spectral attributes covaried in a correlated fashion, the auditory system adapts to efficiently encode the two co-varying dimensions as a single dimension, at the cost of lost sensitivity to the orthogonal dimension. Here we explore the neural basis of this psychophysical phenomenon by recording single-unit responses from primary auditory cortex (A1) in awake ferrets exposed passively to stimuli with two correlated attributes in the temporal and spectral domain similar to that utilized in the psychoacoustic experiments. We found that: (1) the signal-to-noise (SNR) ratio of spike rate coding of cortical responses driven by sounds with correlated attributes was reduced along the orthogonal dimension; while the SNR ratio remained intact along the exposure dimension; (2) Mutual information of spike temporal coding increased only along the exposure dimension; (3) correlation between neurons tuned to the two covarying attributes decreased after exposure; (4) these exposure effects still occurred if sounds were correlated along two acoustic dimensions, but varied randomly along a third dimension. These neurophysiological results are consistent with the Efficient Learning Hypothesis and may deepen our understanding of how the auditory system represents acoustic regularities and covariance. SignificanceIn the Efficient Coding (EC) hypothesis, proposed by Barlow in 1961, the neural code in sensory systems efficiently encodes natural stimuli by minimizing the number of spikes to transmit a sensory signal. Results of recent psychoacoustic studies are consistent with the EC hypothesis, showing that following passive exposure to stimuli with correlated attributes, the auditory system adapts so as to more efficiently encode the two co-varying dimensions as a single dimension. In the current neurophysiological experiments, using a similar stimulus design and experimental paradigm to the psychoacoustic studies of Stilp and colleagues (2010, 2011, 2012, 2016), we recorded responses from single neurons in the auditory cortex of the awake ferret, showing adaptive efficient neural coding of correlated acoustic properties.

neuroscience↗